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ALPHARMA BEEF CATTLE NUTRITION |
Department of Animal Sciences, University of Florida, Gainesville 32611-0910
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Abstract |
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Key Words: cattle • diet synchrony • forage • supplementation
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INTRODUCTION |
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For ruminant animals, the degree of dietary nutrient synchrony in the rumen is not always predicative of the animal performance response, nor is dietary nutrient asynchrony indicative of poor animal performance. Nutrient synchrony occurs in a transient manner in the rumen because most feedstuffs contain both energy and protein that are available for microbial metabolism. However, to elicit improved animal performance nutrient synchrony likely needs to be continuous. Therefore, the desire to increase animal performance would seem to necessitate a greater degree of continual synchrony between energy and protein substrates in the rumen. In forage-fed ruminants, an additional challenge occurs because of the variability in forage intake and forage chemical composition.
What happens if we can actually achieve nutrient synchrony? The theory follows then that we should see an increase in ruminal metabolism (Herrera-Saldana et al., 1990
; Richardson et al., 2003) compared with asynchronous diets. Likewise, an increase in intake and digestibility should occur. Finally, an increase in animal performance should occur through an increase in nutrient extraction and the supply of the end-products of fermentation to the animal.
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CHALLENGES TO NUTRIENT SYNCHRONY |
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outlined the theoretical fermentation of the different components of carbohydrates; soluble sugars, starch and dextrin, and cell wall carbohydrates. Similarly, fermentation profiles of N/protein sources necessary to match the energy component were proposed. The concept of degradation rates and relative proportion of energy vs. protein proposed touches on a key component, that energy and protein release must be complementary to elicit a positive response (Herrera-Saldana et al., 1990). However, the relative degradation rates of feedstuffs are not the only concern in addressing nutrient synchrony. There are additional challenges to nutrient synchrony that must be addressed, including cattle requirements, pasture and forage intake, forage chemical composition, and supplement interactions. Pasture and Forage Intake
One of the greatest challenges that still faces nutritionists, particularly those who work with forage-fed cattle, is the accurate measurement or estimation of forage intake. In the case of grazing cattle, this difficulty is of particular concern (Bargo et al., 2003). Not knowing or having an accurate estimation of forage intake is the first hurdle that must be overcome in the investigation of dietary nutrient synchrony in pasture or forage-fed cattle. Synchronization of nutrients in the diet must first start with knowing what the basal feed-stuff in the diet is supplying. In the case of grazing cattle, the amount of forage that is consumed is often poorly understood (Forbes, 1988; Bargo et al., 2003). Additionally, the diurnal and daily variation in forage intake of grazing cattle complicates the process of dietary nutrient synchrony (Gekara et al., 2005). The variation in forage intake inherently introduces asynchrony in the supply of dietary nutrients to the ruminal microorganism and the animal itself in postruminal digestion. The literature is rife with research that was conducted to estimate forage intake amounts of grazing cattle and understand the patterns of forage intake. Cattle that are fed conserved or harvested forage compared with cattle that are grazing are often utilized as the model for measuring dietary nutrient synchrony when that is the stated objective of the research. In this case, knowledge of the amount of forage that is offered and consumed is known but controlled by the researcher. Likewise, the chemical composition of the forage offered can be assessed prior to initiation of feeding, and attempts at increasing the synchrony of dietary nutrient can be made. In most cases, the limitations that are experienced by grazing cattle in terms of forage intake, forage chemical composition, and forage mass are not apparent in cattle fed conserved or harvested forages. Whereas cattle fed conserved or harvested forages are optimum for research associated with dietary nutrient synchrony, the real-life application of the research needs to be considered.
Forage Chemical Composition
Coupled with the challenge of estimating pasture or forage intake, is the challenge of the chemical composition of the forage that is consumed. The challenge is 2-fold, first estimating and accurately assessing the current chemical composition of the forage that is consumed. Numerous studies (Coleman and Barth, 1973; Fisher et al., 1991; Dubbs et al., 2003) have demonstrated the difference in chemical composition between forage harvested by hand for chemical composition assessment and the chemical composition of masticate samples from esophageal or ruminalfistulated cattle. In the research capacity, access to fistulated cattle to collect masticate samples is feasible, and thus accurate assessment of grazed forage chemical composition may be achieved. The second challenge is that samples must be collected across a wide variety of grazing management strategies, forage availabilities, forage species, growing conditions, forage morphological stages, and environmental conditions. Finally, differences in protein concentration, protein form, and degradability exist between standing forage, hay, and forage silage. Total CP concentration is generally greater for preserved (i.e., hay and silage) compared with fresh or standing forage (Broderick et al., 1992; Messman et al., 1994; Volden et al., 2002). Whereas concentration of degradable protein and true protein are generally greater in fresh or standing forage compared with hay (Messman et al., 1994; Farmer et al., 2001; Volden et al., 2002). All of these constraints present unique conditions in nearly every situation. Indeed, the body of literature that describes actual forage selected and subsequent chemical composition for a wide variety of forage grazing situations is limited. The matrix of conditions that affect chemical composition of pasture and forage presents a daunting scenario for dietary nutrient synchrony.
Cattle Requirements
An issue related to dietary nutrient synchrony is cattle nutrient requirements. Successful achievement of dietary nutrient synchrony is useless if the nutrients supplied are inadequate to meet cattle nutrient requirements for maintenance and the desired level of production (e.g., growth, lactation, or gestation). Similar to pasture-forage supply, cattle nutrient requirements are not static and exhibit a great deal of variation during the productive cycle of any beef animal. DelCurto et al. (1990a) and Beaty et al. (1994), among others, have demonstrated differential responses to supplementation of grazing beef cows during different stages of production. Therefore, not only do requirements change, but the response to nutrient supply is physiological state-dependent.
Supplement Interaction
If the basic underpinning of dietary nutrient synchrony for forage-fed cattle is the forage base, then the introduction of supplements is where manipulation of the diet and nutrient synchrony occurs. However, the inclusion of supplemental feeds creates a complexity in the feeding scenario that may result in an improved or detrimental animal response (Moore et al., 1999). Supplemental feeds oftentimes have physical structure, solubility, degradation, and chemical characteristics that are different from the base forage utilized. The respective differences may be advantageous to the manipulation of diet synchrony. In contrast, the properties of the supplement may exacerbate an asynchronous dietary nutrient supply. In that regard, negative associative effects would be detrimental to the process of dietary nutrient synchrony. Introduction of grain-based supplements may shift rumen microorganism populations (El-Shazly et al., 1961). Likewise, supplemental rumen degradable carbohydrates can result in increased VFA production and elicit ruminal pH depression (Mould et al., 1983; Kennedy and Bunting, 1992; Bargo et al., 2002). Supplemental feedstuffs have differences in solubility, degradation, and chemical composition that influence the relative level of success in synchronizing dietary nutrients observed with a particular supplemental feedstuff.
Determination of the level of synchrony or success in achieving synchrony in a diet is essential. Measurements associated with nutrient synchrony research include ruminal variables: pH, total VFA and individual acid concentrations, and ammonia concentration. Microbial yield, microbial protein, and microbial efficiency also are considered ruminal measures of dietary nutrient synchrony. Ultimately, the success or failure of dietary nutrient synchrony is measured by the animal’s response as BW gain, milk production, or carcass weight accreted. However, successful improvement in one or multiple ruminal parameter measurements may not be indicative of successful live animal improvement.
Ultimately, as nutritionists, we have a multidimensional problem to address when attempting to achieve dietary nutrient synchrony in cattle. The contributing factors of the forage base, cattle characteristics, supplements introduced, and the final rumen milieu where the initial nutrient synchrony starts all present a complicated picture. Simplification of these factors allows research to be conducted to investigate opportunities to improve performance and efficiency through dietary nutrient synchrony. Unfortunately, in many cases, clear simplification is not easy to obtain and does not mirror the nutritional and management scenarios in which beef cattle are produced.
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STRATEGIES TO OPTIMIZE SYNCHRONY |
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Timing of Feed Delivery
A straightforward way to affect the possibility of dietary nutrient synchrony in forage-fed cattle is through the timing or frequency, or both, of supplemental nutrients. In light of forage-fed and, particularly, pasture-fed cattle the supply of forage, or at least accessibility, could be considered relatively constant. Variation in forage intake occurs with diurnal variation associated with grazing. As a result of management, the timing of supply of supplemental nutrients can occur within a day or across multiple days. Timing of supply of supplemental nutrients does not necessarily consider supplemental energy or protein degradation rates, and timing and degradation are not mutually exclusive. The supply of supplemental nutrients acknowledges the situation of nutrient deficiencies from forage-based diets and implicitly implies that supplementation could affect nutrient synchrony. Indeed, utilization of nutrient supply frequency is an underlying application of synchrony of nutrient supply in the total diet.
Supplement Types
In the pursuit of dietary nutrient synchrony in forage-based diets, the main types of supplementations have been energy- and protein-based supplements. The use of energy and protein sources has been demonstrated extensively in the literature. Moore et al. (1999) presented an excellent review of the effects of different supplement types on animal performance, intake, and digestibility. The need for energy or protein supplementation implies an asynchrony of total available nutrients supplied by the forage base that is negatively affecting animal performance. Therefore, the addition of energy or protein should rectify the diet deficiency and achieve some increased level of synchrony of energy and protein in the diet. An important observation is that each particular type of supplement (i.e., energy or protein) also generally supplies other ancillary nutrients. The complement of energy and protein in supplements may increase the likelihood of dietary nutrient synchrony in forage-fed cattle.
Form of Supplemental Nutrients
The form of the supplements offered also can affect the likelihood of nutrient synchrony in the diet of forage-fed cattle. Generalized energy supplement forms include starch-based, simple sugars (e.g., molasses), or fibrous sources (e.g., pulps, soybean hulls). Likewise, protein supplement forms include NPN, natural protein, degradable intake protein (DIP), or undegrdable intake protein (UIP). The utilization of different supplement forms affects the degradation rate and ultimate availability of the targeted nutrients along with ancillary nutrients that are supplied by the supplement choice. The form of the supplements directly addresses the concept of dietary nutrient synchrony discussed by Johnson (1976) in that complementary or synchronized degradation rates should improve animal performance.
Balancing Nutrient Profiles
Direct formulation of supplements and total diets to balance the ratios of energy and protein or energy and protein fractions is a method that directly applies to nutrient synchrony. This approach attempts to balance the supply of ruminal energy substrate (TDN) and protein substrates (CP or DIP). The supply of TDN and protein need not necessarily be equal in amount, but rather supply the substrates in appropriate proportions. Moore et al. (1999) suggested that supplementation with protein or energy improved forage DMI when forage TDN to CP ratio was > 7, indicating a deficiency of N. In general, the ratio approach has proved to be most beneficial for cattle consuming low quality forages in which DIP is limiting. The utilization of ratios of energy and protein substrates suggests that the source of energy is not as critical as the proportion of the energy relative to the protein, particularly DIP. Work by a number of groups has demonstrated the successful utilization of grain-based starch-containing supplements to affect animal performance (Daura and Reid, 1991; Bodine et al., 2001; Bodine and Purvis, 2003). The use of balancing nutrient profiles will be discussed within the confines of energy or protein supplementation.
If dietary nutrient synchrony is to be successful in practice, it is likely that one if not multiple strategies of dietary nutrient synchrony will have to be employed. Often, utilization of frequency and supplement type or frequency and supplement form is incorporated. Likewise, supplement type and balancing of nutrient profiles are utilized. The following discussion will examine the utilization of strategies to affect ruminant animal performance through dietary nutrient synchrony, as achieved by supplementation.
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UTILIZATION OF FEED DELIVERY TO AFFECT NUTRIENT SYNCHRONY |
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The spatial timing of the forage intake and supplement intake has the potential to affect animal performance thorough differential timing of the availability of energy and protein substrates. Kolver et al. (1998) utilized dairy cows that were fed harvested forage and supplemented with a corn-based supplement either at the same time the forage was offered (synchronous) or 4 h after the forage was offered (asynchronous). The different spatial offering of forage and concentrate resulted in different hourly ruminal degradable N to ruminal degradable total nonstructural carbohydrate ratio; however, the daily mean ratio was not different. The synchronous offering of forage and concentrate minimized the hourly differences in N to energy ratio around the feeding events compared with asynchronous offering. However, despite the differences in the hourly ratios, those differences did not elicit substantial differences in cow BW change, milk yield, or milk component yield. Therefore, despite measurable ruminal differences in N:energy over time, there were no measurable differences in performance of dairy cows. Richardson et al. (2003) examined the effect of calculated dietary synchrony index on growing lamb performance. Diet synchrony indices of 3 diets were 0.86 (synchronous), 0.76 (intermediate), and 0.63 (asynchronous). The ADG of growing lambs offered diets that were formulated with different levels of nutrient synchrony were not different (mean = 0.187 kg/d). Likewise, efficiency of gain (mean = 0.178 kg/kg) did not differ among treatments with calculated dietary synchrony index. However, lambs fed the asynchronous diet had lower retained energy (0.079 MJ retained/MJ of intake) compared with lambs fed the intermediate or synchronous diets (0.095 MJ retained/MJ of intake). In this case, diets of different nutrient supply and release did not affect growing lamb performance when lambs were program fed (Richardson et al., 2003). The total supply of nutrients was more influential than the rate of timing of supply of nutrients to lambs. In a frequency of supplementation trial on ranches in Texas, cottonseed meal was supplied at 3 different frequencies (i.e., daily, 3 times per week, or once per week) compared with a control of no supplemental feed (Huston et al., 1999). In 1 experiment, supplementation decreased cow BW loss or percent BW loss by 5.3% compared with nonsupplemented control cows, but frequency had no effect on the magnitude of percent of BW loss, and had no effect on BCS change. In contrast, in a second experiment that was conducted at different locations, cottonseed meal supplementation decreased cow percent of BW loss by 6.4% compared with nonsupplemented control cows, and the decrease in percent BW loss was greater with daily (11% decrease in BW loss) compared with 3 times or once per week (13.6% decrease in BW loss). Likewise BCS change was less with increasing frequency of supplementation. In the case of the second experiment, the more consistent supply of protein and energy associated with cottonseed meal improved cow performance in grazing conditions in Texas. Huston et al. (1999) note that even once-per-week supplementation was beneficial, which was true, but increased frequency of supply with cottonseed meal likely was more beneficial to ruminal fermentation patterns and overall nutrient metabolism. Similarly, Farmer et al. (2001) reported less loss in both BW and BCS with increased frequency of supplementation of a 43% CP supplement to cows grazing tallgrass prairie forage. The loss of cow BW increased by 0.03 kg/d for each day interval increase from 2 to 7 d/wk. The increasing frequency of supplementation elicited a more positive response to the supplemental nutrient. This demonstrates the concept that infrequency of supplementation or asynchronous supply of nutrients may be detrimental to ruminal fermentation and overall animal performance, particularly when the supplement interval is extended.
In a number of trials utilizing mature cows and nutrient synchrony, the ability to elicit an improvement in animal response with timing of supplement supply can be accomplished particularly on low-quality forages. In the situations in which supplement frequency did have an affect on cow performance, the forage base was low-quality and the additional supply of nutrients was beneficial. Graded effects of nutrient supply frequency can be observed (Farmer et al., 2001). In contrast, when more sensitive models were utilized (Hunt et al., 1989; Kolver et al., 1998; Richardson et al., 2003), a synchronized total diet did not elicit an improvement in animal response. These results comprise a range of forage quality. It is likely that in many of the situations, the dietary nutrient density was insufficient to express the animal’s full genetic potential for performance. In these cases, successful synchrony of the diet did not provide a positive influence on performance because animal growth potential was limiting.
Intake and Digestibility
If nutrient synchrony is to affect animal performance, a concurrent change in intake and digestibility is likely warranted. In the work of Kolver et al. (1998) utilizing pasture forage-fed dairy cows, there was no increase in pasture DMI associated with synchrony of pasture and concentrate feeds offered. Thus, total DMI was not increased by synchronizing dietary pasture and concentrate feeding. The intake and digestibility of DM, OM, N, and NDF fraction of the diet was not affected by synchrony of pasture and concentrate offering. Ultimately, the NEl of the diet was also similar between the 2 diets. Currier et al. (2004b) examined the effect of supplemental frequency (daily compared with every 2 d) with different NPN sources on intake and N flow from the rumen in fistulated steers. In a previous study utilizing cows, supplementation increased cow performance compared with nonsupplemented control cows, but there was no effect of supplement frequency on cow BW change, BCS change, or calf birth weight (Currier et al., 2004a). Source of supplemental NPN did not increase straw OM intake (OMI), but daily supplementation with NPN did tend to increase straw OMI compared with that of alternate day NPN supplementation; this effect also was true for total OMI in both steers (Currier et al., 2004b) and wethers (Currier et al., 2004a). However, duodenal OM flow (g/kg of BW) was similar between the 2 supplementation frequencies. The increased intake and digestibility data of Farmer et al. (2001) underscores the effect of supplement frequency on cow performance. A linear increase in daily forage OMI was reported with increasing supplement frequency from 2 to 7 d/wk. There was a 20 g/kg of BW0.75 increase in OMI from 2 to 7 d/wk supplementation frequency. Likewise, there was a linear increase in OM and NDF digestibility with increasing frequency of protein supplementation from 2 to 7 d/wk. The protein source was a natural protein, and thus the constant supply of protein and some additional energy from the supplement was more beneficial and likely elicited a more favorable nutrient synchrony profile than infrequent supplement supply. Bohnert et al. (2002a,b,c) conducted a series of experiments that evaluated the effect of supplement frequency with different protein degradability. In steers offered low-quality meadow hay, a quadratic effect of supplement frequency (daily, every third day, or every sixth day) of DIP or UIP supplementation on hay and total OMI was reported (Bohnert et al., 2002a). Total tract digestibility of OM tended to indicate a linear decrease with decreasing supplement frequency. In all cases, supplying protein more frequently to steers consuming low-quality meadow hay improved forage and total intake and total tract digestibility. Likewise, in wethers consuming low-quality meadow hay, hay consumption and total OMI increased linearly with increasing supplement frequency (Bohnert et al., 2002b). In contrast, OM total tract digestibility was not affected by supplement frequency. Again, these results imply that offering a more consistent supply of supplemental nutrients to achieve a more synchronous supply of energy and protein will improve intake and likely animal performance, as demonstrated by improved cow BW maintenance with more frequent supplementation (Bohnert et al., 2002b).
Forage quality does have an effect on the likelihood of nutrient synchrony being successful. High-quality forages, such as those used in Kolver et al. (1998) or Gekara et al. (2005), may not support dietary nutrient synchrony success, most likely from the excess of N and a potential deficiency of energy. Moore et al. (1999) indicated this may be likely because supplementation generally decreased forage voluntary DMI when forage TDN to CP ratio was < 7. In contrast, studies coupling low-quality forages and supplement frequency demonstrated success in affecting forage DMI and accompanying nutrient synchrony. Even though ruminants have the ability to recycle N, a more consistent supply or synchronized supply of N elicited a better response in terms of intake and digestibility compared with supplement situations where N recycling was expected to occur because of infrequent supplementation (Farmer et al., 2001; Currier et al., 2004a,b). Digestibility was affected by an overall input of nutrients and a consistent input of nutrients. Consistent input of nutrients likely supplies the ruminal microbes with much needed energy and protein substrates. Whereas, infrequent supplementation requires ruminal microbes to go without or limits the supply of needed substrates that in turn decreases digestibility and likely microbial efficiency.
Ruminal Function and Metabolism
Henning et al. (1993) examined the effect of pulse-dosing or gradual supply of energy and protein supplement combinations to a wheat straw diet on the ruminal metabolism in sheep. The combination of pulse-dosing energy and protein represented rapid synchronization of nutrients in the diet; a combination of pulse and gradual supply of energy and protein represented an unsynchronized supply of nutrients in the diet; and the combination of gradual energy and protein supply represented a slow synchronized supply of nutrients. A gradual supply of energy compared with pulse-dosing tended to increase feed intake by approximately 5%. Total ruminal outflow (g/d) and microbial outflow (g/d) were increased by the gradual supply of energy compared with pulse-dosed energy supply. Total ruminal outflow also tended to be increased by 10% with gradual protein supply compared with pulse-dosing of protein. However, microbial outflow was not affected by protein supply pattern. In contrast, true rumen digestibility was decreased 5.6% by gradual protein supply compared with pulse-dosing of protein, but energy supply pattern did not affect rumen digestibility. Similar to microbial outflow, true microbial efficiency (g of microbial N/kg of OM fermented) was increased by 2.3 g of N/kg of OM fermented with gradual supply of energy compared with pulse-dosing of energy, whereas N supply pattern had no effect. These results indicate that the timing of energy supply has a greater effect on the success of nutrient synchrony than does the timing of protein supply. This is likely to be a function of the ability of the ruminal microbes to store N and the ruminant animal’s ability to recycle N, whereas the storage of carbohydrate, energy, or both does not occur. Therefore, the synchronization of the energy supply is consumption dependent.
Kim et al. (1999a, b) conducted 2 experiments that utilized dairy cows fed grass silage and dosed with carbohydrate in a continuous, synchronous (two 6-h infusions after forage feeding) or asynchronous (two 6-h infusions provided 6 h after forage) method. In experiment 1, method of carbohydrate supplementation (sucrose) did not affect ruminal pH or total VFA production compared with the basal diet (Kim et al., 1999b). Ruminal ammonia N was decreased and calculated microbial N was increased by the supplemental carbohydrate, but pattern of supply (i.e., continuous, synchronous, or asynchronous) had no effect on ruminal ammonia N or microbial N. In experiment 2, supplemental carbohydrate (maltodextrin) did decrease ruminal pH and ammonia N concentration, and in the case of ammonia N, a continuous supply of carbohydrate resulted in a greater decrease in ammonia N concentration compared with synchronous or asynchronous supply (Kim et al., 1999a). However, similar to experiment 1, total VFA concentration did not differ between the basal and carbohydrate-supplemented treatments, although microbial N supply was increased with supplementation and synchronous supply increased microbial N 14% more than asynchronous supply. In this case, the rye-grass silage was likely of adequate quality (i.e., in terms of protein and water-soluble carbohydrate) so that the addition of supplemental carbohydrate did not greatly affect ruminal nutrient synchrony and ruminal metabolism.
In the study of Bohnert et al. (2002c), the effect of frequency of supplementation and, thus, nutrient synchrony on ruminal metabolism was examined. On the day that all supplements were offered, ruminal DM fill increased linearly as the length of supplement interval increased. Likewise, ruminal ammonia N concentration increased as frequency of supplementation decreased as did total VFA concentration. Ruminal pH decreased as supplement frequency decreased, an effect of the amount of supplement that was introduced on the day of supplementation. In contrast, on the day that only the daily supplement was offered, the trends were exactly opposite. Total VFA and ammonia N were greater for daily compared with less frequent treatments. Therefore, on the day that all supplements were offered differences between treatments were a function of supplement amount; however, on the "off" days, ruminal metabolism of steers that did not have daily supplements was less favorable compared with the cattle supplemented daily.
The results of Henning et al. (1993) indicated that synchronous supply of energy and protein could elicit a positive response on microbial synthesis. The 2 experiments by Kim et al. (1999a, b) had mixed results on microbial yield. The supply of energy through carbohydrates has as great an influence on nutrient synchrony success as potentially any other factor. Bacteria are limited in their ability to store carbohydrate, and no mechanism exists for the animal to recycle energy back to the rumen. In light of the limitation of energy recycling, a consistent energy supply would be the most beneficial strategy. Finally, matching the N supply to the available energy may be the strategy to adopt; however, that is not to say that synchrony through protein supply may not have benefit.
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EFFECT OF ENERGY SUPPLEMENT AND FORM TO AFFECT NUTRIENT SYNCHRONY |
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Brown and Johnson (1991) examined the ability of source of supplemental energy to affect cull-cow performance. Cows were offered ammoniated stargrass hay such that adequate CP (11.6%) was available from the hay, but overall diet energy supply was limiting and, thus, supplementation of energy was needed. Energy supplementation (i.e., citrus pulp, molasses, molasses + cottonseed meal) increased cow ADG by 0.23, 0.35, and 0.40 kg/d, respectively, more than control cows (0.45 kg/d). There was no difference in ADG between a digestible fiber source in citrus pulp and sugar from molasses. The addition of cottonseed meal, as a source of protein and energy, increased cow performance compared with molasses or citrus pulp alone. The supplemental energy along with a natural protein from cottonseed meal allowed for improved animal performance because of a better nutrient supply.
Similarly, Garcés-Yépez et al. (1997) examined different energy sources for growing steers fed Bermudagrass hay. The energy supplements provided differential amounts of starch and NDF. Energy supplements were corn-soybean meal (C-SBM), wheat middlings, or soybean hulls. Energy supplements also were offered at 2 different levels, low (25%) and high (50%), of the estimated TDN intake. Steer ADG exhibited an inverse relationship with starch level in the supplement particularly at the high level of energy supplementation. In that experiment, the effect of negative associative effects is apparent. Negative associative effects also are a function of nutrient synchrony in the rumen. The energy provided by the supplements with greater fiber concentration were likely complimenting the protein source from the Bermudagrass hay, whereas the energy supplied by the C-SBM did not match the digestion rate and supply of protein from the hay.
In another study that utilized different energy sources (i.e., high fiber or high grain) for growing heifers grazing Bermudagrass, the addition of energy to the diet increased total gain and ADG of the grazing heifers (Bodine et al., 2001). There were no differences between energy sources for heifer performance and efficiency of supplement use. In this case, the DIP supply was key to this situation. The amount of DIP was similar between the 2 energy sources and formulated to meet the requirements of the heifers. Therefore, supply of protein/N for ruminal use was comparable between the 2 treatments and resulted in similar performance.
In another study, Bodine and Purvis (2003) utilized corn, soybean meal (SBM), and a combination of the 2 to supply energy and(or) protein to steers grazing tallgrass prairie. In these supplements, C-SBM was the base supplement that supplied adequate dietary DIP. The amount of corn supplement provided the same amount of energy as C-SBM, whereas the amount of SBM supplement offered the same amount of DIP as C-SBM. Therefore, a different DIP to TDN ratio was achieved in each supplement. The supplement formulations have the potential for differential opportunities for nutrient synchrony within the supplements and total diet. The ADG of steers was greater for the C-SBM supplement in which DIP and energy were balanced. Daily gain was decreased in the supplements that provided a similar amount of energy or protein to equal the C-SBM treatment. Supplements that included corn did decrease the time of grazing by the cattle compared with the nonsupplemented control or steers supplemented only with SBM. Additionally, supplement conversion was greater for the SBM-supplemented steers compared with the corn-supplemented steers, with the C-SBM steers intermediate. The increase in supplement conversion indicated a deficiency of DIP, and the increase in conversion with C-SBM indicates that the tallgrass prairie likely was deficient in both energy and protein.
Supplementation of forage-fed ruminants with different energy sources can improve animal performance (Moore et al., 1999). However, the source and level of supplemental carbohydrate does affect performance. The effect on performance can be a function of matching or synchronizing the availability of energy substrates from the supplement with N from the forage base. The effect of the energy supplement is more pronounced on high-quality forage. When the forage and supplement have nearly equal digestibility and forages have adequate N, forage intake generally suffers. This principle was reviewed by Moore et al. (1999), with TDN to CP ratio above or below 7 being the critical value. The work by Daura and Reid (1991) and Bodine and Purvis (2003) indicate the key to utilization of energy sources is to supply adequate DIP in the total diet to match the dietary supply of energy, thereby synchronizing the supply of digestible energy and available N to grow microbes. By supplying adequate DIP in the diet, starch-based supplements can be utilized without outstanding negative associative effects.
Intake and Digestibility
In the work of Garcés-Yépez et al. (1997), hay DMI was not affected by energy supplement type; however, there was an effect of supplement amount intake. Greater TDN supplementation resulted in a decrease in hay DMI. The depression in hay DMI was not energy substrate-dependent; rather, the decrease in hay DMI was an overall displacement of hay by the supplement. Hay quality was of moderate quality (10.5% CP), and thus, the displacement was a result of the supplements being more digestible than the moderate quality forage. Even though there was an energy supplement source effect on the animal performance, an intake effect attributable to supplement type was not apparent.
The use of corn-based energy supplements decreased steer grazing time on tallgrass prairie pasture and, thus, had an effect on the intake and digestibility (Bodine and Purvis, 2003). The utilization of corn alone or C-SBM supplement decreased both forage DMI and forage digestibility compared with nonsupplemented control and SBM-supplemented steers. The addition of SBM to corn supplement increased digestibility compared with the corn supplement. Therefore, balancing of supplemental energy and protein did positively affect forage intake and digestibility compared with energy alone. This trend was repeated in the total digestible OMI, in that the addition of protein to a starch energy source, resulted in synchrony of nutrient supply in the rumen and had a positive effect on ruminal function. Additionally, when steers that were supplemented with adequate DIP were provided additional energy, total and digestible OMI were increased.
Bodine et al. (2001) offered protein-based, high-fiber energy-based, or high-grain energy-based supplements to steers consuming prairie hay. Supplementation increased hay OMI compared with nonsupplemented control steers, and protein supplementation increased hay OMI to a greater extent. However, there was no difference between energy supplement source, and both increased hay OMI. Likewise, supplementation increased total diet OM digestibility, but fiber-based energy supplementation had greater digestibility than grain-based energy supplementation. In examining the reported starch intake, it would be expected that there would be greater differences in hay OMI and forage digestibility because of the assumed negative associative effects of starch on fiber digestion. However, all diets were formulated to supply sufficient dietary DIP for ruminal digestion of the carbohydrate from the hay and the energy-supplying supplement. Therefore, the key to maintaining acceptable intake and digestion of low-quality forages is to synchronize the supply of DIP and carbohydrate from energy supplements. This is a recurring theme and an important concept for nutrient synchrony in forage-fed animals.
Carey et al. (1993) examined the in situ digestion rate and fiber digestibility of brome hay as affected by different energy supplements. Digestion rates of DM and NDF were not altered by energy supplementation from barley, beet pulp, or corn, although barley did numerically retard the rate of digestion of DM and NDF. The rate of CP digestion was significantly depressed by barely or corn supplementation compared with control and beet pulp. The addition of starch-based energy supplements affected digestion of the CP-associated fiber and NDF fraction because the diet was not balanced for energy and protein.
Supplementation with different energy sources will alter forage intake. The studies discussed herein are just a small sampling of those available. Reference should be made to the review of Moore et al. (1999) for a more through review of the effects of supplementation type on intake, digestibility, and performance across different forage types. There are mixed results for the effect of energy supplementation and potential energy source synchrony on forage intake and digestibility. Again, the key in affecting forage intake and digestibility is the complementary synchrony of DIP and energy in the total diet.
Rumen Function and Metabolism
Supplementation of low-quality tallgrass prairie with protein or energy supplements resulted in lower pH values compared with forage alone (Bodine et al., 2001). The energy supplements resulted in lower pH values compared with protein supplementation, but there was no difference between starch- or fiber-based energy supplements. Ruminal ammonia N in steers was increased after supplementation compared with nonsupplemented steers mainly because the supplements provided additional CP compared with the forage. Likewise, providing supplements increased total VFA concentration and the energy supplements produced greater VFA concentrations compared with protein supplementation. Supplying starch from grain and balancing the diet for DIP resulted in synchronization of the energy and protein supply in the rumen, and greater amounts of VFA were produced.
In the synchrony experiment of Richardson et al. (2003), supplements based on barley and beet pulp were supplied to a forage-based diet for lambs. After feeding these diets to lambs, there was no difference in rumen pH, VFA concentration, or plasma urea N as a result of energy source or level of synchrony. Plasma ammonia N and microbial flow were increased by the barley-based supplement compared with the beet pulp diet. In this case there were not differences in ruminal function and metabolism; however, the greater retention of energy with the synchronized diet may indicate the potential for improved performance.
Lardy et al. (2004) examined the effect of different levels of barley supplementation (i.e., 0, 0.8, 1.6, and 2.4 kg/d) on forage intake, digestibility, and ruminal fermentation in steers fed medium quality (10% CP) hay. During the first 15 h after feeding, ruminal ammonia N decreased linearly with increasing level of barely supplementation. The addition of ruminally available carbohydrate promoted a greater capture of N in the rumen. All levels of barley supplements provided adequate levels of DIP, which also resulted in increased DM, OM, and NDF digestibility, but linearly decreased CP degradation. Thus, providing adequate DIP to complement the addition of energy likely resulted in a more complementary utilization of energy and protein in the rumen. Ultimately, the use of energy-based supplements will influence animal performance and forage utilization, potentially increasing or decreasing the opportunities for nutrient synchrony in the diet. Unfortunately, the level of knowledge about these exact interactions is particularly situation-specific, and robust models that incorporate a broad range of forages and supplements and produce specific results are not widely available.
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EFFECT OF PROTEIN SUPPLEMENT AND FORM TO AFFECT NUTRIENT SYNCHRONY |
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Protein supplementation has been examined equally as a method to achieve nutrient synchrony and improve forage-fed animal performance. To accomplish this, multiple sources and forms of protein supplementation have been examined, as well as combinations of sources and energy. Stateler et al. (1995) examined the addition of different protein sources to compliment the energy supplied by liquid molasses. The addition of energy alone from molasses increased steer performance when grazing dormant bahiagrass forage. The addition of natural protein sources, SBM, or blood-feather meal to liquid molasses increased steer ADG compared with urea as a source of N. In the case of growing cattle, the supply of both DIP and UIP is crucial, and this was indicated by the increased ADG when steers were supplemented with the blood-feather meal by-pass protein sources. The best performance was achieved by the steers that were supplemented with a molasses slurry, which contained urea and blood-feather meal that met both DIP and UIP requirements. In this case, nutrient synchrony of supplying energy from molasses and NPN from the urea was enhanced by the addition of bypass protein.
In 3 selected studies (Bohnert et al., 2002b; Currier et al., 2004a; Farmer et al., 2004), the effect of a progression in the type of N or protein supply on animal performance can be observed. Currier et al. (2004a) examined the effect of 2 different NPN sources (urea or biuret) on mature cow performance. Cow performance did not differ between urea and biuret, but supplemental NPN did improve cow performance compared with control cows. Farmer et al. (2004) examined the percent of DIP in a protein supplement (i.e., 0 or 30%) coming from urea on cow performance when grazing tallgrass prairie. There was no effect of DIP percent from urea on cow performance, but natural protein (0% DIP from urea) was numerically better than a protein supplement containing 30% DIP from urea. Finally, Bohnert et al. (2002b) utilized either a protein that contained DIP or UIP protein sources. Supplying either type of protein improved cow performance compared with control cows, but the 2 protein supplements were not different. Beaty et al. (1994) examined the effect of protein concentration on mature cow performance grazing dormant tallgrass prairie prior to, and including, calving and breeding. Increasing CP percent of the supplement improved cow BW change during the 105 d prior to calving and through calving at d 166. From calving to breeding, low-protein supplements (12 and 21% CP) resulted in less cow BW loss compared with cows offered high CP supplements (31 and 41% CP), which were likely experiencing greater nutrient demands associated with greater milk production. For mature cows consuming low-quality forage, the source of protein is not likely the first limiting factor in terms of cow BW, BCS, or calf birth weight; energy supply from the forage is likely limiting performance. The opportunity for dietary nutrient synchrony likely exists, but is limited by the overall energy of the diet.
In ruminants fed low-quality forages, the supplementation of protein has repeatedly improved animal performance. The improvement in performance generally has occurred because of correcting a protein/N deficiency in the diet, thereby better synchronizing the supply of energy and protein in the rumen. In the experiments reviewed herein, different protein or N sources resulted in similar performance. In many cases, the addition of protein into the system to provide some level of synchrony between energy and protein was positive regardless of the source. Likewise, increasing the proportion, amount, or both of natural protein improved animal performance in a number of experiments. Increasing CP content of the diet does several things. First, it possibly allows for a greater opportunity of energy and protein synchrony just by having more protein available. Second, the additional supplement likely brings with it energy substrates that have different degradation rates than the forage, thereby increasing the dietary nutrient synchrony opportunities. Finally, additional protein allows for N recycling in the ruminant animal, which again may improve the dietary nutrient synchrony opportunities in the rumen.
Intake and Digestibility
The source of NPN (urea or biuret) did not affect straw intake, DM digestibility, or fiber digestibility in a study with lambs (Currier et al., 2004a) or a study with steers (Currier et al., 2004b). Interpretation of these results in light of nutrient synchrony implies that any difference in release rate of the NPN source had little overall effect on intake and digestibility. The supply of N in the rumen, although important, is not the greatest factor controlling intake and digestion.
Similar to the work of Currier et al. (2004b), Bohnert et al. (2002a, b) evaluated the effect of DIP compared to UIP supplementation on forage intake and digestion. Protein supplementation did not increase hay DMI intake in either trial. In this scenario Bohnert et al. (2002b) suggested the maximal NDF intake of 12.5 g · kg of DM–1 d–1 was reached, and thus, intake already was maximized given the fiber level of the forage. Supplementation with DIP or UIP increased DM and NDF digestibility compared with the control diet. It has been well documented that protein supplementation increases digestibility by supplying a complimentary or some measure of synchronous supply of protein for the ruminal microbes to utilize. It was suggested that in this case, the UIP supplement resulted in an improved NDF digestibility because it actually provided a more moderated amount of DIP relative to the energy balance from the forage (Bohnert et al., 2002b). This idea would mirror that put forth by the work of Bodine and Purvis (2003), in that the ratio of DIP to energy is a key driver in animal performance, intake and digestibility, and metabolism, a concept that fits the idea of nutrient synchrony perfectly.
Beaty et al. (1994) observed a linear increase in straw DMI, DM digestibility, and NDF digestibility with increasing percent CP supplement in steers consuming low-quality forage. In this case, the additional protein was supplying ruminal ammonia N, which was likely limiting. Indeed, this is a case where synchronizing the supply of energy from the forage and protein from the supplements elicited a beneficial response. This response has been reported by others including DelCurto et al. (1990a, b).
In most cases supplemental NPN is not stimulatory to forage intake and digestibility (Kropp et al., 1977; Köster et al., 1997). Additionally, differential release rates of NPN products do not stimulate intake or digestibility of low-quality forages. This is a function of NPN supplementation increasing the overall N supply in the rumen, but the ratios of N and protein specifically to energy are not in balance or are synchronized to positively affect intake and digestibility. In contrast, increasing supplemental CP concentration with natural protein sources has been reported to increase forage intake and digestibility, for just the reason stated previously, natural protein does a better job of synchronizing the supply of ruminal degradable protein and energy within the rumen.
Rumen Function and Metabolism
In contrast to the lack of effect of NPN source on intake and digestibility, different NPN sources did have some limited affect on ruminal metabolism (Currier et al., 2004c). Rumen pH was not affected by source of NPN supplementation nor was total VFA concentration. As expected, ruminal ammonia N concentration increased with NPN supplementation compared with nonsupplemented control, but biuret did decrease ruminal ammonia N concentration compared with urea supplementation. Likewise, plasma urea N was increased for NPN-supplemented steers, but again the concentration of plasma urea N was decreased for biuret-supplemented steers. The improved synchrony of N release from biuret with energy from the forage resulted in an increase in bacterial N and bacterial N synthesis for biuret-supplemented steers compared with urea-supplemented steers (Currier et al., 2004b). The increase in bacterial N synthesis should be indicative of an improved ruminal environment and availability of energy and protein substrates. Ultimately, however, there was no improvement in cow performance for biuret compared with urea supplementation (Currier et al., 2004a).
Supplying either supplemental DIP or UIP decreased ruminal pH compared with meadow grass hay-fed control steers and UIP supplementation tended to support a greater ruminal pH compared with DIP-supplemented steers (Bohnert et al., 2002c). Concentrations of VFA increased with protein supplementation compared with control, and VFA concentration tended to be greater with DIP compared with UIP supplementation (Bohnert et al., 2002c). The increase in total VFA production is likely as much a function of overall supplement ingredient profile than a protein effect on VFA production. Ruminal ammonia N concentration was greater in the DIP-supplemented steers (Bohnert et al., 2002c), a result of the diet formulation; however, plasma urea N concentration did not follow this trend (Bohnert et al., 2002a). More bacterial N was synthesized in steers supplemented with DIP compared with UIP, likely because of more energy and rumen available protein from the DIP supplement (Bohnert et al., 2002a). The increase in bacterial N flow indicates a more favorable environment for bacterial synthesis, likely a function of the synchrony of energy from the forage and protein from the supplement. Bacterial protein is of great importance for cattle, particularly cattle that are grazing low-quality forage.
The different release rates of urea and biuret resulted in different effects for ruminal metabolism and absorption of the excess ammonia and its conversion to urea. However, this difference did not equate to differences in animal performance. When using natural protein sources, the true protein/N effect is confounded by the synchrony of protein and energy that natural protein supplies in the rumen. The energy supplied may not be great, but it is likely different than the forage in terms of degradation rate and products of fermentation, thus providing an improvement in the rumen environment.
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CONCLUSIONS |
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In many situations, the forage-feeding system alone, particularly with respect to low-quality forages, likely does not allow for full genetic expression of performance of the animal. Likewise, the forage base alone generally provides an asynchronous diet with respect to the release and amount of important nutrients. When additional feed is introduced to provide additional nutrients in an attempt to synchronize nutrient supply, there can be negative effects. In situations in which moderate to high-quality forages are consumed, substitution of forage for supplement occurs. Additionally, the introduction of antagonistic feedstuffs that result in negative associative effects may compound the asynchronous nature of the total diet. The rumen is a robust environment capable of accommodating a range of dietary situations; however, the rumen does not function as a storage location for energy in the ruminant animal. The limitation of energy storage is likely a limitation in regards to total dietary nutrient synchrony. Measurement of in situ degradation rates of protein and fiber fractions and total protein and fiber amounts is possible for all feedstuffs. However, simply matching these measured chemical compositions and predicted degradation rates will not be sufficient to elicit dietary nutrient synchrony alone. Ultimately, addressing the proportions of energy, protein, organic matter, and degradable intake protein, in combination with many other factors, are plausible methodologies to address total dietary nutrient synchrony.
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Footnotes |
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2 Corresponding author: hersom{at}ufl.edu
Received for publication July 26, 2007. Accepted for publication October 2, 2007.
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LITERATURE CITED |
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This article has been cited by other articles:
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  C. R. Krehbiel, C. A. Bandyk, M. J. Hersom, and M. E. Branine Alpharma Beef Cattle Nutrition symposium: Manipulation of nutrient synchrony J Anim Sci, April 1, 2008; 86(14_suppl): E285 - E286. [Full Text] [PDF]
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Abstract
INTRODUCTION