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ANIMAL NUTRITION |
* Department of Animal Science, Oklahoma State University, Stillwater 74078-6051;
and
Department of Animal and Food Sciences, Texas Tech University, Lubbock 79409-2141
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Abstract |
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 Top Abstract INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONIMPLICATIONSLITERATURE CITED |
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0.28) from those fed the cottonseed diets. Heifers fed the diets containing PCS had greater (P 
0.03) HCW, dressing percent, and LM area than those fed DLCS. Based on our results, whole cottonseed, or products derived from processing whole cottonseed, can replace feedstuffs commonly used in beef cattle finishing diets with no adverse effects on animal performance or carcass characteristics.
Key Words: beef cattle • carcass merit • delinted cottonseed • finishing performance • whole cottonseed
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INTRODUCTION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONIMPLICATIONSLITERATURE CITED |
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One potential problem in the feeding of cottonseed or cottonseed products is gossypol toxicity; however, ruminants have the ability to detoxify large amounts of gossypol within the rumen (Reiser and Fu, 1962
). Diets containing up to 25% (DM basis) whole cottonseed have been reported to be safe for consumption by cattle (Calhoun and Holmberg, 1991). Little research is available regarding the effects of feeding processed cottonseed products (e.g., pelleted cottonseed or delinted cottonseed) on finishing performance and carcass characteristics of beef cattle. Thus, our objective was to evaluate performance and carcass characteristics of finishing beef cattle fed whole cottonseed or processed cottonseed products.
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MATERIALS AND METHODS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONIMPLICATIONSLITERATURE CITED |
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Experiment 1
On November 8, 2002, 91 crossbred steer and bull calves (15% bulls; initial BW = 230 ± 17.7 kg) were shipped from a facility in Meridian, MS, to the Texas Tech University Burnett Center (New Deal, TX). On arrival, each animal was weighed [C & S Single-Animal Squeeze Chute (Garden City, KS) set on 4 Rice Lake Weighing Systems (Rice Lake, WI) load cells], administered a uniquely numbered ear tag in the left ear, vaccinated against respiratory (Prism 9, Fort Dodge Animal Health, Overland Park, KS) and clostridial pathogens (Vision 7 with Spur, Intervet, Millsboro, DE), and administered moxidectin (Cydectin, Fort Dodge Animal Health). When necessary, horns were "tipped" by cutting off the tips of the horns and searing the base with a hot iron. The cattle were sorted into soil-surfaced pens, offered a 65% concentrate diet, and used in a receiving study examining the effects of intranasal lysozyme on health of beef cattle (Rivera et al., 2003). The study protocol required that half (46) of the animals received a nasal dosage of a lysozyme/zinc/carbopol mixture (1 mL per nostril).
On November 21, 2002, 43 additional steers (initial BW = 230 ± 18.6 kg) were shipped from the same facility in Meridian, MS, to the Burnett Center. These cattle were processed in the same manner; however, each steer also was administered a metaphylactic dose of tilmicosin phosphate (1 mL/30 kg of BW; Micotil, Elanco Animal Health, Greenfield, IN). These animals also were sorted into soil-surfaced pens and offered a 65% concentrate diet. On December 5, 2003, all intact males were identified and surgically castrated (15 animals), and the diet was switched to 75% concentrate on the next day. Nine days later, after the cattle were determined to have achieved ad libitum intake, they were switched to an 85% concentrate diet. For the next 4 mo, the steers were limit-fed the 85% concentrate diet in quantities sufficient to achieve an ADG of 0.91 kg. On February 18, 2003, all cattle were transferred from the soil-surfaced pens into partially slotted, concrete-floor pens at the Burnett Center.
Approximately 2 wk before beginning the experiment, the cattle were weighed, and 120 animals with the most uniform BW were selected for use in the experiment. Animals selected for study were stratified by BW into 8 blocks consisting of 15 animals per block. Five steers were assigned randomly to a pen in their corresponding weight block. One of 3 treatments was assigned randomly to pen within each block, such that each block had all of the treatments equally represented. One week before beginning the experiment, cattle were sorted into their treatment pens (concrete, partially slotted floor; 2.9 m wide x 5.6 m deep; linear bunk space = 2.44 m; water trough shared between 2 pens). On d 0 (Exp. 1 initiation), each steer was individually weighed (unshrunk) to obtain an initial BW measurement (initial BW = 381.4 ± 31.7 kg). All BW measurements reported henceforth are unshrunk values.
The composition of the supplement used in Exp. 1 and 2 is detailed in Table 1. Dietary treatments (Table 2) were: CON = conventional 90% concentrate, steam-flaked corn-based, finishing diet; WCS = a finishing diet similar to the CON, in which whole cottonseed replaced the cottonseed meal, tallow, and some of the corn of the CON diet; and EQU = a finishing diet similar to WCS but with whole cottonseed replaced by the individual components of whole cottonseed (cottonseed oil, cottonseed hulls, and cottonseed meal).
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were used for diet formulation for all ingredients except whole cottonseed. Whole cottonseed was analyzed before initiating the experiment for percentages of DM, NDF, CP, and ether extract (Table 2
), and values determined from the laboratory analyses were used in the diet formulation.
Feed samples for each treatment were collected weekly from a mixer/delivery unit (model 84-8, Rotomix, Dodge City, KS), and DM was measured by drying overnight in a forced-air oven at 100°C. At the end of each 28-d period, samples were composited and ground in a Wiley mill (Arthur H. Thomas, Philadelphia, PA) to pass a 2-mm screen. Dry matter, CP, and ADF were analyzed after each period. Ether extract, ash, NDF, Ca, and P were analyzed from a sample composited from each period at the end of the experiment. All chemical analyses of the diets were performed according to the AOAC (1996); fiber analyses were determined according to the procedures of Goering and Van Soest (1970).
Each morning, the 3 diets were each mixed in a 1.27-m3-capacity paddle mixer (Marion Mixers Inc., Marion, IA) and delivered by a drag chain conveyor to the mixer/delivery unit. Diets were then mixed for an average of 3 min in the mixer/delivery unit and delivered to the treatment pens (±0.45 kg) by the use of load cells and an indicator on the unit. The average time from diet mixing to delivery was approximately 10 min.
Feed bunks from each pen in the experiment were appraised visually each morning before feeding to determine the quantity of feed remaining from the previous day. The quantity of feed to be delivered to the pen that day was then programmed, prepared, and delivered. This process was designed for little or no accumulation of feed in the bunk (maximum of 0.5 kg). When a pen of cattle left no feed in the bunk at the time of the bunk evaluation, feed delivered to the pen was increased by 0.2 kg/steer.
As the cattle were being weighed at the end of each period, feed bunks were cleaned, and refusals were weighed (Ohaus electronic scale, ± 0.045 kg; Pine Brook, NJ). A sample of refusals was then taken and dried in a forced-air oven for approximately 24 h to determine DM. Average DMI by a pen was determined by subtracting the DM of the refused feed at the end of the period by the quantity of DM delivered to the pen for the entire period. The corrected total of DM delivered was divided by the number of animal days to determine average DMI by each steer in the pen.
Cattle were weighed individually on d 0, 56, and at their respective shipping dates. On d 0, steers in blocks 1, 2, and 3 were implanted with a single Revalor S implant (Intervet) in the right ear, whereas steers in blocks 4 through 8 were implanted with a single Ralgro implant (Schering Plough Animal Health, Union, NJ) in the right ear. On d 56, steers in blocks 4 through 8 were reimplanted with a single Revalor S implant in the right ear. Cattle were weighed on a pen basis using a platform scale (±2.27 kg) on d 28, 84, and 112. One day before use, each scale was calibrated with 453.6 kg of certified weights (Texas Department of Agriculture).
When a majority of the cattle within each block was determined by visual appraisal to have approximately 28% body fat (Low Choice USDA quality grade), the entire block was shipped approximately 60 km to the Excel Corp. slaughter facility in Plainview, TX. Steers in block 1 were fed for 84 d; steers in blocks 2 and 3 were fed for 105 d; and steers in blocks 4 through 8 were fed for 133 d.
Personnel from Texas Tech University (TTU) followed the cattle to the Excel Corp. slaughter facility to obtain carcass data. One steer from the control treatment was removed from the experiment as a result of urinary calculi; therefore, 119 steers were shipped to slaughter. Measurements included HCW, LM area, marbling score of the LM, percentage of KPH, 12th rib fat thickness at the ³/3 measure of the LM, and USDA yield and quality grades. Yield and quality grades were based on data obtained by TTU personnel rather than by USDA graders at the plant. Dressing percent was calculated from the average HCW of the pen divided by the average final BW of the pen.
Data for BW, DMI, ADG, G:F, HCW, carcass-adjusted variables (calculated as HCW divided by average dressing percent of all pens in the study), and nondiscrete carcass characteristics were analyzed as a randomized complete block design using the MIXED procedure of SAS (SAS Inst. Inc., Cary, NC). Nonparametric quality grade data were rank-transformed and analyzed using the Friedman test (Conover, 1999) by listing the percentage of USDA Choice and Select for each pen within a block and analyzing the percentages as normally distributed data. Pen was the experimental unit. The model statement included terms for treatment as a fixed effect and block as a random effect. Preplanned orthogonal contrasts were used to compare 1) CON vs. the average of WCS and EQU treatments; and 2) WCS vs. EQU. Statistical significance was declared at P 0.10.
Animal performance data also were used to estimate the ME concentrations of the diets through the use of a quadratic equation derived from the NRC (1996). This procedure has been described in detail by Owens et al. (1997); however, one slight alteration was made to this procedure for calculations in the current study. Retained energy (RE) was calculated according to the NRC (1996) using the equation: RE = 0.0635 x EQEBW0.75 x EBG1.097, where EQEBW is equivalent empty BW in kilograms, and EBG is empty body gain in kilograms. The final shrunk BW used to calculate equivalent shrunk BW was the average final shrunk BW of all pens in the experiment. Once the dietary energy concentrations were calculated, an estimation of the ME content of a specific ingredient could be calculated by subtracting the formulation-based energetic content of the diet (less the ingredient to be calculated) from the performance-based ME of the diet. This value was then divided by the DM concentration of the test ingredient to estimate the ME of the specific ingredient.
Experiment 2
One hundred fifty crossbred steers (primarily British x Continental) were selected from a larger group of cattle that were received at the Texas Tech University Burnett Center on October 23 (n = 343) and 25 (n = 79), 2003. All cattle were processed on arrival in the same manner as those in Exp. 1, with the exception of metaphylaxis with Micotil. Over the course of the next 4 wk, steers were housed in concrete, partially slotted-floor pens and gradually adapted to a greater concentrate level until they were receiving a conventional 90% concentrate finishing diet.
All 422 steers were weighed individually on October 30 and 31 to obtain a BW to be used for sorting. The 200 heaviest steers were used for another experiment, and the 222 remaining steers were used as the base to obtain the cattle for the current study. From this base, 150 animals with the most uniform BW were selected (initial BW = 364 ± 9.9 kg). Selected steers were stratified by BW into blocks consisting of 15 animals per block. Steers were assigned to pens in the same manner as in Exp. 1. On November 25, cattle were weighed individually and moved to their assigned concrete, partially slotted-floor pens (as described in Exp. 1), and the treatment diets were initiated.
Dietary treatments (Table 2) were: CON = conventional 90% concentrate, steam-flaked corn-based, finishing diet; WCS = whole cottonseed, the finishing diet with all of the cottonseed meal, added fat, roughage, and a portion of steam-flaked corn replaced with 15% whole cottonseed; and PCS = a finishing diet similar to the WCS, except that PCS (FuzZpellet, Buckeye Technologies, Memphis, TN) was used in place of whole cottonseed. The whole cottonseed and FuzZpellets used in this study were provided by Buckeye Technologies and were prepared from a single lot of whole cottonseed (shipped from North Carolina to the Burnett Center).
All diets were formulated to be isonitrogenous and to provide equal percentages of total fat and NDF from roughage (NDF from alfalfa and cottonseed hulls for CON, and NDF from whole cottonseed for WCS and PCS). Vitamins, minerals, Rumensin and Tylan (Elanco Animal Health; 33 and 11 mg/kg of DM, respectively) were provided by the same premix used in Exp. 1 (Table 3). The CON diet contained additional vitamin E to provide approximately 900 to 1,000 IU/steer daily, which was provided in the form of a ground corn-based premix (formulated at 0.25% of the dietary DM to supply an additional 93.6 IU/kg of DM).
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. Cattle were weighed individually on d 0, 56, and at the end of the study (d 154). On d 0, cattle were implanted with Revalor IS (Intervet) and reimplanted with Revalor S on d 56. Cattle were weighed on a pen basis using a platform scale on d 28, 84, 112, and 140. One steer was removed from the study as a result of low intake and evidence of blood in his feces; therefore, 149 steers were shipped approximately 60 km on d 154 to the Excel Corp. commercial slaughter facility in Plainview, TX. Personnel from Texas Tech University followed the cattle to the Excel Corp. slaughter facility to obtain carcass data as described for Exp. 1. Because of an error in the plant, 2 carcass tags were lost, and only 147 steers had complete carcass data.
An unusually high proportion (70%) of carcasses removed from the primary fabrication line for inspection and possible trimming of questionable areas was in the PCS treatment. These carcasses had bruises or other anomalies not related to treatment, that required extensive trim, and the quantity of trim could not be estimated. Therefore, the HCW and any carcass-adjusted measurements would have been affected (decreased), so the decision was made to eliminate all carcasses removed from the primary fabrication line (regardless of treatment) from the pen average calculations of HCW, dressing percent, and carcass-adjusted measurements for all treatments in the study.
Pen performance and carcass data were analyzed as described for Exp. 1. Preplanned orthogonal contrasts were used to compare: 1) CON vs. the average of WCS and PCS treatments; and 2) WCS vs. PCS. As in Exp. 1, animal performance data were used to estimate dietary ME concentrations.
Experiment 3
One hundred fifty crossbred yearling heifers (318 ± 11.8 kg of initial BW) were delivered to the Willard Sparks Beef Cattle Research Center, Stillwater, OK, on May 15, 2002. On arrival (d –1), heifers were weighed individually and given a uniquely numbered ear tag, after which they were distributed to holding pens, where they were given ad libitum access to prairie hay and water. The next morning (d 0), heifers were vaccinated with IBR-PI3-BVD-BRSV (Bovi-Shield 4, Pfizer Animal Health, New York, NY), treated for control of external and internal parasites (Ivomec Plus, Merial Animal Health, Duluth, GA), had their horns tipped as needed, and were implanted with Synovex-Plus (Fort Dodge Animal Health).
Individual BW measurements (unshrunk) taken on 2 consecutive days after arrival (d –1 and 0) were averaged to determine initial BW. Heifers were stratified by initial BW into 6 blocks consisting of 25 animals per block. Within block, heifers were assigned randomly to 1 of 5 pens, after which each treatment was assigned randomly to a pen within each block. Pens (4.6 m x 12.8 m) were partially covered (sheet-metal shade covering the feed alley, bunk, and approximately 4 m of the pen), soil-surfaced, and contained 4.6 m of bunk space, with 1 fence-line, automatic water tank shared between 2 pens.
Dietary treatments (Table 4) were: CON = conventional 92.5% concentrate (DM basis), dry-rolled corn-based, finishing diet; DL15 = a finishing diet in which cottonseed hulls, supplemental fat, and a portion of cottonseed meal were replaced by a partially delinted cottonseed (DLCS) product (CottonFlo, Buckeye Technologies) at 15% of the dietary DM; DL25 = a finishing diet in which cottonseed hulls, supplemental fat, cottonseed meal, urea, and a portion of the corn were replaced by DLCS at 25% of the dietary DM; PCS15 = a finishing diet similar to DL15, except that PCS (FuzZpellet) replaced the DLCS; and PCS25 = a finishing diet similar to DL25, except that PCS replaced DLCS. All diets were formulated to meet or exceed the NRC (1996) nutrient requirements for growing and finishing cattle. Rumensin and Tylan (33 and 11 mg/kg of DM, respectively) were included in the diets. Heifers were gradually adapted to their final treatment diet by offering approximately 65, 75, and 85% concentrate diets for 7 d each.
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), CP concentration by combustion (Leco, NS2000, St. Joseph, MO), and concentration of NDF and ADF (Goering and Van Soest, 1970).
Two animals were selected randomly from each pen, and blood samples from the same 2 animals were taken on d 0, 28, 56, and 112 via jugular venipuncture for plasma gossypol analyses. The cottonseed products (PCS and DLCS) also were sampled on July 15 and 30, and October 2 for gossypol analyses. Sample preparation was as described by Velasquez-Pereira et al. (1998). Samples of plasma and cottonseed products were shipped on dry ice to the Texas A&M Agricultural Center at San Angelo, TX. High-performance liquid chromatographic procedures were used to determine concentrations of (+)- and (–)-gossypol isomers in plasma (Kim and Calhoun, 1995) and cottonseed products (Hron et al., 1999). Free and total gossypol concentrations in the cottonseed products also were determined by official methods (AOCS, 1985a,b).
After the 150-d feeding period, heifers were shipped approximately 335 km to Tyson Fresh Meats (Emporia, KS) for slaughter. Carcass data (same measurements as in Exp. 1 and 2) were collected by personnel from Oklahoma State University.
Pen performance and carcass data were analyzed in the same manner as in Exp. 1 and 2. For gossypol analyses, repeated measures were taken over days, and the model included fixed effects of treatment, days, and the 2-way interaction (Littell et al., 1998). The optimal covariance structure was determined to be autoregressive (AR1). Preplanned orthogonal contrasts were used to compare: 1) CON vs. the average of the DL15, DL25, PCS15, and PCS25 treatments; 2) the average of DL15 and DL25 vs. the average of PCS15 and PCS25; 3) DL15 vs. DL25; and 4) PCS15 vs. PCS25. As before, performance data were used to estimate dietary ME concentrations.
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RESULTS AND DISCUSSION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONIMPLICATIONSLITERATURE CITED |
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). Similarly, final BW was unaffected (P = 1.00) for the CON vs. WCS and EQU diets. The difference (P = 0.10) in final BW between steers fed WCS and EQU was most likely attributable to gut fill, as the contrast between the 2 treatments in carcass-adjusted final BW diminished in significance (P = 0.21). Carcass-adjusted final BW did not differ (P = 0.16) between steers fed the CON diet and the average of those fed the 2 cottonseed diets.
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0.09) feed than steers fed the EQU diet during every period in the study. Steers fed the cottonseed diets (WCS and EQU) consumed more (P 0.08) feed than steers fed the CON diet from d 0 to 56, 0 to 84, and 0 to end (8.50 vs. 8.11 kg/d). The increase in DMI by cattle fed the cottonseed diets compared with those fed the CON diet was likely a function of the NDF and energy concentrations of the diets, which are normally negatively correlated (diets with greater fiber concentrations tend to be less energetically dense). Krehbiel et al. (2006) reported a linear decrease in DMI as a percentage of BW as the energy density of the diet increased, with the model accounting for 63% of the variation in DMI as a percentage of BW.
Because each diet contained an equal percentage of alfalfa hay and cottonseed hulls, the WCS and EQU diets contained a greater percentage of fiber than the CON diet. The NDF content of the WCS diet was determined to be more than 12% greater than the NDF content of the CON diet, whereas the NDF content of the EQU diet was nearly 9% greater than that of the CON diet. This intake response to NDF has been noted in previous studies (Galyean and Defoor, 2003). Defoor et al. (2002) reported increased DMI by finishing beef heifers as the NDF content of the diet increased. Utley and McCormick (1980) observed an increase in DMI by steers fed a pelleted bermudagrass supplement (9.60% dietary crude fiber) compared with a urea-cottonseed meal–(2.49% dietary crude fiber) or whole cottonseed–(4.87% crude fiber) supplemented diet. Moreover, Bartle et al. (1994) reported that steers linearly increased intake as the roughage level of the diet increased. Galyean and Defoor (2003) suggested that energy dilution of the diet might cause greater feed intakes in cattle fed high-concentrate diets when diets with large differences in NDF content (greater than 5%) are compared. Cattle may compensate, or sometimes overcompensate, by consuming more feed to reach the same energy level when intake does not become limited by fill (Galyean and Defoor, 2003).
Although the WCS and EQU diets were formulated to contain the same proportion of NDF, laboratory analysis indicated the WCS contained approximately 3.5% more dietary NDF than the EQU diet. This difference could be one possible reason steers fed the WCS diet consumed more feed than those fed the EQU diet throughout the experiment; however, as suggested by Galyean and Defoor (2003), the dietary difference in NDF was most likely not great enough to be attributed to energy dilution factors. Another possible explanation for the greater intakes by steers fed the WCS diet compared with those fed the EQU diet is that some of the fat from the WCS diet was protected within the seed coat, limiting its biohydrogenation via ruminal microbes (Baldwin and Allison, 1983). It may then be reasonable to assume that the EQU diets resulted in more free unsaturated fat within the rumen. Unsaturated fatty acids can inhibit ruminal microbes, particularly the cellulolytic organisms, resulting in decreased fiber digestion (Jenkins, 1993; Pantoja et al., 1994). If the fiber portion of the diet was less digestible, it could have been retained within the rumen for a longer period of time, slowing ruminal passage rate and limiting intake. This conclusion may be supported by the findings of Moore et al. (1986), who evaluated different sources of supplemental fat with a high-fiber basal diet (61.8 to 68.9% wheat straw). Ruminal DM digestibility was greater (P < 0.05) for a diet containing whole cottonseed than the ruminal DM digestibilities of diets containing cottonseed oil or animal fat. In contrast, Zinn and Plascencia (1992) showed no statistical difference in ruminal ADF digestibility between a diet containing 5% yellow grease and a diet containing 20% whole cottonseed; however, yellow grease is a more highly saturated fat than the lipids in oil seeds. Brandt and Anderson (1990) reported numerically greater DMI by steers fed a diet containing yellow grease than those fed a diet containing soybean oil.
The ruminal dispersion characteristics of cottonseed hulls might have compounded the effects of fat within the rumen. Cottonseed hulls have been reported to mix with ruminal contents rather than forming a fibrous mat within the rumen (Church, 1988; Moore et al., 1990); this may have limited rumination and thereby particle size reduction of the cottonseed hulls. In contrast, Coppock et al. (1985) concluded that linted whole cottonseed stratified within the rumen and contributed to the fibrous mat.
Neither ADG (P = 0.95) nor carcass-adjusted ADG differed (P = 0.17) between steers fed the CON and cottonseed diets throughout the study. Although steers fed WCS gained BW more rapidly (P 0.05) than those fed EQU from d 0 to 28, 0 to 56, and 0 to 84, the effect dissipated and was not significant (P 0.26) for the entire feeding period or when expressed on a carcass-adjusted basis. Because of the differences in fiber among the diets, period differences in ADG may have been influenced by differences in gut fill and should be viewed with caution.
Due to similar ADG and decreased DMI, steers fed the CON diet had greater (P 0.09) G:F throughout the study than those fed the WCS or EQU diets (0.193 vs. 0.185 from d 0 to end; 0.200 vs. 0.181 on a carcass-adjusted basis). The greater G:F by steers fed the CON diet compared with those fed the cottonseed diets is most likely attributable to the greater energy content of the CON diet compared with the average of the cottonseed diets (3.14 vs. 3.05 Mcal/kg of ME, respectively). This difference also was detected when dietary energy content was calculated using performance measurements, as the CON diet had greater (P < 0.01) dietary ME than the average of the cottonseed diets (3.50 Mcal/kg vs. 3.20 Mcal/kg of ME, respectively). The calculated energetic content of the CON diet based on animal performance was 0.36 Mcal/kg greater than the energetic content based on diet formulation. In a review of grain processing methods, Owens et al. (1997) calculated the ME of steam-flaked corn to be 3.71 Mcal/kg rather than the 3.36 Mcal/kg listed in the NRC (1996). Using the value reported by Owens et al. (1997) for steam-flaked corn, the energetic content of CON based on diet formulation becomes 3.41 Mcal/kg, which more closely agrees with the animal performance values calculated in the current study. Gain efficiency did not differ (P 0.12) between steers fed the WCS and EQU diets throughout the study. It is interesting to note that based on diet formulation, the WCS diet was more energetically dense than the EQU diet (3.10 vs. 3.00 Mcal/kg of ME). Based on animal performance, however, the EQU diet was numerically (P = 0.39) more energetically dense than the WCS diet (3.23 vs. 3.17 Mcal/kg of ME). This result suggests that the whole cottonseed used in the current study was not as energetically dense as the value reported in the NRC (1996).
Solving for the ME content of cottonseed ingredients, the whole cottonseed in the WCS diet was calculated to be 3.90 Mcal/kg, and the ME concentration of the cottonseed components were calculated to be 4.67 Mcal/kg. Nonetheless, using the value of 3.71 Mcal/kg for steam-flaked corn provided by Owens et al. (1997), the energetic content of whole cottonseed was calculated to be 2.33 Mcal/kg of ME, and the energetic content of the cottonseed components was calculated to be 2.82 Mcal/kg of ME. This estimation of ME content of whole cottonseed is 1.20 Mcal/kg less than the value given for whole cottonseed in the NRC (1996). The calculated value for the cottonseed components (3.53% cottonseed meal, 2.32% cottonseed oil, and 6.69% cottonseed hulls; percent included over the CON diet, DM basis) agreed with values reported in the NRC (1996).
Carcass Characteristics.
Neither HCW (P = 0.16 to 0.21) nor LM area (P = 0.47 to 0.50) was affected by treatment (Table 6); however, steers fed the CON diet had greater (P = 0.02) dressing percentages than those fed the cottonseed diets (63.02 vs. 61.81%). This result was most likely caused by the increase in gut fill by the cattle fed the WCS and EQU diets compared with those fed the CON diet. The WCS and EQU diets contained more fiber; therefore, cattle fed the WCS and EQU diets consumed more fiber, potentially causing an increase in ruminal volume and mass. Harvatine et al. (2002) reported a linear increase in the mass of ruminal DM with increasing concentrations of whole cottonseed in the diet.
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nor Huerta-Leidenz et al. (1991) reported differences in carcass fat measurements when diets with up to 30% whole cottonseed were fed.
Experiment 2
Performance.
Because all steers were fed for the same number of days, only measurements from the entire feeding period are shown in Table 7. Initial, final, and carcass-adjusted final BW were not affected (P = 0.54 to 0.89) by treatment; however, steers fed the CON diet consumed more (P = 0.04) feed than those fed the cottonseed diets (WCS and PCS) throughout the entire study (8.46 vs. 8.04 kg/d from d 0 to 154). Dry matter intakes by steers fed the WCS or PCS diet did not differ (P = 0.78) from d 0 to 154. In contrast to Exp. 1, the cottonseed product diets (WCS and PCS) in the current study were formulated to contain the same percentage of NDF from roughage (alfalfa hay, cottonseed hulls, whole cottonseed, and PCS) as the CON diet, which resulted in the CON diet being less energetically dense than the diets containing cottonseed products. The lower energy density of the CON diet likely played a role in the increased DMI by steers fed the CON diet compared with those fed the WCS or PCS diets, as discussed for Exp. 1.
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agrees more closely with that calculated by animal performance than the value reported by Owens et al. (1997). Using the value of 3.71 Mcal/kg of ME reported by Owens et al. (1997), the CON diet contained 3.41 Mcal/kg of ME, which is 0.26 Mcal/kg greater than the value estimated using performance data. Management and environmental factors could explain the difference between the 2 studies. For example, the cattle in Exp. 1 were limit-fed for approximately 4 mo before the study began, whereas the cattle in Exp. 2 were not. Seasonal effects also might have influenced the studies, as Exp. 1 was conducted from April to August, whereas Exp. 2 was conducted from November to April. Because both studies were conducted at the same location and the corn was processed in the same manner, it is unlikely that the energetic value of the steam-flaked corn differed as much as the environmental and management factors.
Performance-based estimates of ME content did not differ (P = 0.82) between the WCS and PCS diets (3.30 vs. 3.28 Mcal/kg, respectively). Using the previously described method of calculation with steam-flaked corn values from the NRC (1996), the ME content of whole cottonseed was calculated to be 3.84 Mcal/kg, whereas the ME content of the pelleted cottonseed product was calculated to be 3.72 Mcal/kg. When the calculations were performed using the 3.71 Mcal/kg of ME for steam-flaked corn reported by Owens et al. (1997), whole cottonseed was estimated to contain 2.09 Mcal/kg of ME, and the pelleted cottonseed product was calculated to contain 1.92 Mcal/kg of ME. Because the NRC (1996) estimate for the ME content of steam-flaked corn more closely matched the performance-based calculation of the CON diet, it is likely that the estimates of ME content for the cottonseed products are more accurate when calculated using the NRC (1996) value for steam-flaked corn in the current study. In fact, those estimates more closely agree with the ME value of 3.43 Mcal/kg reported in the NRC for whole cottonseed.
Carcass Characteristics.
No carcass characteristics were affected (P = 0.12 to 0.87) by treatment. The fact that dressing percentages and marbling scores did not differ between steers fed the CON diet and those fed the diets containing cottonseed products in Exp. 2 may clarify the possible role of dietary fiber or supplemental Vitamin E with respect to the reported differences in dressing percent and marbling score in Exp. 1.
Experiment 3
Performance.
As in Exp. 2, only measurements from the entire feeding period are reported in Table 8. Initial BW was not affected (P = 0.39 to 0.97) by treatment; however, heifers fed the PCS diets (PCS15 and PCS25) had greater final (P = 0.02; 555.4 vs. 539.9 kg) and carcass-adjusted final BW (P = 0.01; 558.0 vs. 536.5 kg) than heifers fed the DLCS diets (DL15 and DL25). Dry matter intake was not affected (P = 0.19 to 0.93) by treatment from d 0 to 150. In contrast to the results of Exp. 2, heifers fed the CON diet did not consume more feed than heifers fed the diets containing cottonseed products (DL15, DL25, PCS15, and PCS25), even though the CON diet was less dense energetically. This might be attributable to differences in dietary NDF content between the 2 studies. In Exp. 2, the CON diet had a greater amount of total dietary NDF than the cottonseed diets (16.28 vs. 13.08%, based on diet formulation), whereas in Exp. 3, the CON diet had less total dietary NDF than the cottonseed diets (17.76 vs. 18.95% for the analyzed values). Thus, in Exp. 2, steers fed the CON diet may have consumed more feed than those fed the diets containing cottonseed products not only because the CON diet was less energy-dense than the WCS and PCS diets, but also because the CON diet contained more NDF than the cottonseed diets. In Exp. 3, although the CON diet was less energy-dense, it contained slightly less dietary NDF than the cottonseed diets, possibly eliminating an increase in DMI by heifers on the CON diet compared with heifers fed diets containing the cottonseed products. The differences in corn processing and sex of the animals between the 2 studies also may have contributed to the dissimilar responses in feed intake.
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The cause of the improved ADG and G:F observed by heifers fed the PCS diets compared with those fed the DLCS diets may be related to the lint remaining in the product. Zinn (1995) reported that a diet containing 15% (DM basis) lint-free whole cottonseed resulted in a decrease in ruminal and total tract N digestibilities compared with a diet that contained 15% (DM basis) linted whole cottonseed. Zinn (1995) concluded that lint-free whole cottonseed must be ground to be of equal feeding value to linted whole cottonseed. Coppock et al. (1985) suggested that lint-free whole cottonseed might not stratify within the rumen, subsequently limiting regurgitation and remastication of the lint-free whole cottonseed and causing a decrease in the digestibility of the seed. In addition, the pelleting process may have improved ADG and G:F. Although pelleting roughage has been reported to increase rate of passage and decrease ruminal digestibility of the product (Minson, 1963), Osbourne et al. (1976) reported that pelleting roughages often decreases the heat increment of the product, which in turn increases the dietary NE of the pellet in relation to the unpelleted product. Because the cottonseed products differed in chemical composition (particularly with respect to the amount of lint), caution should be used when attributing any improvement in performance to the pelleting process, as this is merely speculation.
Performance-based calculation of the ME content of the diets did not differ (P = 0.90) between the CON diet and the average of the cottonseed diets (2.90 vs. 2.91 Mcal/kg, respectively). The greater ADG and G:F by heifers fed the PCS diets compared with those fed the DLCS diets is reflected in the performance-based dietary energy calculations. The PCS diets were calculated to be more (P = 0.08) energetically dense than the DLCS diets (2.96 vs. 2.87 Mcal/kg of ME, respectively). No differences were detected (P = 0.19 to 0.26) when comparing the energetic densities of PCS15 to PCS25 or DL15 to DL25, although it should be noted that both diets containing 25% of the cottonseed products were numerically less energetically dense than the diets containing 15% of the corresponding product (2.91 vs. 3.00 Mcal/kg of ME for PCS25 vs. PCS15; 2.83 vs. 2.91 Mcal/kg of ME for DL25 vs. DL15). This finding may suggest that the heifers were unable to metabolize the diets containing 25% cottonseed products with the same efficiency as heifers fed the diets containing 15% cottonseed products.
Based on diet formulation using ME values from the NRC (1996), the CON diet was calculated to contain 3.12 Mcal/kg of ME, which is 0.22 Mcal/kg greater than the performance-based value. Owens et al. (1997) reported an ME value of 3.21 Mcal/kg for rolled corn, which is slightly less than the 3.25 Mcal/kg reported in the NRC (1996). Using the ME content of 3.21 Mcal/kg for rolled corn, the ME content of the CON diet was calculated to be 3.09 Mcal/kg, which is still substantially greater than the value calculated from animal performance. The reasons for this are unclear, but an adjustment to account for the lower than expected performance is most likely required for the accurate estimation of the ME content of the cottonseed products. Using the NRC (1996) value for rolled corn, the PCS product was calculated to contain between 2.18 (PCS25) to 2.19 (PCS15) Mcal/kg of ME, whereas the DL product was calculated to contain between 1.55 (DL15) to 1.83 (DL25) Mcal/kg of ME. Using the value of 3.21 Mcal/kg of ME for rolled corn reported by Owens et al. (1997), the ME content of the PCS product was estimated to be from 2.30 (PCS25) to 2.40 (PCS15) Mcal/kg, and the DL product was estimated to contain 1.76 (DL15) to 1.94 (DL25) Mcal/kg of ME. The ME content of rolled corn was adjusted so that the total ME of the CON diet (based on diet formulation) matched the performance-based value, in which the ME value of rolled corn was estimated to be 2.97 Mcal/kg. Using this adjustment, the ME content of the PCS product was calculated to be from 2.97 (PCS25) to 3.65 (PCS15) Mcal/kg, whereas the ME content of the DL product was estimated to be from 2.61 (DL25) to 3.02 (DL15) Mcal/kg. The adjusted ME values of the PCS product more closely agree with those calculated in Exp. 2 than the unadjusted values.
Carcass Characteristics.
Heifers fed the PCS diets had greater HCW (P = 0.01; 348.6 vs. 335.2 kg), dressing percentages (P = 0.03; 62.76 vs. 62.08%), and LM areas (P = 0.02; 80.94 vs. 75.53 cm2) than heifers fed the DLCS diets (Table 8). Heifers fed the DL15 diet had a greater (P = 0.05) percentage of KPH fat, as well as a greater (P = 0.03) percentage of heifers grading USDA Choice than heifers fed the DL25 diet. No other carcass characteristics were affected (P = 0.12 to 1.00) by treatment.
Greater HCW of heifers fed the PCS diets was a function of the greater ADG and final BW compared with those fed the DLCS diets. The increase in dressing percent of heifers fed the PCS diets could be a result of the increased rate of passage of the PCS product resulting from the pelleting process, ultimately decreasing the ruminal fill of heifers fed the PCS diets compared with those fed the DLCS diets. The increased LM area of heifers fed the PCS diets was most likely a function of heavier HCW compared with heifers fed the DLCS diets, as no differences (P 0.25) were observed among treatments when LM area was expressed relative to HCW (data not shown). Heifers fed the DL15 diet were 12.8 kg heavier (final BW) than heifers fed the DL25 diet, which may have contributed to the greater KPH fat in heifers fed the DL15 diet compared with those fed the DL25 diet. The cause for the difference in the percentage of carcasses grading USDA Choice is unclear, but it may be worth noting that heifers fed the DL25 diet did not perform as well as heifers fed the DL15 throughout the finishing period, possibly affecting quality grade.
Gossypol Concentrations.
The concentration of gossypol in the cottonseed products used in the study is presented in Table 9. In addition, data from the plasma gossypol analyses are presented in Table 10 and Figure 1. Treatment x day interactions were significant (P < 0.01) for total, (+) isomer, and (–) isomer plasma concentrations. Averaged across treatments, total plasma gossypol concentrations increased (P < 0.01) from d 0 to 28 (0.82 to 4.08 µg/mL), decreased numerically (P = 0.59) from d 28 to 56 (4.08 to 3.93 µg/mL), and then increased (P < 0.01) from d 56 to 112 (3.93 to 4.69 µg/mL). Total plasma gossypol concentrations of heifers fed the DL15, DL25, and PCS25 diets followed this general trend; however, heifers fed the CON diet reached a peak in plasma gossypol concentrations on d 28 and exhibited decreased concentrations on d 56 and 112. Total plasma gossypol of heifers fed the PCS15 diet increased with increasing time on feed. The decrease in plasma gossypol concentrations (after d 28 for heifers fed CON, and from d 28 to 56 for heifers fed DL15, DL25, and PCS25) may indicate that these heifers were able to detoxify the compound more rapidly once adapted to the gossypol concentrations of the diets. It is unclear why heifers fed the PCS15 diet did not follow a similar trend in plasma gossypol concentration, but is likely of little significance because heifers fed the PCS15 diet had the lowest plasma gossypol concentrations of cattle fed the cottonseed diets (PCS15, PCS25, DL15, and DL25). The treatment x day interaction was not significant (P = 0.70) for the percentage of each isomer in the total plasma gossypol concentration.
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Because no significant differences were observed in any performance or carcass measurements between heifers fed the CON diet and the average of heifers fed the diets containing cottonseed products, it seems that the concentrations of gossypol in the cottonseed products and the plasma of heifers fed those products were safe for finishing cattle. This finding agrees with that of Calhoun and Holmberg (1991), who reviewed scientific literature and noted that diets with up to 25% of the dietary DM as whole cottonseed did not produce any noticeable toxicity in finishing cattle. However, plasma gossypol levels of heifers fed the DL15 and DL25 diets exceeded the safe upper limit of 5 µg/mL proposed by Calhoun et al. (1995). This result could be another factor in the decreased ADG and G:F of heifers fed the DLCS diets compared with heifers fed the PCS diets. We consider this unlikely, however, because DMI was not affected and no behavioral abnormalities were reported.
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2 Corresponding author: jakecranston{at}hotmail.com
Received for publication November 17, 2005. Accepted for publication March 10, 2006.
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