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ANIMAL PRODUCTION |
Department of Animal Sciences, University of Kentucky, Lexington 40546-0215
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResults and DiscussionLiterature Cited |
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Key Words: Alfalfa • Ewe • Fat • Fescue • Lactation • Lamb
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionLiterature Cited |
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). Few studies have investigated the feasibility of supplementing fat to meat-type ruminants during lactation, whereas the dairy cattle industry routinely adds fat to promote milk production. Increased milk yields in dairy animals have been related to increased energy availability when supplemental dietary fat is directly incorporated into milk fat (Palmquist et al., 1993). Ruminally inert fats have been developed to avoid the decline in dietary fiber digestion previously associated with fat supplementation (Jenkins and Jenny, 1989; Sklan et al., 1990). This provides the potential to offset the expense of adding fat to lactation diets by feeding high-fiber, less-costly forages; milk production is not decreased as a result of the increase in dietary nutrient density (Davis, 1993).
Hernandez et al. (1986) and Casals et al. (1999) reported that 4-wk lamb weights were increased when supplying fat to ewes consuming high-forage diets. Increased milk yields and milk fat content were found in ewes fed rumen-inert fat (Alba et al., 1997; Casals et al., 1999). Although milk yield and milk fat and protein contents have been related to preweaning lamb performance (Torres-Hernandez and Hohenboken, 1980; Hernandez et al., 1986; Lynch et al., 1991), increasing the long-chain components of milk fat through dietary fat supplementation may increase lamb use of milk energy to improve nursing offspring growth (Palmquist et al., 1993; Casals et al., 1999). The objective of this research was to evaluate the nutrient digestion, milk production and composition, and potential lamb production of meat-type ewes when an endophyte-free, fescue hay-based diet was supplemented with the calcium salts of palm oil fatty acids or hydrogenated tallow.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionLiterature Cited |
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). A total mixed diet consisting (as-fed basis) of 52% concentrate:48% alfalfa hay (alfalfa; n = 4) was formulated as fed in a previous experiment (Appeddu et al., 1995) and served as a positive control. Endophyte-free fescue hay (‘Kenhy’) replaced alfalfa hay to form the second treatment (fescue; n = 4). The third treatment (fescue + fatty acids; n = 4) consisted of the fescue diet supplemented with 3.7% calcium salts of palm oil fatty acids (Megalac; Church and Dwight Co., Inc., Princeton, NJ). An alfalfa-based diet with added fat was not included in this experiment because Appeddu et al. (1995) reported no differences in ewe milk measures or lamb growth between alfalfa-based diets with and without fat.
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). The proportions of soybean meal and corn were altered in fescue-based diets to compensate for the lower protein content analyzed (see later text for methods) for fescue (11% CP) vs. alfalfa hay (15% CP). The fescue + fatty acids diet was formulated to be more nutrient dense than the other diets, so a lower amount of the fat-supplemented diet could be offered. Hays were coarsely chopped to a 2- to 4-cm length before mixing diets.
Before lambing, ewes were group-fed twice daily at a rate of 0.7 kg of alfalfa hay and 0.46 kg of corn/animal. Following parturition, each ewe and her lambs were individually penned (1.2 m x 8 m) in an open-sided barn. Minimum amounts of straw were used as bedding on a dirt floor, and a concrete slab provided an outdoor run. Each ewe received 1.8 kg of alfalfa hay and 0.7 kg of shelled corn (as-fed basis) from d 0 to 4 of lactation, and then each was adjusted to dietary treatments from d 4 to 9 of lactation. Ewes were allotted to dietary treatments randomly as they lambed, and only ewes nursing twin lambs were included. Diet amounts were based on individual initial ewe BW taken on d 4 of lactation and were fed to meet the nutritional requirements of ewes nursing twin lambs (NRC, 1985). Daily rations remained constant from d 9 to 56 after lambing. Total mixed diets were offered in equal amounts at 0800 and 1600. Lambs were not offered creep feed and were separated from ewes for 60 min at each feeding. This was done to evaluate ewe milk traits and lamb performance solely as a function of ewe diet. Any feed remaining was removed before lambs were returned. All animals were treated according to the animal care and use guidelines of the University of Kentucky.
Experiment 2.
Seventeen fall-lambing, Polypay ewes (3 to 5 yr of age) nursing twin lambs were randomly allotted to one of three dietary treatments (Table 1
). The control diet was a 52% concentrate:48% fescue-based diet (fescue; n = 6) comparable to that fed in Exp. 1. The second diet (fescue + fatty acids; n = 5) was formulated in a manner similar to the fescue + fatty acids diet used in Exp. 1. The third treatment contained 3.1% hydrogenated tallow (Rumical; Griffin Industries, Inc., Cold Spring, KY) mixed into the concentrate portion of the fescue diet (fescue + tallow; n = 6). As was done in Exp. 1, diets were formulated to supply ewe nutrient requirements at equal protein, energy, and Ca intakes. A lower percentage of tallow was used due to the higher fat content (minimum 98%), according to the manufacturer’s label, compared with fatty acids (minimum 83.5% fat).
To increase time on experimental diets, gestating ewes were randomly divided into three pens at an estimated 2 wk before the start of lambing. Pregnant ewes were group-fed one of three diets containing 40% concentrate:60% endophyte-free fescue hay with no fat, 3.9% fatty acids, or 3.4% tallow (as-fed basis). The concentrate portion of the gestation diets also contained corn (28.6, 24.2, or 22.3%), soybean meal (3.0, 4.3, or 5.2%), and vitamin A, D, E mix (0.2, 0.2, or 0.2%) for treatments with no fat, fatty acids, or tallow, respectively. Diets were fed at 2.90, 2.75, and 2.75% of an average 80-kg BW for ewes consuming diets with no fat, fatty acids, or tallow, respectively, and met the nutrient requirements of ewes in late gestation (NRC, 1985). Two days after lambing, each ewe with twin lambs was moved to an individual pen and remained on the same prelambing diet until d 4 of lactation. Thereafter, daily rations consisted of feeding lactation diets (Table 1) based on the same prelambing treatment (no supplemental fat, fatty acids, or tallow) and individual ewe BW taken on d 2 of lactation. Diets were fed to meet the nutrient requirements for lactating ewes nursing twin lambs (NRC, 1985). Feeding procedures were the same as described in Exp. 1, and dietary treatments continued through d 59 after lambing.
Measurements
In both experiments, representative samples of lactating ewe diets were collected daily, composited on a weekly basis, dried in a forced-air oven (50°C), and ground to pass a 1-mm screen in a Wiley mill (Thomas-Wiley model 4, Thomas Scientific, Philadelphia, PA). Diets were analyzed for DM, ash (AOAC, 1990), NDF, ADF (Goering and Van Soest, 1970), and fat (acid hydrolysis method; AOAC, 1990). Lignin was determined (Goering and Van Soest, 1970) in diets from Exp. 1 only. Crude protein was determined using a macro nitrogen analyzer (Foss Heraeus Analysensyteme GmbH, Hanau, Germany) that automated the Dumas procedure (AOAC, 1990). Gross energy was analyzed using the isoperibol operation on a Parr bomb calorimeter (Parr Instrumentation Co., Moline, IL). Orts were collected after each feeding, dried (50°C), and weighed for calculation of ewe OMI.
Apparent nutrient digestibilities were determined using chromic oxide. A mixture (as-fed basis) of 88% ground corn, 7% Cr2O3, and 5% corn oil was top-dressed at each feeding to supply Cr2O3 at 0.35% of the diet from d 26 to 35 and d 35 to 44 of lactation in Exp. 1 and 2, respectively. Fecal grab samples were collected at 0600, 1200, 1800, and 2400; 0400, 0800, 1400, and 2000; and 0200, 1000, 1600, and 2200 over the last 3 d of the marker feeding periods. Fecal samples were dried in a forced air oven (50°C) and ground through a 1-mm Wiley mill screen. Orts and fecal samples were composited by dry weight for each ewe over the collection period and analyzed for nutrients as described for diet samples. Diets, orts, feces, and the chromic oxide mixture were prepared for chromium determination using a wet ash procedure (Williams et al., 1962), and were analyzed via atomic absorption with a nitrous oxide/acetylene flame. Fecal output and digestibilities of OM, CP, NDF, ADF, and GE were calculated using the equations of Van Soest (1994).
Ewe milk production was determined at 7-d intervals from d 14 to 56 and d 8 to 57 of lactation in Exp. 1 and 2, respectively. Following the morning feeding, each ewe received an i.v. injection of oxytocin (40 IU) and was machine-milked. After a 3-h separation period from lambs, ewes received a second oxytocin injection and were milked. The second milking was weighed and multiplied by eight to estimate 24-h milk production. A subsample was preserved with bronopol and shipped to Milk Marketing, Inc. (Strongsville, OH) for determination of fat, protein, and lactose (Exp. 1) or fat and protein (Exp. 2) by infrared analysis (AOAC, 1990). Total milk solids (milk DM%) were determined by the Majonnier method (AOAC, 1990).
The fat composition of ewe diet and milk samples was analyzed by direct transesterification of the fat component into fatty acid methyl esters (Lepage and Roy, 1986). Milk fat composition was determined in weekly milk samples in Exp.1, and on d 8, 36, and 57 in Exp. 2. Hexane fractions were harvested and analyzed by gas chromatography using a temperature-programmed, carbowax fused, silicia capillary column (Perkin Elmer; Norwalk, CT). Fat peaks were identified using the retention times of a reference standard ranging from 14:0 to 18:3 (carbon chain length:number of unsaturated bonds).
Ewes and lambs were weighed at the start of treatments and weekly until weaning on d 56 (Exp. 1) and d 59 (Exp. 2). Ewe BCS was evaluated by visual and handling appraisal on a scale of 0 (emaciated) to 5 (obese). Twin lamb weights were expressed as kilograms of lamb produced per ewe. Final lamb weights were adjusted to 60 d and for sex, birth weight, birth type, and ewe age (SID, 1988). Changes during lactation were determined for ewe weight and BCS, and twin lamb gain. Efficiencies per ewe OMI and ewe fat intake were determined for ewe weight change, milk production, milk fat yield, and lamb gain.
Statistical Analyses
Data were analyzed using PROC MIXED of SAS (SAS Inst., Inc., Cary, NC) using a completely randomized design. Data collected over lactation were analyzed using a repeated measures model, which included dietary treatment, lactation day, and treatment x lactation day. Ewe was considered to be a random effect. Twin lamb data were evaluated as a function of the ewe. When a significant treatment effect was observed (P < 0.05), differences among treatment means were separated using pairwise t-tests. When treatment x lactation day was significant (P < 0.05), treatment comparisons were made by lactation day. Data collected only once (digestibilities, 60-d adjusted weaning weights, overall changes, and production efficiencies) were analyzed using a one-way ANOVA.
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Results and Discussion |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionLiterature Cited |
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) in the fescue + fatty acids diet (Exp. 1) and fescue + fatty acids and fescue + tallow diets (Exp. 2). Crude protein content was similar between the alfalfa diet and fescue diet in Exp. 1, whereas it was lower in the fescue diet in Exp. 2 vs. 1. Because diets were formulated similarly for both experiments, this difference in dietary CP may be attributed to fluctuations in the nutrient composition of dietary ingredients. As planned, protein content was higher in diets with supplemental fat in both experiments. In contrast, measured GE content was not higher in diets with fatty acids or tallow compared with diets without added fat. Calculated GE values of diets supplemented with fat were higher than measured values, ranging from 4.6 to 4.7 Mcal/kg diet OM (NRC, 1996). This discrepancy in calculated vs. actual GE content may be due to the assay not detecting the total heat of combustion in diets with added fat. Other researchers have reported similar difficulties in determining higher GE values in ruminant diets supplemented with fat (Sklan et al., 1990; Alba et al., 1997). The results of Andrew et al. (1990) further suggest that the energy values of diets supplemented with fat may be more accurately expressed on a metabolizable or net energy basis.
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Hay type did not change dietary fat composition. In both experiments, the fescue + fatty acids diet had higher percentages of 16:0 and 18:1, similar 18:0, and lower 18:2 and 18:3 (Exp. 1) than the fescue diet. Replacing fatty acids with tallow in Exp. 2 increased the proportion of 18:0 and decreased 18:1 and 18:2. Proportion of 16:0 was similar between the fescue and fescue + tallow diets. The 14:0 fatty acids were either undetectable or detected only in small percentages.
Ewe Intake and Digestibility
As planned, ewes allotted to diets supplemented with fatty acids or hydrogenated tallow were offered, and therefore consumed, less (P < 0.05) OM than those fed alfalfa or fescue diets without added fat (Table 3). Diet amounts offered in Exp. 2 were initially similar to Exp. 1, but were reduced within 10 d after lambing when large amounts of orts were recovered across all treatments. As a result, the average amount of OM consumed in Exp. 2 was 18.5% less than in Exp. 1. Although not determined, factors such as weather conditions, inherent differences among ewes, and metabolic adjustments caused by feeding experimental diets before parturition could have contributed to lower intakes in Exp. 2.
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), results suggest differences in cellular locations or the organic structures of lipids may have caused digestibility differences (Van Soest, 1994). In Exp. 2, fat digestibility was higher (P < 0.01) in ewes fed the fescue + fatty acids diet than when the fescue diet was fed (Table 3). The lowest fat digestibility (P < 0.01) was found in ewes consuming the fescue + tallow diet. Differences in fat digestibilities between diets supplemented with fat may be attributed to differences in their fat composition (Table 2). Researchers have reported 16:0 and 18:1, as primarily found in the fescue + fatty acids diet, to have higher digestibility coefficients than 18:0, which was predominant in the fescue + tallow diet (Wu et al., 1991; Weisbjerg et al., 1992; Børsting et al., 1992). The lower fat digestibility of the fescue + tallow diet contributed to it having a lower total OM digestibility (P < 0.01) than the fescue diet (Table 3).
Ewe protein intakes were similar within experiment. The higher (P < 0.05) protein digestibility of diets with supplemental fat in both experiments may be attributed to the higher level of soybean meal used in these diets (Table 1) as a nitrogen source. Lower (P < 0.01) NDF and ADF intakes in ewes fed the alfalfa vs. fescue diet (Table 3) resulted from differences in fiber contents of the hays (Table 2). Decreased (P < 0.01) fiber intakes in ewes fed fat-supplemented diets were due to offering lower total amounts of these diets (Table 3). However, NDF and ADF digestibilities were lower (P < 0.05) when feeding the alfalfa diet than with the fescue or the fescue + fatty acids diet in Exp. 1. In support of this finding, Hoffman et al. (1993) reported fiber digestibility of legumes to occur at a faster rate, but to a lesser extent, than grasses.
Supplementing with fatty acids and tallow decreased (P < 0.05) NDF and ADF digestibilities of these diets in Exp. 2. A similar trend was observed when comparing the NDF digestibility of the fescue + fatty acids diet with the fescue diet in Exp. 1. In contrast, Ohajuruka et al. (1991) did not find lower OM or fiber digestibilities in dairy cows supplemented with either the calcium salts of fatty acids or an animal/vegetable fat blend in a 60:40 forage:concentrate diet. Because the fatty acids and tallow sources used in Exp. 1 and 2 were manufactured to be ruminally inert, the decreased NDF digestibility in diets with added fat was more likely caused by a nutrient deficiency or a nutrient imbalance in the rumen. In support of this, a lower proportion of corn was formulated in diets with supplemental fat (Table 1), which would reduce the amount of ruminally available energy (Palmquist et al., 1993). Ruminally available nutrients were decreased further by feeding smaller amounts of diets with supplemental fat, especially in Exp. 2 (Table 3). Unchanged fiber digestibilities reported in other experiments (Ohajuruka et al., 1991; Palmquist et al., 1993) may have been due to offering fat-supplemented diets to dairy cows at equal rates or free choice as compared with diets without supplemental fat, thus preventing a significant decrease of ruminally available nutrients.
Ewes fed the fescue + fatty acids diet had the lowest (P < 0.05) GE intake in Exp. 1, whereas supplemental fat tended to increase ewe GE intake in Exp. 2. Diets with added fat had numerically higher GE digestibilities in Exp. 2, causing the fescue + fatty acids and fescue + tallow diets to have higher (P < 0.05) DE contents than the fescue diet. A similar trend was observed in Exp. 1. Expression of energy content on a DE basis was more in line with the expected increase in available energy resulting from fat supplementation. Ewe nutrient intakes in Exp. 1 met daily protein (435 g CP) and energy (8.6 Mcal DE) requirements for 80-kg ewes nursing twins in the first 6 to 8 wk of lactation (NRC, 1985). While protein and digestible energy intakes were similar across treatments in Exp. 2 (Table 3), lower dietary intakes caused CP and DE to be 14 and 27% below lactating ewe requirements.
Milk Production and Composition
Daily milk production in Exp. 1 declined (P < 0.001) as lactation progressed, but yields were not changed by hay source or fatty acid supplementation (Table 4). In Exp. 2, an interaction (P = 0.03) between dietary treatment and milk yields over lactation was detected (Figure 1). Ewes fed fescue + tallow tended (P < 0.06) to have lower milk yields than those fed the fescue + fatty acids diet on d 29 (2.15 vs. 2.54 kg/24 h; Figure 1). On d 43, ewes supplemented with tallow produced less (P < 0.07) milk than those fed the fescue diet (1.90 vs. 2.29 kg/24 h). Overall, ewes fed the fescue + tallow diet numerically produced the least amount of milk (Table 4). This may have resulted from the lower digestibility of the fescue + tallow diet decreasing available nutrients below the level needed to maintain milk production similar to other diets.
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), feeding fescue + fatty acids to meet ewe nutrient requirements did not increase milk production above the alfalfa or fescue diet. Appeddu et al. (1995) also reported no increase in the milk yields of meat-type ewes when supplementing an alfalfa hay-based diet with fatty acids. Casals et al. (1999) detected no differences in milk production between fat-supplemented and unsupplemented grazing dairy ewes; however, these researchers did not measure total nutrient intakes. In contrast, Alba et al. (1997) found a tendency for increased milk production after 35 d of lactation when dairy ewes were supplemented with fatty acids to achieve higher energy intakes. The results of these and other experiments suggest that the ability of dietary fat to increase milk production may depend on the genetic potential of the ewe to increase production (Scott et al., 1995) as it consumes more dietary nutrients (Schauff and Clark, 1992; Schauff et al., 1992b; Teh et al., 1994). The observation that ewe milk production was numerically similar between Exp. 1 and 2, with a lower amount of feed consumed per day in Exp. 2, further suggests ewe lactation potential may have been reached (Table 3).
The percentage of milk fat was higher (P < 0.01), but lactose content was lower (P < 0.05), in milk produced by ewes fed the fescue + fatty acids diet than those fed the fescue diet in Exp. 1 (Table 4). In Exp. 2, dietary treatment affected milk protein content by the end of lactation (interaction; P < 0.01). Ewes fed fescue + fatty acids produced milk with a lower protein content than those fed the fescue diet on d 50 (4.6 vs. 5.4%; P < 0.01) and 56 (5.0 vs. 5.8%; P < 0.01). Although milk component yields were similar across treatments in Exp. 1, ewes fed the fescue + fatty acids diet produced more milk fat (P < 0.05) than those fed fescue + tallow in Exp. 2.
An increase in milk fat content or yield is commonly observed during fat supplementation of dairy cows (Grummer, 1991; Palmquist et al., 1993) and dairy ewes (Alba et al., 1997; Casals et al., 1999). Appeddu et al. (1995) reported a tendency for milk fat content to be higher in meat-type ewes by the end of lactation, although fat supplementation was not started until d 19 after lambing. Supplemental fat also has been shown to decrease percentages of milk protein and lactose in dairy cows (Coppock and Wilks, 1991; DePeters and Cant, 1992) and ewes (Appeddu et al., 1995; Alba et al., 1997). Similar to the results of Exp. 2, Casals et al. (1999) reported milk protein content decreased as lactation progressed in fat-supplemented ewes. Whereas other researchers (Appeddu et al., 1995; Alba et al., 1997; Casals et al., 1999) have reported declines in milk protein and lactose yields, no changes in the production of these components were detected when fat was supplemented in either Exp. 1 or 2.
Milk Fat Composition
Supplementing with fatty acids decreased (P < 0.01) the proportion of milk fat 14:0 in both experiments (Table 4). Other researchers have reported lowered percentages of 14 carbon and shorter chain lengths in the milk fat of dairy cows supplemented with fat (Grummer, 1991; Schauff and Clark, 1992; Alba et al., 1997). This decrease may be attributed to an increased incorporation of preformed, longer-chain fats (
16 carbon) into milk fat, which has been shown to inhibit the acetyl-CoA carboxylase pathway and thus prevent the elongation of shorter-chain fats during de novo milk fat synthesis (Grummer, 1991; Palmquist et al., 1993). Proportion of 14:0 did not decrease in the milk of ewes fed fescue + tallow in Exp. 2, suggesting smaller amounts of long-chain fats were supplied to the mammary gland by this treatment than with the fescue + fatty acids diet.
Although the proportion of milk fat 16:0 was not changed in Exp. 1, the highest percentage of 16:0 (P < 0.05) was found in the milk of ewes fed fescue + fatty acids in Exp. 2. Fatty acid 16:0 may either be synthesized by the mammary gland or incorporated directly into milk fat (Grummer, 1991; Palmquist et al., 1993). Therefore, a maintenance or increase in this fatty acid suggests a sufficient level of 16:0 was supplied by the fescue + fatty acids diet (Table 2) to offset the depressed synthesis of 16:0 often observed when feeding other fat sources (Grummer, 1991). The finding that the fescue + tallow diet did not change milk 16:0 (Table 4) again suggests that this diet did not supply enough fat to the mammary gland to alter milk fat composition.
Although 18:0, 18:1, 18:2, and 18:3 comprised over 40% of the fat composition of ewe diets (Table 2), no treatment differences were detected in their proportions in ewe milk fat (Table 4). Other researchers have found increased percentages of 18.0 and 18:1 when feeding fat (Schauff et al., 1992a; Alba et al., 1997). Although the 18-carbon-chain-length fatty acids in milk fat arise primarily from preformed sources (Grummer, 1991; Palmquist et al., 1993), restricting intakes to meet ewe nutrient requirements may have prevented more significant changes in milk fat composition in Exp. 1 and 2. On average, ewes in Exp. 2 produced milk fat with lower percentages of 18:0, but higher 18:1, than in Exp. 1. Although lower ewe nutrient intakes in Exp. 2 may have contributed to this difference (Garnsworthy and Huggett, 1992), it was not possible to differentiate between body and dietary contributions to milk fat in these experiments.
Ewe and Lamb Measures
Because animal numbers were limited due to experimental restrictions of ewes to lamb in the fall and to bear twin lambs, only preliminary effects of feeding fat on weight changes and production efficiencies are discussed. Ewe weights and BCS are shown in Table 5. In Exp. 1, ewes fed fescue + fatty acids lost the most weight (P < 0.05), but no differences were detected for changes in body condition. Losses in ewe weight and body condition were similar across treatments in Exp. 2. Differences between experiments agree with the review by Chilliard (1993), who reported inconsistent changes in body reserves when supplemental fat was fed to dairy cows. This author concluded that changes in BW and condition during fat supplementation depend on the extent of the increase and improved energetic efficiency of milk production while milk fat de novo synthesis is decreased. Another influencing factor may have been the difference in initial ewe BCS, which was lower in Exp. 1. Although milk production was not changed, ewes supplemented with fatty acids in Exp. 1 were least efficient (P < 0.05) in using dietary nutrients to minimize BW loss. In contrast, Garnsworthy and Huggett (1992) determined that feeding fatty acids caused thin dairy cows to produce less milk and maintain body reserves, whereas higher conditioned cows supplemented with fat lost more body fat and produced milk with a higher fat content.
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). Offering larger amounts of diets in Exp. 1 caused ewes to produce less milk per unit of feed than in Exp. 2 (808 ± 57.7 vs. 948 ± 54.5 g milk/kg ewe OMI).
Twin lamb performance was similar across treatments in Exp. 1 (Table 5). In Exp. 2, ewes fed the fescue + tallow diet weaned lighter (P < 0.05) lambs than those fed fescue + fatty acids. Results suggest lower milk yields and milk fat production of ewes fed fescue + tallow (Table 4) contributed to lower lamb performance. Ewes fed fescue + fatty acids produced a higher (P < 0.05) lamb ADG per ewe OMI in Exp. 2 (Table 5) as a result of feeding this diet at a lower rate (Table 3). In Exp.1, lamb gain per unit of ewe dietary fat intake was more efficient (P < 0.05) for the fescue + fatty acids diet than for the alfalfa diet (1.9 vs. 3.1 ± 0.26 g/g). Conversion of ewe dietary fat to lamb gain was intermediate for the fescue diet (2.6 g/g). Ewes fed the fescue diet in Exp. 2 produced more (P < 0.01) lamb gain per unit of fat consumed by ewes (4.0 ± 0.12 g/g) than those fed fescue + fatty acids (2.5 ± 0.12 g/g) or tallow (2.4 ± 0.12 g/g). Lamb gain per unit of ewe milk fat production was similar across treatments in Exp. 1 (1.9 ± 0.45 g/g) and Exp. 2 (2.0 ± 0.36 g/g). Results indicate increasing dietary fat in ewe diets does not proportionally increase lamb gain. Furthermore, neither milk fat yield nor composition was changed enough by fat treatments to increase the efficiency of milk fat conversion into lamb gain.
Casals et al. (1999) found a numerical increase in lamb weaning weights at 4 wk of age and a more efficient conversion of milk into lamb gain when feeding fat to dairy ewes. Hernandez et al. (1986) reported a 1-kg increase in lamb weight by 35 d of lactation when meat-type ewes were fed fat. However, other researchers did not find increased lamb performance when ewes were supplemented with fat (Appeddu et al., 1995; Alba et al., 1997; Espinoza et al., 1998). Twin lamb gain decreased as lactation progressed in both of the current experiments (P < 0.001), from an average of 0.54 kg/d (d 15 to 22) to 0.27 kg/d (d 50 to 57). These results suggest lamb nutrient requirements exceeded milk nutrient production (Torres-Hernandez and Hohenboken, 1980; Hussein and Jordan, 1990). Managing lambs to consume only ewe milk in both experiments may have prevented nonmilk nutrients as normally consumed by lambs, such as creep feed or high-quality pasture, from interacting with changes in milk production or composition to accelerate lamb growth when meat-type ewes were supplemented with fat. Further evaluation is warranted to determine the effects of supplementing fat to meat-type ruminants when lactation potential is higher, forage quality is lower, and/or when lambs have access to feed sources other than ewe milk.
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Footnotes |
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2 Correspondence: Health Sciences Division, Southwestern Oklahoma State Univ., 100 Campus Dr., Weatherford 73096 (phone: 580-774-3148; fax: 580-774-7159; e-mail: lisa.appeddu{at}swosu.edu).
Received for publication July 31, 2003. Accepted for publication June 1, 2004.
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionLiterature Cited |
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