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Department of Animal Science Cornell University, Ithaca, NY 14853
Corresponding author: T. R. Overton; email: tro2{at}cornell.edu.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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16) fatty acids to milk fat. Changes in milk yield, milk fat content, and milk fatty acid composition were not apparent until after the second week of lactation. Yield of 3.5% fat-corrected milk, milk protein content, milk protein composition, and calculated energy balance were not affected by treatment. Postpartum concentrations of glucose, nonesterfied fatty acids, and ß-hydroxbutyrate in plasma and hepatic content of glycogen and triglycerides were similar between treatments. These data imply that with CLA treatment in early lactation, dairy cows decreased milk fat synthesis and appeared to respond by partitioning more nutrients toward milk synthesis rather than improving net energy balance.
Key Words: conjugated linoleic acid • milk fat • lactation • transition cow
Abbreviation key: CLA = conjugated linoleic acid, NCN = noncasein nitrogen, NEB = net energy balance, TN = true nitrogen, TP = true protein
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Economics generally favor prevention of milk fat depression on commercial dairy farms, but there are some scenarios in which reduced output of milk fat could be advantageous (Bauman et al., 2001; Perfield et al., 2002). These include markets where producers are regulated by a quota system based on milk fat and situations in which animals cannot consume sufficient energy to meet requirements such as occurs during heat stress or when poor weather limits forage growth in pasture-based systems. Parturition and early lactation is an additional period when intake is inadequate to meet nutrient requirements, so cows are dependent on the use of body reserves. If an imbalance occurs during this period, stress or metabolic disorders can occur, and prolonged negative energy balance can also compromise reproductive performance (Bell, 1995; Butler, 2001). Current management recommendations and most experimental approaches to decrease the severity and duration of negative energy balance involve strategies to maximize DMI during this transition period. However, the energy deficit also could be less pronounced if the fat content of milk were reduced. Our objective was to determine the effect of feeding a supplement containing rumen-protected CLA on milk fat synthesis at parturition and during early lactation in dairy cows. To obtain a more complete evaluation, we monitored lactational performance, metabolic status, and variables related to reproductive performance.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Cows were fed diets as TMR that were formulated using the Cornell Net Carbohydrate and Protein System (Fox et al., 1992) to meet or exceed predicted requirements for energy, protein, minerals, and vitamins (NRC, 2001). All cows were fed the same basal diet during the prepartum period beginning between 28 and 21 d before expected parturition and then switched to a common diet during the postpartum period. Ingredient and nutrient composition of the diets fed during the prepartum and postpartum phases of the experiment are provided in Table 1
. Feeds were sampled weekly throughout the experiment, and DM content was determined by drying at 54°C until static weight. Amounts of individual feed components in the TMR were adjusted weekly based on changes in the DM content of feed components. Feed samples were composited at 4-wk intervals and analyzed by wet chemistry methods for CP, ADF, NDF, ether extact, and minerals (Dairy One Cooperative Inc., Ithaca, NY). Cows were fed ad libitum, with fresh feed provided each morning after milking. Orts were weighed and recorded daily. Water was available at all times.
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After parturition, cows were milked three times per day and yields were recorded at each milking. Through the 20-wk treatment period, milk samples were collected from each milking on one day per week and composited. The composite samples were stored at 4°C with a preservative (bronopol tablet; D&F Control System, San Ramon, CA) until analyzed for fat, protein, and lactose using infrared analysis (AOAC 2000: method 972.160), and SCC by an optical fluorescent method (AOAC 2000: method 978.26) (Dairy One Cooperative Inc.). The calibration reference methods for the infrared milk analysis were as follows: fat by modified Mojonnier ether extraction (AOAC 2000: method 989.05), Kjeldahl true protein (AOAC 2000: method 991.22), and lactose by difference of oven drying total solids (AOAC 2000: method 990.20) minus the sum of modified Mojonnier ether extraction, Kjeldahl true protein (AOAC 2000: method 991.22), estimated nonprotein nitrogen (0.19% on a protein basis), and estimated ash [(true protein x 0.596) + 0.5379]. Additional aliquots of the composite milk samples collected on wk 1, 2, 4, 6, 8, 12, 16, and 20 were stored at -20°C (without preservative) until analyzed for fatty acid and protein composition.
Blood samples were collected every other day beginning 1 wk before treatment (21 d prepartum) and continuing through 56 DIM, and thereafter once weekly until the study terminated (140 DIM). Blood was collected via venipuncture from the coccygeal vessels during the 30-min interval following the morning milking and before providing fresh feed. Sodium heparin (100 U/ml of blood) was used to prevent coagulation. Plasma was harvested following centrifugation (2800 x g, 15 min at 4°C) and stored at -20°C until analyses for metabolites and progesterone.
Liver samples were obtained from each cow via percutaneous trochar biopsy (Veenhuizen et al., 1991) on 1 d during the week preceding assignment to treatment and on d 10 and 21 postpartum. Liver was blotted to remove excess blood and connective tissue, snap frozen in liquid nitrogen, and stored at -80°C until analyzed for triglyceride and glycogen content.
Milk Fatty Acid Analysis
Milk fat was extracted using the method of Hara and Radin (1978) and fatty acid methyl esters were prepared by base-catalyzed transmethylation according to Christie (1982) with modifications by Chouinard et al. (1999a). Fatty acids in the rumen-protected supplements were methylated using 1% sulfuric acid in methanol as described by Christie (1989). Fatty acid methyl esters were quantified using a gas chromatograph (GCD system HP 6890+; Hewlett Packard, Avondale, PA) equipped with a SP-2560 fused silica capillary column (100 m x 0.25 mm [i.d.] with 0.2-µm film thickness; Supelco, Bellefonte, PA) under conditions previously described (Perfield et al., 2002). Fatty acid peaks were identified using pure methyl ester standards (Nu-Chek Prep, Elysian, MN). Additional standards for CLA isomers were obtained from Natural Lipids Ltd AS (Hovdebygda, Norway). A butter oil reference standard (CRM 164; Commission of the European Community Bureau of References, Brussels, Belgium) was used to determine recoveries and correction factors for individual fatty acids as well as acting as a reference sample for routine quality control.
Milk Protein Analysis
Total N (TN) (AOAC, 2000; method number 991.20) and N fractions of milk were determined using macro-Kjeldahl techniques. Milk NPN consisted of N that was soluble in 12% trichloroacetic acid (AOAC, 2000; method number 991.21). Noncasein N (NCN) was determined by precipitating casein at pH 4.6 and filtering, leaving the filtrate for N analysis (AOAC, 2000; method number 998.05). These milk N fractions were used in calculations as follows: CP equaled (TN x 6.38); true protein (TP) equaled (TN - NPN) x 6.38; casein protein equaled (TN - NCN) x 6.38; and whey protein equaled (NCN - NPN) x 6.38. Milk NCN and NPN were multiplied by 6.38 to convert to protein equivalents so they could be compared with other protein fractions.
Plasma and Tissue Analysis
Plasma glucose was determined by enzymatic analysis (glucose oxidase) using a commercial kit (kit 510-A; Sigma Chemical, St. Louis, MO). Plasma concentrations of NEFA were analyzed by enzymatic analysis (NEFA-C; WAKO Pure Chemical Industries, Osaka, Japan) using modifications described by McCutcheon and Bauman (1986) and Sechen et al. (1990). Plasma concentrations of BHBA were quantified (BHBA dehydrogenase) using a commercial kit (kit 310-UV; Sigma Chemical). All spectrophotometric measurements were conducted using a Versamax tunable microplate reader (Molecular Devices, Sunnyvale, CA). Interassay variation was maintained at <5%.
Plasma collected during the postpartum period was assayed for progesterone by radioimmunoassay (Staigmiller et al., 1979; Nara and First, 1981). Intra- and interassay CV were 5 and 13%, respectively. Ovulation was identified by three consecutive samples with progesterone levels greater than 1 ng/ml.
Glycogen content of liver was determined according to the procedures described in Hawk and Bergeim (1926) with modifications. Frozen liver tissue was pulverized in liquid nitrogen and approximately 0.1 g of powdered liver tissue was placed in a 15-ml polycarbonate centrifuge tube with 1.2 ml of 30% KOH. The tube was capped, vortexed, and placed in a boiling water bath for 20 min. The mixture was brought to room temperature, 1.4 ml of 95% ethanol added, and centrifuged at 4°C for 20 min at 1730 x g in a Beckman GS-6KR centrifuge. The supernatant was removed and the pellet was washed twice with 60% ethanol, using 10 ml the first time and 5 ml the second. Following each wash, the mixture was centrifuged under the same conditions as described above. After the second wash the pellet was resuspended in 8 ml of 0.2 N acetate buffer. Two hundred microliters of hydrolyzed liver sample was combined with 30 µl of amyloglucosidase (Sigma A-3514; Sigma Chemical) and incubated at 55°C for 1 h to convert liver glycogen to glucose. Glucose was then analyzed as described for plasma.
Liver triglyceride content was determined using the Folch extraction method (Folch et al., 1957) followed by a colorimetric method for estimating serum triglycerides (Fletcher, 1968) with modifications described by Foster and Dunn (1973).
Statistical Analysis
Daily intake and milk yield values were reduced to weekly means before data analysis. Pretreatment values for DMI, BW, BCS, blood metabolites, and liver composition were used as covariates during analysis of covariance applied to their corresponding measurements during the treatment period. Analysis of variance was conducted using the MIXED procedure of SAS (2001) for a completely randomized design with repeated measures. The model included the effects of treatment, time, and the interaction of treatment and time, with the random variable being the cow x treatment interaction. Parity was included as a term in the original model, but was not significant and was eliminated from the final model. Days to first ovulation for the two treatments were compared using a two-tailed t-test (Number Cruncher Statistical System; NCSS, 2000), median days to first ovulation was evaluated using nonparametric survival analysis (NCSS, 2000), and the number of cows with days to first ovulation less than or equal to 30 d was evaluated by chi-square analysis (NCSS, 2000). Least squares means are reported throughout, and significance was declared at P < 0.05.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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). Likewise, plasma concentrations of glucose, NEFA, and BHBA were similar between treatment groups during the prepartum period (Table 2).
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. During this period, CLA-supplemented animals tended (P < 0.13) to yield approximately 3 kg/d more milk. Milk fat percentage was decreased by 12.5% for the CLA-supplemented group over the 20-wk period (P < 0.001), but milk fat yield was reduced by only 7.5% (P < 0.11) because of the increased milk yield (Table 3). The numerical differences in milk yield and milk fat percentage were offsetting, such that yield of 3.5% FCM and the net energy required for milk synthesis were essentially identical between the two treatment groups (Table 3). Temporal patterns for milk yield, milk fat percentage, and 3.5% FCM are shown in Figure 1. The yield and fat content of milk were nearly identical for the two treatment groups during the first 2 wk postpartum, and then differences occurred that persisted through the remainder of the period. In contrast, there were no significant differences in content of protein and lactose in milk between treatment groups throughout the treatment period (Table 3).
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). The temporal pattern of NEB also was similar between groups during the entire period of supplementation (Figure 2). Postpartum BW (Table 3; Figure 3) of cows fed CLA tended (P < 0.09) to be increased compared with controls; postpartum BCS (Table 3; Figure 3) tended (P < 0.14) to follow a similar pattern.
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). When averaged over the entire postpartum treatment period, the reduction in the yield of the short- and medium-chain fatty acids (<16 carbons) was proportionally greater, causing a shift such that the milk fat of cows receiving CLA tended (P < 0.09) to have a greater content of long-chain fatty acids (>16 carbons) (Table 4). Statistically significant (P < 0.05) increases in content of trans-C18:1 fatty acids in milk fat also were measured; however, the total changes represented less than 0.3% of the total fatty acids. Similar to the temporal pattern of response observed for milk yield and milk fat content, the shift in milk fatty acid composition occurred after the second week of lactation and persisted through the remainder of the treatment period (Figure 4). In contrast, milk fat content of trans-10, cis-12 CLA was elevated during the first week of lactation and remained constant over the entire 20-wk period (Figure 5). Pairs of fatty acids comprising the desaturase index (Perfield et al., 2002) were not different between treatment groups (Table 4), indicating that 
9-desaturase was not affected by CLA supplementation.
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). Consistent with the lack of change in yield and content of protein in milk during the entire 20-wk treatment period, there were no differences between treatment groups for any of the specific protein or N fractions in milk.
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. Plasma concentrations of glucose and NEFA were not affected during either d 2 through 56 of lactation or d 63 through 140 of lactation. Consistent with the lack of effect of treatment on the temporal pattern of calculated NEB described above (Figure 2), the similar temporal pattern for plasma NEFA concentrations between treatments confirms the lack of effect on mobilization of body fat reserves (Figure 6). Concentrations of BHBA in plasma were increased (P < 0.01) during d 63 through 140; however, given the lack of effect (P > 0.15) of treatment on plasma BHBA concentrations from d 2 through 56 of lactation and the small magnitude of the effect during d 63 through 140, this effect is not likely to be of biological significance. Concentrations of glycogen and triglycerides in liver were not affected significantly by treatment (Table 6).
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Several variables of reproductive performance are presented in Table 7. Concentrations of progesterone in plasma from cows during early lactation were used to determine days to first ovulation. Cows fed rumen-protected CLA during the transition period and early lactation tended to have lower mean days (P < 0.13) and median days (P < 0.07) to ovulation, whereas the number of cows whose first ovulation occurred on or before 30 DIM was similar (Table 7). Although the number of cows assigned to each treatment was too small to assess other reproductive parameters statistically, it is interesting to note that the CLA treatment group had a numerical advantage in number of cows that became pregnant and conception rate. Overall, there was no evidence that supplementation with CLA had any negative effects on reproduction variables.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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).
In the present study, CLA supplementation did not affect milk fat content until several weeks after the initiation of lactation (Figure 1). Likewise, there was no shift in milk fatty acid composition until several weeks postpartum (Figure 4). This differs from studies conducted with cows during established lactation where abomasal infusion of CLA (Baumgard et al., 2000, 2001) or feeding rumen-protected CLA (Giesy et al., 2002; Perfield et al., 2002) resulted in an immediate reduction in milk fat content and shift in milk fatty acid composition. A delayed effect of treatment also was observed by Selberg et al. (2002) when CLA supplementation was initiated 28 d prepartum.
An explanation for the lack of a CLA response in milk fat during the first few weeks postpartum is unknown. A CLA isomer that causes a reduction in milk fat is trans-10, cis-12 CLA (Baumgard et al., 2000), and our analysis indicates it was consistently transferred to milk fat throughout the treatment period (Figure 5). Thus, the lack of an effect immediately postpartum is unlikely to be related to any difference in uptake of trans-10, cis-12 CLA by the mammary gland. The source of fatty acids for milk fat synthesis is also a consideration, and this differs during the early postpartum period. The NEB characteristic of the onset of lactation is associated with an increased mobilization of body fat reserves, and this results in an increased mammary uptake of circulating NEFA and their use to synthesize milk fat triglycerides (Bell, 1995). However, it is not obvious why an increased contribution of NEFA for milk fat synthesis would completely abolish the CLA-induced reduction in milk fat. Another consideration is the mechanism and studies investigating the effect of trans-10, cis-12 CLA on milk fat synthesis have shown the mechanism involves coordinated decreases in mRNA abundance for key enzymes involved in the production of milk fat (Baumgard et al., 2002). Perhaps at the onset of lactation the essential cellular signaling systems are attenuated such that trans-10, cis-12 CLA is unable to elicit the coordinated reduction in the expression of genes for key lipogenic enzymes. Additional studies will be required to understand the basis for the delayed response to CLA, but the overall effect is that CLA supplementation did not reduce milk fat synthesis in the immediate postpartum period.
Results from the present study with transition cows also differ in other ways from those observed with administration of CLA to cows in established lactation. In established lactation, CLA administration or feeding affected the yield and content of milk fat, but milk yield and the yield of other milk components were relatively unaffected (Baumgard et al., 2000, 2001; Chouinard et al., 1999a; 1999b; Giesy et al., 2002; Perfield et al., 2002). In the present study the CLA-supplemented group exhibited an apparent increase in milk yield, beginning several weeks postpartum and continuing throughout the remainder of the treatment period (Figure 1). While statistically the milk yield increase (~3 kg/d) was only a trend (P < 0.13), it is underpinned by the simultaneous temporal pattern changes involving an increase in milk lactose yield (pattern not shown), a decrease in milk fat percentage (Figure 1), and shift in the fatty acid composition of milk fat (Figure 4). Thus, feeding rumen-protected CLA to early-lactation cows had a net effect of shifting nutrient partitioning, where energy spared from the reduction in milk fat was used to increase milk synthesis so that NEB was unchanged (Figure 2). This shift in nutrient partitioning when dietary CLA supplements were fed also has been reported by others. An increase in milk yield coinciding with decreased milk fat content was reported in studies in which cows were fed CLA supplements in early lactation (Giesy et al., 1999; Selberg et al., 2002) or on pasture-based systems (Medeiros et al., 2000). These studies have been reported only in abstract form, but are all situations in which energy intake would likely be less than optimal. In the case of pasture-fed cows where amino acid supply would likely be in excess, supplementation with rumen-protected CLA also resulted in a simultaneous increase in milk protein yield (Medeiros et al., 2000; Gulati et al., 2001).
The present study is the first to supplement CLA during the first 20 wk of lactation, an interval in which cows would typically be returned to reproductive service. Effects on reproduction were of special interest because studies with avian species indicated that CLA supplements resulted in high embryonic mortality and reduced hatchability of eggs (Aydin et al., 1999a, 1999b). However, no adverse effects were observed for conception, maintenance of pregnancy throughout the treatment period, or for the remainder of the pregnancy (Table 7). Perfield et al. (2002) reported that CLA supplementation over the last 20 wk of the lactation cycle caused no adverse effects on the maintenance of pregnancy or the development of the fetus. The CLA isomers are metabolized and a portion of their beneficial effects—for example, effects on enhancing immune function—are postulated to involve the formation of eicosanoids (Pariza et al., 2000). Polyunsaturated fatty acids, such as linoleic acid, may affect prostaglandin synthesis through a variety of mechanisms, which may contribute to a reduction in embryonic mortality (Mattos et al., 2000). Due to the limited number of animals per treatment group, it is difficult to make any definitive conclusions about the reproductive benefits of CLA supplementation, but all of the numerical changes in reproductive variables were all positive. Larger scale experiments will be required to elucidate the mechanisms underpinning these potential effects of CLA.
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CONCLUSIONS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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ACKNOWLEDGEMENTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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FOOTNOTES |
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2 Presented in part in abstract form at Annual Meeting of the American Dairy Science Association July 25, 2001 Indianapolis, IN [Bernal-Santos, G., J. W. Perfield II, T. R. Overton and D. E. Bauman. Production responses of dairy cows to dietary supplementation with conjugated linoleic acid (CLA) during the transition period and early lactation. J. Dairy Sci. 84(Suppl. 1):82. (Abstr.)] and at the 63rd Cornell Nutrition Conference, October 18, 2001 Rochester, NY [Overton, T. R., G. Bernal-Santos, J. W. Perfield II and D. E. Bauman. Effects of feeding conjugated linoleic acids (CLA) on metabolism and performance of transition dairy cows. Proc. Cornell Nutr. Conf. pp. 179–187].
3 Present address: Universidad Autónoma de Querétaro, Facultad de Ciencias Naturales, Medicina Veterinaria y Zootecnia, Querétaro, Qro. CP 76000, Mexico.
Received for publication December 16, 2002. Accepted for publication May 5, 2003.
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REFERENCES |
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on parturition in swine. J. Anim. Sci. 52:1360–1370.
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