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Department of Animal Science Cornell University, Ithaca, NY 14853
Corresponding author:
D. E. Bauman; e-mail:
deb6{at}cornell.edu.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONACKNOWLEDGEMENTSREFERENCES |
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200 d prepartum) and continued for 140 d until dry off. Twenty-three cows completed the study; those receiving CLA supplement had a lower milk fat test (2.90 versus 3.80%) and a 23% reduction in milk fat yield (927 versus 1201 g/d). Intake of DM, milk yield, and the yield and content of true protein and lactose in milk were unaffected by treatment. Milk fat analysis indicated that the CLA supplement reduced the secretion of fatty acids of all chain lengths. However, effects were proportionally greater on short and medium chain fatty acids, thereby causing a shift in the milk fatty acid composition to a greater content of longer-chain fatty acids. Changes in body weight gain, body condition score, and net energy balance were not significant and imply no differences in cows fed the CLA supplement in replenishment of body reserves in late lactation. Likewise, maintenance of pregnancy, gestation length, and calf birth weight were unaffected by treatment. Overall, feeding a dietary supplement of rumen-protected CLA to pregnant cows over the last 140 d of the lactation cycle resulted in a marked reduction in milk fat content and yield, and a shift in milk fatty acid composition, but other milk components, DMI, maintenance of pregnancy, and cow well-being were unaffected.
Key Words: conjugated linoleic acid • CLA • milk fat • lactation • cow
Abbreviation key: CLA = conjugated linoleic acid, NCN = noncasein nitrogen, NEB = net energy balance, TN = total nitrogen, TP = true protein
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONACKNOWLEDGEMENTSREFERENCES |
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Trans-10, cis-12 CLA can be produced by rumen biohydrogenation under certain dietary circumstances (Griinari and Bauman, 1999). Consistent with the biohydrogenation theory of milk fat depression, there is an inverse relationship between milk fat content of trans-10, cis-12 CLA and milk fat yield (Bauman and Griinari, 2001). Economics usually favor milk fat on commercial dairy farms, but there are some scenarios when reduced output of milk fat could be advantageous. These include markets where producers are regulated by a quota system based upon milk fat and situations where animals cannot consume sufficient energy to meet requirements. Examples of the latter could include the transition period and early lactation, or adverse environmental effects such as heat stress and poor weather conditions for sufficient growth of forage in pasture-based systems.
Most investigations of the effect of CLA on milk fat in dairy cows have lasted only a few days and used abomasal infusion as a convenient experimental method to bypass rumen fermentation. Three recent abstracts report studies using early lactation animals in which the diet was supplemented with rumen-protected CLA. Two of the studies were less than 11 wk in duration (Giesy et al., 1999; Medeiros et al., 2000), while the third covered the first 20-wk of lactation (Bernal-Santos et al., 2001). There have been no investigations of the effects of supplementing rumen-protected CLA during the later stages of lactation. Effects on replenishment of body reserves during the later stages of the lactation cycle would be of interest because CLA supplementation has been shown to reduce body fat accretion in growing animals (Dugan et al., 1997; DeLany et al., 1999; Ostrowska et al., 1999; Azain et al., 2000). Likewise, maintenance of pregnancy would be of interest in CLA-treated cows because birds fed dietary supplements of CLA produced eggs with high embryonic mortality and reduced hatchability (Aydin et al., 1999a, 1999b). Thus, our objective was to assess the effects of CLA supplementation during established lactation on production parameters, replenishment of body reserves, and maintenance of pregnancy, as well as the overall health of the animal.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONACKNOWLEDGEMENTSREFERENCES |
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). The CLA supplement provided 30.4 g/d of CLA, and the four predominant CLA isomers were: trans-8, cis-10 (9.2%), cis-9, trans-11 (25.1%), trans-10, cis-12 (28.9%), and cis-11, trans-13 (16.1%).
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). Feeds were sampled weekly throughout the experiment, and DM content was determined by drying the feed at 110°C for 18 h. The diet composition was 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, and minerals (Dairy One, Ithaca, NY). Cows were fed ad libitum, with fresh feed provided after each morning milking. Orts were weighed and recorded daily. Water was available at all times.
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Blood samples were collected on 1 d/w beginning the week prior to treatment and continuing on wk 1, 2, 3, 4, 8, 12, 16, and 20. Blood was collected via venipuncture from the coccygeal vessels over the 30 min interval following the morning milking and prior to providing fresh feed. Sodium heparin (100 U/ml of blood) was used to prevent coagulation. Plasma was harvested following centrifugation (2,800 x g, 15 min at 4°C) and stored at –20°C until analyses for blood metabolites.
Body weights and body condition scores of each animal were recorded 1 d/w throughout the study. Cows were body scored on a five-point system (Wildman et al., 1982) by two individuals and the average of these two scores was the assigned value. Daily observations and general health records were recorded throughout the study. Cows were also observed through the dry period, with calf sex and birth weight recorded at the subsequent parturition.
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). The oven temperature was initially 80°C, then ramped at 2°C/min to 190°C and maintained for 15 min. Inlet and detector temperatures were 250°C and the split ratio was 100:1. The hydrogen carrier gas flow rate was 1 ml/min, hydrogen flow to the detector was 25 ml/min, airflow was 400 ml/min, and the flow of nitrogen make-up gas was 45 ml/min. 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.
Milk Protein Analysis
Total N (TN) and N fractions of milk were determined using macro-Kjeldahl techniques (AOCS, 2000). Milk NPN consisted of N that was soluble in 12% trichloroacetic acid. Noncasein N (NCN) was determined by precipitating casein at pH 4.6 and filtering, leaving the filtrate for N analysis. From these milk N fractions, the following were calculated: 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 also converted to protein equivalents by multiplying by 6.38 to allow comparison with other protein fractions.
Blood Metabolite Analysis
Plasma glucose was determined by enzymatic analysis 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). Plasma concentrations of BHBA were quantified using a commercial kit (kit 310-UV; Sigma Chemical). All analysis was done using a Versamax tunable microplate reader (Molecular Devices, Sunnyvale, CA). Inter-assay variation was maintained at < 5%.
Statistical Analysis
Pretreatment values for each variable measured were used for covariate adjustment. Daily intake and milk yield values were reduced to weekly means before data analysis. Analysis of variance was conducted using the General Linear Models procedure of SAS (1998) for a completely randomized design with repeated measures. The model contained the effects of treatment, week of treatment, cow within treatment and the interaction of treatment by week. The overall effect of treatment was tested using cow within treatment as the error term. Least squares means are reported throughout, and significance was declared at P < 0.05.
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RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONACKNOWLEDGEMENTSREFERENCES |
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. Supplementation with CLA decreased milk fat content and milk fat yield by 23 and 18%, respectively. However, DMI, milk yield, and content and yield of milk protein and milk lactose were unaffected by treatment. A total of 23 cows completed the full 20-wk of treatment. Two of the seven cows that did not complete the study were removed due to health (displaced abomasum) or physical injury (stifle injury), and the remaining five dried off early. Animals were assigned to the study based on stage of pregnancy rather than stage of lactation, and the animals that dried off early averaged 400 DIM. Performance results over the full 20-wk for the 23 cows that completed the study (Table 4) were virtually identical to those for all cows over the first 10-wk of treatment (Table 3). Subsequent data presentation describes the 23 animals that completed the study.
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). Studies involving pure CLA isomers have demonstrated that abomasal infusion of 10 g of trans-10, cis-12 reduced milk fat synthesis by 44%, but infusion of the same amount of cis-9, trans-11 CLA had no effect (Baumgard et al., 2000). There was a curvilinear relationship between the dose of trans-10, cis-12 CLA and milk fat yield, with the maximum reduction in milk fat yield approximately 50% (Baumgard et al., 2001; Peterson et al., 2002). In contrast to milk fat, the yield of milk protein and milk lactose were unchanged (Table 4), and the temporal pattern of the decline in milk yield was nearly identical between treatment groups (Figure 1). The lack of effects of CLA on the yield of milk and milk protein are consistent with other investigations using cows in established lactation (Chouinard et al., 1999a; 1999b; Baumgard et al., 2000, 2001). However, all of the previous studies of established lactation have been short-term (up to 5 d) involving abomasal infusion of the CLA.
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The decrease in milk fat yield in the CLA-supplemented group had occurred by the first sampling at the end of the first week of treatment and remained consistent throughout the 20-wk treatment period (Figure 2). The reduction in fat yield resulted from a decrease in the secretion of all milk fatty acids (Table 5). However, the reduction in the yield of the short and medium chain fatty acids (< C16) was proportionally greater, causing a shift so that milk fat of cows receiving CLA had a greater content of long chain fatty acids (
C18) (Table 6). This shift in milk fatty acid composition is similar to that reported in short-term studies involving abomasal infusion of a similar mixture of CLA isomers (Loor and Herbein, 1998; Chouinard et al., 1999a, 1999b) or pure trans-10, cis-12 CLA (Baumgard et al., 2000). Abomasal infusion studies with the trans-10, cis-12 CLA isomer have also demonstrated that the magnitude of the shift in the milk fatty acid composition and the reduction in milk fat yield increases as the dose of this CLA isomer increases (Baumgard et al., 2001). The rumen-protected CLA supplement was composed of four CLA isomers, and cows receiving the supplement had an increase in both yield and concentration of trans-10, cis-12 CLA in milk fat (Tables 5 and 6). The content of cis-9, trans-11 CLA, another CLA isomer in the supplement, also was increased in milk fat (Table 6); the, yield of this isomer was reduced by treatment (Table 5), however, because of the overall reduction in milk fat yield. The remaining two isomers in the supplement (trans-8, cis-10 CLA and cis-11, trans-13 CLA) were not detectable with the analytical system that was used.
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The enzyme 
9-desaturase plays an essential role in the maintenance of cellular membrane fluidity through introduction of a cis-9 double bond in fatty acids (Ntambi, 1999). In mammary, 9-desaturase plays an additional critical role in the maintenance of milk fat fluidity (Kinsella, 1972). There are four pairs of fatty acids in milk fat that represent product/substrate for 9-desaturase, and their ratio in milk fat can serve as a proxy for 9-desaturase in the mammary gland (Bauman et al. 2001). These pairs are called the desaturase index and they are: C14:1/C14:0, C16:1/C16:0, C18:1/C18:0, and cis-9, trans-11 CLA /trans-11 C18:1. Abomasal infusions of high doses of CLA isomer mixtures reduced the ratios in milk fat, indicating a decrease in quantity or activity of 9-desaturase (Chouinard et al., 1999a; 1999b). Baumgard et al. (2001) showed that the trans-10, cis-12 CLA reduced the desaturase index, whereas the cis-9, trans-11 isomer had no effect. Studies involving growing rodents have demonstrated that the trans-10, cis-12 isomer affected both enzyme activity and gene expression for 9-desaturase (Lee et al., 1998; Bretillon et al., 1999; Park et al., 2000). In the present study, there was no indication of a reduction in 9-desaturase based on ratios of the fatty acid pairs, and in fact there was a small but significant increase in the ratios (Table 6). This lack of reduction in the desaturase index is likely related to dosage. Whereas high doses of trans-10, cis-12 CLA (7.0 and 14.0 g/d) shifted desaturase index, lower doses had no effect even though milk fat yield was reduced (Baumgard et al., 2001; Peterson et al., 2002). When 9-desaturase is markedly reduced by extremely high doses of CLA, effects on lipid fluidity may impair the formation and secretion of milk fat and the turnover of cellular membranes. This could explain the apoptosis observed in some in vitro cultures when cells were incubated with high concentrations of CLA (Ip et al., 1999) and could be the basis for the decline in milk synthesis observed when lactating dairy cows are abomasally infused with extreme levels of CLA (150 g/d) (Bell and Kennelly, 2001).
Specific protein fractions and TP are also important when considering the manufacturing properties of milk. Specific milk proteins were compared between treatment groups and no significant differences were observed (Table 7). Thus, results suggest that the manufacturing properties related to milk proteins were unaffected by the use of CLA supplements during established lactation.
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). We observed affects on DMI, BW or BCS (Table 4). The temporal patterns of DMI, BW and BCS were nearly identical between CLA-supplemented and control treatment groups (Figures 3 and 4). Thus, cows receiving CLA were able to replenish their body reserves in a typical manner. Body reserves are of particular importance to milk production in early lactation, and the milk yield over the first 6 wk of the subsequent lactation was similar for the two treatment groups (44.5 ± 4.2 kg/d for control and 47.1 ± 5.4 kg/d for CLA-supplemented groups). The ability of CLA supplemented cows to replenish body fat reserves contrasts with studies involving growing animals in which CLA supplements have been shown to reduce body fat accretion in rats (Azain et al., 2000), mice (DeLany et al., 1999), and pigs (Dugan et al., 1997; Ostrowska et al., 1999). Baumgard et al. (2002) noted that the CLA doses used in studies with growing animals are several-fold greater than those used in lactation studies, including the present study. Consequently, the different effects on body fat may be related to dose, but could also be related to other factors such as physiological state and/or species differences.
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)]. In the case of growing rodents, some studies have suggested a mechanism whereby CLA reduces body fat accretion through an increase in energy losses (DeLaney et al., 1999; West et al., 2000). This involves an increase in heat production and a reduction in efficiency of nutrient use. The present study provides no evidence that CLA adversely affecting metabolic efficiency. The lack of treatment differences in calculated NEB (Table 4) agrees with the lack of any treatment differences in BW gain and BCS (Figure 4). Nevertheless, the effect of CLA on bioenergetics will be an area of continued interest as others seek to verify and extend our results.
The present study was also the first to feed rumen-protected CLA to pregnant dairy cows, and relevant variables are presented in Table 9. Pregnancy was maintained for all animals, and no differences were observed between treatment groups for gestation length. Parturition and calf health also appeared normal, and there were no treatment effects on average birth weight. The maintenance of pregnancy was of concern due to studies that showed a high embryonic mortality and reduced hatchability of eggs from birds fed a diet supplemented with CLA (Aydin et al., 1999a, 1999b). These adverse effects are probably related to the dose of CLA (0.5% of the diet) and its affect on 9-desaturase, as eggs from CLA-supplemented birds had a marked reduction in lipid content of unsaturated fatty acids. Cyclopropenoid fatty acids found in some feeds (e.g. cottonseed) also inhibit 9-desaturase, and this can impair reproduction in birds and mammals (Phelps et al., 1964). Dietary supplements of unsaturated fatty acids overcame the adverse reproduction effects of cyclopropenoid fatty acids in birds and rodents (Phelps et al., 1964; Nixon et al., 1977). Recently, it was demonstrated that addition of olive oil to the diet of CLA-supplemented birds also prevented the adverse effects on reproduction (Aydin et al., 2001). Thus, the lack of an effect of CLA on pregnancy is consistent with the absence of any adverse effects on 9-desaturase as seen in milk fat values for the desaturase index ratios (Table 6). In other studies that had objectives unrelated to reproduction, there were no apparent complications in the maintenance of pregnancy or fetal development when dietary supplements of CLA were fed to rats (Chin et al., 1994) or sows (Bee, 2000; Poulos et al., 2000).
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ACKNOWLEDGEMENTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONACKNOWLEDGEMENTSREFERENCES |
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FOOTNOTES |
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2 Present address: Universidad Autónoma de Querétaro, Facultad de Ciencias Naturales, Medicina Veterinaria y Zootecnia, Querétaro, Qro. CP 76000, MEXICO.
Received for publication January 23, 2002. Accepted for publication April 2, 2002.
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONACKNOWLEDGEMENTSREFERENCES |
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