Submitted to: American Society of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/6/2006
Publication Date: 3/15/2007
Citation: Lake, S.L., Weston, T.R., Scholljegerdes, E.J., Alexander, B.M., Rule, D.D. 2007. Effects of postpartum dietary fat and body condition score at parturition on plasma, adipose tissue, and milk fatty acid composition of lactating beef cows. American Society of Animal Science. Vol. 85, 717-739. Interpretive Summary: Previous work has indicated that maintenance of greater body condition during lactation in beef cattle to supplementation with linoleic acid, whereas dietary oleic acid increased milk fat synthesis. Additionally, beef cows in low body condition maintained condition and had the metabolic capacity to increase fat accretion during the first 60 d of lactation. We hypothesized that the aforementioned nutrient partitioning effects of dietary lipids and body condition are associated with changes in fatty acid composition of tissues involved with nutrient partitioning. Therefore, two experiments were conducted with lactating Angus crossed beef cows to determine the effects of postpartum lipid supplementation, body condition at parturition, and day of lactation on fatty acid profiles in plasma, fat tissue, and milk. Cows were fed hay and either a low-fat supplement or supplements with cracked, high-linoleate safflower seeds or cracked, high-oleate safflower seeds from d 3 to 90 of lactation. Dietary lipid supplementation and day of lactation effected plasma and milk fatty acid composition in beef cows during early lactation. Cows in a low body condition appeared to deposit greater amounts of dietary fatty acids in fat tissue. However, the metabolic demands associated with lactation seemed to divert nutrients away from adipose tissue in beef cows during early lactation.
Technical Abstract: Two experiments were conducted with lactating Angus X Gelbvieh beef cows to determine the effects of postpartum lipid supplementation, BCS at parturition, and day of lactation on fatty acid profiles in plasma, adipose tissue, and milk. In Exp. 1, 36 primiparous cows (488 +/- 10 kg of initial BW; 5.5 +/- 0.02 initial BCS) were given ad libitum access to hay and assigned randomly to a low-fat (control) supplement or supplements with cracked, high-linoleate safflower seeds (linoleate) or cracked, high-oleate safflower seeds (oleate) from d 3 to 90 of lactation. Diets were formulated to be isonitrogenous and isocaloric; safflower seed diets provided 5% of DMI as fat. Plasma and milk samples were collected on d 30, 60, and 90 of lactation. Adipose tissue biopsies were collected near the tailhead region of cows on d 45 and 90 of lactation. In Exp. 2, 3-yr-old cows achieving a BCS of 4 +/- 0.07 (479 +\- 36 kg of BW) or 6 +/- 0.07 (580 +/- 53 kg of BW) at parturition were used in a 2-yr experiment (n = 36/yr). Beginning 3 d postpartum through d 61 of lactation, cows were fed diets similar to those of Exp. 1. Adipose tissue and milk samples were collected on d 30 and 60, and plasma was collected on d 31 and 61 of lactation. Responses to postpartum dietary treatment were comparable in both experiments. Cows fed linoleate and oleate had greater (P +/ 0.001) total fatty acid concentrations in plasma than cows fed control. Except for 15:1, milk fatty acids with '18 carbons were greatest (P +/- 0.01) for cows fed control, whereas milk from cows fed linoleate had the greatest (P +/- 0.02) 18:1trans-11, 18:2n-6, and cis-9, trans-11 CLA. Milk from cows fed oleate had the greatest (P +/- 0.001) 18:1cis-9. In Exp. 1, total fatty acid concentrations in adipose tissue samples decreased at d 90 compared with d 45 of lactation, but the fatty acid profile of cow adipose tissue was not affected (P = 0.14 to 0.80) by dietary treatment. In Exp. 2, the percentage of cis-9, trans-11 CLA in adipose tissue of cows with a BCS of 6 decreased (P = 0.001) from d 30 to 60 of lactation. Plasma and milk fatty acid composition reflected alterations in postpartum diet. Less medium-chain fatty acids and more 18-carbon fatty acids in milk were indicative of reduced de novo fatty acid synthesis in the mammary gland of beef cows fed lipid supplements; however, the metabolic demands of lactation prevented the deposition of exogenously derived fatty acids in adipose tissue through d 90 of lactation.