Effects of short-term oilseed supplementation on plasma fatty acid composition, progesterone and prostaglandin F metabolite in lactating beef cows.

Twenty-four 3-year-old Angus cows (512.2±21.6 kg) and six ruminally cannulated beef heifers (523.1±16.9 kg) were used to determine the impact of feeding oilseeds starting at the beginning of estrous synchronization until maternal recognition of pregnancy on plasma fatty acid composition. Starting ~60 days postpartum cows were synchronized with the Select Synch+controlled internal drug-release (CIDR) device and timed artificial insemination (AI) protocol. The day CIDR was inserted; cattle were randomly assigned to one of the three treatments being grazing only (CON) or a supplement containing whole soybeans (SOY); or whole flaxseed (FLX). Cattle continued to receive these diets for 28 days. Blood was collected every 3 days until 10 days after insemination and then every day until 18 days after insemination. All cattle grazed a common pasture and supplemented cattle were individually fed their respective supplements once daily. Ruminally cannulated heifers were used to evaluate the impact supplements had on forage intake, which was reduced (P=0.05) with oilseed supplementation. Feeding oilseeds increased total fatty acid intake (P<0.001) across treatments with SOY having greater (P<0.001) 18:2n-6 intake than either CON or FLX. Likewise, cattle fed FLX had greater (P<0.001) 18:3n-3 intake than either CON or SOY. There was a treatment×time interaction (P≤0.05) for all fatty acids identified except for 20:5n-3 (P=0.99). Within 3 days after the start of supplementation, plasma concentrations of 18:2n-6 increased (P<0.001) for cattle fed SOY compared with CON or FLX, whereas flax-fed cattle did not exhibit an increase (P=0.02) until day 15 of supplementation over that of CON. Plasma concentrations for 18:3n-3 was greater (P<0.013) for FLX than both CON and SOY by day 12. Feeding flaxseed tended to (P=0.07) increase and increased (P=0.01) plasma concentrations of 20:4n-6 by day 18 over CON and SOY, respectively. Overall, treatment did not affect serum concentration of progesterone (P=0.18) or prostaglandin F metabolite (P=0.89). However, day after breeding had an effect on serum progesterone (P=0.01) with day 16 after timed AI being lower compared with other days. Feeding oilseeds during the time of estrous synchronization will not only increase the energy density of the diet but will provide key fatty acids around the time of maternal recognition of pregnancy.