Level and source of fat in the diet of gestating beef cows. II. Effects on the postpartum performance of the dam and the progeny

Citation

Añez-Osuna, F., Penner, G.B., Campbell, J., Dugan, M.E.R., Fitzsimmons, C.J., Jefferson, P.G., Lardner, H.A., McKinnon, J.J. (2019). Level and source of fat in the diet of gestating beef cows. II. Effects on the postpartum performance of the dam and the progeny, 97(7), 3120-3141. http://dx.doi.org/10.1093/jas/skz172

Plain language summary

A study was conducted to evaluate the effects of level and source of fat in diets of pregnant cows on the post-calving performance of cows and calves. Cows were assigned to one of three diets with the same energy and protein levels including a low-fat and two high-fat diets, which included either canola seed (CAN) or flaxseed (FLX). No differences in cow body weight or calving to weaning average daily gains were found. Body condition scores during the first 6 weeks after calving were greater for low fat compared to high fat diets with no difference between high fat diets. Backfat thickness over the ribs was greater for low fat compared to high fat cows at calving and at weaning with no difference between CAN vs. FLX cows. Over the first 6 weeks after calving, no difference was observed for milk yield. Milk protein concentration was greater for CAN compared to FLX. Milk fat from FLX cows had greater conjugated fatty acids than CAN cows during the first 6 weeks after calving. Pregnancy rate of high fat cows tended to be greater than low fat cows, with no difference between CAN and FLX cows. Calves from high fat cows were 2.7 kg heavier at birth than low fat cows. From calving to weaning, average daily gains of calves born to CAN cows was 60 g per day greater than calves born to FLX cows, with no difference for calves born to low fat vs. high fat cows. At slaughter, calves from high fat cows had greater pre-slaughter body weight (+26 kg) and hot carcass weights (+16 kg) compared to low fat cows, with no difference between CAN vs. FLX. These results show that feeding a HF diet during pregnancy results in heavier calves at birth and slaughter, and superior calf weight gains from birth to slaughter, as well as heavier carcasses, possibly due to a developmental (genetic) programming effect.

Abstract

A study was conducted to evaluate the effects of level and source of fat in the diet of gestating beef cows on the postpartum performance of the dam and the progeny. Each year, 75 mature pregnant (183 ± 4.8 d until calving) Angus cows with similar BW (663 ± 21.5 kg) and BCS (2.6 ± 0.12; 1 to 5 scale) were randomly assigned to 1 of 15 outdoor pens. Each pen was assigned to 1 of 3 iso-caloric and iso-nitrogenous treatments: a low-fat diet (LF; 1.4 ± 0.12% EE) and two high-fat diets (HF; 3.3 ± 0.20% EE) including a canola seed-(CAN) or a flaxseed (FLX)-based pelleted feed. Diets were formulated to meet the requirements of pregnant beef cows and fed until calving. Data were analyzed as a randomized complete block design with contrasts for the effects of level (LF vs. HF) and source (CAN vs. FLX) of fat. No differences (P ≥ 0.21) were found for BW or calving to weaning ADG of cows. The average BCS during the first 42 d of lactation was greater (P<0.01) for LF compared with HF (2.63 vs. 2.51) with no difference (P = 0.35) for CAN vs. FLX cows. Subcutaneous fat thickness over the ribs was greater (P ≤ 0.01) for LF compared with that of HF cows at calving (5.7 vs. 4.3 mm) and at weaning (4.3 vs. 3.7 mm) with no difference (P ≥ 0.11) for CAN vs. FLX cows. Over the first 42 d of lactation, no difference (P ≥ 0.23) was observed for 12-h milk yield. Milk protein concentration was greater (P = 0.03) for CAN compared with FLX (3.11 vs. 3.01%) cows, whereas no difference (P ≥ 0.28) was observed for any other milk component. Milk fat from FLX cows had greater (P < 0.01) CLA and CLnA concentrations than that of CAN cows during the first 42 d of lactation. Pregnancy rate of HF cows tended (P = 0.07) to be greater than that of LF cows with no difference (P = 0.77) for CAN vs. FLX cows. Calves from HF cows were heavier (P ≤ 0.01) at birth (42.9 vs. 40.2 kg) than those from LF cows. From calving to weaning, ADG of calves born to CAN cows was greater (P = 0.03) that that of calves born to FLX cows (1.19 vs. 1.13 kg/d) with no difference (P = 0.18) for calves born to LF vs. HF cows. At slaughter, progeny of HF cows had greater (P ≤ 0.03) shrunk BW (605 vs. 579 kg) and HCW (355 vs. 339 kg) compared with those from LF cows with no difference (P ≥ 0.16) for progeny of CAN vs. FLX cows. These results show that feeding a HF diet over gestation results in heavier calves at birth and at slaughter, and superior calf gains from birth to slaughter as well as heavier carcasses, possibly due to a developmental programming effect.