Level and source of fat in the diet of gestating beef cows: I. Effects on the prepartum performance of the dam and birth weight of 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: I. Effects on the prepartum performance of the dam and birth weight of the progeny, 97(7), 3103-3119. http://dx.doi.org/10.1093/jas/skz171

Plain language summary

A study was conducted to evaluate the effects of level and source of fat in the diet of pregnant beef cows on the pre-calving performance of cows and the birth weight of calves. Cows were assigned to one of three diets with the same energy and protein levels including a low-fat (LF) and two high-fat diets (HF), where one HF diet included canola seed (CAN) and the other HF diet included flaxseed (FLX). Data were analyzed to separate the effects of level (LF vs. HF) and source (CAN vs. FLX) of fat. After 160 days on trial, the body weight (BW) of LF cows and the proportion of overconditioned cows were greater than those of HF, with no difference between CAN and FLX for BW and proportion of overconditioned cows. Feeding FLX diet during gestation resulted in cows with a greater concentration of conjugated linolenic acid and n-3 fatty acids when compared with cows fed the CAN diet. By the end of gestation, the concentration of non-esterified fatty acids (NEFA) in the blood of LF cows was lower than that of HF cows, and FLX cows had greater NEFA concentration in the blood than CAN cows. Cows receiving the LF diet during gestation gave birth to lighter calves compared with those receiving the HF diets, with no difference between calves born to CAN and FLX cows. In conclusion, these results suggest that the type of fatty acid in the diet of pregnant beef cows affected the fatty acid profile and that feeding a high-fat diet during pregnancy results in heavier calves at birth.

Abstract

A 2-yr study was conducted to evaluate the effects of level and source of fat in the diet of gestating beef cows on their prepartum performance and birth weight of progeny. Each year, 75 multiparous (≥3 calving) pregnant Angus cows were stratified by BW (663 ± 21.5 kg) and BCS (2.6 ± 0.12; 1 to 5 scale) and randomly assigned to 1 of 15 outdoor pens. Subsequently, each pen was randomly assigned to 1 of 3 (n = 5) treatments: a low-fat diet (LF; 1.4 ± 0.12% EE) consisting of grass-legume hay, barley straw, and barley grain, or 1 of 2 high-fat diets (HF; 3.3 ± 0.20% EE) that included either a canola seed (CAN) or a flaxseed (FLX) based pelleted feed. Diets were formulated to meet the requirements of pregnant beef cows during the last 2 trimesters of gestation (0.183 ± 4.8 d), adjusted for changes in environmental conditions, and offered such that each pen on average received similar daily amounts of DE (31.2 ± 2.8 Mcal/cow), CP (1.36 ± 0.13 kg/cow), and DM (12.9 ± 1.0 kg/cow). Data were analyzed as a randomized complete block design with contrasts to separate the effects of level (LF vs. HF) and source (CAN vs. FLX) of fat. After 160 d on trial, conceptus corrected-BW (CC-BW) of LF cows (708 kg) and the proportion of overconditioned cows (13.2%) were greater (P ≤ 0.04) than those of HF, with no difference (P ≥ 0.84) between CAN and FLX for CC-BW (697 kg) and proportion of overconditioned cows (3.6% vs. 2.9%). Feeding FLX diet during gestation resulted in cows with a greater (P ≤ 0.01) concentration of conjugated linolenic acid (0.12% vs. 0.05%) and n-3 (0.58% vs. 0.37%) fatty acids, and a tendency (P = 0.09) for conjugated linoleic acid concentration (1.05% vs. 0.88%) to be greater in subcutaneous adipose tissue (SCAT) when compared with cows fed the CAN diet. By the end of gestation, serum NEFA concentration of LF cows (592 μEq/L) was lower (P < 0.01) than that of HF cows, and FLX cows had greater (P < 0.01) serum NEFA concentration than CAN cows (636 vs. 961 μEq/L). Cows receiving the LF diet during gestation gave birth to lighter (P < 0.01) calves compared with those receiving the HF diets (40.2 vs. 42.9 kg), with no difference (P = 0.24) between calves born to CAN (42.4 kg) and FLX (43.3 kg) cows. In conclusion, these results suggest a partitioning of the ME in pregnant beef cows that is dependent on the type of dietary energy, resulting in heavier calves at birth for cows fed high-fat diets. Also, the type of fatty acid in the diet of gestating beef cows affected the fatty acid profile in SCAT and serum NEFA concentration.