Abstract A two-year study was conducted to evaluate the effects of level and source of fat in the diet of gestating beef cows on their pre-partum 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 one of fifteen outdoor pens. Subsequently, each pen was randomly assigned to one of three (n=5) treatments: a low-fat diet (LF; 1.4±0.12% EE) consisting of grass-legume hay, barley straw, and barley grain; or one of two 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 two trimesters of gestation (183±4.8 d), adjusted for changes in environmental conditions, and offered such that each pen on average received similar daily amounts of digestible energy (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 over-conditioned 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 over-conditioned cows (3.6 vs. 2.9%). Feeding FLX diet during gestation resulted in cows with a greater (P≤0.01) concentration of CLnA (0.12 vs. 0.05%) and n-3 (0.58 vs. 0.37%) fatty acids, and a tendency (P=0.09) for CLA concentration (1.05 vs. 0.88%) to be greater in subcutaneous adipose tissue (SCAT) when compared to 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 to 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. This content is only available as a PDF. © The Author(s) 2019. Published by Oxford University Press on behalf of the American Society of Animal Science. All rights reserved. For permissions, please e-mail: firstname.lastname@example.org. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)
Journal of Animal Science – Oxford University Press
Published: Nov 9, 21
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