Effects of low vs. high dietary fat and source of fat on the performance of gestating beef cows and subsequent effects on progeny
Añez-Osuna, F., Penner, G. B., Fitzsimmons, C. F., Dugan, M. E. R., Campbell, J., Jefferson, P. G., Lardner, H. A. and McKinnon, J. J. 2017. Effects of low vs. high dietary fat and source of fat on the performance of gestating beef cows and subsequent effects on progeny. ASAS-CSAS Joint Annual Meeting (JAM), July 8-12, 2016, Baltimore, MD, USA.
A two-year study was conducted to evaluate the effects of dietary fat inclusion and source of fat on performance of gestating beef cows and subsequent effects on progeny. Each year, 75 mature pregnant Angus cows were stratified by BW and BCS (Scottish System: 1 to 5), and randomly assigned to 15 pens (5 cows/pen). Subsequently, each pen was randomly assigned to one of three (n=5) treatments: a low-fat diet (LF; 1.4±0.03% EE) consisting of grass hay, barley straw, and barley grain, and two high-fat diets (HF) where barley grain was substituted with a canola seed (CAN; 3.3±0.02% EE) or a flaxseed (FLX; 3.3±0.05% EE) based pelleted feed. Diets were formulated to meet the requirements of pregnant beef cows during the last two trimesters of gestation (184±0.9 d) and adjusted for changes in environmental conditions (2.6±0.02 Mcal/kg of DE and 10.5±0.09% of CP). Data was analyzed as a randomized complete block design with contrasts carried out to separate the effects of fat (LF vs. HF) and source of fat (CAN vs. FLX). At the start of trial, all treatments had similar (P=0.37) BW corrected for conceptus (659±3.820.7 kg), and similar (P≥0.33) proportion of thin (0.7±0.69%), optimal (95.2±3.04%), and fat (4.1±2.80%) cows. After 160 d on trial (24±0.9 d pre-calving), corrected BW of LF cows (711±2.2 kg) and proportion of fat cows (15.2±8.8%) were greater (P≤0.04) than those fed HF, with no difference (P≥0.47) between CAN and FLX for corrected BW (698±4.6 vs. 702±4.4 kg) and proportion of fat cows (3.7±3.3 vs. 5.6±4.3%). From calving to weaning, no differences (P≥0.22) were observed for performance of cows. Birth weight of bull-calves from cows fed LF (41±0.5 kg) was lighter (P<0.01) than those from cows fed HF, while no difference (P>0.70) was observed between calves from cows fed CAN (45±0.7 kg) and FLX (45±1.2 kg). At weaning, ADG and BW of steer-calves from LF cows (1.17±0.02 kg/d and 251±3.7 kg) were similar (P≥0.74) to those from HF, while ADG and BW of steer-calves from CAN cows (1.20±0.03 kg/d and 261±5.4 kg) were greater (P≤0.04) than those from FLX cows (1.11±0.04 kg/d and 245±6.9 kg). In conclusion, differences observed in corrected BW and BCS between cows fed low vs. high-fat diets before calving and the difference between their bull-calves at birth, suggest a differential partitioning of ME by gestating beef cows which is dependent on the form of dietary energy.
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