Effects of Low Vs. High Dietary Lipid and Source of Lipid on Performance of Gestating Beef Cows and Subsequent Effects on Progeny

A two-year study was conducted to evaluate the effects of dietary lipid inclusion and source of lipid on performance of gestating beef cows and subsequent effects on progeny. Each year, 75 multiparous (≥3 calving) 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-lipid diet (LL; 1.4±0.03% EE) consisting of grass hay, barley straw, and barley grain, and two high-lipid diets (HL) 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), adjusted for changes in environmental conditions, and to be iso-caloric (DE: 2.6±0.02 Mcal/kg) and iso-nitrogenous (CP: 10.5±0.09%). Data were analyzed as a randomized complete block design with contrasts to separate the effects of lipid (LL vs. HL) and source of lipid (CAN vs. FLX). At the start of trial, all treatments had similar (P=0.37) corrected (for conceptus) BW (659±3.8 kg), and similar (P≥0.33) proportion of thin (0.7±0.69%), optimal (95.2±3.04%), and over conditioned (4.1±2.80%) cows. After 160 d on trial (24±0.9 d pre-calving), corrected BW of LL cows (711±2.2 kg) and proportion of fat cows (15.2±8.8%) were greater (P≤0.04) than those fed HL, with no difference (P≥0.47) between CAN and FLX for corrected BW (698±4.6 vs. 702±4.4 kg) and proportion of over conditioned cows (3.7±3.3 vs. 5.6±4.3%). From calving to weaning, no differences (P≥0.22) were observed in ADG, BW, BCS, milk yield, and milk composition of cows. Birth weight of bull-calves from LL cows (41±0.5 kg) was lower (P<0.01) than those from HL cows, while no difference (P=0.70) was observed between bull-calves from CAN (45±0.7 kg) and FLX (45±1.2 kg) cows. At weaning, ADG and BW of steer-calves from LL cows (1.17±0.02 kg/d and 251±3.7 kg) were similar (P≥0.74) to those from HL, while steer-calves from CAN cows had greater (P≤0.04) ADG (1.20±0.03 vs. 1.11±0.04 kg/d) and BW (261±5.4 and 245±6.9 kg) than those from FLX cows. In conclusion, differences observed in corrected BW and BCS between cows fed low vs. high-lipid 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.