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Two studies were conducted to evaluate the effects of fat and the type of fatty acid (MUFA vs. PUFA) inclusion in the diet of beef cows during the pre- and postpartum period on the performance of the dam and the progeny. In study 1, replicated over three years, 36 second- and third-calving lactating Angus cows were stratified by BW (554±15.5 kg) and days postpartum (38±1.5 d), and randomly assigned to 9 paddocks (4 cows/paddock) where cows grazed cool-season grass (CSG) pastures (12.5±2.5% CP and 56.5±2.9% TDN). Each paddock was randomly assigned to one of three replicated treatments: a non-supplemented control (CON), and two supplemented (SUP) treatments where cows were offered either a canola seed (CAN) or a flaxseed (FLX) based pellet targeting 300 g/cow/d of supplemental fat (EE) over 42 d. Data were analyzed as a RCBD with contrasts for the effect of fat supplementation (CON vs. SUP) and source (CAN vs. FLX). Results indicate that CON had greater (P=0.01) forage utilization and tended (P=0.08) to have greater estimated forage DMI compared to SUP, while no difference (P≥0.76) was observed between CAN and FLX. At the end of the trial, all treatments resulted in positive ADG, maintained or increased BCS and SCFT, and reduced serum NEFA concentration with no difference (P≥0.20) among treatments. No differences (P≥0.12) were observed for pregnancy rate, calving distribution and calving to calving interval. In study 2, replicated over 2 years, 75 multiparous (≥3 calving) pregnant Angus cows were stratified by BW (663±21.5 kg) and BCS (2.6±0.12), and randomly assigned to 15 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) and two high-fat diets (HF; 3.3±0.20% EE) which included a CAN or a FLX pelleted feeds similar to those used in study 1. Diets were formulated to meet the requirements of pregnant beef cows during the last two trimesters of gestation (183±4.8 d), and offered such that each pen on average received similar amounts of DE (31.2±2.8 Mcal/cow/d), CP (1.36±0.13 kg/cow/d), and DM (12.9±1.0 kg/cow/d). Data were analyzed as RCBD with contrasts for 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. Feeding FLX diet over gestation resulted in subcutaneous adipose tissue (SCAT) with 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 when compared to 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 over 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 and FLX cows. 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 to HF (2.63 vs. 2.51) with no difference (P=0.35) for CAN vs. FLX cows. Subcutaneous fat thickness over the 12/13th ribs was greater (P≤0.01) for LF compared to 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) between CAN and FLX cows. Over the first 42 d of lactation, no difference (P≥0.23) was observed for 12-h milk yield. However, milk protein concentration was greater (P=0.03) for CAN compared to FLX (3.11 vs. 3.01%) cows while 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 (95.4%) tended (P=0.07) to be greater than that of LF cows with no difference (P=0.77) between CAN and FLX cows. From calving to weaning, ADG of calves born to CAN cows was greater (P=0.03) than that of calves born to FLX cows (1.19 vs. 1.13 kg/d) with no difference (P=0.18) between calves born to LF and 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 to those from LF cows with no difference (P ≥ 0.16) between progeny of CAN and FLX cows. Expression of evaluated genes in muscle tissue of male calves was not significantly affected by either the level or source of dietary fat during gestation. These results indicate that reproductive performance of lactating young beef cows was not affected by the level or source of fat in their diet likely as a result of sufficient good quality pastures. On the contrary, a prepartum high-fat diet tended to increase the pregnancy rate of beef cows at the end of the breeding season. Also, a prepartum high-fat diet resulted in a reduced amount of subcutaneous adipose tissue in the dam but heavier calves at birth, which suggests a partitioning of the ME dependant on the type of dietary energy. Moreover, a high-fat diet during gestation resulted in improved birth to slaughter performance and superior HCW at slaughter of the progeny.



Beef cows, Gestation, Fat supplementation



Doctor of Philosophy (Ph.D.)


Animal and Poultry Science


Animal Science


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