Effects of postpartum fat supplementation and source on the reproductive performance of lactating young beef cows grazing cool-season grass pastures

Abstract

ABSTRACT Objective The objective was to evaluate the effects of fat supplementation and source on reproductive performance of young lactating Angus beef cows grazing cool-season grass (CSG) pastures. Materials and Methods Over 3 yr, 36 second- and third-calving, lactating (38 ± 1.5 d postpartum) Angus cows (554 ± 15.5 kg of BW) were assigned randomly to 9 paddocks (4 cows per paddock) of CSG pastures. Each paddock was assigned randomly to a nonsupplemented control (CON) or 2 supplemented (SUP) treatments in which cows received 300 g/cow per day of supplemental fat (ether extract) from a canola seed–based (CAN) or flaxseed-based (FLX) pellet for 42 d before start of the breeding period. Data were analyzed as a randomized complete block design contrasting the effects of fat supplementation (CON vs. SUP) and fat source (CAN vs. FLX). Results and Discussion Results indicate that cows in CON had greater (P = 0.01) forage utilization and tended (P = 0.08) to have greater estimated forage DMI compared with cows in SUP, whereas no difference (P ≥ 0.76) was observed between CAN and FLX treatments. By the end of the trial, all treatments resulted in positive ADG, maintained or increased BCS and s.c. fat thickness, and reduced serum nonesterified fatty acid concentrations 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. The failure to find treatment differences in growth and reproductive performance is likely a result of greater-than-expected nutrient content (CP: 12.5 ± 2.5%; TDN: 56.5 ± 2.9%) of CSG pastures and similar nutritional status across treatments. Implications and Applications These results indicate that prebreeding fat supplementation and source had no beneficial effects on reproductive performance of young, lactating Angus beef cows grazing good quality CSG pastures.