Abstract
Rumen-protected omega-6 (ω-6) fatty acids have been investigated for their potential to enhance reproductive success in beef cattle. However, limited research has explored ω-6 supplementation across different physiological stages, particularly in both cows and heifers. This study evaluated the effects of ω-6 supplementation during late gestation, post-breeding, and before and after fixed time artificial insemination (FTAI) on cow reproductive function, calf pre-weaning growth, and young cow development. In the first experiment, 73 mature cows were assigned to a low-fat rumen unprotected control (UPFA) or a high-fat rumen-protected ω-6 supplement (100 g/hd/d; RPFA) for 37 days pre-partum (PRE) and/or 49 days post-AI (POST) in a 2×2 factorial arrangement. Supplement intake varied among cows, but body weight remained unaffected (P = 0.52). Plasma ω-6 concentrations increased with supplement intake across the PRE and POST periods (P < 0.05). Reproductive outcomes, including postpartum estrus activity (P = 0.81) and FTAI estrus response (P = 0.13), were unaffected. Although corpus luteum (CL) area did not differ (P = 0.16), PRE RPFA-POST UPFA cows had elevated plasma progesterone concentration (P = 0.006) and POST RPFA cows tended to have greater conception to FTAI (P = 0.08). POST RPFA calves tended to have greater midsummer weights (P = 0.09), while UPFA born calves exhibited greater total protein concentrations in blood at 24 hours old (P = 0.07). The second experiment investigated the effects of ω-6 supplementation on primiparous and young, multiparous cows. Eighty cows received either no supplement (CON, n = 40) or a high-fat rumen-protected ω-6 supplement (100 g/hd/d; TRT, n = 40) for 10 days before FTAI and 21 days after FTAI. Body weight remained similar throughout the trial (P ≥ 0.27). Estrus response to FTAI (P = 0.35) and CL area on d 7 (P = 0.15) were not affected; although, CON cows had greater d 7 plasma progesterone (P = 0.03). Conception rates did not differ (P = 0.82). Overall, free choice ω-6 supplementation altered the plasma fatty acid profile but did not significantly impact reproductive outcomes or calf growth from birth to weaning. In young, primiparous and multiparous cows, ω-6 supplementation did not enhance reproductive performance or conception rates following FTAI. These findings suggest that ω-6 fatty acid supplementation does not markedly improve reproductive efficiency in beef cattle across different physiological stages and may be highly dependent on supplement intake.