Impact of Body Condition Change Post-Breeding on Reproductive Performance of Beef Cows
Whittier, William D.
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Body condition score (BCS) is a commonly used tool for evaluating the nutritional status of beef cows. Good nutritional status of beef cows is one of the essential components for improved reproductive performance. The objective was to evaluate the impact of change in body condition during 2 months after breeding on the AI pregnancy success in beef cows. Angus cross beef cows (N = 2571) from 11 locations were included in this study. All cows were given a BCS (1-emaciated; 9-obese), by the same clinician in each location at the initiation of the synchronization (CO-Synch+CIDR) protocol and again at pregnancy diagnosis, 60 to 70 days later. Cows were fitted with Kamar heat detection patches at CIDR removal and observed three times daily for estrus expression until timed insemination. Cow’s Cows’ pregnancy status was determined by per-rectal palpation or using ultrasonography. Variables included in the model (PROC MIXED) were change in BCS (no change or gain vs. loss), cows expression of estrus at or prior to AI (activated, partially activated, or lost Kamar) or not (intact Kamar), age of the dam (2, 3 to 6 and >6 years), days post calving at initiation of synchronization (30 to 60, 61 to 80 and > 81 days) and appropriate 2-way interactions. Season (location) and AI sires were considered as random effects. The results showed AI pregnancy rate was influenced by change in the BCS [No change or gain: 55.3%; (1034/1870) vs loss: 50.1% (352/703); P<0.05] and cows that showed estrus at or prior to AI [estrus: 57.8% (825/1423) vs no estrus: 48.9% (560/1148); P<0.0001]. In conclusion, cows that lost body condition between breeding and pregnancy diagnosis had lower AI pregnancy rates compared to cows that maintained or gained body condition. It is essential to feed cows following breeding to maintain their BCS in order to optimize their conception rates.