Estrous Synchronization Increases Early Calving Frequency, Whichenhances Steer Progeny Value

Calving records collected between 2000 and 2008 at the Gudmundsen Sandhills Laboratory, Whitman, NE, were used to determine the effect of estrous synchronization on calving distribution and the impact of time of calving on carcass characteristics. Calves born between 2000 and 2006 resulted from non-synchronized 60 d breeding seasons between 1999 and 2005 (n = 2075). Calves born in 2007 and 2008 resulted from synchronized 45 d breeding seasons in 2006 and 2007 (n = 521). Estrus was synchronized with a single injection of prostaglandin F2α administered 108 h after bulls were turned in with cows. Cow pregnancy rate after synchronized or nonsynchronized breeding seasons was similar (P = 0.48). Twelve percent more (P < 0.001) synchronized cows calved during the first 21 d compared to non-synchronized cows. Average calving date and percentage of male calves were similar (P ≥ 0.23). The weaning BW of calves born to synchronized dams was 9 kg greater (P < 0.001) than calves from non-synchronized dams. The effect of calving distribution, defined as percentage calving in the 1, 2 or 3 21 d of the season was evaluated in the steer progeny born between 2001 and 2007 (n = 659). Steers were fed in the feedlot and slaughtered after 218 d on feed. As the time of calving increased, male calf birth weaning BW decreased (P < 0.001). Time of calving did not affect feedlot ADG (P = 0.90). As time of calving increased, HCW, marbling score and yield grade decreased (P < 0.001). Although the percentage of steers achieving USDA small grade was not affected (P = 0.17) by time of calving, the percentage of steers receiving a USDA quality grade of modest or greater and the total carcass value declined (P ≤ 0.001) as time of calving increased. Estrous synchronization with a single injection of prostaglandin F2α resulted in more cows giving birth earlier, even though the breeding season was 15 d shorter. Calves born earlier in the season are heavier at weaning and produce a heavier, more valuable carcass.