A comparison of spring- and fall-calving beef herds grazing tall fescue

Nineteen years of beef cow herd records were obtained from the Research and Education Center at Ames Plantation, near Grand Junction, Tennessee. The cow herds were under the same management, and all cows were strictly culled for reproductive failure, age, and low performance of their calves. The cows primarily grazed tall fescue (Lolium arundinaceum Schreb.) with the wild-type endophyte (Neotyphodium coenophialum) that is known to cause the symptoms of tall fescue toxicosis. For 19 yr the total number of cows and calves were 478 and 1,534 for the spring-calving herds and 474 and 1,727 for the fall-calving herds, respectively. Phenotypic parameters were days to first calf, calving interval, number of calves born, birth BW, weaning weight (WW), adjusted 205-d WW, ADG from birth to weaning, and weight/day of age. The data were analyzed from a historical standpoint using herd as a fixed effect and years as replicates. Heifers in the spring-calving herd averaged 27 d older (P < 0.0001) at calving than the fall-calving heifers. The spring-calving herd had a shorter calving interval (P < 0.05) and produced fewer calves per cow (P < 0.05). Although calves born in the spring and fall herd had similar birth BW (P = 0.751), the calves born in the spring had a higher ADG and higher 205-d WW than did those born in the fall. Even though the spring-born calves gained faster and had higher 205-d WW, the fall-calving herd increased the income of the farm because of greater number of calves and reduced need for replacement heifers.