Weaning and post-weaning performance by fall-born calves weaned on different dates from endophyte-infected tall fescue pastures managed with two different rotation frequencies

A number of studies have reported performance by spring-calving cows grazing Neotyphodium-infected fescue [E+, Lolium arundinaceum (Schreb.) Darbysh.], but post-weaning calf performance from the majority of those studies is limited. Furthermore, both pre- and post-weaning information pertaining to fall-calving cows and their calves grazing E+ is particularly limited. A 3-year study was initiated in April 2000 near Batesville, AR (USA) to investigate the impact of rotational management (twice monthly vs. twice weekly) program and weaning date [mid-April (EARLY) vs. early June (LATE)] on production of fall-calving cow-calf pairs grazing E+ overseeded with ladino (Trifolium repens L.), and red clover (Trifolium pretense L), lespedeza (Lespedeza stipulacea Maxim.), and crabgrass (Digitaria sanguinalis (L.) Scop.). A secondary objective of the study was to evaluate calf performance both at weaning and after weaning until either breeding of the heifers or slaughter of the steers. Calves weaned later had greater (P < 0.05) actual weaning weights, but weaning date × year interactions were detected (P < 0.05) for most measurements at weaning. Weight loss during a simulated transport and sale, as well as the days required to regain the lost weight were lower (P < 0.05) by EARLY than by LATE in 2 of 3 years, and intake (kg DM/100 kg BW) was higher by EARLY than by LATE in 2 of 3 years. Antibody titers to infectious bovine rhinotracheitis and bovine virus diarrhea measured prior to vaccination and at weaning were greater (P < 0.05) from EARLY than from LATE. Heifer weight at breeding was greater (P < 0.05) from LATE than from EARLY in 1 year and numerically greater (P ≥ 0.11) from LATE in the other 2 years. Initial and final feedlot BW and gain did not differ (P ≥ 0.16) among previous treatments in 2 of 3 years. Therefore, carryover effects of weaning date or rotational grazing on calves previously grazing E+ tall fescue may be mitigated during a subsequent backgrounding period such that impacts on subsequent breeding or feedlot performance is minimized.