HERBAGE ALLOWANCE X YEARLING HEIFER PHENOTYPE INTERACTIONS FOR PREWEANING CALF GROWTH ON HUMID PASTURE AND SEMIARID RANGELAND

Preweaning growth data were obtained during 4 yr on 349 Braford-sired calves from Brahman-Hereford Fl first-calf females. These females were allotted to either semiarid rangeland (Uvalde) or humid improved past ure (Overton) as weanlings and to one of four herbage allowance levels at each location as yearlings. Females were wintered on systems in lo cal industry practice and maintained on various allotted herbage level s both as yearlings and during first lactation. The desired range in h erbage allowance (400 to 2,800 kg of DM per 100 kg of BW at Uvalde and 80 to 460 kg of DM per 100 kg of BW at Overton) was accomplished by a djusting stocking rate monthly from April to weaning (October). Herbag e allowance and yearling heifer characteristics (hook height, conditio n score, or weight) were treated as continuous, independent variables in regression analyses. Preweaning daily gain responded to increased h erbage allowance differently for the two locations. Generally, at Over ton, herbage allowance influenced suckling calf growth to a greater ex tent than for the Fl yearling variables, but at Uvalde this trend was reversed. Heifers with larger yearling heights had first calves that g rew faster to weaning for both locations and all herbage allowances, a lthough the relationship was stronger for greater herbage allowances a t Overton (herbage allowance x yearling weight interaction, P <.07). T his interaction was not detected (P >.15) at Uvalde. Interactions betw een herbage allowance and yearling condition score were detected (P <. 05) at both Overton and Uvalde, but these interactions were different( P <.15) at the two locations. At Uvalde, calf daily gain increased mor e with increased herbage allowance for females that had greater yearli ng condition than for those with less condition. At Overton, the oppos ite effect was observed: yearlings of lower condition had calves that benefited the most. For humid improved pastures, yearling females with lower condition scores had calves that grew faster, especially at hig h herbage allowances. In contrast, for semiarid rangeland, fatter year ling females had calves that grew faster, especially at high herbage a llowance.