Herbage Allowance x Yearling Heifer Phenotype Interactions for Preweaning Calf Growth on Humid Pasture and Semiarid Rangeland

Preweaning growth data were ob- tained during 4 yr on 349 Braford-sired calves from Brahman-Hereford F1 first-calf females. These fe- males were allotted to either semiarid rangeland (Uvalde) or humid improved pasture (Overton) as weanlings and to one of four herbage allowance levels at each location as yearlings. Females were wintered on systems in local industry practice and maintained on various allotted herbage levels both as yearlings and during first lactation. The desired range in herbage 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 adjusting stocking rate monthly from April to weaning (Oc- tober). Herbage allowance and yearling heifer charac- teristics (hook height, condition score, or weight) were treated as continuous, independent variables in regression analyses. Preweaning daily gain responded to increased herbage allowance differently for the two locations. Generally, at Overton, herbage allowance influenced suckling calf growth to a greater extent than for the F1 yearling variables, but at Uvalde this trend was reversed. Heifers with larger yearling heights had first calves that grew faster to weaning for both locations and all herbage allowances, al- though the relationship was stronger for greater herbage allowances at Overton (herbage allowance x yearling weight interaction, P .15) at Uvalde. Interactions between 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 more with increased herbage allowance for females that had greater yearling condition than for those with less condition. At Overton, the opposite 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 high herbage allowances. In contrast, for semiarid rangeland, fatter yearling females had calves that grew faster, espe- cially at high herbage allowance.