Herbage allowance x yearling heifer phenotype interactions for the growth of Brahman-Hereford F1 first-calf females grazing humid pasture and semiarid rangeland.

Growth data were collected over 4 yr from 349 Brahman-Hereford F1, first-calf, lactating females that had been allotted as weanlings to either semiarid extensive rangeland (Uvalde) or humid improved Bermudagrass pasture (Overton) and to one of four herbage allowance levels at each location as yearlings. Heifers were wintered according to systems in local practice and maintained on allotted forage levels both as yearlings and during their first lactation. Heifers were bred to Braford bulls to calve as 2-yr-olds in January to March. Herbage allowance (400 to 2,800 kg of DM/100 kg BW at Uvalde and 80 to 460 kg of DM/100 kg BW at Overton) was maintained by adjusting stocking density monthly from April to weaning (October). Herbage allowance and yearling heifer hook height, condition score, or weight (taken on April 15) were continuous independent variables in regression analyses. Final heifer weight, height, and condition responses to increased herbage allowances were related to yearling phenotypes differently (P < .01) for the two locations. At Uvalde, yearling condition score interactions were especially important in that heifers that had more condition (especially those > 5 for 1 to 10 with 10 = fattest) as yearlings retained more (P < .05) weight and condition and grew more (P < .05) in height than did those of lower yearling condition. These females also responded to increased herbage allowance by gaining advantage (P < .05) in these variables, whereas those of lower yearling condition made smaller advances. At Overton, yearling condition played little role in subsequent growth. The yearling variable that had the greatest interactive effect was height. Shorter yearling heifers (< 123 cm) responded (P < .07) to increased herbage allowance so that they had greater final condition and grew more rapidly in height than those taller as yearlings.