Genotype x environment interactions for postweaning performance in crossbred calves grazing winter wheat pasture or dormant native prairie

Data from 403 calves from Angus, Brahman, and reciprocal-cross cows sired b y Polled Hereford bulls were used to evaluate the impact of postweaning bac kgrounding forages on postweaning BW, gains, and carcass traits. Calves wer e born (spring of 1991 through 1994) and reared on either endophyte-infecte d tall fescue or common bermudagrass pastures. After meaning, calves were t ransported 360 km to the Grazinglands Research Laboratory, west of El Reno, Op, and, within breed and preweaning forage, were assigned to one of the f ollowing winter stocker treatments: l)winter wheat pasture or 2) dormant na tive prairie plus supplemental CP. In March, winter stocker treatments were ended and calves were grazed as a single group on cool-season grasses unti l early July (1992; 1993, and 1994) or late May (1995), when the feedlot ph ase began. In the feedlot, calves were fed a high concentrate diet for an a verage of 120 d until a backfat thickness of > 10 mm was reached. Calves we re shipped in truck load lots to Amarillo, TX (350 km), for processing and collection of carcass data. Averaged over calf breed group, calves wintered on wheat pasture gained faster (P < 0.01) during the stocker phase (0.71 v s 0.43 kg); had heavier (P < 0.01) final feedlot weights (535 vs 512 kg); l ower feedlot (P < 0.01) ADG (1.37 vs 1.53 kg); heavier (P < 0.01) carcass w eights (337 vs 315 kg); larger (P < 0.01) longissimus muscle (84.9 vs 81.8 cm(2)); higher percentage (P < 0.01) of kidney, heart, and pelvic fat (2.32 vs 2.26); and higher (P < 0.01) dressing percentage (62.2 vs 61.3) than ca lves backgrounded on native prairie. Maternal heterosis for stocker ADG was evident in calves backgrounded on native prairie but not on winter wheat ( P <less than> 0.10), but the two environments were similar in maternal hete rosis for feedlot ADG and carcass traits. Calves wintered on native prairie were restricted in growth and expressed compensatory gain during the feedl ot phase but not during the spring stocker phase. Dormant native grasses ca n be used to winter stocker calves excess to the winter wheat pasture needs , but ownership of these calves would have to be retained through the feedl ot phase to realize any advantage of built-in compensatory gain. Finally, t hese data suggest that expression of maternal heterosis for weight gain is more likely in calves backgrounded on native prairie than in calves grazed on winter wheat.