Supplementation of rangeland primiparous Bos indicus x Bos taurus beef heifers during lactation. 1. Effects on dam milk production and liveweight, bull calf growth, live carcass characteristics and metabolic hormone concentrations

The practice of feeding replacement-breeding bulls on high energy diets after weaning to meet liveweight (LW) and carcass expectations between 18 and 24 months of age negatively affects reproductive potential. This experiment reports upon the effects of an alternative management strategy aimed at improving calfhood nutrition in rangeland-reared bulls to enhance LW and live carcass characteristics at 2 years. Following artificial insemination (AI cohort; n = 26), or natural mating, subsequent to the addition of bulls at 39 d post-AI (NM cohort; n = 36), primiparous Santa Gertrudis heifers grazing rangeland pastures with bull calf progeny were allocated at parturition to receive either nil supplement (control; CON) or provided with unrestricted access to a pelleted vegetable protein meal-based supplement containing 35% CP (SUPP) until weaning at 199 ± (SD) 26 d. The mean estimated pellet consumption by SUPP heifers during lactation was 2.6 ± (SEM) 0.5 kg DM daily. Grazing diet quality measurements indicated nutritional restriction of CON heifers until at least 115 d of lactation. This was confirmed by lower blood urea nitrogen concentrations at 88 d (P