HERBAGE INTAKE, INGESTIVE BEHAVIOR, AND GROWTH-PERFORMANCE IN UNBRED AND ONCE-BRED HEREFORD X FRIESIAN HEIFERS

The once-bred heifer beef production system involves mating heifers at 15 months of age to calve as 2-year-olds. This study compared the per formance of once-bred Hereford x Friesian heifers mated to Limousin or Charolais sires and the herbage intake of once-bred and never-bred he ifers during periods corresponding to late pregnancy and early lactati on in the former group. Heifers carrying Limousin-sired (LS) calves ha d gestation lengths slightly longer than those carrying Charolais-sire d (CS) calves (290.4 versus 286.6, pooled SE (PSE) = 1.2 days, P < 0.1 0), but there was no effect of calf sex on gestation length. The avera ge birth weight of calves was 40 +/- 1 kg, there being no difference b etween female and male, or LS and CS, calves. Dystocia caused mortalit y rates of 19% in calves and 9% in heifer dams. Female calves had 9 kg lower weaning weights at 142 days of age than male calves, whereas th e CS calves had greater weaning weights than LS calves (218.3 versus 2 04.9 kg, PSE = 3.6 kg, P < 0.01). Dam weaning weights were 443.5 versu s 394.7 kg (PSE = 9.5 kg, P < 0.01) and 437.5 versus 400.7 kg (PSE = 9 .5 kg, P < 0.05) in heifers suckling female versus male and LS versus CS calves, respectively. During late pregnancy, pregnant heifers had s imilar ingestive behaviour, herbage intake, and liveweight gains to ne ver-pregnant heifers when offered a restricted pasture allowance of 7 kg dry matter (DM)/head per day. During early lactation, however, neve r-pregnant and lactating heifers consumed 9.19 versus 11.36 kg organic matter (OM)/head per day, (PSE = 0.63 kg OM/head per day P < 0.05) at a pasture allowance designed to permit ad libitum intakes. During thi s period, liveweight gains of 1.70 versus 0.61 kg/day (PSE = 0.28 kg/d ay, P < 0.05) were recorded for the never-pregnant versus lactating he ifers. Results are discussed in the context of beef production from un bred and once-bred heifers.