HERBAGE INTAKE, GROWTH-PERFORMANCE, AND CARCASS AND MEAT QUALITY CHARACTERISTICS OF ONCE-BRED HEREFORD X FRIESIAN HEIFERS WEANED AT 12 OR 21 WEEKS OF LACTATION

Beef-breeding cows are traditionally weaned at about 7-8 months of cal f age in New Zealand but early weaning may have advantages in once-bre d heifer beef production systems. This study compared the growth perfo rmance, and carcass and meat quality characteristics, of 31 once-bred Hereford x Friesian heifers mated to Angus (17 heifers) or Charolais ( 14 heifers) sires from which calves were removed at either 12 weeks (D ay 84 of lactation = L84) or 21 weeks (Day 147 of lactation = L147) of lactation. These are referred to as the ''W84'' (calves weaned at Day 84 and their darns) or ''W147'' (calves weaned at Day 147 and their d arns) groups respectively. During L84-L147, W84 heifers had higher dai ly liveweight gain (LWG) than the W147 heifers (0.79 versus 0.51, PSE = 0.07 kg/day, P < 0.01). Calves weaned at L84 had significantly lower daily LWG than W147 calves during the period L84-L147 (0.73 versus 1. 30, PSE = 0.05 kg/day, P < 0.001). This resulted in 30 kg lower (P < 0 .001) liveweight in W84 versus W147 calves at the time of weaning for the latter group. During the period L137-L147, the W84 versus W147 hei fers had herbage organic matter intakes (estimated using intraruminal chromium controlled-release capsules) of 3.01 versus 3.50 (PSE = 0.16) kg DM/100 kg LW per day (P < 0.05). Heifers whose calves were removed at L147 spent more time grazing (P < 0.01) and ruminating (P < 0.10), and less time idling (P < 0.01) than the W84 heifers. Overall, weanin g time did not significantly affect the carcass and meat quality chara cteristics of W84 or W147 heifers. Results are discussed in the contex t of weaning time effects on the productivity and carcass and meat qua lity traits of once-bred heifers.