Estimation of herbage intake of Angus heifers from growth rate and milk production selection lines

Abstract

Herbage intake was measured using n-alkanes (at age 10 and 13 months) and the pre- and post-grazing technique (at age 12 and 14 months) in 80 Angus heifers selected for high (Hi-Gr) or low (Lo-Gr) growth rate or high (Hi-Milk) or low (Lo-Milk) milk production. Average liveweight and estimated herbage intake at 10 months were 240.2±0.4 kg and 3.47±0.1 kg dry matter (DM)/head per day respectively. The respective values at 13 months of age were 287.2±1.9 kg and 6.50±0.36 kg DM/head per day. No differences in estimated herbage intake among the genetic lines were detected using n-alkanes at 10 or 13 months of age. Average liveweight at 12 months of age was 247.1±0.7 kg and mean estimated intakes were 4.86±0.26, 4.17±0.26, 4.37±0.26 and 3.00±0.26 kg DM/head per day for the Hi-Gr, Lo-Gr, Hi-Milk and Lo-Milk lines, respectively. The Lo-Milk line had lower (P<0.05) estimated intake than the other three lines. At 14 months of age, average liveweight was 272.5±0.6 kg and estimated intakes were 6.99±0.18, 6.52 kg±0.18, 6.71±0.18 and 7.28±0.19 kg DM/head per day for the Hi-Gr, Lo-Gr, Hi-Milk or Lo-Milk lines, respectively. Lo-Milk heifers had higher (P<0.05) intakes than heifers from the Lo-Gr and Hi-Milk lines. No statistical difference in intake between the Lo-Milk and the Hi-Gr lines was detected. In general, the Hi-Gr heifers outperformed the heifers from other lines.