| dc.description.abstract |
Semen from Hereford (H), Friesian (F), Charolais (C) and Brahman (B) bulls was used to inseminate H and F cows in August and September of each year from 1970 to 1973. After weaning at 8 months of age, the heifer progeny were grazed on improved pastures and oestrus was detected by sterilized bulls fitted with chin-ball harnesses. Average daily liveweight gains (kg/day) from weaning to 21 months and liveweights (kg) at 21 months were: HH, 0.44, 373 ; FH, 0.47, 402; CH, 0.47,402; BH, 0.45, 374; HF, 0.42, 428; FF, 0.43, 427; CF, 0.44, 451; BF, 0.40, 401. Mean ages (days) and liveweights (kg) at puberty, and the proportions (%) of heifers reaching puberty by 15 months of age were: HH 464, 290, 41; FH 347, 263, 85; CH 470, 326, 38; BH 568, 336, 14; HF 277, 285, 100; FF 298, 294, 98; CF 309, 313, 97; BF 397, 306, 64. Heterosis in HF and FH crosses for age and weight at puberty were - 59 days and - 17.4 kg respectively. These results indicate that, relative to the use of straightbred Hereford heifers, early breeding in the progeny would be facilitated by crossing Hereford with Friesian, unaffected by crossing with Charolais, but made more difficult by crossing with Brahman, in a temperate environment. |
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