Abstract 277

Hunter,-RA; Siebert,-BD

Division of Tropical Animal Science, CSIRO, Tropical Cattle Research Centre, North Rockhampton, Qld. 4702, Australia.

Australian-Journal-of-Agricultural-Research. 1986, 37: 5, 549-560; 23 ref.

The effects of genotype, age and liveweight (LW), pregnancy and lactation on the voluntary feed intake by cattle of roughage diets of different qualities were studied. Diets ranged from poor quality (low-nitrogen, high-fibre) spear grass (Heteropogon contortus) hay on which intakes were low (11 g DM/kg LW) to good quality lucerne hay (26 g DM/kg LW). On the poorest-quality diet, differences in intake between Bos taurus and B. indicus were not significant. On the higher quality diets Herefords ate significantly (P < 0.05) more than Brahmans. In addition, as the quality of the diet improved from speargrass through to lucerne, the breed difference in favour of the Herefords became progressively greater and the variability between animals progressively smaller as a proportion of intake. Another study showed that with increasing age and liveweight of steers, intake per unit body weight declined, the rate of decline being significantly (P < 0.05) greater on good-quality lucerne than on a poor-quality speargrass diet. There was no significant difference between Aberdeen-Angus and Brahman steers in the rate of decline of intake of each diet with increasing age and liveweight of the steers. Another experiment in which intake of pregnant and lactating heifers was estimated showed that the amount of feed eaten by pregnant heifers increased with increasing liveweight in late pregnancy, with intake per unit liveweight remaining constant. Lactating cows ate 35% more on a liveweight basis than their non-pregnant, non-lactating counterparts.