Effect of maize supplementation, seasonal temperature and humidity on the liveweight gain of steers grazing irrigated Leucaena leucocephala/Digitaria eriantha pastures in north-west Australia

Abstract

Brahman Shorthorn steers (213±4·6 kg initial weight) were grazed on a pangola (Digitaria eriantha cv. Steudel) pasture interplanted with leucaena (Leucaena leucocephala cv. Cunningham) in rows 1·8–2·7 m apart in the Ord River Irrigation Area (ORIA) in north-west Western Australia. The leucaena comprised a mean of 46% of the diet but ranged from 100% of the diet on day 1 to c. 18% on day 7 of a 7-day grazing period, within the rotational grazing system. It was suggested that the low herbage allowance of leucaena may have restricted the intake of the steers, reducing the quantity and quality of the herbage consumed.

The steers were also supplemented with maize during the dry and wet seasons (1992 and 1992/93). The maize supplement was offered at 0, 0·5, 1·0, 1·5 and 2·0 kg/head per day, over a 168-day period. Maize supplementation at 1·5 kg maize per head per day resulted in an increase in the liveweight gain of the steers grazing leucaena/pangola pastures in the dry season from 0·73±0·05 kg/day (mean±S.E.) for no supplementation to 1·1±0·05 kg/day for 1·5 kg/head per day of maize. Maize supplementation up to 2·0 kg/day did not further increase the liveweight gain. A high rate of substitution of leucaena and pangola intake for the maize supplement occurred.

There was a large seasonal difference in liveweight gain (mean 0·89 v. 0·63 kg/day for the dry and wet seasons respectively; P<0·001) irrespective of the level of maize supplementation. This seasonal difference in liveweight gain was not primarily a function of the herbage on offer, but was most probably a direct function of the effect of the seasonal temperature and humidity influencing the feed intake and growth rate of these Brahman crossbred cattle.

This system produced some of the higher liveweight gains recorded per hectare for a grazing system (1570–2110 kg/ha per year), as a result of the very good individual liveweight gains (250-340 kg/head per year) and high stocking rate (6·25 head/ha).