Effects of providing supplements during the wet season on beef production in the Darwin district of the Northern Territory.

Abstract

The effects of four wet season supplementation regimes on the pregnancy rates, mortality and liveweight of 870 Brahman x Shorthorn cross cattle (cows, bulls, heifers and steers) were investigated on Mt Bundey Station from 1980 to 1984. Treatments imposed were (i) Control (no wet season supplement), (ii) Mineral (supplementation with 13 minerals during the wet season), (iii) +Protein (the same minerals plus non-protein nitrogen and protein over the wet season), and (iv) Strategic (consecutive use of salt, mineral and non-protein nitrogen/protein supplements over the early wet, mid wet and late wet season periods respectively). Each treatment was replicated twice and all received a dry season supplement of non-protein nitrogen plus minerals while stocked at one breeder to 14 ha on native pasture. The pregnancy rate of lactating cows in the +Protein regime in 1982 was 77% compared with 60% for the other three regimes (P<0.05). The pregnancy rates in 1983 for both the +Protein (57%) and Strategic (54%) regimes were higher (P<0.05) than the Control (40%) and Mineral (31%) regimes. Mortality rates of breeders and heifers ranged from 2 to 5% in the Mineral, +Protein and Strategic regimes, compared with 8% (1982) and 12% (1983) (P<0.05) in the Control groups. Post pregnancy diagnosis losses were 8% in the +Protein regime compared with 16% in the other regimes (P<0.05). Breeders were 25 to 30 kg heavier in the +Protein than in Control regimes (P<0.05). Liveweight gain of steers in the +Protein regime was 11 to 31% higher than the other three regimes in two of the three steer drafts. Calf weight per breeder in the +Protein treatment was 55% higher in 1983 and 44% higher in 1984 than the other three regimes. It is concluded that wet season supplementation with non-protein nitrogen/protein and minerals has the potential to substantially increase herd productivity in the monsoonal tallgrass region. The response to the wet season +Protein regime, and the absence of a similar response to the Mineral regime, despite a phosphorus, sodium and sulphur deficiency in the pasture, was attributed to an overriding nitrogen requirement. Other factors affecting herd productivity were, paddock variability which was attributed to variation in the proportion of upland compared with floodplain/riparian land units in each paddock and seasonal differences related to the length of the preceding dry season.