Intake of lick block supplements by cattle grazing native monsoonal tallgrass pastures in the Northern Territory.

Abstract

Four supplementation treatments to investigate wet seasons responses were imposed on eight Brahman/Shorthom cross herds totalling 870 animals of all classes (cows and calves, bulls, heifers and steers). They grazed 12,300 ha of native pasture in the Darwin district of the Northern Territory. The treatments were: (i) control (no wet season supplement), (ii) Mineral (Ultraphos - supplementation with 13 minerals during the wet season), (iii) +Protein (Ultrapro-50 - the same 13 minerals plus non-protein nitrogen (WN) and true protein over the wet season), and (iv) Strategic (strategic use of salt, mineral and hTN supplements over the early wet, mid wet and late wet seasons respectively). All treatments received an hTN plus mineral supplement (Uramol) during the dry season. Supplement intakes by the herds were measured monthly for three years. Intake of Salt, Ultraphos and Ultrapro-50 supplements averaged 43, 124 and 149 g/animal/day respectively during the three wet seasons. Losses of the molasses-based block formulations due to rain were small (7%) during the wet season. However, up to one third of each pure salt block was eroded. Intake of Uramol during the three dry seasons averaged 182 g/animal/day across all herds. No urea toxicity problems were noticed over the three years of the supplement programme, despite high intakes during the dry season. All animals consumed some supplement. However, levels of supplement intake: (i) increased with the seasonal decrease in native pasture quality, (ii) decreased with an increase in proportion of paddock burnt, (iii) varied between animal classes, with lactating cows consuming 64% more supplement than non-lactating cows in two of the three years, and (iv) varied between individuals within classes. Individual intake varied widely (from 10 to 835 glanirnallday for lactating cows) with no significant correlation between individual intake and the pregnancy rate or average daily liveweight gain.