Energy and protein supplementation of lactating dairy cows offered urea treated whole-crop wheat as the sole forage

Abstract

Whole-crop wheat treated with 40 kg urea/t/DM was examined in two experiments as the sole forage offered ad libitum. The objective was to evaluate the nutritive value of the forage, and the response in milk production to energy and protein supplements. In Experiment 1, 12 Holstein Friesian lactating cows in three 4 × 4 Latin squares were offered four concentrates, A—6 kg/day of 208 g CP kg/DM, B—6 kg/day of 276 g CP kg/DM, C—8 kg day of 208 g CP kg/DM and D—10 kg/day of 208 g CP kg/DM. The apparent digestibility of the forage was measured at maintenance and ad libitum levels of feeding with four Holstein Friesian heifers in a changeover design. In Experiment 2, six Holstein Friesian lactating cows in two 3 × 3 latin squares were offered, E—4 kg/day of a concentrate containing 166 g CP kg/DM, F—4 kg/day of 333 g CP kg/DM (additional soya-bean meal) and G—4 kg/day of 329 g CP kg/DM (additional soya-bean meal and fish meal). Digestibility of diets was measured in the same cows by the total collection of faeces. In experiments 1 and 2, respectively, mean in vivo DOMD (g/kg/DM) of urea treated whole-crop wheat was 646 and 738, and mean DM intakes (kg/day) were 14.12 and 18.68. These high forage intakes produced only moderate levels of milk production. Estimated energy balances indicated that on average 48 MJ ME intake in Experiment 1, and 70 MJ ME intake in Experiment 2 could not be accounted for in the ME requirements estimated from measured animal performance. This indicates a low efficiency of utilisation of the digested energy of urea-treated whole-crop wheat. Milk production responses to concentrate level were similar to those observed with other types of forage. Additional protein in the supplement from fish meal but not from soya-bean meal significantly increased milk yield.