Attempts to improve the utilization of urea-treated whole-crop wheat by lactating dairy cows

This paper reports the results of three experiments designed to attempt to improve the efficiency of milk production from diets based on a 1 : 2 dry m atter (DM) mixture of grass silage and whole-crop wheat (WCW) harvested at 550 to 600 g DM per kg and treated with 40 g urea per kg DM. In the first e xperiment a control diet of the forage mixture offered ad libitum with 9 kg fresh weight (FW) per day of a concentrate mix was compared with seven tre atments in which the forage or the concentrates were varied. Eight multipar ous cows were used in a four-period incomplete change-over design with 4-we ek periods. Caustic treatment of the WCW increased DM intake (P < 0.001) bu t tendencies for higher yields of milk and milk protein were not significan t. Replacement of 2 kg FW concentrates per day by the same weight of molass es as a 24-h pre-soak of the forage (molasses pre-treatment) or added to th e forage at feeding increased DM intake (P < 0.001) but did not increase mi lk yield or yield of milk solids. Molasses pre-treatment and molasses added to the concentrates reduced milk protein concentration (P < 0.05). Replace ment of 2 kg FW concentrates per day by the same weight of ground wheat inc reased DM intake when added to the concentrates (P < 0.001) but not when ad ded to the forage and milk yield was unaffected by either method of additio n. The ground wheat tended to result in higher milk protein concentrations than the molasses. Increasing the digestible undegradable protein content o f the concentrates had no significant effect on food intake or milk product ion. In the second experiment diet digestibility and energy and nitrogen (N ) balance were measured for the control diet and three of the treatments fr om experiment I in four multiparous cows in a 4 X 4 Latin-square experiment with 5-week periods. There were no significant effects on food intake or m ilk yield. Caustic treatment reduced starch digestibility (P < 0.001) and i ncreased neutral-detergent fibre (NDF) digestibility (P < 0.05) but had no effects on energy utilization. It also reduced N intake (P < 0.01) and urin e N losses (P < 0.001) by reducing the ammonia concentration of the WCW. Mo lasses added to the forage or concentrates reduced milk protein concentrati on (P < 0.05) and digestibility of both starch and NDF (P < 0.05) but energ y utilization was unaffected. In a further Latin-square experiment with the same treatments and four fistulated lactating cows, caustic treatment redu ced daily mean ammonia concentration (P < 0.01) and increased daily mean pH (P < 0.01) in the rumen. It is concluded that these treatments did not gen erally improve the value of WCW although caustic treatment increased milk y ield and milk protein yield consistently but not significantly. However pra ctical problems may limit its use on the farm. Urea-treated WCW must be acc epted as being a relatively low-energy food although with high intake chara cteristics, and future work should concentrate on evaluating WCW harvested at an earlier stage of maturity.