Intake and digestibility of urea-treated whole crop wheat and liveweight gain by dairy heifers

Abstract

Whole crop wheat (WCW) was harvested at 550–650 g dry matter (DM) kg −1 in each of 3 years. Each crop was mixed with 40 kg urea t −1 DM and stored anaerobically. In Experiment 1, nine Holstein Friesian heifers of 370 kg liveweight were offered WCW ad libitum in a 3 × 3 Latin square design. The three treatments were: no supplement (W); a supplement of 2.0 kg day −1 molassed sugar beet pulp (WB); a supplement of 1.8 kg day −1 molassed sugar beet pulp + 0.2 kg day −1 fishmeal (WBF). Experiment 2 was similar except that WB consisted of molassed sugar beet pulp fed at 20% of WCW DM intake and WBF consisted of molassed sugar beet pulp fed at 15% of WCW DM intake and fishmeal at 5%. This method of proportionate allocation of feeds enabled a comparison to be made of the effect of liveweight (three groups with initial liveweights of 136, 267 and 340 kg). In both experiments, intake and digestibility were measured. In Experiments 1 and 2, the mean digestible organic matter in the dry matter (DOMD) of the WCW was 654 g kg −1 and 635 g kg −1, respectively. The supplements tended to increase neutral detergent fibre and acid detergent fibre digestibility and reduce starch digestibility. The mean DM intake of WCW was depressed by the WBF supplement. There were no significant effects of heifer size on digestibility but intake per kilogram liveweight declined with increasing size. Experiment 3 had a continuous design with 20 Holstein Friesian heifers of 165 kg liveweight. The treatments were: W (as above); a supplement of 1.0 kg day −1 molassed sugar beet pulp (WB); a supplement of 0.2 kg day −1 fishmeal (WF); a supplement of 0.8 kg day −1 molassed sugar beet pulp + 0.2 kg day −1 fishmeal (WBF). The mean liveweight gains over 9 weeks for W, WB, WF and WBF respectively were 0.65 kg day −1, 0.79 kg day −1, 0.76 kg day −1 and 0.88 kg day −1. These were lower for all treatments than predicted from estimated metabolisable energy (ME) intakes. The possible reasons for this are discussed. The blood urea levels for treatment W were reduced by treatment WB, and levels increased for all treatments over time.