THE EFFECTS OF FORAGE TYPE (MAIZE-LABLAB OR OAT-VETCH) AND LEVEL OF SUPPLEMENTATION (WHEAT-MIDDLINGS) ON FOOD-INTAKE, DIET APPARENT DIGESTIBILITY, PURINE EXCRETION AND MILK-PRODUCTION OF CROSSBRED (BOS-TAURUS X BOS-INDICUS) COWS

An experiment was carried out to evaluate the effects of forage type a nd level of concentrate supplementation on forage intake, diet apparen t digestibility, purine excretion and milk production. Twelve crossbre d cows (Bos taurus X Bos indicus), in early lactation, were allocated to the following six dietary treatments: maize-lablab forage (ML) or o at-vetch forage (OV), offered ad libitum, and supplemented with either 0, 2.5 or 5.0 kg per cow per day of a supplement (wheat middlings). A four-period, partially balanced, change-over design was used and the treatments were arranged as 2 X 3 factorial. Mean organic matter (OM) intake was 670 g higher with cows on ML-based diets compared with thos e on OV-based diets (P < 0.01). The apparent digestibilities of crude protein (CP) and neutral detergent fibre (NDF) were similar for cows g iven ML- or OV-based diets but the apparent digestibility of OM was hi gher for ML diets (P < 0.05). Values of the degradation parameters (a, b and c) of DM and NDF were greater for ML forage than for the OV for age. Forage type did not affect daily milk yield nor excretion of puri ne derivatives in urine used to estimate microbial-nitrogen supply (P > 0.05). The concentration of milk fat and total solids in the milk we re similar for the two forage types offered but the concentration of m ilk protein was slightly higher for the cows given ML-based diets (P < 0.05). Daily OM intake increased by 3.75 and 2.70 kg per cow per day (P < 0.001) respectively, when the amount of concentrate increased fro m 0 to 5.0 kg per cow per day for the ML- and OV-based diets. The CP a pparent digestibilities of the diets were higher when the diets were s upplemented with concentrates but there was no effect of supplementati on on the apparent digestibilities of OM and NDF. The supply of microb ial-nitrogen increased linearly with increasing level of concentrate s upplementation (P < 0.05). Milk yield increased linearly when the leve l of concentrate supplement increased from 0 to 5 kg (P < 0.001), resu lting in 0.39 and 0-29 kg more milk per day per kg additional concentr ate given in cows on ML and OV, respectively. There was also a tendenc y for a quadratic effect (P < 0.12), especially with ML diets, showing that when the level of concentrate increased from 0 to 2.5 or from 2. 5 to 5.0 kg/day, the milk yield increased respectively by 0.62 and 0.1 5 kg/day per kg additional concentrate given.