INFLUENCE OF THE NATURE OF THE CONCENTRAT E ON ZOOTECHNICAL PERFORMANCES OF DAIRY-COWS RECEIVING A COMPLETE DIET

The influence of concentrate (wheat or sugar beet pulp + corn gluten f eed) on milk yield and composition, rumen volatile fatty acids and som e blood parameters was studied with a crossover design using 36 dairy cows (22 primiparous) during 2 experimental periods of 6 weeks each. T he cows were fed ad libitum with a complete diet consisting, in large part, of maize silage. The 2 diets had the same energy concentration ( 1.57 Mcal/kg dry matter [DM]) and crude protein (14.20%). The nature o f the supplement had no significant effect on mean daily total DM inta ke (18.0 kg) and mean daily milk production (22.2 kg/d). The most affe cted was the fat content of the milk, fat-corrected milk and fat yield which increased with the fibrous concentrate (+3.2 g/kg milk, P < 0.0 5, +1.1 kg, P < 0.10 and +73 g/d, P < 0.01, respecfively) (table II); the true protein content of the milk and the body weight were signific antly higher with the starchy concentrate (+0.7 g/kg, P < 0.05 and +58 0 g/d, P < 0.01, respectively). The proportion of acetic acid in the r umen fluid was significantly lower (-3%, P < 0.05) and the proportion of propionic acid higher (+2%, P < 0,05) with the starchy concentrate (table III). The nature of the concentrate had neither a significant e ffect on the non-esterified fatty acids and beta OH-butyrate contents, nor on the uremia (table IV and fig I). The glycemia was significantl y increased for the diet with the starchy concentrate (+0.02 g/l, P < 0.05) (fig 2).