INFLUENCE OF THE SUPPLY OF WHEAT OR POTATOES AS A COMPLEMENT IN A TOTAL MIXED RATION FOR DAIRY-COWS - INTERACTION WITH THE FORAGE NATURE

The effect of starch source used as an energy concentrate (wheat or po tato pelling residues) was studied in interaction with forage nature ( maize silage or grass silage) in a latin square design with 24 dairy c ows. The diets, consisting of maize silage + straw or grass silage, fo rmaldehyde-treated soyabean meal, formaldehyde treated rapeseed and so yabean meal and wheat or potato pelling residues, had, for the same fo rage, similar energy and crude protein concentrations. The dry matter intake was significantly (P < 0.01) higher with the potatoes (+ 1.3 kg DM/cow/day) and with the maize silage (+ 2.1 kg DM/cow/day). The milk yield was not significantly affected by the treatments. With the maiz e silage diets, the fat content of the milk, the fat corrected milk an d the fat yield were significantly higher with the potatoes (respectiv ely + 2.6 g/kg, + 1.7 kg/day and + 103 g/day compared with wheat, P < 0.05 when the nature of the energy concentrate had no significant effe ct with the grass silage diets. The true protein content, the protein yield and the gain in body weight were significantly lower with the gr ass silage diets (respectively - 0.9 g/kg, - 43 g/day and - 327 g/day compared with grass silage, P < 0.01). The non protein nitrogen and ur ea contents of the milk and the uremia were significantly higher with the maize silage diets (respectively + 24, + 42 and + 55 mg/L compared with grass silage, P < 0.01) and with the wheat (respectively + 6, 24 and + 20 mg/L compared with the potatoes, P < 0.05).