EFFECT OF THE STARCH NATURE OF THE ENERGY CONCENTRATE AND OF A METHIONINE SUPPLY ON THE REARING PERFORMANCE OF DAIRY-COWS

The effect of two starch sources (potatoes and wheat) as a supply of r umen-protected methionine is studied in a latin square design using 12 dairy cows. Both diets are composed of maize silage, wheat straw soyb ean meal, formaldehyde-treated mixed meal (rape and soybean) and miner als supplemented by wheat or potato peeling residues. The diets have s imilar contents of energy (0.91 UFL/kg dry matter [DM]) and protein (1 05 g PDI/kg DM). They are supplied with or without 19 g of rumen-prote cted methionine. No effect was observed on the DM intake (22.1 kg/day) , the milk yield (27.0 kg/day), the lactose content (50 g/kg), the pro tein yield (912 g/day) and the weight gain (338 g/day). The fat conten t, the fat yield and the yield of standard milk (4% of fat) were lower with the wheat diet (respectively, 34.2 vs 38.0 g/kg for potato diet, P < 0.01; 958 vs 1 045 g/day, P < 0.01; 25.5 vs 26.5 kg/day, P < 0.10 ); however. the ureamia and the nonprotein nitrogen content of the mil k were higher (respectively, 0.38 vs 0.27 g/L, P < 0.01; 320 vs 272 mg /L, P < 0.01). The methionine supply increases the protein content (33 .0 vs 32.2 g/kg, P < 0.01) but there is no significant effect of the s tarch source on this parameter.