Influence de l'apport de blé ou de pommes de terre dans une ration complète pour vaches laitières : interaction avec la nature du fourrage

Abstract

Summary — 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 potato pelling residues) was studied in interaction with forage nature (maize silage or grass silage) in a latin square design with 24 dairy cows. The diets, consisting of maize silage + straw or grass silage, formaldehyde-treated soyabean meal, formaldehyde-treated rapeseed and soyabean meal and wheat or potato pelling residues, had, for the same forage, 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 maize silage diets, the fat content of the milk, the fat corrected milk and the fat yield were significantly higher with the potatoes (respectively + 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 effect with the grass silage diets. The true protein content, the protein yield and the gain in body weight were significantly lower with the grass 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 urea 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).