Aptitude à la coagulation du lait de vache. Influence de la race, des variants génétiques des lactoprotéines du lait, de l'alimentation et du numéro de lactation

National audienceOne hundred and thirty Holstein (41), Montb6liardes (42) and Tarentaises (54) dairy cows in first or second lactation received during winter one of two levels (high, H ; low, L) of energy intake, and were later fed identically at pasture. Three times in winter and twice at pasture, individual measurements of milk chemical composition and coagulation properties were performed. Milk from Holstein cows had lower casein and calcium contents, and poorer coagulation properties (curd firming time and curd firmness) than that from Montbéliardes and Tarentaises (P<0.01). These differences practically disappeared when taking into account the distribution of the different kappacasein variants and milk casein content. kappa-BB milks had coagulation properties 20 to 50% superior, according to characteristic, to those of AA milks. In the 3 breeds, animals from the H group had casein contents higher by 1.4 g/1 than those of the L group, which induced a significant improvement in curd firming time, curd firmness and cheese yield. Turning out to pasture induced an increase of 0.02 unit in milk pH, and improved milk coagulation properties. These changes did not appear to result entirely from the parallel increase in milk casein content. Coagulation properties were poorer in first lactation than in second lactation.Cent trente sept vaches laitières de race Pie-Noir (41), Montbéliarde (42) ou Tarentaise (54), en première ou deuxième lactation, ont reçu au cours de l’hiver deux niveaux d’alimentation énergétique (haut: H et bas : B), et ont été ensuite alimentées de manière identique au pâturage. Des mesures individuelles de la composition chimique du lait et de son aptitude à la coagulation ont été réalisées 3 fois pendant l’hiver et 2 fois au pâturage. Chez les Pie-Noir, les taux de caséines et de calcium et l’aptitude à la coagulation (temps de raffermissement et fermeté du gel) ont été inférieurs (P