This study aimed at comparing the effects of once-a-day (OAD) milking during the descending phase of lactation between cows from the two most common breeds in France (Holstein and Montbéliarde). This study was carried on during two successive summers on a total of 50 Holstein and 38 Montbéliarde cows. During 7 weeks, half of the cows from each breed was milked OAD while the other half was milked twice a day (TAD). The animals were also followed for the next 3 or 5 weeks when they were all milked TAD, to check for any residual effect of OAD milking. The behaviour of OAD cows was observed around milking time. The incidence of diseases, the main performance variables (milk production, milk flow rate, live weight and body condition score), the detailed composition of milk (fat, protein, lactose, somatic cells, minerals, pH, free fatty acid (FFA), nitrogen fractions and enzymes) and some technological variables (clotting time and curd firmness) were measured on all cows.
Some signs of disturbance were observed in the OAD cows at the time when milking was omitted: some cows mooed, some went close to the exit of the paddock, some leaked milk prior to milking. However, these signs disappeared after 2 days. After the experimental period, the live weight and the body condition score of TAD and OAD cows did not differ significantly. OAD cows produced 4.5 kg/day less than TAD (P < 0.001), this being more marked in Holstein (5.7 kg/day, P < 0.001) than Montbéliarde (3.3 kg/day, P < 0.001) cows. The milk contents of fat, whey protein, casein, total protein and phosphorus, and its plasminogen activity, were higher with OAD cows while lactose and FFA contents, and lipoprotein lipase activity were lower, with no interaction observed with breed. During the subsequent 3 weeks, when all cows were again milked TAD, OAD cows still produced 1.7 kg/day less milk (P < 0.01) with slightly higher fat and protein content.
OAD milking for 7 weeks during the descending phase of lactation decreased milk production but increased milk content of most components, with a low residual effect. Montbéliarde cows were less affected by OAD milking than Holstein cows.