Effects of lambing season and stage of lactation on ewe milk quality

Abstract

A total of 240 bulk milk samples were collected and examined from January to July of 2000. The milk samples were obtained from 5 intensively managed flocks of Comisana ewes located in southern Italy. Milk sampling was performed separately on the ewes which had lambed in the autumn (October and November) of 1999 (ALB, autumn lambing) and in the winter (January and February) of 2000 (WLB, winter lambing). For each lambing season, 6 sampling cycles were carried out during early-, mid- and late-lactation (less than 60 days from 100 to 130 days and from 150 to 180 days in lactation, respectively), using the bulk milk of four consecutive milkings. In all the farms, the ewes received hay and concentrates during the winter season, while during the spring and summer season ewes grazed and were supplemented with hay and concentrates. The milk yielded by the WLB ewes recorded lower fat and protein contents compared to that of the ALB ewes (6.71 vs. 6.93% and 5.15 vs. 5.39%, respectively), as well as deteriorating renneting and hygienic characteristics. Irrespective of the lambing season, a higher SCC was recorded in late, compared to early- and mid-lactation milk (6.16 vs. 5.93 and 5.87log10somatic cells/ml) as well as a marked worsening in coagulating behavior. Reduced cheese-making efficiency was associated with a reduction in the casein and fat content of milk from the ALB ewes, and decreased calcium and phosphorus content in the WLB ewe milk. For both lambing seasons increased plasmin activity was recorded in the milk. Results suggest that ovine milk quality is strongly affected by the combined effects of seasonal changes in climate and herbage availability and variations in ewe metabolic status with the advancement of lactation. Proper housing sanitation, flock management and milking procedures play a major role in optimizing the quality of ewe milk during the late-lactation when several factors concur to increase the risk for mastitis, such as the involution of the mammary epithelium, rises in ambient temperatures, and worsening in air and surface hygiene. During the summer season, strategies to reduce the impact of high temperatures on lactating ewes and an appropriate administration of mineral elements with the feed diets are necessary to sustain the yield and quality of milk and cheese in ewes.