Factors affecting the milk yield and composition over lactation of prolific D'man ewes in Tunisian oases.

This work aimed to investigate milk potentiality and the influence of some non-genetic factors both on milk yield production and composition in prolific D'man sheep. Observations were performed in eighty lactating D'man ewes maintained under an intensive oases system in Southern Tunisia. Daily milk yield was determined at 7-day intervals using oxytocin + hand milking method. Chemical milk composition was determined by Lactoscan. Total productions over lactation (milk, fat, and protein) were estimated using the Fleischmann method. Daily milk yield averaged 1.64 ± 0.02 l. It increased to a plateau from the third to the fourth week of lactation, and decreased gradually to the tenth week. D'man ewes produced 128.91 ± 3.14 l of milk, 9.23 ± 0.26 kg of fat, and 5.26 ± 0.12 kg of total proteins. Overall, milk contained 16.17% of total solids, 7.08% of fat, 4.04% of proteins, 4.32% of lactose, 9.09% of solids-not-fat, and 0.73% of ash. Lambing season affected the daily milk yield and milk composition, where fat and total proteins were highest in autumn. Total solids, lactose, solids-not-fat, and ash were higher in winter than in autumn and summer. Ewes reared multiple lambs produced more milk than those reared singles. Dams nursing triplets or more had the highest milk total proteins, and the lowest total solids and fat levels. Adult ewes produced more milk compared to younger and older ewes, and their milk contained higher total solids, fat, and ash levels than milk from young ewes. Ewes with asymmetric udder produced less and more concentrated milk than ewes with symmetrical udder. Daily milk yield was negatively correlated to total solids, fat, and total proteins amounts. In contrast, litter survival at weaning was positively correlated to the amounts of total milk, fat, and total proteins.