Abstract: The purpose of this study was to investigate the changes of milk yield and milk composition in East Friesian sheep during lactation and their correlation with the hardness and water-holding capacity (WHC) of rennet-induced curd. The results showed that during the whole lactation period, milk yield changed significantly, which was 2.8% and 17.1% higher and 19.9% lower than the average level at the early, middle and late lactation stages, respectively. The contents of total solids, protein, casein, fat and calcium increased evidently and lactose content increased only slightly but not significantly. Curd hardness increased obviously from the early to the middle stage of lactation, but moderately from the middle to the late stage. WHC declined markedly from the early to the middle stage, but gently from the middle to the late stage. Curd hardness and WHC were significantly correlated with the contents of casein, fat and calcium in sheep milk (P < 0.01). Curd hardness increased with increasing content of casein and calcium, but decreased with increasing content of fat in sheep milk. Curd WHC decreased with the increase in casein and calcium contents, but increased with the increase in fat content in sheep milk. There was a significantly negative correlation between curd hardness and WHC (P < 0.01). The above findings may provide a reference for the development of sheep milk products.

Key words: sheep milk; lactation; milk production; curd hardness; water-holding capacity