Effect of the stage of lactation on milk composition, its properties and the quality of rennet curdling in East Friesian ewes

Abstract

The evaluation of the effect of the stage of lactation on milk composition, its properties and the quality of rennet curdling was carried out over the period of three successive years using milk samples (<I>n</I> = 162) obtained from a total of 27 ewes of the East Friesian (EF) breed, reared on a small sheep farm in Juřinka in the region of Wallachia. The stage of lactation had a highly significant effect on the contents of all milk components. However, only the contents of total solids (TS), solids non-fat (SNF), fat (F), protein (P) and casein (CN) gradually increased with the advancement of lactation. The stage of lactation also had a highly significant effect both on all the properties of milk and the rennet curdling quality (RCQ). All phenotypic correlations between the particular contents of TS, SNF, F, P, CN and urea nitrogen (UN) were positive and high (<I>P</I> ≤ 0.001). On the other hand, all phenotypic correlations between milk yield and particular contents of TS, SNF, F, P, CN and UN were negative and high (<I>P</I> ≤ 0.001). The majority of phenotypic correlations between rennet clotting time (RCT) and the other particular parameters was insignificant. However, the phenotypic correlations between lactose (L) and RCT and between pH and RCT were positive and high (<I>P</I> ≤ 0.001) whereas the phenotypic correlation between titratable acidity (TA) and RCT was negative and high (<I>P</I> ≤ 0.001). The majority of phenotypic correlations between the rennet curdling quality (RCQ) and the other particular parameters was insignificant. Nevertheless, the phenotypic correlations between pH and RCQ and between RCT and RCQ were positive and high (<I>P</I> ≤ 0.001) whereas the phenotypic correlation between TA and RCQ was negative and high (<I>P</I> ≤ 0.001).