The composition of sheep milk and its production per lactation are influenced by a large number of factors; however, the most important factors are breed, nutrition, health of the animals, environment and the number and stage of lactation. The effect of the stage of lactation on milk composition in different sheep breeds was studied by Jelínek et al. (1990), Maria and Gabina (1993) 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 (n = 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 (P ≤ 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 (P ≤ 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 (P ≤ 0.001) whereas the phenotypic correlation between titratable acidity (TA) and RCT was negative and high (P ≤ 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 (P ≤ 0.001) whereas the phenotypic correlation between TA and RCQ was negative and high (P ≤ 0.001).

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Effect of parity (PA), stage of lactation (SL) and interaction of PA x SL on daily milk yield (DMY), composition (contents of total solids, fat, total protein and lactose) and quality (somatic cell and bacteria counts) of organic sheep milk were evaluated using 20 ewes of East Friesian which were reared on an organic farm in Habří. Ewes were on the 2nd (n = 10) and 3rd (n = 10) lactation. During the experiment ewes were reared on permanent pasture. The milk records and samplings were carried out on average 75th, 132th and 190th day of lactation. All parameters were determined by standard methods. The PA had a significant effect only on somatic cell count (SCC). On the other hand, SL had a significant effect on daily milk yield (DMY), contents of total solids (TS), total protein (TP) and lactose (L). The SL also had a significant effect on total bacteria count (TBC), psychrotrophic bacteria count (PBC), total coliform count (TCC) and SCC. The interaction of the PA x SL had a significant effect on DMY, TS and TP contents and PBC. Positive and significant correlations were found among the SL and contents of TS and TP. Significant and positive correlation was observed between the PA and SCC, but on the other hand, significant and negative correlation was found between the SL and SCC.