Original scientific paper
Impact of parity and litter size on dairy traits in Istrian ewes
2019, 20 (2) p. 556-562
The aim of the study was to determine the influence of parity and litter size on dairy traits in Istrian ewes. The following traits were analysed: lactation milk yield (LMY), daily milk yield (DMY), fat yield (FY), fat content (FC), protein yield (PY), protein content (PC), lactose yield (LY), and lactose content (LC). Lactation records (n=6481) collected on 2786 ewes were analyzed using a statistical model adjusted for unbalanced data structure accounting for all the available sources of phenotypic variability. Parity had a statistically significant effect on all the investigated traits (P<0.01, P<0.001). LMY DMY, PY and LY peaked in third, FY, FC, and PC in fourth, and LC in second lactation. The estimated differences between parities with maximum and minimum production for LMY, FY, PY, and LY were 21.6 kg, 1.1 kg, 1.25 kg, and 0.98 kg, respectively. Litter size had a significant effect on all the investigated traits (P<0.01, P<0.001) except the FC (P<0.05). Multiple litters led to higher yields but to lower contents of dry matter components in the milk. The results of the study should contribute to better understanding of the phenotypic variability of some economically very important dairy traits in ewes.