The Impact of Age at First Lambing on Milk Yield and Lactation Length in a Population of Istrian Sheep under Semi-Intensive Management

SIMPLE SUMMARY: The impact of age at first lambing on dairy traits has been poorly investigated in sheep, especially in semi-intensive husbandry systems. Insufficient information on this issue, especially scientifically proven, leads to many speculations among breeders. The aim of this study was to examine the impact of age at first lambing on days in milk, daily milk yield, and total milk yield. The study was conducted on field data routinely collected in a population of Istrian sheep bred under selection. It was determined that the prolongation of the first mating of lamb ewes to the second year of life is not beneficial to milk production. In conclusion, ewes reared under semi-intensive dairy orientated systems could be successfully bred in their first year of life in order to reduce their unproductive non-milking phase. ABSTRACT: This study aimed to examine the impact of ewe’s age at first lambing (AFL) on days in milk (DIM), average daily milk yield (DMY), and total milk yield (TMY). Symmetrical bimodal distribution of AFL enabled classification of maidens in those mated in the first (47%) or second year of life (53%). After accounting for all available sources of phenotypic variability with the linear mixed model for repeated records, it was estimated that AFL had a statistically significant effect only on DIM (p < 0.001). The litter size had a significant effect only on TMY (p < 0.001), while the effect of the parity was significant for all the examined traits (p < 0.001). The results of the study suggest that prolongation of age at first mating to the second year of life is not justified in dairy-orientated sheep farms. However, more evidence on this issue is needed for generalization, especially considering some other traits that can impact profitability of dual-purpose sheep farms (reproduction traits, growth rate of lambs, etc.).