engleski

Influence of season of birth on the age at first lambing and reproductive performance in ewe

Sheep are widely known as domestic livestock species with marked seasonality of breeding activity. The annual cycle of daily photoperiod has been identified as the determinant factor of this phenomenon, while environmental temperature, nutritional status, social interactions, lambing data and lactation period are considered to modulate it. In temperate climates, breeding generally occurs in autumn to give birth in spring. Seasonal reproduction is a serious problem for the sheep industry, reducing effectiveness of accelerated lambing programs, restricting flexibility to integrate lambing into other farm activities, and limiting access to favourable seasonal markets. Genetic differences in seasonal breeding patterns are present among and within some sheep populations, leading to opportunities to reduce seasonality by selection. Selection programmes are based on desirable characteristics such as extended breeding season combined with high reproductive performance. Possible characteristic influencing future reproductive performances might be the season in which the ewe was born. In this investigation a total number of 290 ewes were analysed according to their birth date, age at first lambing, litter size and lamb's birth weight at first lambing. Ewes were from the population known for their all-year-breeding ability, unselected and randomly sampled. Village farm management concerning mating and feeding procedures for all ewe lambs were quite similar and typical for conditions in continental region of Croatia. Statistical procedure ANOVA (Statistica - Stat. Soft. Inc., 7.1) was used to analyse significant differences between groups of ewes born in different seasons. All ewes were divided according to their birth date to autumn born (n=102), winter born (n=44), spring born (n=85) and summer born (n=59). The overall mean age at first lambing for all ewes was 444.5 days. Winter born ewes were the youngest at the time of their first lambing with the age of 402.7 days which was statistically significant (p<0.01) compared to the age of summer (467.0 days) and autumn (462.9 days) born ewes. The age of spring born ewes at first lambing was intermediate (428.4 days) and significantly (p<0.05) shorter to the age of summer and autumn born ewes. Litter size at first lambing for the autumn, winter, spring and summer born ewes was 1.16, 1.09, 1.05 and 1.08 respectively. No statistically significant influence (p>0.05) of ewe's birth season on their lamb birth weight was observed. The overall mean birth weight of male lamb singles was 3.74 kg with the highest value of those which were lambed by autumn born ewes (3.79 kg) and the lowest value of those lambed by summer born ewes (3.61 kg). Slightly lower mean birth weight was determined for female single lambs (3.61 kg), the highest in lambs lambed by spring born ewes (3.73 kg) and lowest in lambs lambed by summer born ewes (3.50 kg). Differences between twin lambs were small and non-significant. The results suggest that season in which a ewe was born might be a possible predictor of its early maturity.

sheep; seasonality; reproductive performance

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