Unlike other livestock species, we mostly rear sheep extensively, which is why they are still mainly bred seasonally. Exceptions are certain breeds that can lamb out of season. Seasonal rearing of sheep is influenced by many factors, such as photoperiod, geographic latitude, exposure to rams, and the body condition of ewe. Sheep breeds originating from tropical regions tend to lamb out of season in their native habitat but do not always show this trait in temperate zones. Similarly, some seasonal breeding sheep breeds lamb out of season in tropic regions in both tropical and temperate zones. Out-of-season lambing in sheep first appeared at Neolithic Period because environmental conditions were favourable. The lambs that were born out of season were only able to survive due to extra care provided by Neolithic breeders and were therefore able to pass on the out-of-season lambing trait to the next generation. There are several production systems for sheep breeds that lamb out of season and where sheep can lamb more than once per year. Out-of-season lambing is an economically important trait as it allows continuous production of lambs for slaughter throughout the year. Due to many factors, classical selection for this trait is slow and inefficient, so scientists are trying to identify genetic markers with positive effects on this trait that would allow genomic selection and greater and faster genetic gain. Based on the literature review, we conclude that environment likely has a greater influence on the occurrence of out-of-season lambing than genetic factors.
|
