[en] Lambing percentage is one of the most significant factors affecting profitability on New Zealand sheep farms. Since the early 1990s, lambing percentage has increased at about 1% per year from a relatively stable level of approximately 100%, and top performing sheep farms are now consistently achieving 150% or more. As lambing percentage increases, the proportion of ewes bearing twins and triplets increases accordingly. Lamb mortality rate in these multiples is higher than in singles, with triplets being particularly susceptible. Consequently, lamb survival has become increasingly important to the New Zealand sheep industry. Sheep Improvement Ltd (SIL, New Zealand's national sheep genetic evaluation system provided by Beef & Lamb NZ) records lamb survival to weaning but genetic improvement has been limited due to the low heritability of the trait and the current method of recording.
