An approach to functional longevity in Latxa dairy sheep

Abstract

Productivity and profitability of sheep farming are strongly influenced by the productive performance of ewe during it lifetime. For that, it is relevant to quantify the genetic and non-genetic factors affecting functional longevity in order to consider its inclusion as a trait in a breeding scheme. In this investigation, a Weibull proportional hazard model was applied to study the length of productive live as functional longevity indicator in Latxa dairy sheep breeds. The time from the first calving to the date of culling was individually calculated using records from 28,466 Latxa Cara Rubia (LCR), 26,045 Latxa Cara Negra from Euskadi (LCNEAE) and 10,385 Latxa Cara Negra from Navarre (LCNNAF) from commercial flocks, born between 2000 and 2018. The culling risk associated to the age at first lambing, number of lambs born per lambing and total milk yield produced per lactation was estimated using a likelihood ratio test, and the genetic component of longevity was estimated using a sire-maternal grandsire model. The results concerning the relative culling risk showed that ewes having their first lambing at 2 years of age had around 1.30 times more risk of disposal compared with those of 1 year, regardless of the Latxa population. Similarly, it was found that LCR and LCNEAE having 2 o 3 lambs born per lambing had 1.20 and 1.34 higher risk to be culled in comparison to having 1 lamb, whereas the risk was 1.04 in LCNNAF. In contrast, the probability to be culled was drastically reduced by around 1.50 in all the Latxa populations as the milk yield moved from low to intermediate levels and by around 3.0 times when it moved from low to high. Regarding the genetic parameters of longevity, heritability values ranged from 0.042 to 0.061, which indicates that it is under low additive genetic control. Furthermore, a decreasing genetic was observed, although the decrease rate was smaller during recent years possibly due to the parallel improvement on udder traits. In the light of the results of this first longevity study in Latxa, it is possible to infer that ewes’ on-herd durability is negatively affected by a reproductive delay and a high prolificacy, whereas the higher the milk production, the lower the risk. Moreover, given the genetic findings, it can also be deduced that although selection on longevity is viable, the genetic progress may be a long process.