Effects of the level of early productivity on the lifespan of ewes in contrasting flock environments

Abstract

Selection for high levels of prolificacy has allowed substantial improvements in the production efficiency of New Zealand (NZ) sheep farms, but the consequences on ewe lifetime performance are mostly unknown. In this study, the relationship between the level of prolificacy early in ewes' productive lives and their probability to survive later (i.e. stayability) was evaluated in two contrasting NZ flock environments. Records were obtained from 6605 ewes from four ram breeder flocks representing either a moderate ( n = 2) or a highly variable ( n = 2) nutritional environment. All ewes lambed for the first time at 2 years of age and were mated the following year. The number of lambs born during the first 2 years of productive life (NLB 2-3 ) was used as a measure of early prolificacy. Effects of NLB 2-3 on stayability to 4, 5, 6, 7 and 8 years old were analysed using logistic regression. Curvilinear effects (logit-transformed) were detected ( P < 0.05) until stayability to 6 years and to 8 years old in the highly variable and the moderate environment, respectively. The NLB 2-3 that resulted in maximum expected stayability to various ages was 3.9 to 4.2, and 4.5 to 4.7 lambs in the highly variable and in the moderate flock environments, respectively. In addition, ewe stayability was reduced when the proportion of the litter that survived from birth to weaning (i.e. ewe rearing ability) was submaximal during the early productive life. High prolific ewes had a low rearing ability whatever the environment whereas the rearing ability of lowly prolific ewes was apparently more sensitive to the nutritional environment. The poor maternal performance of ewes with low levels of NLB 2-3 led to a premature culling by breeders whereas the high early reproductive effort associated with high levels of NLB 2-3 seemed to be at the cost of ewes' survival, even in the moderate flock environment. In conclusion, the flock environment influenced the level of early prolificacy beyond which ewe longevity was reduced. It is suggested that further selection for high and early prolificacy in NZ flocks is likely to impair ewes' lifetime productivity.

Ewe Wastage in New Zealand Commercial Flocks: Extent, Timing, Association with Hogget Reproductive Outcomes and BCS

“…Using a bioeconomic model, Farrell reported that for a New Zealand North Island Hill Country sheep farm with 21% of the flock lost annually due to wastage, a reduction in wastage to 5% could increase cash profit by 33% [1]. Combined, this indicates that it is important for replacement hoggets to remain in a flock, and be productive, for a sufficient period to be economically efficient [6,9,10].…”

Factors Associated with Ewe Death and Casting in an Extensively Farmed Sheep Flock in New Zealand

“…Studies investigating ewe mortality rates and timing in extensive outdoor pastoral farming systems have largely focused on data collection at key production times (i.e., weaning, pre-mating, mid-pregnancy, and pre-lambing) with the estimation of mortality rates based on sheep missing at these times [8,[12][13][14]. A large New Zealand study identified that the majority of ewes that went missing and were presumed to have died, or were reported as dead, did so over the mid-pregnancy to weaning period, but the causes of death were not investigated [8].…”

Prediction of reproductive performance of ewes based on the early production data, ewe birth rank, dam age, and dam birth rank

“…Reproductive indicators measured earlier in life might be helpful in making a selection and culling decisions, given that they are, to some extent, associated with the ewes' total or lifetime reproductive performance. Authors of several studies used this presumption in an effort to explain or predict ewe reproductive performance (Lee and Atkins, 1996;Amer et al, 2007;Lee et al, 2014;Kleemann et al, 2016) or its stayability (Douhard et al, 2016).…”