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

Abstract

Ewe wastage is the combination of on-farm mortality and premature culling. Internationally, there is limited research on actual wastage incidence and causes in commercial sheep flocks. To the authors’ knowledge, this is the first study that reports both lifetime wastage and detailed annual wastage in a sample of commercial New Zealand flocks. This study utilized data collected from 13,142 ewes from four cohorts on three commercial New Zealand farms (Farm A 2010-born, Farm A 2011-born, Farm B, Farm C), during the period 2011–2017, as they aged from replacement hoggets to 6-year-old ewes (Farm A and Farm B) or 3-year-old ewes (Farm C). Data collection visits occurred at three or four key management times each year, namely pre-mating, pregnancy diagnosis, pre-lambing and weaning. At each visit, body condition score (BCS) was assessed and any ewes that were culled or had died on farm were recorded. As this was a lifetime study, each ewe was assigned an outcome and corresponding ‘exit age’. By the end of the study, all ewes that had exited their respective flocks, were classified as either prematurely culled, or dead/missing, or if still in the flock, as censored, and either the exact date or interval in which they exited the flock was recorded. Semi-parametric competing risk (premature culling vs. dead/missing), interval-censored survival models were developed to: 1. describe the association between hogget reproductive outcomes and risk of subsequent wastage, and 2. assess pre-mating BCS as a predictor of wastage in that production year. Of the 13,142 enrolled ewes, 50.4% exited their respective flocks due to premature culling and 40.0% due to on-farm dead/missing, giving a total of 90.4% that exited due to wastage. Annual mortality incidence ranged from 3.5 to 40.2%. As a hogget, wastage incidence ranged from 7.6 to 45.4%. Pregnancy or rearing a lamb as a hogget did not increase risk of subsequent wastage. In all years, pre-mating BCS was a predictor of ewe wastage, with odds of wastage lower with increasing BCS. Therefore, farmers should focus on improving pre-mating BCS to 3.5/5.0 by assessing ewe BCS at weaning, allowing poorer-BCS ewes to be managed to gain BCS before re-breeding.

Mortality of Dairy Sheep during the Peri-Parturient Period: Results of a Field Investigation in Greece

“…The importance is similar in dairy-and meat-production systems. In a recent study of ewe wastage in meat production systems in New Zealand, a much higher removal rate from the flocks from mating to lambing were noted [11] compared to this study. This can be explained if one considers that in dairy systems, ewes would be milked until 30 to 45 days before the expected lambing ( i.e., farmers would provide care and infrequently cull animals until after the end of the lambing period).…”

The Number of Offspring Weaned from Ewe Lambs Is Affected Differently by Liveweight and Age at Breeding

“…Although the mechanisms that underpinned the effect of own birth type on reproductive performance in the current study were not tested, they are likely to be related to management and environment rather than genetics. Multiple-born and reared lambs are known to gain weight more rapidly following weaning [ 34 ], and higher growth rates from weaning to breeding have been associated with more ewes achieving estrus for a given liveweight [ 35 ]. In addition, the higher reproductive performance of these multiple-born lambs at 6 to 9 months of age in our study was not as evident at their second breeding at 19–20 months (Rosales-Nieto unpublished data).…”

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

“…Ewe deaths affect the productivity and profitability in sheep farming systems [1,2] and are an important issue in terms of potential animal welfare implications and market (consumer) perceptions [3,4]. Reported ewe mortality rates in extensive outdoor grazing systems, such as in New Zealand, Australia and UK, are reported to be in the range of 2.8-27% [5][6][7][8][9][10][11]. Two recent New Zealand studies have reported average ewe mortality rates of around 7-13% per annum but with considerable variation between flocks, agegroups, and years [8,9].…”

“…Reported ewe mortality rates in extensive outdoor grazing systems, such as in New Zealand, Australia and UK, are reported to be in the range of 2.8-27% [5][6][7][8][9][10][11]. Two recent New Zealand studies have reported average ewe mortality rates of around 7-13% per annum but with considerable variation between flocks, agegroups, and years [8,9].…”

“…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]. Few studies have reported on the relationship between productive parameters such as live weight, body condition score (BCS), litter size, and ewe mortality in outdoor grazing systems worldwide [8,12,14,15].…”