Abortion and Lamb Mortality between Pregnancy Scanning and Lamb Marking for Maiden Ewes in Southern Australia

Abstract

The contribution of abortions to the overall mortality of lambs born to maiden (primiparous) ewes in Australia remains unclear. This cohort study aimed to quantify abortion and lamb mortality for ewe lambs and maiden Merino two-tooth ewes. Lamb mortality from pregnancy scanning to marking were determined for 19 ewe lamb and 11 Merino two-tooth ewe flocks across southern Australia. Average lamb mortality from scanning to marking was 35.8% (range 14.3–71.1%) for the ewe lambs and 29.4% (range 19.7–52.7%) for the two-tooth ewes. Mid-pregnancy abortion was detected in 5.7% of ewes (range 0–50%) in the ewe lamb flocks and 0.9% of ewes (range 0–4.4%) in the two-tooth ewe flocks. Mid-pregnancy abortion affecting ≥2% of ewes was observed in 6/19 ewe lamb flocks and 2/11 two-tooth ewe flocks. Lamb mortality from birth to marking represented the greatest contributor to foetal and lamb mortality after scanning, but mid-pregnancy abortion was an important contributor to lamb mortality in some ewe lamb flocks. Variability between the flocks indicates scope to improve the overall reproductive performance for maiden ewes by reducing foetal and lamb losses. Addressing mid-pregnancy abortion may improve the reproductive performance in some flocks.

Lower Reproductive Rate and Lamb Survival Contribute to Lower Lamb Marking Rate in Maiden Ewes Compared to Multiparous Ewes

“…The difference in reproductive rate between these age groups was less than other studies, which have ranged from 75 to 124% [ 7 , 14 ], whereas the difference in lamb survival between these age groups tended to be greater than most other studies where the difference was less than 10% [ 14 , 17 , 18 , 19 ]. The wider variation in marking rate, reproductive rate and lamb survival between individual flocks of non-Merino ewe lambs was similar to these and other studies, including Clune et al [ 9 ] and Thompson et al (unpublished data). Improved understanding of the degree of variation and causes of poorer reproductive rate and lamb survival in maiden ewes will inform extension and adoption programs to improve maiden ewe reproductive performance.…”

“…The 58% difference in marking rate for non-Merino ewe lambs compared with multiparous ewes across 40 farms in our study was similar to the difference recently reported from nine commercial farms representing more than 300,000 records in New Zealand (72 vs. 142%) [ 14 ]. Likewise, marking rate was more variable between flocks for non-Merino ewe lambs compared with multiparous non-Merino ewes, with the overall average and variation in marking rate between flocks of non-Merino ewe lambs being similar to results reported by both Shorten et al [ 14 ] and Clune et al [ 9 ]. The 22% difference in marking rate for Merino two-tooth ewes compared to multiparous ewes across 39 farms was greater than the differences measured by Kleemann and Walker [ 10 ] on 14 farms in South Australia (70 vs. 86%) and a recent survey of 1200 Merino producers across Australia (79 vs. 93%) [ 15 ].…”

“…The weak and generally non-significant correlation between the reproductive performance of ewe lambs and their multiparous counterparts in the current study hinged on the more variable performance of ewe lambs, whereas the performance of maiden two-tooth ewes was more consistent when compared with their multiparous counterparts on the same farm. Comparisons between studies suggest that the responses in reproductive rate to improved live weight at the start of the mating period and live weight gain during the mating period are much greater for ewe lambs than in multiparous ewes regardless of breed [ 8 , 9 , 20 , 21 , 22 ]. Recently Paganoni et al [ 23 ] also reported that the effects of live weight and condition score at mating on reproductive rate were greater in ewe lambs compared to two-tooth non-Merino ewes within the same flocks, and the difference between these age groups was greater than the difference between two-tooth and multiparous Merino ewes.…”

“…There has been less work on the performance of ewe lambs in Australia compared to New Zealand. Thompson et al [ 8 ] and Clune et al [ 9 ] recently reported considerable variation in reproductive rate and or marking rates between different flocks of ewe lambs. In these studies, the average reproductive rate was 108%, and foetal and lamb losses between scanning and marking exceeded 35%.…”

“…In these studies, the average reproductive rate was 108%, and foetal and lamb losses between scanning and marking exceeded 35%. Lamb mortality in the perinatal period was the primary cause of lamb mortality after scanning, although abortions were an important contributor in some flocks [ 9 ]. However, neither study compared the performance of ewe lambs and multiparous ewes or focussed on the relative contributions of reproductive rate and foetus and lamb survival to the poorer and more variable marking rates for ewe lambs.…”