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

Abstract

Suboptimal reproductive performance of maiden (primiparous) ewes remains a source of inefficiency for the Australian sheep industry. However, the extent and causes of the poorer reproductive performance of maiden ewes on Australian sheep farms are not well understood. Here, we show the reproductive performance of maiden ewes relative to their multiparous counterparts on the same farms across Australia using a cohort survey. The difference in marking rate for non-Merino maiden ewe lambs compared to multiparous ewes was 58% (74 vs. 132%; p < 0.001), and this was attributable to a 50% difference in reproductive rate (109 vs. 159%; p < 0.001) and 16% difference in lamb survival to marking (67 vs. 83%; p < 0.001). The difference in marking rate for maiden Merino two-tooth ewes lambing at approximately 2 years-of-age compared to mature multiparous ewes was 22% (80 vs. 102%; p < 0.001) and this was attributable to a 24% difference in reproductive rate (108 vs. 132%; p < 0.001) and 3% difference for lamb survival (75 vs. 78%; p < 0.05). Positive correlations for reproduction traits (reproductive rate, lamb survival and marking rate) between maidens and multiparous ewes were observed for maiden Merino two-tooth ewes (p < 0.001), but these correlations were weak or non-existent for non-Merino ewe lambs. Strategies to improve both reproductive rate and lamb survival can address the poorer and more variable reproductive performance of maiden ewes.

Breeding Ewe Lambs: An Australasian Perspective

“…It is accepted that the reproductive performance of ewe lambs is consistently lower than that of both 2 year old and mature ewes [ 10 ]. A recent survey of farmers in Australia found that the reported reproductive rate of ewe lambs and mature ewes differed by 50% [ 16 ]. The lower number of lambs weaned per ewe lamb presented for breeding is due to a number of factors ( Table 1 ).…”

“…Variation exists among breeds and genotypes with regard to timing and live weight at puberty, proportion of ewe lambs displaying estrus (i.e., puberty achievement) within season, length of reproductive season, pregnancy and reproductive rates, and lambing percentage [ 10 , 16 , 81 ]. Therefore, farmers have scope to select breeds or genotypes most suitable to be bred as ewe lambs.…”

Heritability and Genetic Parameters for Semen Traits in Australian Sheep

“…Semen traits could similarly play a role in influencing litter size in livestock species, including sheep which, in turn, may influence the profitability of sheep enterprises. Given maiden ewes have significant abortion and lamb mortality rates compared to multiparous ewes [ 12 , 13 ], improving semen quality and quantity traits through selective breeding may also afford opportunities to improve maiden ewe reproduction rates. As such, every ejaculate collected should be routinely assessed to determine quality prior to use in artificial breeding programs.…”

Seropositivity to Campylobacter and association with abortion and lamb mortality in maiden ewes from Western Australia, South Australia and Victoria

“…In Australia, the causes of foetal and lamb losses between pregnancy diagnosis in mid‐pregnancy and lamb marking for maiden ewes are not well studied. Furthermore, it is not clear whether infectious diseases are an important contributor to the poorer reproductive performance reported for maidens compared to multiparous ewes 5–8 …”

“…Furthermore, it is not clear whether infectious diseases are an important contributor to the poorer reproductive performance reported for maidens compared to multiparous ewes. [5][6][7][8] Ovine campylobacteriosis caused by Campylobacter fetus or Campylobacter jejuni is one of the most frequently diagnosed causes of ovine abortion in Australia. 9,10 Transmission occurs via ingestion of feed and water contaminated by faeces or aborted material, with no evidence of venereal spread in sheep.…”