Breeding Ewe Lambs: An Australasian Perspective

Abstract

A number of potential advantages have been identified for breeding ewe lambs at 7 to 9 months of age, including increased lifetime productivity and profitability. However, breeding at this young age in extensive pastoral systems, such as in Australasia, can be associated with a number of disadvantages resulting in uptake of this management procedure being relatively low. This review highlights the known differences between ewe lamb and mature ewe reproductive performance, thus differing in their management. The review then summaries the scientific literature of factors that affect ewe lamb reproductive success, with a focus on recent studies conducted under extensive pasture-based conditions in Australasia. In particular, this review outlines the importance of ewe lamb live weight and body condition score on their productivity. The potential long-term consequences of breeding a ewe lamb at a young age in terms of her future success and that of her offspring to weaning are briefly outlined. In addition, the potential impacts of selecting progeny born to ewe lambs as future replacement ewes are discussed. Throughout this review, optimal management guidelines from prior to breeding the ewe lambs until rebreeding at 2 years of age are provided. Lastly, areas requiring future research are identified and discussed.

Keywords: ewe lamb; performance; reproduction.

Figure 1

The cumulative proportion of ewes that attained puberty each week of the breeding period in the South Island of New Zealand (adapted from [11]). Note: In New Zealand, mature breeding begins in March/April, and the shortest day occurs on 21 June.

Figure 2

The effect of ewe lamb body condition score (A) and breeding liveweight category (B) on ewe lamb fertility rate (ewes pregnant per 100 ewes presented for breeding; white bars) and reproductive rate (number of fetuses per 100 ewes presented for breeding; black bars). Adapted from [17].

Figure 3

The relationship between percentage of mature weight and (a) fertility and (b) fecundity of 8 month old Romney crossbred ewe lambs (logit predictions and 95% confidence intervals are shown; adapted from [107]).