Reducing the labour requirement at lambing through breeding

Both ewe mothering ability and lamb vigour can be improved through breeding. In fact all improvements made through breeding are permanent and cumulative being passed on from one generation to the next as Teagasc researchers Áine O’Brien and Donagh Berry and Alan Bohan, Sheep Ireland explain.

Main Messages

• Lambing accounts for over 25% of the labour requirement throughout the year
• Improving ewe mothering ability and lamb vigour immediately after birth could reduce the labour requirement
• Both ewe mothering ability and lamb vigour can be improved through breeding

Introduction

Genetics is the study of genes and genetic variation. All improvements made through breeding are permanent and cumulative being passed on from one generation to the next. While other factors such as management factors or environmental factors can change throughout the lifetime of an animal, the genetics of the animal remains unchanged and is fundamental to the performance of the animal. The heritability of a trait is an estimate of the extent of the performance that is explicably under genetic control. On sheep farms, lambing accounts for over 25% of the labour requirement across the year (Figure 1) representing more than double the labour requirement at any other key time points such as weaning, mating, or housing. Therefore measures that could potentially reduce the labour requirement or time spent per ewe should be considered. Two such traits that are currently under investigation are ewe mothering ability and lamb vigour. 

Lambing-related traits

Lambing-related data were available on over 60,000 animals. Data were collected from both flock-book recorded animals and crossbred animals through the Central Progeny Test flocks. Lambing-related data were collected by both producers and trained Sheep Ireland technicians. For any trait to be included in a breeding index, it must fulfil three key criteria: 1) it must be under some genetic control, 2) it must be of social or economic importance, and 3) it must be (easily) measurable on a large scale.

Ewe mothering ability

Ewe mothering ability was measured on a five point scale (Table 1). The overall prevalence of “poor” mothering ability (i.e., score 1, 2, and 3) was 16.1%. Considerable differences among sire groups existed in the prevalence of “poor” mothering ability (i.e., score 1, 2, and 3) of their progeny (Figure 2). All 150 sires included in Figure 2 had a minimum of 30 daughters that lambed in at least two flocks. As management practices and environment were expected to be the same for daughters of sires in the same flocks, this would indicate that genetic differences among sires account for a significant proportion of the differences on the prevalence of poor mothering ability in daughters of sires.  In fact, 6% of the differences in ewe mothering ability are under genetic control. 

Lamb vigour

Similar to ewe mothering ability, lamb vigour was measured on a five-point scale (Table 1).

The prevalence of “poor” lamb vigour was 19.9%. Considerable differences among sire groups existed in the prevalence of poor lamb vigour (i.e., score 1, 2, and 3; a lamb took at least 30 minutes to stand) of their progeny (Figure 3). All 309 sires included in Figure 3 had at least 30 progeny with these progeny being born in at least two flocks. Similar to ewe mothering ability, the prevalence of “poor” lamb vigour varied within sire progeny. The heritability estimate of lamb vigour in Irish lambs is 41% which is quite high for such a trait. Therefore the genetics of the lamb is responsible for 41% of the differences observed in lamb vigour among individuals. 

Conclusions

The prevalence of poor mothering ability and poor lamb vigour varied between the progeny of sires. Since it was expected that factors such as management were uniform for progeny of all sires in the same flocks, genetic differences between sires account for a large proportion of the differences in prevalence among progeny. The heritability of ewe mothering ability and lamb vigour is 6% and 41%, respectively. This supports that in the future, where both traits are included in a breeding index, the selection of sires with a superior breeding value for ewe mothering ability of lamb vigour in order to improve both traits. Subsequently the labour requirement at lambing could be reduced.