Development of an improved field protocol to assess lamb vigour

Summary

Lamb vigour scores (LVSs) are usually assessed during tagging and measurement of the lamb within the first 12 to 18 hours of life and are based on a combination of subjective assessments of the degree of struggling and vocalisation, and the rate of the lamb’s return back to the ewe. The trait has a low heritability and has been shown to be genetically associated with lamb survival to 3 days of life. However, it is unclear which behavioural elements of LVS are most important and at what point after birth is it best to assess.

This study assessed individual elements of the LVS at intervals in the first 24 hrs post-birth, in 236 lambs. Furthermore, a subset of ewes were fitted with SmartTag sensors in order to assess whether key pre-partum behaviours, that could be used to predict the birth, could be remotely assessed using wireless sensor technology.

The objectives of the project were

• to develop improved field-based measures/protocols for the assessment of lamb vigour; and
• to develop prediction algorithms of lambing behaviour in ewes and neonatal lamb behaviour using a novel remote sensing measurement platform (Smart Tags).

Sire variation was evident in bleat responses following restraint at 3 and 4 h post-birth. Sire rankings were similar at 3 and 4 h post-birth and there was also some congruence with EBVs for time to bleat. The rankings were less consistent at 8 and 12 h post-birth, suggesting that the trait has some repeatability particularly early post-partum. The bleat response of lambs can be a simple, practical test to assess lamb vigour in the field. It should be carried out after the ewe and lamb have moved away from the birth site, and preferably before the lamb is 12 hours old. However, questions remain with respect to how best to estimate the age of a lamb in the field, once mother and lamb have moved away from the birthing site; and also the impact of stressful procedures such as tagging and birth weighing on the lamb’s bleat response. Further research is recommended to address these questions.

In terms of remote sensing, many challenges were encountered during the data collection phase of the experiment, however, clear evidence of changing behaviours was obtained. Unfortunately, within the time constraints of the project, we were unable to complete development of a birthing predictor. Further work is required to develop a true predictive algorithm, which should then undergo pilot testing prior to in-field validation.