Impact of mob size during lambing on twin lamb survival from Merino and maternal ewes

Summary

The literature review undertaken highlighted the lack of clear recommendations for sheep producers on lambing paddock management, particularly regarding the impact of ewe mob size on resultant marking percentage.  The template designed in this project to record mob-paddock observations and lambing results has proven to be highly effective for collecting detailed information on key variables influencing lambing results.  A total of 750 mob-paddock observations were collected and the information collected has been used to further define the relationship between the number of ewes in a lambing paddock and marking percentage.
It was found that ewe mob size has a significant impact on marking percentage.  Across the 750 mob-paddock observations 20% of the variation in marking percentage was due to the ewe mob size at lambing (p<0.001).  the strength of this relationship reduced when the data was analysed in breed groups (r-squared of 11% for merino ewes and 10% for non-merino ewes), although it was still statistically significant (p><0.001).  the strength of this relationship reduced even further when the analysis was undertaken for ewe breed and parity (single and twin bearing mobs) separately, primarily due to a significant reduction in the number of cases in each grouping.  similarly, it was difficult to determine the effects of other variables such as ewe stocking rate, condition score, feed-on-offer, shelter and weather on the relationship between ewe mob size and marking percentage.>
The impact of the number of ewes in the mob at lambing on marking rate was significant in non-merino twin and single bearing ewes (p<0.001).  for every 100 extra non-merino ewes in the mob at lambing twin lamb marking rates declined by 9% in twins and 5% in singles.  the number of merino ewes in a mob at lambing was also found to significantly affect twin lamb marking rates (p><0.01) but was not significant for single lamb marking rates (p>0.10).  For every 100 extra merino ewes in the mob at lambing, twin lamb marking rates declined by 6%.
This project has provided encouragement for further work to be undertaken in this area, to aid in the quest to improve the survival of lambs born.  Lamb survival continues to be a significant wastage point in the flocks surveyed, with only 75% of the foetuses conceived resulting in live lambs at marking.  This outcome appears to be influenced significantly by ewe mob size at lambing, particularly for twin born lambs.  Across all the data collected (750 paddock-mob records), for every 100 extra ewes in the mob at lambing, marking percentage decreases by about 10% (p<0.001).  the majority of producers in this study (62%) have already demonstrated a willingness to manipulate single and twin bearing mob sizes at lambing, however they require more precise guidelines to optimise their decisions regarding mob size at lambing.  hence, further investigation is warranted given that very limited research has been undertaken on the relationship between lambs born per day (governed by mob size, parity, joining length and pattern) and lamb survival rates.>