Proximity sensors fitted to ewes and rams during joining can indicate the birth date of lambs

Knowing the birth date of lambs is important for the accuracy of breeding values, particularly when ranking potential sires for liveweight and growth. We used proximity sensors to measure the daily interactions between ewes and rams to test the hypothesis that the birth date of lambs could be predicted from the time of highest interactions between ewes and rams during joining. This was a pilot project with two plots of ewes (29 or 42 ewes per plot) and one ram per plot for a 26 day joining period. The day in which the ewe had the highest ratio of interactions with the ram relative to the other ewes in the plot was selected typically as the estimated day of conception. A threshold ratio of 1.5 was used which eliminated six ewes (the number of interactions between the ewe and ram compared with the average number of daily interactions for all ewes with the ram in the plot). The prediction of the date of birth was within five days of the actual birth date for 100% of the ewes (n = 55) and within two days for 82% of the ewes. Eighty five percent of the variation in date of birth of lambs was explained by the estimated date of conception. Using the remote sensors was a discreet way of measuring mating behaviour that proved to be a good tool for predicting the birth date of lambs. This can help breeders improve the accuracy of breeding values and the ranking of sires for early growth traits.