Knowing the approximate date of birth of lambs is important to enable more precise management of ewes during pregnancy and lambing and for improving the accuracy of breeding values, particularly when ranking potential sires for liveweight and growth. When birth date is not recorded, growth traits for animals that are born earlier in the lambing cycle are overestimated and can subsequently decline when they sire progeny with a natural range in birth dates. Birth date is difficult and expensive to measure in large flocks, and for this reason is not recorded routinely, particularly in extensive sheep production systems. There have been several published studies where sensors have been used to predict birth date in cattle and sheep for welfare purposes but all of them have used direct or indirect indicators of parturition to estimate when birth is commencing with mixed results. To our knowledge few studies using sensors have attempted to predict date of birth by measuring movements and behaviour at the time of conception so that date of birth can be estimated well ahead of the birth event for sheep.
Date of conception can be estimated by fitting rams with harnesses and crayons that mark ewes when they are showing oestrus behaviour. However, this procedure is laborious and intrusive, involving repeat mustering of the sheep to assess and record crayon marks. Consequently this technique is only appropriate as a research tool or for artificial breeding purposes. New sensor technology that measures the “closeness” or proximity of sheep to each other offers a new method of measuring interactions between ewes and rams that could assist in estimating the day of conception remotely and practically. For example, remote sensors were used recently to measure the maximum number of interactions between ewes and lambs to determine their pedigree. It is well documented that rams and ewes are attracted to each other with increased preference during oestrus. Using sensors to measure the interactions between ewes and rams during oestrus may then identify accurately date of conception and, from this date of birth can be predicted. We therefore hypothesise that by measuring the number of interactions between ewes and rams during joining, as an indicator of date of conception we can predict the date of birth of lambs accurately.