Not sure if its relevant but our lambs have been on the smaller side this year. This appears to be a common problem in our area this year with even our local agriculture suppliers and even vet nurses at our practice that have sheep all having the same problems of lambs just not as big as they normally would be, our local butchers have also found lower lamb weights. Our yield off the hay field wasn't as good this year so for us it is likely the weather and amount of rain we've had this year has affected our grass growth and quality.