Performance recording is an effective method of identifying sheep and cattle with the best genetics for economically important traits. Selective breeding has allowed considerable genetic gain in the breeds which have embraced this technology – with improvements in growth rate being a key area of focus. Growth rates are easily measured and highly heritable, meaning that they offer themselves to substantial genetic progress in both cattle and sheep.
Livestock breeders should however bear in mind the positive relationship between birth weight and weights later in life (and the subsequent positive relationship between increasing birth weight and difficulties at lambing/calving). As growth rates increase, so too will birth weight and this can result in more difficult births – although in purebred populations some of this increase will be offset by an increase in the mother’s mature size and pelvic area.
On both pedigree and commercial farms, difficulties at birth are a major economic setback, and can lead to the loss of the offspring and sometimes the mother. In cattle, difficulties at calving also significantly lengthen calving intervals.
With the majority of the country’s lambing and calving periods just around the corner, pedigree breeders reminded of the importance of recording birth weight and calving/lambing ease to monitor this important trait. This will allow the identification of sires that not only have good genetic merit for growth rate, but also produce progeny that are born without assistance.
Birth weight is taken around the time of birth. Sheep producers tend to place lambs in a bucket held under a spring balance.
Lambing/calving ease is assessed using a 6 point scoring system:
1 Unassisted delivery, short duration (shorten than half an hour)
2 Unassisted delivery, long duration (longer than half an hour)
3 Minor assistance needed, little effort required
4 Major assistance required
5 Veterinary assistance
6 Elective caesarean
For more information click on Recording Lambing Ease and Birth Weight