Path to higher birth weights?
Path to higher birth weights?
GENETIC index selection for improved growth rates in pedigree flocks also increases lamb birth weights, according to an MLC-funded study at the University of Wales.
Yet increasing birth weights should cause no concern for producers and will help the survival of small lambs, says MLC senior geneticist Gert Nieuwhof.
Janet Roden, of the Institute of Rural Studies, analysed birth weights using Sheepbreeder records from 10 breeds. Data shows a small, yet positive increase in birth weights.
"The highest rate of genetic change in purebred populations was 0.017kg/year in the Charollais breed. But at this rate it would take about 60 years for the average flock birth rate to increase by 1kg," says Dr Roden.
Mr Nieuwhof believes small lambs will benefit from higher birth weights. "In the long term, the number of very low birth weight lambs, less than 2-3kg, will be reduced, which will help improve survival rates."
At the other extreme, exceptionally large lambs have a slightly lower chance of survival, due to prolonged and difficult births. But Dr Roden is not anticipating greater problems.
"Selection, based on indexes currently in use, would result in improved mature weight of ewes, so any increase in lambing difficulties is likely to be negligible."
Project leaders have discussed whether there is a need to work on an estimated breeding value for limiting lamb birth weights, but Mr Nieuwhof says producers concerned about high birth weights should look at the management of pregnant ewes. *