Great care needed when selecting breeding traits
Published 03/04/2013 | 05:00
PROFESSOR Hugh Blair, also from New Zealand's Massey University gave a presentation that looked at the use of genetics to improve sheep farm profitability. He started off by highlighting the dangers of selecting for just one trait.
He used the example of how selection for wool production in the Romney had a negative impact on fertility.
The increased wool coverage of the Romney increased her body temperature, which in turn reduced embryo survival.
This trait has now been reversed and the Romney is much more similar, in physical appearance at least, to the animal which originally arrived in New Zealand.
Despite these drawbacks, genetic selection has lead to annual increases of 250g per year in weaning weight over the last 20 years.
The production of replacement rams was analysed. The total ram supply for commercial farms is dependent on the 10,000 rams that annually enter breeders' flocks.
This highlights the need for the nucleus flocks to select traits which reflect profitability on commercial farms, rather than those traits which are important in the show ring. It was also pointed out that the production costs are a relatively new consideration in New Zealand sheep breeding.
For this reason, there is a negative weighting on mature weight in the current breeding index to try to control maintenance costs. However, this can be adjusted if there is a fear that lambs are becoming too small.