Selecting For Production

Press, Volume CIX, Issue 32032, 5 July 1969, Page 8

Selecting For Production

The first field day for members of the Dorset Down section of the New Zealand Sheepbreeders’ Association was held at Lincoln College last week When about 50 breeders from all parts of the country were present.

After a morning session at which matters including breed policy and development were discussed, the

breeders visited the college's stud sheep farm where selection and breeding for production was the central theme of discussions led by Dr D. S. Hart, reader in animal science at the college, assisted by-Mr A. Sutherland, the stud sheep farm manager. Also in attendance were Professor A. E. Henderson, professor of wool science, and Professor I. E. Coop, professor of animal science. The use of index methods of selection were outlined, with reference being made to the method of selection and breeding which the college has been using with other meat breeds for the last 11 or 12 years, with selection being based on the two production characters of lamb birth weight and growth rate from birth to weaning. The Dorset Down stud was used to present examples of animals which were rated as high producing and low producing under the index system. It was pointed out that in this stud the selection programme had only been in progress for three lambings as the college had only recently begun breeding Dorset Downs as a result of the gifts of Dorset Down stud ewes from breeders. The breeders were invited to criticise groups of top index ram hoggets and top index ewe hoggets and also the bottom groups of these hoggets. These animals were each discussed in relation to their production index and how they appeared as representatives of the breed. Finally the breeders were asked to select out of a group of eight ram hoggets the sheep that they would keep first as a stud sire and the ram that they would cull first. Previously the group had been arranged by the college staff so as to contain six rams in the middle of the index, together with the top ram of the year on index and bottom ram.

The outcome was that only four of the assembled breeders were able to pick the top index ram as their top choice.' It was a good demonstration to breeders that where breeding is being done for productive characters—in this case birth weight and growth rate, which are essential for a prime lamb sire of any breed—eye judgment Is of little avail and selection has to be done on the production records of the sheep. This point was further emphasised by the report on the six sires used to sire these rams last year. The range in the growth rate of all of the progeny of each sire from birth weight to weaning was between 0.6151 b live-weight gain a day for the top sire and 0.5651 b a day for the progeny of the lowest sire. This represented quite a considerable difference in the breeding performance of stud sheep and from the point of view of stud breeding indicated that one sire’s progeny should be considered as strong candidates for any future culling. , Some breeders wondered, on the basis of questions posed, whether selection for birth weight was important enough to use and whether in fact it might eventually turn out to be detrimental, but it was pointed out that birth weight was regarded as being about a sixth of the prime lamb’s final drafting weight and it was therefore fairly necessary to use this character as forming part of the selection index, although by far the major emphasis of the index was on growth rate. The value of birth weight was that it could be sufficient to separate two rams, whose growth rate figures proved to be the same.

It was also emphasised that all production indices were only valid within the flock and on the farm where they were derived, and the last thing that anyone should do was to compare the figures obtained on one farm with those obtained on another. For example, the college growth rate figures were derived from weaning weight less birth weight divided by age in days, whereas many other breeders recorded growth rate by taking weaning weight and only dividing it by age. This would obviously give a much higher rate of growth and this

showed how impossible it was to compare different studs.

In these circumstances ; breeders were advised to seek to buy the top index sheep in whatever stud they ! were buying from. During the afternoon Mr K. J. Oliver gave a demonstration on faults in Dorset Down) sheep and breeders were also; given the opportunity to in-| spect all of the Dorset Down) sheep on the college property j —these had been assembled in their various groups.