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21. Use bloodlines to increase lamb survival rates

In Merinos, the crossing of bloodlines can lead to substantial lifts in reproduction results, according to NSW Agriculture. The claim follows studies by Dr. Sue Mortimer at the Trangie Agricultural Research Centre and Dr. Kevin Atkins of Orange Agricultural Institute.

Eight bloodlines covering the range of fine to broad wool types were crossed in a wide variety of ways to examine the effects of heterosis (hybrid vigour) on reproduction. The work started with simple bloodline crosses, where purebred rams of one bloodline were mated to purebred ewes of another bloodline.

Compared with purebred mating, the simple crosses were four per cent more fertile and had a seven per cent increase in lambs weaned per ewe mated. When the "crossbred" females were mated, they had a further eight per cent higher reproduction rate than purebred females.

This latter increase, due to maternal heterosis, was principally through a higher survival rate of the lambs from "crossbred" mothers and through slightly higher twinning rates, Dr. Mortimer said.

Much of the higher level of lamb survival and improved lamb turnoff achieved from first cross and second cross joining, as compared to a straight Merino x Merino joining, is realised as a result of hybrid vigour alone. Thus, by searching around amongst different bloodlines of rams used in first and second cross enterprises, it should be possible to realise similar results to those found in the Trangie work.

Mortimer, S.I., Atkins, K.D. (1997). Improvement of Merino reproductive performance through bloodline substitution and crossing. Proc. Assoc. Advmt. Anim. Breed. Genet. 12:404-407.