3 November 1995


Increasing the number of lambs reared when breeding from ewe lambs usually leads to increased profitability. Harry Hope reports on how a pre-tup shear benefits the bottom line

SHEARING ewe lambs before tupping increases conception rate, as well as lamb birthweight and liveweight gain in lowland flocks. This is the result of a three-year trial at ADAS Drayton, Warwicks.

The extended trial involved 216 Border Leicester x Swaledale Mule ewe lambs, bought in the first two weeks of September from 1988 to 1990, inclusive.

They grazed as one group on predominantly perennial ryegrass swards with whole barley offered at the rate of 225g a head a day until housing in early January. Lambs were also dosed for worms on arrival, then introduced to the farm vaccination programme against clostridial diseases, enzootic abortion and foot rot.

At the same time they were weighed, and again at housing, post lambing and before ram introduction the following year. They were also condition scored.

Those selected for shearing were clipped about one month before ram introduction, while the other group were shorn the following May.

Suffolk tups were raddled so mating dates and returns could be recorded twice a week. They ran with the ewe lambs from late October to mid-December for three 17-day cycles.

At housing in early January, ewe lambs were wormed and for the first two years grass silage was offered ad lib. The supplement was changed to a proprietary sheep pencil, with the rate kept at 225g a head a day to lambing.

In the third year silage was not available and cereal straw offered ad lib. The supplement was 0.59kg whole wheat; 0.20kg soyabean meal and 0.02kg minerals a head/day. Booster injections (Heptavac-P and Clovax) were given at least six weeks before the expected onset of lambing.

The average maximum temperature between shearing and housing over the three years was 11.5C (52F) and the average minimum 4.3C (41F).

Lambing performance was the number of lambs and birthweights. Individual lamb weights were measured subsequently at six weeks old, weaning and sale.

When liveweight details from ewes at mating were analysed, (excluding barreners), unshorn and shorn ewes weighed 65.9kg and 65.6kg, respectively.

Mating performance is shown in the table above. Numbers of ewe lambs mated in each cycle was fairly similar for both treatments, but there was a tendency for the profile to be more peaked for the shorn treatment.

Single returns between the two treatments was similar and this indicated the wool from unshorn ewe lambs did not hinder mating, even though they were not crutched before rams went in.

The other table describes lamb performance from birth to sale and splits lambs into twins and singles born and reared as such.

It excludes fosterings and twins when one lamb died at an early age. Liveweight and liveweight gain for single lambs was improved significantly by shearing before mating. The trend was similar for twin lambs, but the difference was statistically significant for the sale weight only.

The reason for increased birthweights was likely to have been the reduction of heat stress over the housing period.

While the fleece of shorn ewe lambs would have re-established after shearing in September, the quantity during housing would not have been as great as for unshorn animals. Further studies at Drayton are investigating shearing at housing for ewe lambs which have already been shorn before tupping.

Researcher Pat Johnson explains that while the mechanism for birthweight increase due to shearing at the pre-tupping stage may seem to be understood, the reason for increased conception is less so.

He cites dated work (Allen and Lamming 1961) which showed that a higher plane of nutrition can reduce the age at puberty and also increase ovarian and uterine weight. But no effect was found on ovulation rate or fertilisation of ova.

Age at puberty does seem to be relevant to the Drayton findings and apart from the more peaked conception for shorn ewe lambs, the mating performance was similar for both treatments. This suggested that shearing may help to prevent mortality at the embryo stage.

Reduction in heat stress and increase in feed intake might be relevant to the reduced mortality and the need for further studies on embryonic mortality is suggested.n