Romney survey selects the top sheep

Press, Volume CXII, Issue 33067, 7 November 1972, Page 29

Romney survey selects the top sheep

(By

C. A. MARTIN,

Romney Sheep Breeders' Association)

Twinning is an important factor in sheep production and Profound effect on lambing percentages. On any farm, additional lambs, provided there is room for them, must mean extra financial return to their owners, but more important still, they provide greater scope for better selection of flock replacements.

More critical selection for all aspects of sheep production must lead to improved flock performance, which in turn elevates the whole level of production. Therefore twinning provides an ascending spiral of performance. From the work of the New Zealand Romney Survey it is known that there are stud flocks with a lambing potential of up to 175 per cent, this being total lamb drop, expressed as a percentage over ewes lambing. Flocks with this potential based on ewes to the ram, have docked around 160 per cent The over-all average potential of stud Romney flocks in New Zealand over the five years of investigation by the survey has been consistently in the vicinity of 146 per cent. This means that almost half the ewes under survey which lambed gave birth to twins and at this rate two out of every three lambs in these stud paddocks are twins. When the question is asked—how can the twinning potential be expressed, the answer would be the same for all breeds of sheep in New Zealand. With present knowledge there appears to be several main factors involved in increasing lamb production and therefore in increasing twinning within a flock. Probably the most rm-

portant single factor in encouraging the expansion of twinning potential would be the implementation of a restricted mating period in any flock.

At all levels of sheep production the aim must be to introduce the very best twotooth ewe flock replacements each year. The body weight factor in sheep production has been wellexpounded and is of extreme importance. Late dropped lambs, without special treatment, tend to be poorer two-tooth ewes and subsequently the poorer, older ewes.

The late dropped lambs are therefore undesirable as regards body weight, and also from the fertility point of view, because they are mainly the progeny of the less fertile ewes — those that come into season very late or those that return to service once or more.

In 34 days of mating, under stud mating throughout New Zealand, 87 per cent of all ewes have conceived — by 42 days this figure has risen to at least 97 per cent In commercial flocks with the massed mating technique these figures are higher, and although they do vary slightly from district to district, the withdrawal of rams after 34 days of effective mating, and their replacement with another breed, would mean

that a relatively small number of ewes are involved in this late mating. These would be the less fertile ewes and there would be no possibility of their progeny, either ewes or rams, coming back into the flock. Flocks in which this technique of mating has been adopted for some years find that their lamb production has improved steadily, and this means that their incidence of twinning has increased. Some of these farmers have subsequently reduced mating well below 34 days with their breed type rams and they report added improvement. In any restricted mating, the efficiency and performance of the rams must be studied, and this would involve thorough examination of every ram before mating and close observation over this vital period. More important it would also involve a complete study of the productivity background of the rams used.

In the collection of detailed lambing information throughout New Zealand, the survey has found that ewes which lamb in the first 34 days of lambing consistently produce at a higher level — these ewes which conceive in this restricted period are in the upper bracket of fertility.

The total lamb drop, in 17-day periods, in large numbers of stud ewes under survey in one year, was as follows:— First 17 days, 52 per cent of all ewes produced twins; second 17 days, 60 per cent of all ewes produced twins ;third 17 days, 39 per cent of all ewes produced twins; subsequently, 23 per cent of all ewes produced twins. The other important aspect of restricted mating is that the less number of days involved the less will be the number of ewes involved which have returned to service. Examination of good stud records shows that ewes which conceive to a single service are generally superior producers. Information taken from a group of studs where the relative records were available showed that two-tooth ewes which conceived to single service dropped 131 per cent of lambs, compared to 105 per cent from those which returned to service. Four years’ subsequent lambing from the same two groups of ewes was 149 per cent and 120 per cent respectively, A restricted period of effective mating will improve the number and standard of lambs bom and reared — they will be better in both quality and potential. In any flock, as emphasised previously, the degree of selection of two-tooth ewes for flock replacements depends mainly on lambing percentages. Final selection depends on many factors—conformation

(and in Romneys, requirements are changing on this aspect), wool, size and body weight are all considerations, but other unseen factors are equally, if riot, more important. On Romney studs, good records enable accurate assessments to be made and in every ewe being considered, their potential for production, based on that of their dam and both grand dams must be considered. Details such as lambs bom and reared (including weaning weights); number of times returned to service; the degree'“of assistance at lambing; wool weight, count and quality—all of these must be taken into account. A more refined examination may be in sire and family groups. Another test for selection in commercial flocks could be the use of “teasers” on ewe hoggets and the information gained on how they were covered at a period when they were seven to eight months old, utilised. New Zealand and overseas workers have shown an improvement in subsequent lamb production from ewes which come into oestrus and cycle at the hogget stage. In the selection of rams, the relative considerations discussed for ewes are more important, and as a degree of selection is so very' much more intense, each facet of selection can be more emphasised. Close analysis of the production of sisters and half-sisters is an extremely important guide oh a ram’s potential. Management of a ewe flock is a major factor in its ability to express its twin-

ning potential. Body weights and mating techniques are involved in management. The Romney survey, in flock slaughter experiments has shown, together with other workers in the same field, that the embryonic loss factor in the first 30 days of pregancy is a serious matter. Extremely important points in the survey investigations showed that just over 40 per cent of ewes which produced twin ovulations finished up carrying one live foetus or lamb (an irrecoverable loss) and 23 per cent of all fertilised eggs did not survive to the thirtieth day. It follows that the first 30 days of pregancy is a critical period—a time when ewes should be handled carefully, and not shorn, footrotted and yarded as has been the case on many farms. Many aspects of sheep production have been discussed but all bear a close relationship to the factors which will allow the Romney flocks of New Zealand to express the twinning potential that they undoubtedly contain. There is increasing awareness among many breeders throughout the country for the need to maintain and use improved recording systems. The National Flock Recording and the Romney Stud Fertility Schemes are evidence of this concept, the main aims being to find and utilise the superior sheep.