Raising Productivity Of Sheep Flocks

Press, Volume CVI, Issue 31362, 6 May 1967, Page 8

Raising Productivity Of Sheep Flocks

If farmers did only two things—culled barren ewes and bred bigger and better flock replacements—this would make a great difference to the productivity of their flocks, Mr C. A. Martin, field officer of the New Zealand Romney Survey, said in Feilding this week, discussing the work of the survey which was established in 1961 by the New Zealand Romney Sheepbreeders’ Association and the Meat and Wool Boards.

Mr Martin said it was estimated that if every egg shed within every breeding ewe was fertilised and carried successfully right through to birth and to weaning, New Zealand would be better off to the extent of 16 million lambs a year. Five factors were listed by Mr Martin as leading to increased lambing percentage. They were:— (1) Ask for the productive background of the rams you buy. He said that in many cases these records were available.

(2) Check your rams regularly and look after them. (3) Breed bigger and better ewe flock replacements. (4) Cull barren ewes and identify ewes which carry their lambs to full time but then lose them. (5) Find out why any sheep dies (lambs, including abortions), hoggets, ewes and rams.

Survey work in studs and ordinary flocks has shown that single lambs are on average 51b heavier than twins at weaning, but as the year progresses the twins gradually catch up with the singles, says a recent commentary on work of the Survey. This means that the culling of hoggets on size can eliminate some twins, but if culling is done at the twotooth stage there will not be the tendency to select against twinning. It is not the twin lamb but rather the late lamb which tends to be the tail-ender. In weight, under similar conditions, the late-born lamb never catches up with early and middle-drop lambs. There is a tendency for late lambs retained as ewes to produce late lambs and, therefore, poorer lambs.

Beneficial In an all-out effort to produce high grade two-tooth ewes it will, therefore, be a benefit to eliminate late lambs. This can be done by a restricted period of mating ewes with the Romney ram. If the Romney rams are replaced by Southdowns after six weeks of mating all late lambs will be killed and all lambs retained for breeding would come from ewes which came into season early, held to the ram and were, therefore, of higher fertility. When two-tooths do present lambs, the most valuable sheep in any flock are the two-tooths which have twins and rear them well. They must be retained, but barren two-tooths must be culled and go to the works.

The barren ewe is regarded as a problem on many farms. The Romney Survey has investigated this question and suggests that increased production would result from the culling of all barren twotooth ewes. It has been common practice for dry twotooths to be given a second chance and then those dry again as four-tooths are culled. About 80 per cent of dry two-tooths will lamb as four-tooths but their production is very low compared with ewes which lambed as two-tooths and the subsequent production of their progeny is at the lower level. The retention of these ewes tends to infuse a lowerproducing trait into the flock. To investigate this the Romney Survey extracted

from good stud records the subsequent lamb production figures from a group of ewes dry as two-tooths and retained, compared with the same number of two-tooths which reared their own lambs. The following table gives the results:— Lambing p.c. Wets Drys 5 years aggregate' 149 78 4 years, excluding two-tooth lambing 158 113 5 years lambing of original ewes, plus that of all female progeny .. 130 112 In the same way production records have been taken from many studs comparing the

life-time production of three groups of ewes which as twotooths were barren or had singles or twins. In every case the barren ewes retained showed up in a very poor light. From this investigation there was no doubt that ewes which produced twins as two-tooths produced the highest life-time results. The wet/dry ewe is one which carries her lamb to full time but loses it The reasons for these lamb losses are variable, but it is important to define them. Adverse

weather conditions at the time of lambing could have killed the lambs and therefore the blame for the loss cannot be levelled at the ewe.

However, at lambing time, various factors considered, if the cause of a lamb loss can be directly attributed to the ewe herself she should be identified for culling. From work done by the survey it would appear that the wet/dry condition is repeatable, but the degree would be dependent on the original reasons for the ewes losing their lambs. Body Weight Work done by the survey has also shown that as the body weight of two-tooths increases so also does their lambing percentage. When tupping weights of large numbers of two-tooths were correlated with subsequent lambing percentage, it was found that those ewes which had body weights of 811 b to 901 b produced 55.6 per cent of lambs and those between 1211 b and 1301 b 107.2 per cent of lambs docked. The survey has demonstrated that benefits accrue from good body weights in ewes both in ovulation and lamb production, but there is also an indication that excess body weight tends to have a depressing effect on subsequent production and this has been confirmed by weighing projects conducted by the survey.

Some work done by the survey has indicated that as a general assessment body weight has some effect on wool production, but the degree of variation in the wool produced by sheep of identical weights, and conversely the variation in body weights of ewes producing the same weight of wool, shows that selection on wool weights would not necessarily lead to improved body weights. Rams Mr Martin said that young, new rams coming to a property should not be put with old rams but on a good, fresh paddock and after mating they should be put on good feed to enable them to make a quick recovery. One of the things requiring most intensive investigation was ram performance, he said.

A report on semen testing done by the survey said it was once again obvious that semen testing prior to mating could only be regarded as a guide to the inidividual ram’s ability to produce good semen samples. A later comment was that over-all fluctuations in ram performances suggested that there was a great deal of work needed on factors affecting ram semen. The selective grazing habits of rams also required investigation, together with the many factors affecting ram fertility.