Scientist looks at breeding from ewe hoggets

Press, 3 April 1980, Page 10

Scientist looks at breeding from ewe hoggets

In the ‘ accompanying item Professor A. R. Sykes, of the Animal Sciences Group at Lincoln College, discusses breeding 'front ewe hoggets — a means, of increasing production without any expansion of existing flocks.

At this time of the year decisions have been made on culling and replacement, which influence the over-all level of stocking and peformance of the flock throughout the whole of the coming year. It is sensible that consideration is given to other factors, which are important in influencing the output of the ewe flock, and in particular the advantages or otherwise of breeding from ewe lambs. It is important nationally, at a time when the Government is rightly stressing the need and

ability to increase output from the traditional primary industry. I recently read the reports of work carried out by A. R. Leslie during the 1930 s in ' which consideration was being given to the problems' of first breeding from two-tooth as opposed to four-tooth ewes on the college’s Ashley Dene property. Concern was expressed that the move to breeding from two-tooths. could, irreparably impair the lifetime performance, of the sheep. Since those days major advances in knowledge of fertiliser ' requirements, plant breeding, irrigation, grassland management and in the nutrition, health control and general management of sheep flocks have enabled regular breeding from sheep as two-tooths across a wide range of environments. On some/properties this move is being taken one stage further and-sheep are bred at eight months of age, arid indeed it has been the policy on Ashley Dene in recent years to adopt this practice/ ’with varying degrees of; Success. • The impetus towards earlier breeding of ~ewe Jambs occurs for three reasons. - ? , First, the greater the proportion of sheep in a flock which are contributing. effectively ■ to sales of wool and Jamb, the more, efficient will be the use of the most scarce farm'/' resource \ — /feed energy..? Apart from the ’ ■wooft’/Whichlr they/; grow, ; hogget . replacements .are carried by. the main ewe. flock so - far- as a contribution towards.lamb production; is /.concerned.. .The. maintenance. . requirement ;6f a sheep ' flock . constitutes over 80 per cent of its total, annual feed re'quirement. The greater the amount of product over which ; this requirement can be spread the lower is its cost for each" unit produced. ■ / ■ Looked at from another

viewpoint, we can calculate that in a flock with a lambing percentage of 120 and a breeding life of four years only 2.5 per cent of herbage energy consumed and available to the anils converted to energy in the lamb carcase. Breeding from the same animal as a hogget and retaining it in the flock for four lambings would increase this efficiency to almost 3 per cent. These are both low values, but the latter is 20 per cent greater than the former. If reliable breeding at this stage could be achieved without subsequent loss of performance, the increase in efficiency would be equivalent to an increase in lambing percentage from 120 to 145 per cent. This is equivalent to the genetic progress which might be achieved by many years of intensive selection for fer--tility within the flock, and can be achieved almost immediately. Second, on most properties, particularly those with irrigation development, where continuity of herbage growth is now much' more secure, there are, feed surpluses in spring, summer and autumn which are not made effective use :of. Indeed, because of ■this total annual herbage production can be depressed.. Winter carrying capacity generally limits stocking rate. A flock - structure which allows the maximum number of wintered stock to contribute to production of lambs to consume spring and summer herbage ensures that a balance of annual food demand is achieved, which better fits the annual pattern of herbage growth. Good husbandry.and■good pasture management are thus made easier, and the necessity for conservation is decreased. ■ Third, New Zealand as a trading nation places heavy reliance on an ability to adapt rapidly to changing world demand for food commodities. The problem of the beef cycled with a two and a half to threeyear lag between the decision to increase beef output and .the ability, to put the result of that decision on /to the market are currently plain. In' the-, sheep industry a decision - to bre6d from some of the existing ..11.8M ewe hog- . gets, which are maintained annually,' would provide a response^-to. increased world demand fof meat within/' eight months and. with no increase in the • total number of breeding livestock to be. maintained.'.. Given that there are ad- > vantages ; to be gained from early!- breeding what are likely to be the keys to success?

Hpggets ■ will. . show oestrus and produce eggs for fertilisation at about 200 days of. age, but this, can vary depending on breed and nutrition and date of birth. Of major

importance is the bodyweight which the hogget attains during the breeding season (March-July/);: For New Zealand, breeds a critical average weight, for hoggets in late March, to ensure satisfactory breeding/ /is about ■ -35 kg: , ; At bodyweights greater than this we can anticipate that 90 per cent of lambs .will show heat, accept the; ram and conceive; The; heavier the bodyweight, the more likely that all lambs will be cycling '/when the ram is introduced, and the greater the ; .chance of a tight lambing. As: in the mature ewe, there; is. some evidence that’ a high -plane of nutrition during the breeding season will ‘ increase/ the proportion of hoggets which will show heat. To achieve a weight of 35kg in late ■ March requires an .average growth rate from birth of about 150g/day. Most lambs are capable of growing .at 300g/day from birth so this is a perfectly reasonable target. Care must be given to the nutrition and health of • the growing lamb, and the lamb land ewe must be managed to promote continual rapid growth in the former. Lamb weaning should not be delayed to the stage that the-ewe competes unfairly .with the lamb for herbage - while producing

little milk for the lamb. Lambs can be weaned at' 20 to 25kg bodyweight (8 . to 10 weeks) on-to good .clover-dominant or lucerne pastures;’ ’ and provided they -arg moved-- .throughquickly./tb select highly nutritious*. herbage,- growth"

rate will not be checked. The ewe should then follow and clean up pasture in preparation for regrowth of further highly • digestible lamb feed to maintain succession through summer and in the autumn. Ewe bodyweight recovery need not be prejudiced by this practice provided that bodyweights are monitored and targets for a gradual return of a pre-mating bodyweight of 55 to 60kg are aimed for by mid-February. It is essential that trace element deficiencies, gastro-in-testinal parasitism and other health problems are effectively controlled by dosing and grazing man1 agement during this growth phase, but that, is a subject in itself. Ewe. hoggets, like twotooth ewes, are.more reticent in seeking out the ram than mature ewes and because of their', small anatomical size the open-, ing of the female reproductive tract, the vulva, is smaller. Penetration by the ram is, therefore, more difficult. Mating practices should ensure that the ram does not have to travel long distances to seek out the hogget. A ratio of rams: hoggets of about 1:80 . should be used and ..small . paddocks with ample . feed selected. To ease -•mating a hogget crutching is desirable. Choice of the small rams from those available is advisable and a marking (black faced) . ..ram would be a husbandry aid in case these lambs need to be quit early as "stress develops in a dry ' season. It is unlikely that ‘lambs from these ewes would be used for breed- - ing replacements and colour marking will save confusion at drafting. A compromise must be struck between allowing continuing growth of the hogget, while controlling of the foetus to minimise lambing difficult-' ..ids LL Good nutrition for the hogget during the first .yThree months of pregnancy ,to allow continuing body ; growth can be achieved with little danger to sub- * sequent health because, unlike the mature ewe, ; body tissue will be deposited as bone and muscle > rather than as abdominal . fat,. A target ..weight gain during this period should be-8 kg, though 4 kg may be the "most that can be expecJed.gPUripg the last.

six weeks of pregnancy increase in liveweight should be limited to 7-8 kg to avoid excessive lamb birth weights. Ewe hoggets, where bred, are often not mated until a month after the main ewe flock. This ensures that they lamb on to the main flush of spring herbage growth and are not pinched, for feed during lactation. This is important to prevent excessive weight loss. Lambs from this category of ewe should also be weaned early, at 6-8 weeks, to ensure that the hoggets achieve weights of 50-55 : kg . before breeding as twotooths. On the assumption that hogget, weight at lamb weaning- is about 4045 kg a weight gain of 150 g/day should be budgeted for between : weaning and late Feburary. The important point to remember is that these Jambs are. a bonus and should be quit as stores if feed supplies suggest, that the hoggets may be stressed. Provided these objectives are met subsequent performance as a ewe will not be compromised. Indeed scientific evidence suggests that if these growth targets are achieved,. ewes bred from as ewe hoggets will be equally productive as those bred as two-tooths. There is scientific evidence that the act of promoting growth rates to achieve weights at eight' months of age, which ensure hogget oestrus occurs, will result in superior lifetime reproductive performance. One of the problems of breeding from ewe hoggets is the question of how to manage two hogget flocks — one which accepts the ram and the other which doesn’t. , Experience, suggests that general flock fertility would be improved by selling those which don’t cycle as stores or for manufacture during the winter period. It would be unrealistic to think that wool production would not be penalised. However, with the bodyweight targets outlined we would not anticipate the depression in wool growth to be significantly greater than tjeat expected in breeding jfompared with Of more importance is the decision cf, when to shear those in-iamb hoggets. This needs careful consideration and will be resolved either by shearing

as lambs in early January and again prior to lambing in September, or delaying until February as lambs and then shearing in early December after their lambs are weaned. Ewe lambs are inexperienced mothers and will give birth to smaller lambs than mature ewes. Care is obviously needed in provision of undis-, turbed, sheltered paddocks with good feed supplies. The fact that lambing will be delayed should reduce the risk of inclement weather coinciding with low feed supplies. Clearly, I have made some generalised statements. There undoubtedly will be variation between breeds and within breeds in hogget ’ performance. The bulk of the data I have referred to. comes from Romney, Perendale, Bord e r-R omney and Coopworth breeds, but dominantly the latter two. We have little information for Corriedales and .we need more, reliable data on effects on lifetime performance. In keeping with the role of the college in initiating investigational work to service the developing needs of the agricultural industry, Ashley Dene is now being used to evaluate several aspects of life time performance of cross-bred sheep involving Coopworth, Booroola Merino, Border Corriedale and Corriedale breeds. An important aspect of the programme is that half of each breed group will be allowed to mate as hoggets and the other half retained to mate as twotooth ewes. These trials will help us to assesswhether technology has improved sufficiently since the earlier studies to now allow further progress in. improving flock output by regularly breeding from ewe lambs.