Invermay investigation of Effects of Hogget Mating on Lifetime Performance of Ewes

New Zealand Journal of Agriculture, Volume 99, Issue 6, 15 December 1959, Page 537

Invermay investigation of Effects of Hogget Mating on Lifetime Performance of Ewes

THOUGH far from being general on New Zealand farms, the practice of mating ewe lambs has had adherents for many years. The opinions of these farmers are generally favourable but not always precise. Little accurate information on subsequent productive performance seems to be available. Lifetime productivity of ewes which have reared lambs as yearlings is therefore being investigated at the Department of Agriculture's Invermay Research Station. The initial phase of this investigation was discussed in a paper by K. H. C. LEWIS, Scientific Officer, at this year's Invermay Farmers' Conference. This article is an adaptation of that paper.

SO far has hogget mating been thought to be outside accepted management that until recently there has been almost a complete lack of published information on the breeding season of the Romney ewe lamb. Such information has been reviewed by Ch’ang and Raeside (1), who have also made an important contribution. Available overseas information supports the practice. Careful work with the Hampshire breed in U.S.A. (2) showed that the growth rate over five years was not affected once the difference due to the yearling, lactation was recovered at the 4-tooth stage.

Two-tooth lambing performance was slightly inferior, but lambing over the remainder of the productive life was comparable. These results and other work < (3, 4) indicate that the initial advantage in lamb production from the additional mating is held over the sheep’s lifetime. Further overseas research (5) showed that at 16 months of age hoggets which have reared lambs had lighter carcasses, narrow in both fore and hind quarters, bones of normal length but thinner, and retarded muscle and fat development. However, a year later at the normal 2-tooth weaning there were no apparent differences in carcass conformation. The conclusion was therefore that mating of ewe lambs did not permanently

check their growth provided they were adequately fed. It was on this background and after three seasons of preliminary investigation at the Station that the long-term Invermay experiment was begun. Stock and Management From the Station flock about 300 ewe lambs were selected, broadly for adequate development, and divided by restricted randomisation on weight into two groups. One identified group of 100 was returned to the Station hogget flock as a control. At 83 lb average live weight in early May 1958, these hoggets were considered to be well developed. Though their, exact age was not known, they were born in late September or early October and thus were eight to eight and a half months old at the onset of their breeding season. One raddled Southdown ram was put with 198 ewe hoggets on 16 April to await activity and two further rams were added on 5 May. Matings were recorded once daily from markings. Observation and recording continued until 30 June, 67 days after the first recorded heat period. One ram remained with unmarked ewes until

28 July. Favourable conditions for mating were provided by using paddocks of 3 to 4 acres. The feeding of the control group followed normal Station practice for ewe hoggets. No attempt was made to flush the mated group, which was carried on grass with hay supplements until early July and then boxed with the Station hoggets until 10 September. The group then went on to grass with a limited oat supplement. No difficulty was experienced in promoting satisfactory development in all experimental animals. In spring the lambing group was given preferential treatment up to weaning while control animals were less favourably grazed so that they did not become too fat. RESULTS Onset and Pattern of Heat Isolated animals showed heat (which may not have been the onset) on 25 April, but there was then inactivity for 10 days. Moderate but consistent activity started on 3 May and continued throughout that month. Isolated onsets only were recorded after the first week in June, the latest being 29 June. The mean date of onset, 22 May, was comparable to that found by Ch’ang and Raeside (1) in North Island Romney ewe lambs. As the rams were removed from ewes exhibiting heat at the end of June, the pattern of the return to inactivity is not known. Results showed that earlier onsets favoured concep-

tion and that 70 per cent of barren ewes either did not exhibit heat or had but one cycle. TABLE I—RELATIONSHIP BETWEEN WEIGHT AT MATING AND HEAT ACTIVITY Per Live No. cent weight Range lb lb Exhibiting heat . . 179 91 83.79 57-95 Pregnant .. 132 67 83.90 Not pregnant .. 47 24 83.50 Heat absent .. 17 9 78.00 68.94 Table 1 shows body weight at approximate time of onset for various classes of performance. There was a significant difference of 5.8 lb (1 per cent) in live weight between ewes showing and not showing heat. Though there was a definite relationship between live weight at puberty and commencement of heat, the success of consequent matings appeared to be unrelated to live weight. Lambs of weights throughout the entire range of the group exhibited heat. Lambing The average lengths of 115 gestation periods ranging from 139 to' 152 days were: Days 102 single births . . . . 145.1 13 twin births .. .. 146.0 These were derived from the oncedaily recording of matings and births at similar times each day. The mean date of birth was 19 October. . Lambs were weighed and tagged at birth. Congenital abnormalities and

mortality were fully recorded, though often the cause of death could not be diagnosed accurately. Whenever possible lambs were fostered on to ewes which lost their lambs to keep them lactating. The flock generally was placid with a strong mothering instinct not greatly inferior to that of mature ewes and rather better than that of 2-tooths. There . was a high incidence ol abnormal presentations, nine being of the head and one foreleg type. Rectifying these conditions was more difficult than in 2-tooths because of the small pelvic girdles. However, malpresentation was not a major , cause of lamb mortality. The few births classified as “assisted” were mainly those in which the vulva was constricted. One ewe had pre-natal bearing trouble, and died after producing twins. This was the only ewe lost at lambing. Table 2 shows lambing performance. TABLE 2—SUMMARY OF LAMBING PERFORMANCE Barren Exhibiting heat .. .. 47 Heat absent .. .. . . 17 Total . . . . . . 64 Normal births .... .. .. 100 Abnormal births ~ ;. r . Born alive: Assisted .. . . .. . 4 Malpresentations .. 11 ' Total ■.. .... 15 Born dead: . Assisted . . .. . . 1 Malpresentations .. 3 Premature .. .. 4 Normal .. . . .9 Total 17 Total 196

Birth Weight The mean birth weights of single and twin lambs are shown in Table 3. Earlier experience had consistently shown a mean birth weight of 8 to 8| lb for Southdown-cross singles, about 1 lb lower than the same cross .

TABLE 3— BIRTH WEIGHT OF LAMBS No. Weight Range lb ■; lb Singles: Male . . 63 8.82 1« on irl9 a Female .. 50 7.61 J 4.8-12. b Twins: Male . . 16 7.34 Ir-to 4698 Female .. 10 6.76 J 7,12 4.b-».rf

born to 2-tooth ewes. The birth weights of the limited number of twins were relatively high compared with those of singles and might indicate an appreciable reserve in foetal development. The possibility that where lambing was prolonged late into spring exceptionally good feeding conditions in late pregnancy might result in increased birth weights was not supported by results. No difference was found in the sex-corrected weight of single lambs born before and after 19 October, the mean birth date of all lambs. Nevertheless the contribution of heavier lambs to abnormal births was high.

Of 20 births of lambs weighing 10 lb or more, only 35 per cent were normal, 45 per cent were assisted or malpresentations, and 20 per cent of the lambs were born dead. The frequency of abnormalities in the birth weight range 9 to 9.9 lb was about the same as for all births, 76 per cent of which were normal. Twin Births Ewes bearing twins were allowed to rear their lambs except where removal of the lamb was necessary for its survival, but of 14 sets only five were reared intact to weaning. Four sets were broken by death or mothering

off at birth and five by deaths after tailing.

In spite of relatively high birth weight and apparent viability at birth, twin births made an excessive contribution to lamb losses; 13 of 28 lambs failed to survive to weaning. The growth rate from birth to weaning (0.283 lb per day) was below that for singles. Though heavier losses and lower live-weight gains are expected with multiple births, it is probably unwise to allow ewe hoggets to rear both twins, particularly where foster mothers can readily be found.

Lamb Losses

. Fewer lambs survived to weaning (Table 4) than might be expected with favourable weather and close shepherding. Eighteen per cent of those born died before tailing and 27 per cent before weaning. Four of the 14 deaths after tailing were due to white muscle disease, the -influence of which in births and subsequent losses was not clear. Such wastage has not been characteristic of hogget lambing on earlier experience. Nevertheless young stock may prove to be more susceptible to conditions inducing white muscle disease in their progeny, , and all the available precautions should be taken.

TABLE 4—LAMB LOSSES

Per cent of ewes mated Lambs born (inc. prematures) 146 73.7 Lambs born at term .. .. 142 71.7Lambs born alive .. .. 129 65.2 Lambs surviving 24 hours . . 124 62.6 Lambs surviving to tailing.. 120 60.6 Lambs surviving to weaning 106 53.5

Lamb Growth to Weaning

Though a warm, dry spring favoured lamb growth, a ; summer that became progressively drier made feed suitable for fully lactating ewes difficult to find. The mean age at weaning was 89 days, the ages ranging from 52 to 114 days. Thus there was a rather wide range in nutrition and environment. The average gain of 0.394 lb per day for single lambs from birth to weaning was satisfactory, but fell short of results obtained with earlierborn lambs from 2-tooth ewes in a similar environment.

The ewes were obviously able to produce sufficient milk. Though udders were variable in size, they were shapely and teat development was

good. There seemed to be a definite

relationship between a lamb’s growth rate in the early part of lactation and the size of the ewe’s udder, but as lactation began at different dates up to 30 days apart, accurate estimation of the relationship may not be possible.

Growth and Development of Hoggets

The mean weight of lactating ewes at weaning (16 January) was 108 lb, some 8j lb lighter than barren and dry ewes and 6J lb lighter than controls (similar, unmated hoggets). A precise estimate of the effect of lactation on body weight was not possible in this trial, because both control and barren ewes were fed differently from productive ewes for some part of the year.

In two previous trials lactating hoggets had reached 110 to 115 lb at weaning and had become comparable with non-milking hoggets in body weight and appearance 9 months later. The resilience of young stock to early stress (such as lactation) has been established (6). With good feeding and management the trial ewes are expected to recover condition completely.

Wool Production

All lambs were shorn in April before the start of tupping. Unskirted

fleece weight at shearing, in November

is shown in Table 5.

TABLE S—WOOL PRODUCTION

No. *lb Heat absent .. .. ..15 5.69 Exhibiting heat: Barren .. .. .. 43 5.93 Lactating .. .. 128 5.47 Control 100 5.27

On the average ewes had been in milk for 36 days before shearing.. The extent to which wool production was affected by pregnancy and lactation is perhaps best represented by the difference between the fleece weight of lactating ewes and barren ewes which showed heat. The latter sheared about i lb more. However, the comparison is not straightforward, because the two classes of ewes were separated before and throughout lambing. ' ■ CONCLUSIONS Over 100 lambs have been reared from ewe hoggets. Only overseas reports carry an assurance that breeding from well reared hoggets is not detrimental to the animals’ subsequent production. So far the Invermay trials indicate that pregnancy and lactation produce no major stresses. However, though effects on the ewes’ development may be expected. to disappear before the 4-tooth mating, earlier pregnancy may have important effects on longevity, particularly on the soundness of teeth and udders.

Records accumulated during . the lifetime of the experimental flock .of ewes which have reared lambs 'as yearlings will enable relationships to be established between yearling and subsequent breeding performance. Their relative value as aids in selection of hoggets for mating can then be assessed.

At this stage the farmer on the better class of land may choose to tap the productive potential of his hogget flock. A trial mating, of a small number of hoggets may be desirable to test the soundness of the step. If lambs exhibiting heat in May have only one or perhaps two cycles before rams are removed to avoid very late lambs, lambing percentages cannot be expected to be more than 50 to 60. ■: References 1. Ch’ang, T. S., and Raeside, J. 1., ?(A Study of the Breeding Season of Romney Ewe Lambs”, “Proceedings of the New Zealand Society of Animal Production”, Vol. 17, p. 80 (1957). 2. Spencer, Schott, et al, “Journal of Animal Science”, Vol. 1, p. 27 (1942). 3. Bowstead, J. E., “Effect of Breeding Immature Ewes”, “Scientific Agriculture”, Vol. 10, p. 429 (1930). 4. Briggs, H. M., North Dakota Agricultural Experiment Station Bulletin No. 285, “Some Effects of Breeding Ewe Lambs” (1936). 5. Palsson, H., “Animal Breeding Abstracts”, 1955, Vol. 23, p. 53. 6. Coop, I. E., “Effect of High and Low Plane Rearing of Hoggets on Lifetime Productivity”, “Proceedings of the New Zealand Society of Animal Production”, Vol. 16, p. 31 (1956).

Animal Diseases Expert for Conference in Manila QR S. JAMIESON, Chief Advisory ■ Officer (Infectious ’ Diseases Control), Department of Agriculture, will represent New Zealand at theFourth Joint Food and Agriculture Organization and International Office of Epizootics Far East Meeting on Animal Health in . Manila in December. / At the meeting each representative report on the history of various animal diseases in his country and detail present and proposed measures to combat them. These diseases include rinderpest and foot-and-mouth disease, diseases in young animals, and poultry diseases. Though many of the diseases listed for discussion have never occurred in New Zealand, they are a constant threat and in view of New Zealand's increasing trade with Asia it is most necessary that we know what steps other countries are taking against them.

* Unskirted fleece„ weight