ABORTION, BARRENNESS, AND FERTILITY IN SHEEP. Fertility.

Otago Witness, Issue 2408, 26 April 1900, Page 4

ABORTION, BARRENNESS, AND FERTILITY IN SHEEP. Fertility.

The reports from 606 English flockmasters, recorded by Mr Walter Heape, show the proportion of lambs for 107,603 ewes as 120.4 ncr cent. When the flock

percentages of lambs are analysed, it is found that the most usual proportion of ilambs for all purebred flocks is between 110 and 120 per cent., that somewhat more than 50 per cent, of the flocks have less than 130 per cent, of lambs, and that, as a rule, the highest percentage of lambs is experienced in small flocks. TLe statistics show that out of 85 flocks pf 100 ewes, 50 of them have over 130 per cent, of lambs ; out of 40 flocks of 300 ewes, eight have over 150 per cent, of lambs ; whereas out of 11 flocks of more than 1000 ewes, only one flock has more than 130 per cent- of lambs. The percentage of twins recorded by 237 flockmasters for 68,536 ewes is 30.02 per cent. Roughly analysing the totals obtained for all purebred flocks, if 30 ewes produce twins, that is 60 lambs, out of a total of 120 lambs, the remaining 60 lambs will require another 60 ewes for their production ; 90 ewes then will produce 120 lambs, and as 7 per cent, of the ewes are either barren or abort their young, and 3 per cent, of the ewes on an average die, the 100 ewes which are necessary for the production of 120 lambs are accounted for. In the following account, unless otherwise stated, the fertility of a breed is considered in relation to the percentage of twins produced by its ewe?.

The difference in the fertility of ewes of various breeds is very remarkable ; both the percentage of lambs and the percentage of twins slioje verjr marked variation in

different breeds, and indicate clearly that fertility is a racial characteristic in sheep, probably a much more definite character than is usually recognised.

According to the records of twins, tha breeds may be divided into those of firstclass fertility, consisting of the Sufiolks and Shropshires : of second-class , fertility, Dorset horns, Oxford Downs, Kents, and Lincolns ; and of third-class fertility,' Hampshire Downs and Southdowns. The most fertile of all breeds is the Suffolk,' with 52.22 per cent, of twins ; and this is a low estimate of the capacity of thesa ewes, for if the flocks which are run im the home county are taken alone, they show 60.46 per cent, of twins. It is a very, remarkable return, and is only beaten among purebred sheep by six small flocks of WensleycUles, which record 61.21 percent, of twins. The Sbropshires come next; -\iith 48.64 per cent., and here again the estimate is low. for nine flocks in Staffordshire record 54.97 per cent, of twins. Then the Dorset horns, with 37.55 per cent., the Oxford Downs, with 35.02 per cent., and the Kents, with 31.38 per cent., all show fairly consistent returns ; the Lincolns, with 29.03 per cent., are recorded low, if the returns are to be trusted of nine flocks in Yorkshire, which record 47.57 per cent, of twins ; while ths -Hampshire Downs, with 24.09 per cent., and the Southdowns, with 18.67 per cent, are representative returns. In reference to the lasL-named, Mr Heape says:— "The return fGr Southdowns calls for "special notice; it is so low as to be worthy the serious a.ttent:on of flockmasters of that breed. Ifc is noi low on account of losses by abortion and barrenness ; the figures represent the fertility of the breed in comparison with the fertility of other breeds, a;:d, if my records are representative, which I see no reason to dembt, special care in the selection of breeding ewes, from the point of view of fertility, seems imperative."

The returns for crossbred flocks show that several pure breads are more fenlle than the average crossbred ewe. In this connection it is interesting to observe that i lie hi-hly-fertik Suffolk and Wensleydale fwet. when crowed, aie slightly le;-n prolific ihan wlien bred \i ith ram 5 ; of their own breed; v. hilo, on the other hand, the fertility of L'ox'set horn ewes, when crossed Avith Down rams, is greatly increased. In the case of this latter breed, as already noted, the aid of Down rams is very usually called for by Dorset horn fiookrnasters lor pwes T.hieh foil to get in lomb with Dorset horn ruins, and, it is found that, wLereas a considerable number of Dorset horn ewes may fail to become pregnant to rams of their own' breed, they larely fail when, covered by Down rams. Mr Heape had also evidence from several sources that Dorset Lorn ewes which slip lamb-: got by Dorset horn rams will bear lambs got by Down rams. It would appear from the f-bove facts that Suffolk and Wensleydale ewes reach the maximum of their fertility with rams of their own breed, while Dorset horn ewes require a cross in order that they may bo stimulated to the greatest generative activity.

The Causes Which Induce Ewes to Produce Twins. — The primary cause is probably constitutional ; the racial character of the fertility of different breeds indicates that. Fui'ther, there is reason to believe that twin lambs produce more twins than single lambs, and that the influence of here-^ dity is brought to bear. In that case, where tLe fertility of a flock is below the average ,the careful selection of the breeding ewes will probably increase its fertility.

The Condition of Ewes. — There is overwhelming evidence that flocks in good condition at tupping time have a higher subsequent percentage of fertility than ewes in pooi 1 condition at tupping time. The returns for the Suffolk", Kent, Hampshire Down, Dorset horn, and Lincoln breeds f-how chis clearly. By '" good condition" is meant not "fat," but strong, healthy,' vigorous breeding condition. In 'confirmation of this view are the records of the time in the lambing season during which most twins are born. Altogether, "275 flockmastera have expressed" their opinion, on the point ; of these, 26 say most twins are born in the middle of the lambing season ; 56 say late ; 61 say a1!a 1 ! through the eeason ; and 152 (more than half) say early in the season, and of these latter many add tint unless such is the case the crop of lambs will be small.

Some flockmasters and many shepherds maintain that the production of twins is due to the ram. It cannot be a question of the amount of .«psrmatoza evacuated by the ram during copulation ; -where there is sufficient to fertilise one ovum there is sufficient for a hundred ; and unless it can be proved tLat the production of ovum from the ovary of a ewe is influenced by copulation (and it is quite certain that this is not I=o in the case of horses and cattle ■ — see " Veterinarian," vol. 71, 1898, on " Insemination of Marcs"), it follows that the production of twins instead of a single lamb is a matter with which the ewe alone is concerned, and that it is not influenced by the ram. That being so, if most twins are born at early lambing time, they are produced by the ewes which first come in season, and, apart from artificial stimulus, such as " flushing," these are the ewes which are the keenest breeders, whose generative system is in the most vigorous? and healthy condition, and it is to their breeding vigour the production of twins is due. Further evidence of this is afforded by the fact, of which many flockmasters are assured, that ewes which go over or abort — that is to say, ewes whoso breeding vigour is impaired — very seldom - produce twins to a second service. There is? still another point connected with this question which it may be profitable to note, and that is, in the two breeds with the lowest percentage of twins — namely,; the Soiithdowns and Hampshire Downs, there is the greatest diversity of opinion among flockmasters regarding the time of birth of their twins, and that among the former, whose ewes are the least prolific of all breeds, most of them record " late "' as the time when twins are usually born. ;It may be argued from this either tks&

Southdown ewes mature late, or that those Southdown flockmasters who have forwarded returns suffer from their anxiety to produce early lambs ; but, however that may be, flocks in which twins ove produced late are not highly fertile flocks.

The Feeding of Ewes. — Different methods of feeding may accelerate or retard the time of season for ewes. It seems quite possible that a ewe may be a vigorous breeder in spite of the h fact that she has been kept jback ; at the same time there is abundant evidence in the returns to show that ewes which are slow to come in season do not produce many twins. Forcing ewes for early lambing does not appear to be attended with high returns of fertility as a rule. At the same time, the greatest " fall of twins seems to be induced by assisting, rather than checking, the breeding inctinot : it is nob assumed that the "flushing" of ewes is a wise proceeding, but it is undoubtedly well to have them in strong, improving* condition when the rams are put to them, in order to ensure a good fall of twins.

The age of the ewes may doubtless affect the fertility of -a flo.ck. In some breeds, notably the Dorset horns, young ewes bear fewei twins than older ewes ; this is apart from the fact that young ewes are more uncertain breeders than two or three-shear ewes.

The Age of the Rams. — Where ram lambs are used, the opinion is very generally held that they gee the largest proportion of twins. It has been already affirmed that the ram is not responsible for twins, and the returns show that where ram lambs iare used, a full share of twins is get from ewes which are not .served by ram lambs.

The Use of Ram Lambs. — Various opinions are held regarding the advantage, or otherwise, attending the use of ram lambs for breeding pin-pose?. Apart from the view, elsewhere disposed of. ihat the percentage of twins is influenced by the use of ram lambs, it is of interest to compare the percentages of lambs got and of barren ewes in relation to the age of the ram. According to tee returns, ram lambs ato rarely used except in tlie following breeds : in the" Sufiolks, 49 per cent, of the* rams used ?re ram lambs ; in the Hampshire Downs, 55 per cent, are ram lambs ; in the Dorset horns, 28 per cent, are ram lambs ; while in the Southdowns, 18 per cent., and in the Oxford Downs, 13 per cent., are ram lambs. The number of flocks available for analysis in these two last-named breeds was too small for comparison, but in tlie three other breeds, Mr Heope divided the flocks into A. Those in which all the rams used are ram lambs.

B. Those in which 50 per cent, or more are ram lambs.

C. Those in which less than 50 per cent.

are mm lsinbs.

D. Those ~n which no ram lambs are used at all.

Tht; result of the calculations for the SuSolks, in which 36 flocks, consisting of 7170 ewefj, were concerned, shows that the best results were obtained by 13 B flocks ; the worst results hj seven A Hocks ; while eight C flocks give slightly batter returns than eight D flocks ; and it would appear from these statistics that the u?e of ram lambs to a limited extent gives better reGults than where no ram lambs are used, but that it is advisable to use no ram lambs rather than to rely wholly upon them for breeding purposes. The order, therefore, js B, C, D, A.

In t}ie Hampshire Down breed, 50 flocks, consisting of 24,860 ewes, were made use of in the analysis, and the result obtained was that seven flocks-, C, showed the best results, and five D flocks the worst, and this latter is true, in spite, of the fact that eight A flocks had double as maiYy barren ewss as the D flocks. Here again a moderate use of ram lambs is attended with good results. Thirty B flock's in this breed gave better results than the D flocks, the order ■being 0, A, B, D. Jn the Dorset horn breed, in which 29 flocks, consisting of 9020 ewes were concerned, in spite of the reduced proportion of ram lambs used on the whole for brecdong purposes, six C flocks again gave the best results, and a moderate proportion of r.im lambs is again shown to be of advantage. There were nine B flocks, 13 D flocks, and only one A flock in this breed. Here the order is, omitting the one A flock, C, D, B.

With regard to barren ewes, the A and B flocks have invariably tho. highest percentage in all three breeds, the uncertainty of ram lambs as breeders being thus indicated.

From these results it would appear that if ram lambs are not actually responsible for twins, they are still associated with their production, and it might be argued that the latter statement is directly opposed Ao the former ; but that is not so, and when it; is remembered, tiiafc nun lambs arc very

generally put to the ewes first, and the older rams not until afterwards, it is seen 1 that ram lambs may be associated Avith twin-getting, because they serve the ewes which first come in season, and these, as lips been already shown, are the ewes . which produce the most twins.