ARCHIVE FILE
This article was published in 1949
See the original document
INSTITUTE OF INSPECTORS OF STOCK OF N.S.W. YEAR BOOK.
Stilboestrol Trial for Earlier Lambs
H. R. PEISLEY. B.V.Sc., Inspector of Stock, Warialda.
SUMMARY
There is a demand in Australia for April-May lambs instead of May-June lambs, but the earlier lambs usually cannot be obtained owing to the occurence of the anoestrous period in early summer.
A field trial made into the possibility of inducing an earlier lambing with injections of the synthetic oestrogen, Stilboestrol, in the anoestrous period is described. (For clarity it has been considered desireable to include much of the preliminary data which appeared in our publication last year on this, as then uncompleted, field trial).
A total of 356 maiden merino ewes aged 14 to 17 months, was divided by random selection into 179 controls and 177 for experimental injections. The latter were again randomised into eight groups, each of 20 to 25 ewes; four of these groups were injected with 1.5 mg. diethyl stilboestrol in 1 ml. arachis oil; two groups subcutaneously and two groups intramuscularly. One each of these received a second injection similar to the first, and by the same route, 16 days after the first injection. The remaining four groups were treated in a similar manner, but with only 0.75 mg. diethyl stilboestrol in 1 ml. arachis oil.
Lambing counts were made on four occasions; the first being 168 days after the initial injection. Granger (1947) believes the average gestation period for Merinos to be 151 days.
At the 168th day, eleven (approx. 12 per cent.) early lambs were recorded in the single injected sheep, as against none in those given a repeat injection a cycle-length (16 days) later; and as against two (approx. 1 per cent.) early lambs in the controls.
Within the limits of this trial it would appear that the size and route of stilboestrol administration can be disregarded and that: i. a single injection will give a percentage of earlier lambs; ii. a repeat injection a cyclelength (16 days) later will act as an abortifacient; iii. the fertility of those ewes which receive a stilboestrol injection during the anoestrus period and do not then conceive, is not markedly affected during the usual oestrous season immediately following.
LITERATURE
In all countries there is apparently an anoestrous period in merino ewes, extending over approximately 10 to 12 weeks in normal seasons. Quin and Van der (1943) describe a suppression of sexual activity in South Africa from September to December, and mention a similar anoestrous in Europe during the early summer months.
This corresponds closely to Australian experience. Kelly and Shaw (1943) describe this anoestrous period as occurring in late spring and early summer and mention that it may be associated with "silent" heat.
A similar anoestrus is described by Cole and Miller (1935) working with Southdowns, Shripshires and Hampshires.
It is accepted that in merino sheep the female sexual cycle is suppressed rather than absent. Granger observes that two "silent" heats, in which all features of heat except sexual desire are present, is the general rule before fully expressed oestrous cycles occur, and again at the transition from the oestrous to the non-oestrous season; while even in the centre of the non-oestrous season some changes in the sexual organs characteristic of the oestrous cycle may be detected by microscopic examination.
The physiological explanation of the phenomena has not as yet been determined, but Hammond (1944) has suggested that the anoestrous and "silent heat" might be associated with a temporary insufficiency of gonadotrophic and follicular hormones; and that the resumption of normal pituitary and ovarian function appears to be related to the nutritional state. This view supported by the common field obervation that the anoestrous period is prolonged in drought years and contracted in flush seasons.
Various attempts have been made in the past 15 years to contract the anoestrous period with hormone or hormone-like preparations, the two types most usually employed being (1) the gonadotrophic hormones as obtained from the anterior lobes of the pituitary and also found in pregnant mare's serum and human pregnancy urine; and (2) the oestrogenic hormones which occur naturally in the ovaries, placenta and human pregnancy urine, and synthetically as such chemical compounds as diethyl stilboestrol, stilboestrol diproprionate and stilboestrol di-n-butyrate.
Quin and Van der Wath (ibid.) mention that apart from their direct stimulating effect on the uterus, vagina and mammary glands, various oestrogenic compounds administered in adequate quantities will exert a peculiar trigger-like action on the anterior lobe of the pituitary itself. Although the exact mechanism is not known they suggest that the judicious use of oestrogens might be as effective in initiating ovulation and oestrous as are the gonadotrophic hormones themselves.
In their Onderstepoort experiment stilboestrol dipropionate and pregnant mare's serum were tried (the stilboestrol being in dose rates of 1 mg. to 5mg. given intramuscularly in oil) and the conclusion was that, while the results of different workers are at variance, the evidence suggests that in cows and heifers induced ovulation is accompanied more regularly by the onset of oestruous and the initiation of normal cycles that is the case in ewes. The experiment resulted in a high percentage of ovulations with stilboestrol, but only 17 per cent. came into heat sufficiently evident to allow service. Evidence is presented showing that seasonal anoestrous in merino ewes is closely associated with a decreased physiological response of the uterus and vagina to oestrogens.
Hammond (ibid.) attempted to induce fertility in ewes with a single injection of pregnant mare's serum and stilboestrol. He mentions that from previous work by Hammond, Hammond and Parkes oestrogens will generally induce heat in anoestrous ewes and will quite often cause ovulation, while' pregnant mare's serum and other follicle stimulating preparations will consistently bring about ovulation. Like the first ovulation of the natural breeding season this is not normally accompanied by heat, but an induced ovulation is sometimes followed a cycle later by spontaneous ovulation and heat.
Hammond found that on slaughter all sheep he gave pregnant mare's serum had ovulated; approximatelv 92 per cent. given pregnant mare's serum followed by stilboestrol 24 hours later had ovulated. None of the animals given pregnant mare's serum alone, however, came on heat. Both in those sheep treated with stilboestrol alone and those given stilboestrol at or after gonadotrophin injection, the majority of those failing to ovulate came on heat and most of those ovulating failed to come on heat. Further, in most cases the timing of ovulation and heat was such that he considered it very unlikely that fertilisation would occur.
Montgomerie and Brownlee (1941) recommended 1 mg. stilboestrol diproprionate for treatment of anoestrus in the ewe.
Austin (1946) in reviewing the literature, observes that as regards the synthetic oestrogens stilboestrol and hexoestrol, very variable results have been obtained by different workers, and that they have reported everything from no effect at all to oestrous without ovulation, ovulation without oestrous, as well as full oestrous response in which ovulation does occur.
LOCAL FIELD TRIAL
In view of the variability in the stilboestrol results recorded, and the real demand that exists in parts of this State for earlier lambs, a test under field conditions was considered worth while.
This demand emanates from such considerations as better markets if lambs are available in August-September, and to be ready then a late summer drop is desirable. In the west, Barley Grass starts to seed about October and this dry feed is not suitable for weaning; on the colder tablelands the frosty, bleak May-June weather is not suitable for laming; in the south, with October shearing, the unweaned lambs are subjected to much undesirable handling.
In November, 1947, Mr. J. Lynch, Tumut, made available for the trial the lamb drop from June-August, 1946. A total of 356 merino ewes was drafted from 376 wethers. These were the progeny of Merribee ewes mated with Merribee and North Bungaree rams and lambed at Tumut.
The 356 ewes were randomised by alternate selection through a drafting race into 179 controls and 177 for experimental injections. The latter again were randomised by alternate selection into four groups—A, B, C and D—and were injected, respectively, with 1.5 mg. diethyl stilboestrol subcutaneously, 1.5 mg. diethyl stilboestrol intramuscularly, 0.75 mg. diethyl stilboestrol subcutaneously, 0.75 mg. diethyl stilboestrol intramuscularly. The vehicle in each injection was 1 ml. arachis oil.
These injections were made on the morning of 3rd November, 1947, and the controls and experimental sheep were depastured together with eight fresh young rams. The rams were raddled to determine whether there was an onset of oestrus, but no attempt was made to assess the number on heat. On 6th November, the sheep were examined in the paddock and it was noted that several injected sheep, and one wether, had been mounted by the rams, but none of the controls. On this date four more rams were raddled and released into this experimental flock. An employee reported on 9th November that the rams were working, mainly on the injected ewes, but also on an occasional control.
On 19th November, that is, one cycle-length (16 days) after the initial injection, the sheep were yarded again and drafted into their respective groups; and on the date groups A, B, D and D were subdivided by alternate selection into A1, A2; B1, B2; C1, C2; D1 and D2. Of these, A1, B1, C1 and D1 were given repeat injection of the same size and by the same route as on 3rd November; A2, B2, C2 and D2 were not given any further treatment.
When yarded for these injections on the 19th. the rats were observed working on both controls and injected sheep while in the yard, and from their great loss of condition, in spite of the good feed, must have worked strenuously during the preceding 16 days. They were reinforced from this date with more fresh rams.
These injections are summarised in Table 1:—
TABLE 1
| Group | No. of ewes | First injection | Diethyl stilboestrol mg. | Route | Second injection | Diethyl stilboestrol mg. | Route |
|---|---|---|---|---|---|---|---|
| A1 | 23 | 3/11/47 | 1.5 | s/c | 19/11/47 | 1.5 | s/c |
| A2 | 22 | 3/11/47 | 1.5 | s/c | - | - | - |
| B1 | 20 | 3/11/47 | 1.5 | i/m | 19/11/47 | 1.5 | i/m |
| B2 | 21 | 3/11/47 | 1.5 | i/m | - | - | - |
| C1 | 24 | 3/11/47 | 0.75 | s/c | 19/11/47 | 0.75 | s/c |
| C2 | 25 | 3/11/47 | 0.75 | s/c | - | - | - |
| D1 | 21 | 3/11/47 | 0.75 | i/m | 19/11/47 | 0.75 | i/m |
| D2 | 21 | 3/11/47 | 0.75 | i/m | - | - | - |
The different Groups were identified with different Tar Brands.
On 19th April, 1948, that is 168 days after the initial injections, the sheep were mustered at Cootamundra, having been moved there from Tumut in the intervening months. The flies had been bad, there had been some losses and a few brands were not visible; while a few others had been removed with the dressing of "strikes." A total of 338 ewes were mustered and were drafted into 167 injected ewes, 136 controls and 35 on which the brands were not visible. At a later date, after some thought, it was decided that most of not all of these 36 sheep were "controls" and were treated as such at future counts.
There were only ten lambs, two being in the controls and wight in the injected sheep. In addition to these, three "wet" ewes which had lost their lambs (probably taken by crows) were discovered in the injected lot. There were no lambs in the the small lot with no visible brands.
The result to this date is summarised in:—
TABLE 2
| Total muster 19/4/48 | Inject ewes | Inject ewes lambs | Inject "wet" | Controls | Control lambs | Control "wet" ewes | Marks not visible | Lambs | "Wet" ewes |
|---|---|---|---|---|---|---|---|---|---|
| 338 | 167 | 8 | 3 seen | 136 | 2 | none seen | 35 | nil | none seen |
Dissecting the results of the 13 ewes which had lambed at that date:—
TABLE 3
| Group | A1 | A2 | B1 | B2 | C1 | C2 | D1 | D2 | Controls | Total |
|---|---|---|---|---|---|---|---|---|---|---|
| Number of lambs | - | 4 | - | 2 | - | 2 | - | 3 | 2 | 13 |
The rams were left running with the ewes throughout the summer to indicate the relative fertility of injected ewes to control ewes. The lambing results at each count in the succeeding months is shown in the following:—
| Date | Days after initial inject | Days after second inject | Inject ewes mustered | Lambs of inject ewes mustered | Controls mustered | Lambs of controls mustered | Gross total ewes mustered | Gross total Lambs |
|---|---|---|---|---|---|---|---|---|
| 3/11/47 | Day injected | Day injected | 177 | - | 179 | - | 356 | - |
| 19/4/48 | 168 | 152 | 167 | 11 | 136 (+35 nvb) | 2 | 338 | 13 |
| 17/5/48 | 196 | 180 | 179 | 35 | 172 | 41 | 351 | 76 |
| 9/7/48 | 249 | 233 | 183 | 54 | 169 | 58 | 352 | 112 |
| 19/9/48 | 321 | 305 | 183 | 59 | 172 | 65 | 355 | 124 |
It will be seen from the above figures that there were slight discrepancies in the figures at each muster. This is regrettable but it is considered that the two flocks are substantially the same and it is susupected that only some 6 to 10 controls have "boxed" with the injected sheep. Such was unavoidable, the sheep have been moved several times in the course of the trial, the paddocks were not thoroughly stock-proof and the musters have not always been complete.
ANALYSIS
The results suggest that the size of the dose und the route of administration, as used in the trial, are of no practical significance, the three significant groupings of these results being:— (a) ewes which received a single injection; (b) ewes which received a second injection a cycle-length (16 days) later, and (c) controls.
Within the limits of this trial it appears likely that:-
1. A sheep experiencing, or approaching, "silent heat" when injected with stilboestrol, can conceive;
2. A ewe having conceived following the first injection, then a second injection a cycle-length (16 days) later acts as an abortifacient (cf. Table 3);
3. In the event of a ewe being injected with stilbeostrol during the anoestrous period and not conceiving, such treatment does not adversely affect the normal oestrous season, or in any way impair the subsequent fertility of the ewe.
PRACTICAL APPLICATIONS
1. As eleven earlier lambs, (approx. 12 per cent.) were recorded in the groups given a single stilboestrol injection, as compared with no lambs in those given a repeat injection 16 days later, and two earlier lambs (approx. 1 per cent.) in the controls, stilboestrol injection could well be tried on a larger scale. Twelve per cent., or 120 earlier lambs per 1,000 ewes would be of value in some districts.
Further, it must be remembered that this was recorded in a trial using maiden ewes, aged only 14 to 17 months, and that these ewes were subjected to much undesiralle treatment during the trial period, including the bad fly and worm summer, crows and a movement by road, while in lamb, from Tumut to Belbowrie, a distance of some 70 miles.
In spite of the undesirable treatment of these young maiden ewes, they have produced 35 per cent. lambs, or, 32 per cent. in the injected sheep and 37 per cent. in the controls. Kelly ( 1946) referring to the same southern area of this State, a merino stud flock in the Riverina, mentions three lines of maiden ewes numbering 326, 300 and 486 respectively, which were mated at the ages of 19 months, 24 months and 30 months respectivley and resulted in 43 per cent., 38 per cent. and 42 per cent. lambs; or disregarding the actual age groups of these maiden ewes, 41.3 per cent. conceived at the first opportunity to do so. He further points out that the percentage of ewes which gave birth to a lamb was not higher than 74 per cent. until the ewes were from 3 to 4 years of age.
Bearing in mind the adversities which the sheep in this trial suffered, and their particular juvenility, the 35 per cent. lamb drop compares favourably with that recorded by Kelly. From the preceding and Kelly's further observation that there is an "upward trend associated with increasing age in the accession to sexual maturity" it follows as a reasonable probability that while 12 per cent. early lambs were obtained with a single injection in these juvenile ewes, an appreciably greater percentage increase might be expected if the trial were conducted with more mature sheep, say 4-year-old ewes.
2. There is also an indication that the stilboestrol injections had no lasting deleterious effect on the fertility of the trial ewes. Consequently, a sheep owner desirous of obtaining a percentage of earlier lambs, and prepared to make available a line of mature ewes for a further trial, with say 1 mg. stilboestrol subcutaneously, is not likely to have a lower percentage of lambs, but such will be born from April to June, instead of May to June, if the stilboestrol is injected during November.
3. The repeated injection of stilboestrol a cycle-length (16 days) later appears to have acted as a reliable abortifacient. While this is of no practical value in routine sheep management, it may have some veterinary application in small animal practice and occasionally in studs.
CONCLUSION
Sufficient success has been obtained with a single injection of stilboestrol during the anoestrous period in young maiden ewes, namely 12 per cent. early lambs compared to 1 per cent. in the controls, to warrant a further trial with older sheep and simplified by using one dose rate administered either subcutaneously or intramuscularly.
ACKNOWLEDGEMENTS
It is desired to thank Mr. J.N. Lynch, Tumut, for the provision of sheep, labour and time to conduct this trial—he has been of every assistance throughout; Mr. W. L. Hindmarsh, B.V.Sc., M.R.C.V.S., D.V.H., Chief, Division of Animal Industry, Department of Agriculture, Sydney, for providing references and advice; Prof. R. M. McGunn, D.V.Sc., B.Sc., B.Sc.Agr., M.R.C.V.S., Faculty of Veterinary Science, University of Sydney; and Mr. W. Granger, B.V.Sc., Chief, Division of Animal Industry, Papua-New Guinea, for advice freely given.
REFERENCES
Austin, C. R. (1946)—Aust. vet. J. 22: 2, 50.
Cole, H. H. and Miller, R. F. (1935)—Amer. J. Anat., 57: 39-97. Cited by Animal Breeding Extracts 4: 1, 48.
Granger. W. (1947)—Aust. vet. J. 23: 6, 144.
Hammond, J., Jnr. (1944)—J. Endocrinol. 4: 169.
Kelly, R. B. and Shaw, H. E. B. (1943)—C.S.I.R. Bull 166: 18.
Kelly, R. B. (1946)—C.S.I.R. Bull 205: 17-20.
Montgomerie, R. F. and Brownlee, G. (1941)—Vet. Rec. 53: 567. Cited by Animal Breeding Abstracts 9: 291.
Quin, J. I. and Van der Wath, J. G. (1943)—Onderstepoort J. vet. Sci. 18: 139.