(Received 18th September 1961)

Transcription

1 SEX BEHAVIOUR OF PUREBRED AND CROSSBRED MERINO AND BLACKHEAD PERSIAN EWES D. M. JOUBERT Faculty of Agriculture, University of Pretoria, South Africa (Received 18th September 1961) Summary. Data are presented on a number of aspects of the sex behaviour of four breeds of sheep in South Africa. In crossbred Dorset of 399- Horn : Persian ewes, puberty was reached at an average age days. Autumn-born lambs, however, showed their first signs of oestrus 6-2 days later than those born in winter. Ewes generally exhibited a seasonal pattern in their sex activity with a peak in autumn and the lowest level in spring. This was most pronounced in the Merino and least so in Blackhead Persians. Crossbred ewes by Dorset Horn sires occupied an intermediate position. The mean length of the oestrous cycle was 16-9 days, oestrus lasting 29-2 hr. Significant differences between breeds were found for the duration of oestrus, the period being shorter in purebred than in crossbred ewes. Dorset Horn : Persian lambs were born after a gestation period of days. It was also observed that the males were being carried slightly longer than the female lambs. A period of lactation anoestrus was observed in all the breeds, but in crossbred Dorset Horn : Merino and Dorset Horn : Persian ewes, oestrus was first recorded at respectively 42 and 51 days post partum, as compared with 90-1 days for purebred Blackhead Persians and days in the case of Merino ewes. INTRODUCTION Though sex physiology is not a very old branch of the biological sciences, sheep were amongst the first animals studied by pioneers such as Heape (1899) and Marshall (1903). In South Africa, Kupfer (1928) is usually credited with initiating the study of the subject. Following a term of research in this country, he published a lengthy report on ovarian changes and the periodicity of oestrus of various farm animals, including sheep. Kupfer was also the first to compare local data with results obtained from his native Central Europe. a series of so-called These early investigations were soon followed up by Studies in sex physiology by a team of veterinarians and animal scientists. The report of Quinlan & Mare (1931), once more on physiological changes in the ovary, was the first important paper by these workers to deal specifically with the ewe. Though quite a few publications appeared soon afterwards, the treatise by Roux (1936) entitled Sex physiology of sheep is undoubtedly the 41

2 42 D. M. Joubert most comprehensive of all and is still recognized by many as one of the classic papers on the subject. Despite close identity in structure, striking differences have been reported in the function or rhythm of function of the genital organs between breeds of sheep, among others by both Heape and Marshall, and also somewhat later, by Marshall & Hammond (1925). Early South African research was in the main confined to Merino sheep. Consequently there is a need for further sex physiology studies on the many other important breeds that play a role in the wool and mutton industries of this country. Figures are now given on certain aspects of the sex behaviour of, wherever possible, four breeds of sheep ; other wise of crossbred Dorset Horn : Blackhead Persian sheep only. In view of the vast literature on the subject and the very thorough reviews available for further consultation (Asdell, 1946; Robinson, 1951; Hafez, 1952), references will be restricted mainly to previous South African studies. MATERIAL AND METHODS The data for analysis were collected over a period of 20 years at the Experi mental Farm of the University of Pretoria. Records are included that were kept as a matter of routine. Information was also obtained from a project that was designed to permit investigation of the seasonal sex activity of sheep. Four breeds of sheep were considered : purebred Merino (woolled breed) ; purebred Blackhead Persian (non-woolled breed) ; crossbred Dorset Horn : Merino and crossbred Dorset Horn : Persian (intermediate types). Particularly large numbers of crossbred Dorset Horn : Persian ewes were available for study since they were used extensively in long-term breeding programmes that eventually produced a new non-woolled breed of sheep, namely the Dorper. Oestrus was recorded by teasing ewes with vasectomized rams twice daily, at 6 a.m. before turning the sheep to pasture and again after 5 p.m. when they returned to their pens for the night. It was possible to calculate the length of the oestrous cycle and also the duration of oestrus from these records. The latter figures are obviously subject to error. The method applied does not allow for accurate determination of either commencement or cessation of oestrus. It is, however, the usual one employed where routine observations are made on large numbers of animals. Together with figures from the mating and lambing registers, the data render possible in addition an analysis of postpartum oestrus and of the duration of pregnancy. Observations on oestrus were commenced following the selection of young ewes for breeding purposes at an age of 5 to 6 months. Hence the age at which puberty is reached could be investigated. The lambing season of the Dorset Horn : Persian flock was regulated for reasons of management, from the beginning of April to the end of June. The age at puberty could therefore be studied on both early or autumn-born (1st April to 15th May) and late or winter-born (16th May to 30th June) lambs. To investigate seasonal sex activity, ten sexually mature ewes for each of the four breeds referred to above were kept in pens for 3 consecutive years. They received a maintenance ration of lucerne hay and maize, plus minerals.

3 Sex behaviour in ewes 43 The ewes were teased twice daily for oestrus during the entire period, but were never bred from. For purpose of analysis, the data have been converted to monthly means. RESULTS Age at puberty The results in Table 1 indicate that crossbred Dorset Horn : Persian ewes reach puberty at an average age of 399- days. It is clear, however, that appreciable variation may occur, as shown by a range of 195 to 82 days. Though the number of winter-born lambs analysed constitutes a decided minority, there is strong evidence that they tend to reach puberty at an earlier age than autumn-born lambs. The mean difference of 6-2 days statistically highly significant (P<0-01). is in fact Sex season The total number of oestrous periods recorded for each month during 3 years of observation are given separately for the four breeds in the first Table 1 age at puberty of autumn- and winter-born ewe lambs Age Group No. ewes (days ± s.e.) Range Autumn-born Winter-born ± ± to to 82 All ewe lambs ± to 82 columns of Table 2. Statistical analysis of these figures shows that the variation that occurs between months is highly significant (P<0-01). In the second columns of the Table, the mean number of oestrous periods per ewe has been calculated, again on a monthly basis. According to the method of calculation, in theory the maximum possible figure is 1-8 periods per month, i.e. a 30-day month divided by a 1-day cycle. The results clearly indicate seasonal variation in the sex activity of the ewes which fluctuates from a low level in spring to a peak in autumn. On the other hand, appreciable differences occur between breeds as shown by the graphs in Text-fig. 1. The mean annual number of cycles per ewe for the four breeds studied is as follows: Merino, 8-13; Dorset Horn : Merino, 10-9; Blackhead Persian, 16-1 ; Dorset Horn : Persian, Except for the very slight difference between the latter two examples, inter-breed differences are all statistically highly significant (P<0-01). The average figures suggest a strong tendency for Merino ewes to go into anoestrus for 1 month of the year (October) and very limited sex activity for at least 3 months. Blackhead Persian ewes on the contrary appear to be much less

4 44 D. M. Joubert seasonal in their breeding habits, without any evidence of a prolonged anoestrous period. Crossbreeding with Dorset Horn rams in both instances in creased the degree of sex activity, but a stronger seasonal pattern remains evident in the Merino crossbreds. Table 2 sex season of purebred and crossbred merino and blackhead persian ewes Month Total oestrous periods Merino per D.H. : Mer. Total oestrous periods per Total oestrous periods Persian per ewe D.H. : Total oestrous periods Total Per Merino Dorset Horn : Merino O 1-8 Blackhead : Persian Dorset Horn : Persian _1_I_1_1_L ONDJFMAMJJAS ONDJFMAMJJAS Text-fig. 1. The sex season in ewes of four breeds of sheep. Periodicity of oestrus Data are provided in Table 3 on the length of the oestrous cycle of crossbred Dorset Horn : Persian ewes. The results have been arranged in such a way that the periodicity up to the sixteenth consecutive cycle could be examined in a

5 Sex behaviour in ewes 45 limited number of ewes. According to the results, deviations from the weighted mean of days for successive cycles are very slight and not significant. The ranges, on the other hand, indicate that appreciable variation in cycle length does occur, from 12 to 25 days in isolated cases. A slight tendency is also evident for the range to decrease with an increase in the cycle number. Duration of oestrus The 4290 observations recorded on oestrus at 12-hr intervals (Table 4) give a weighted average duration of hr, with individual oestrous periods ranging from 12 to 50 hr. The monthly means show no seasonal trend, but breed differences are fairly distinct. Oestrus is shortest in the Merino, followed by the Blackhead Persian. In crossbred ewes out of these breeds by Dorset Table 3 periodicity of oestrus in crossbred dorset horn : head persian ewes black Cycle number No. observations Range to to to to to to to to to to to to to to to to 1-0 Total/ to 250 in the Merino crosses. All inter Horn sires, oestrus is prolonged, particularly breed differences are statistically highly significant (P<0-01). Duration of pregnancy Pregnancy in Dorset Horn : Persian ewes by rams of identical breeding lasted, on an average, days (Table 5), with a range of 13 to 160 days. The data do not include any twin births. The results show that ewes that carry male foetuses tend to have a very slightly longer period of gestation. Statistically, this difference of 0-4 days is significant at the 5% level of probability. Post-partum oestrus The results in Table 6 on the period from lambing to the first subsequent sign of oestrus, give a weighted all-breed mean of 1-8 days and a range of 2 to

6 46 D. M. Joubert Table 4 DURATION OF OESTRUS IN PUREBRED AND CROSSBRED MERINO AND BLACKHEAD PERSIAN EWES Merino D.H. : Mer. Persian D.H. : Per. No. observations Month (hr) (hr) (hr) (hr) January February March April May June July August September October November December Range 12-0 to to to to 43-4 Table 5 duration of pregnancy in crossbred dorset horn blackhead persian ewes Male Female Sex No. observations period (days ± S.E.) 146- ± ± 0-12 Range 13 to to 152 All lambs ± to 160 Table 6 POST-PARTUM OESTRUS IN PUREBRED AND CROSSBRED MERINO AND BLACKHEAD PERSIAN EWES Breed Merino D.H. : Mer. Persian D.H. : Per. No. observations period Range 51 to to 2 8 to to 149 Total/ to 283

7 Merino, Sex behaviour in ewes days. Though the data on Merino and crossbred Merino ewes are rather limited, breed differences are fairly distinct. It is particularly evident that cross breeding with the Dorset Horn reduced the period of lactation anoestrus by nearly half. Further examination of the range reveals that 64% of the Merino ewes came on heat within 5 months of lambing. The figures for the other breeds are: Dorset Horn : Merino, 100%; Blackhead Persian, 82%; Dorset Horn : Persian, 100%. DISCUSSION Owing to the restricted breeding season of sheep there is, according to Ham mond (1960), no fixed age at which puberty is attained. Referring to the report of Hammond Jr. (1944), he indicates that lambs born early in the year are generally older at their first oestrus than late-born lambs; furthermore, that lambs born very late in the season do not reach puberty until the breeding season of the following year. Though the Dorset Horn : Persian sheep used in the present investigation are less subject to the influence of seasonal sex activity (Text-fig. 1), a fairly restricted breeding season was nevertheless enforced. The conditions arising from a fixed lambing season, which extends over a period of but 3 months, therefore closely simulate those that Hammond has in mind. And the results obtained on the subject of puberty agree closely with his statement quoted above. Hafez (1952) studied the age at puberty of Suffolk and Scottish Blackface ewes and reported mean ages, respectively, of 240 and 238 days. In his study of Egyptian Rahmani and Ossimi ewes (Hafez, 1953), he found the respective ages and days. The present results clearly agree more closely with those of the latter investigation, but this is not surprising since the sheep under discussion are also out of indigenous African stock. The sex season of Merino sheep in South Africa has been studied by Kupfer (1928), Quinlan & Mare (1931), Marais (1936), Roux (1936) and Hugo (1955). Despite the somewhat conflicting results in regard to the occurrence and duration of an anoestrous period, it is generally agreed that the intensity of sex activity fluctuates seasonally, with the period March to June as peak months. The present results support this contention. The duration of sex activity in crossbred sheep (Suffolk : Persian and Merino : Persian) was studied by Roux (1936) in the cold-temperate eastern Transvaal, and by Hugo (1955) in the semi-arid Karroo. The results of Roux do not support the present finding of an extended breeding season as compared with purebred Merinos. In fact, the sex season of the crossbred ewes studied by him was 4 to 6 weeks shorter than that of Merino ewes. Hugo's investigation enabled him to classify different breeds and types of sheep according to duration of the sex season as follows : (a) Short season British mutton breeds (excepting Dorset Horn), either pure or crossbred with Merino or Blackhead Persian; (b) Inter mediate season either pure or crossbred with German Merino or Dorset Horn, and also Dorset Horn : Blackhead Persian. Persian crossbreds ; and (c) Long season

8 48 D. M. Joubert The present results support Hugo's classification except that crossbred Dorset Horn : Persian ewes fall with the Blackhead Persians in the longseason group. The results of Hugo on pure Blackhead Persians indicate a less restricted breeding season than that for pure Merinos. He nonetheless believes that individual animals go into anoestrus, but at different times of the year of the trends with the exception, of course, of the peak months. The slopes reported by Hugo for sex activity understandably, therefore, differ but little from those of the present investigation. The results obtained on the periodicity of oestrus agree closely with those of previous South African investigators. Quinlan, Mare & Roux (1930, 1932) and Quinlan & Mare (1931) found the mode of the cycle to be 1 days, while Roux (1936), working on the same breed, reported a mean length of 16 days 18-6 hr. These authors stress the degree of variation which ranges from 6 to 'silent' heats. The tendency observed in Table 3 for the range to decrease with an increase 68 days, but pay no regard to possible in the cycle number may be explained in terms of age of the ewes. In cattle, Joubert (1954) reported a tendency for irregularity of immediate post-pubertal cycles, before the anticipated rhythm sets in. In a personal communication in 1953, A. V. Nalbandov referred to a similar tendency in sheep. Obviously the initial cycles with wider range, include large numbers of young which irregularity of rhythm occurs more frequently. After consulting the available literature, Asdell (1946) concludes that the mean duration of oestrus in sheep is from 30 to 36 hr, with but little difference between breeds. On the other hand, as early as 1900 Heape drew attention to the fact that domestication has been responsible for considerable prolongation of oestrus. Significant inter-breed differences have also been reported by other workers (McKenzie & Phillips, 1930). Previous studies on Merino sheep by ewes in Quinlan & Mare (1931) and Roux (1936) gave a mode from 36 to 48 hr (0% of cases) and a mean of about 30 hr. The present results, though generally indicating shorter periods than the above, confirm the significance of breed differences. In this connection, the longer oestrous periods of crossbred ewes are of particular interest and, no doubt, also of practical importance. The results obtained on the duration of pregnancy in crossbred Dorset Horn : Persian ewes fit in well with those of many previous investigators (see Asdell, 1946). The principle that the sex of the lamb tends to affect gestation length is also well established (Starke, Smith & Joubert, 1958). Of the parent breeds, data are available in the literature only on pregnancy in the Dorset Horn for which Daley & Eastoe (1943) reported a mean length of days. Of the indigenous sheep of Southern Africa, to which Blackhead Persians belong, only the Ronderib-Afrikaner has received attention, Quinlan, Claassens, Bonsma & Rose (1939) reporting a mean period of days. Various authors have reported on the delay of oestrus following parturition as a result of lactation in sheep (vide Hafez, 1952). The connection between this phenomenon and the inherent milking capacity of the ewe is particularly evident from the present results. Milk yields of the four breeds under discussion as determined by Bonsma (1944) for 11-week lactation periods gave the following results: Merino, 2039 ± 68-0 oz; Dorset Horn : Merino, 3301 ±

9 Sex behaviour in ewes oz; Blackhead Persian, 101 ± 38-0 oz; Dorset Horn : Persian, 3314 ± oz. The average milk yield of the purebred ewes is clearly appreciably lower than that of crossbred ewes by Dorset Horn sires. Observation of the strain on the condition ewes in question confirms that suckling causes a great of the dam in the ewes of low milking capacity. One is therefore led to agree with Hafez (1952) that post-partum oestrus appears to have a genetic basis, but conditioned by inherent constitutional and lactational qualities. ACKNOWLEDGMENTS The important contribution of Dr J. S. Starke, formerly professor and head of the department of Animal Husbandry in the University of Pretoria, towards planning and execution of the project is gratefully acknowledged. Thanks are also due to the many persons who through the years assisted with the recording and analysis of data. I am indebted to Messrs J. P. Steenkamp and V. E. de Kock for constructive criticism of the manuscript. REFERENCES Asdell, S. A. (1946) Patterns of mammalian reproduction. Comstock, New York. Bonsma, F. N. (1944) Milk-production studies with sheep. Bull. Dept. Agrie. S. Afr. No Daley, C. J. & Eastoe, R. (1943) Breeding habits of the Dorset Horn. Agrie. Gaz. N.S.W. 54, 5. Hafez, E. S. E. (1952) Studies on the breeding season and reproduction of the ewe. J. agrie. Sci. 42, 189. Hafez, E. S. E. (1953) Puberty in remale farm animals. Emp. J. exp. Agrie. 21, 21. Hammond, J. (1960) Farm animals, 3rd edn. Edward Arnold, London. Hammond, J. jr. (1944). On the breeding season in the sheep. J. agrie. Sci. 34, 9. Heape, W. (1899) Abortion, barrenness and fertility in sheep. J. roy. agrie. Soc. 10, 21. Heape, W. (1900) The sexual season of mammals and the relation of proestrum to menstruation. Quart. J. microscop. Sci. No. 13, 1. Hugo, W. J. (1955) Die probleem van lae vrugbaarheid by Suid-Afrikaanse skaapkuddes. D.Sc. (Agrie.) Dissertation, Univ. Stellenbosch. Joubert, D. M. (1954) The influence of high and low nutritional planes on the oestrous cycle and conception rates of heifers. J. agrie. Sci. 45, 164. Kupfer, M. (1928) The sexual cycle of female domesticated mammals. 13 & Wth Ann. Rep. Dir. Vet. Educ. & Res. S. Afr. p Marais, I. P. (1936) Untersuchungen ü. d. Sexualzyklus bei Merinoschafen. Dissertation, Univ. Leipzig. Marshall, F... ( 1903) The oestrous cycle and the formation of corpus luteum in the sheep. Phil. Trans. B, 196, 4. Marshall, F. H. A. & Hammond, J. (1925) The physiology of animal breeding, with special reference to the problem of fertility. Res. Monogr. Min. Agrie. & Fisheries, Lond. No. 2. McKenzie, F. F. & Phillips, R. W. (1930) Some observations on the estrai cycle in the sheep. Rep. Univ. Missouri, June 30. Quinlan, J. & Mare, G. S. (1931) The physiological changes in the ovary of the Merino sheep in South Africa, and their practical application in breeding. 1/A Ann. Rep. Dir. Vet. Educ. & Res. S. Afr. p Quinlan, J., Mare, G. S. & Roux, L. L. (1930). Gland grafting in Merino sheep. Preliminary observations on its influence: (a) On body-development, wool-production and progeny, (b) On senility. \&th Ann. Rep. Dir. Vet. Educ. & Res. S. Afr. p. 63. Quinlan, J., Mare, G. S. & Roux, L. L. (1932) The vitality of the spermatozoon in the genital tract of the Merino ewe, with special reference to its practical application in breeding. 18/ Ann. Rep. Dir. Vet. Educ. & Res. S. Afr. p Quinlan, J., Claassens, C. C, Bonsma, H. C. & Rose, P. D. (1939) Observations on the gestation period of Ronderib-Afrikander sheep. Onderstepoort J. vet. Sci. 12, 251. Robinson, T. J. (1951) Reproduction in the ewe. Biol. Rev. 26, 121. Roux, L. L. (1936) Sex physiology of sheep. Onderstepoort J. vet. Sci. 6, 465. Starke, J. S., Smith, J. B. & Joubert, D. M. (1958) The birth weight of lambs. Res. Bull. Dep. Agrie. S. Afr. No. 382.