Abstract:
MATING BEHAVIOUR OF MERINO EWES M. A. deB. BLOCKEY* and I. A. CUMMINGS Summary Observations of mating behaviour were made on Merino ewes of three ages, each group being joined separately. The mean duration of oestrus on 2% and 5 year old ewes, 22.0 and 19.0 h. respectively, did not differ significantly but both differed significantly from that in 1% year old ewes, 12.6 h. The behavioural patterns at mating were similar in both maiden ( 1% years) and older ewes. The distribution of time of onset of oestrus in relation to overnight camping of ewes and sexual activity of rams is discussed. As maiden ewes displayed the range of behavioural characteristics observed in older, oestrous ewes, it is concluded that maiden ewes have an innate mating ability. I. INTRODUCTION Mattner, Braden and Turnbull (1967) have shown that mature ewes actively seek out and follow the male to initiate sexual contact, and that they gather about the ram and compete for its attention. Whether young, maiden ewes are capable of initiating the sexual encounter or competing for the ram's favour, is unknown. This paper describes the results of a study of the effect of age on the mating . behaviour of Merino ewes. II. MATERIALS AND METHODS (a) Animals anId Management Eighty-nine fine wool Merino ewes were transferred from a commercial flock in WesTern Victoria to the State Research Farm, Werribee, where observations were made. The group comprised 3 1 maiden ewes (11% years old), 3 1 uniparous ewes (2% years old) and 27 multiparous ewes (5 years old). In April 1969, oestrual activity was synchronized by injecting each ewe with 20 mg progesterone on each of six alternate days. Observations were made on the second oestrus after progesterone treatment. On May 12, the l%, 2% and 5 year old ewes were joined separately on three adjacent 0.4 ha paddocks, each group with an entire Dorset Horn ram in its third season of mating. An observation tower 6m in height and surmounted by a canvas hide was erected immediately outside the paddocks. Black calico saddle cloths numbered with reflective silver paint were attached to the midsides of each ewe and ram. For night observations, a :>Department of Agriculture? Victoria. TDepartment of Physiology, University of Melbourne. TABLE 1 behavioural signs, results from these two groups were pooled; the pooled results are presented in Table 1. The difference of 7.9 h in duration of demonstrable oestrus between maiden and older ewes was highly significant (P <O.OOl) but no significant differences were demonstrated in the proportion of ewes initiating sexual contact or engaging in such competitive activity as interception, aggression or following (Table 1). The average times of day that ewes displayed their first sign of oestrus and rams participated in sexual contact are shown in Figure l(a) and (b) respectively. 346 From 06151200 h, 46 per cent of ewes exhibited their first sign of oestrus; in the same period, sexual activity of rams was most intense with a peak in the two hours about sunrise. Ewes camped from 1800 to 0600 with only occasional grazing (Figure lc). IV. DISCUSSION McKenzie and Terrill (1937) and Lambourne (1956) found that maiden ewes of British breeds had a significantly shorter oestrous period than older ewes. Data presented here indicate that maiden Merino ewes also have only a short duration of oestrus. This suggests that short oestrous periods accompanied by a reduced nutiber of services (Lambourne 1956) could contribute to the low levels of fertility often found in maiden ewes. The present study confirms the finding of Scott (1958) that sheep camp ovemght with little grazing activity. In this study, rams participated in little sexual activity during the hours of darkness, but about sunrise, engaged in much investigational activity. A high proportion of ewes exhibited their first signs of oestrus at this time. This is consistent with the results of Hutchinson, O'Connor and Robertson (1964) who found that a high proportion of Welsh Mountain ewes mated between 0630-0730 hr. As in the present study, there was either a diurnal variation in time of onset of oestrus, or oestrus in some ewes remained undetected during the night as a result of the nocturnal inactivity of ram and strong camping tendency of ewes. Lindsay and Robinson (1961) suggested that young ewes may have to learn to mate or, alternatively, to compete with older, more experienced ewes. However, in the present study, the maiden ewes initiated sexual contact, competed for the ram's favour and demonstrated all other behavioural characteristics observed in older oestrous ewes. Unless the behaviour of the maiden ewes was influenced by that of the older ewes adjacent to, but separated from them, it can be concluded that the maiden ewes displayed an innate sexual behaviour and no further experience with rams is necessary to intensify it. V. ACKNOWLEDGMENTS The authors are grateful to Mr. R. Jardine for assistance with the analysis of results; to Messrs. C. G. Winfield, R. Baxter, L. Cahill, A. Makin, D. Rizzoli, E. Stanton, Mrs. M. Drew and Miss B. Mole for technical assistance, and to Drs. R. H. Watson and J. R. Goding for the interest they have shown in the experiment. Financial assistance for this project was provided by the Wool Research Trust Fund. VI. REFERENCES B ANKS, E. M. (1964). Behaviour 23: 249. H UTCHINSON , J. S. M., O ' CO N N O R , P. J., and R OBERTSON , H. A. ( 1964). J. agric. Sci., Camb. 63: 59. L AMBOURNE, L. J. (1956). Proc. Ruakura Farmers' Conf. p. 16. L INDSAY , D. R., and R OBINSON , T. J. ( 1961) . J. agric. Sci. Camb. 57: 137. MATTNER, P. E . , BRADEN, A. W. H., and T URNBULL , K. E. ( 1967). Aust. J. exp. Agric. Alzirn. Hub. 7: 103. M C K E N Z I E, F. F., and TERRILL, C. E. (1937). Bull. MO. agric. Exp. Stn No. 264. S COTT, J. P. ( 1958) ., 'Animal Behaviour' (University of Chicago: Chicago). 347