A new approach to controlled breeding in sheep using the ram effect.

Abstract

Animal Production in Australia A NEW APPROACH TO CONTROLLED BREEDING IN SHEEP USING THE 'RAM EFFECT' Y. COGNIE*, S.J. GRAY**, D.R. LINDSAY**, C.M. OLDHAM**, D.T. PEARCE** and J.P. SIGNORET* SUMMARY Ewes which are induced to ovulate by the introduction of rams, the 'ram effect', often have short cycles caused by short life-span corpora lutea (CL). In two experiments we studied the use of progestagens to prevent short life-span CL and to ensure synchrony at the next ovulation. Treatment with intravaginal progestagen sponges before the introduction of rams induced 34 of 35 ewes to ovulate and display oestrus. The 'ram effect' with and without a single injection of progesterone induced ovulations in 27 of 35 and 32 of 35 ewes but only 7 and 5 of these showed oestrus. At the following cycle all 27 of the ovulating ewes treated with progesterone were in oestrus between days 15 and 20 after the introduction of rams compared with only 11 of the 32 ovulating ewes which received no progesterone. In a second experiment it was shown that synchrony at the second oestrus was improved as the dose of progesterone increased from 5 to 20 mg. INTRODUCTION Current techniques for the synchronisation of oestrus and controlled breeding of sheep use exogenous hormones and are relatively expensive. It has recently been demonstrated in the sheep that some synchrony can be obtained using the 'ram effect', first shown by Underwood et al. (1944) and this has been used commercially (Corke 1980). However,oestrus induced by rams is dispersed over a period of about a week and the distribution of ewes in oestrus is concentrated at the beginning and end of this period. This problem has been defined as one of inducing a viable corpus luteum (CL)after 'teasing' by the introduction of rams. The biphasic spread of the first oestrus is caused by the variable life span of the ram-induced CL. Ewes normally ovulate in response to rams by the second day after 'teasing' and this ovulation is generally 'silent' -unaccompanied by overt oestrus. About half of the ewes have a normal CL which leads them to re-ovulate, this time with oestrus, around day 18-19. In the other half, the ram-induced CL regress prematurely causing a short cycle and a second 'silent' ovulation occurs around day 7 followed by a CL which persists for a normal life span. This results in a second grouping of oestrus around day 24 (Oldham and Martin 1978). These short cycles have never been observed when the induced ovulation follows a long-term treatment with progestagen-impregnated sponges (Oldham et ai?. 1980). In addition, the long-term treatment with progesterone induces oestrus with the first ovulation and successful insemination is possible (Hunter et al. 1971). Cognie et al. (1981) showed that progesterone before it regresses. The always followed by a CL of normal life amount of progesterone before ovulation the short life-span CL does produce some resulting second 'silent' ovulation is span. This suggests that even this small may be sufficient to ensure a normal CL. In this paper we test the hypothesis that a single treatment with a small amount of progesterone associated with the 'ram effect' can eliminate the short life-span CL. This should eliminate in turn,the wave of oestrous ewes around day 24 and synchronise ovulation and oestrus about day 18-19 after the introduction of rams. * Station de Physiologie de la Reproduction, INRA, 37380 Nouzilly, France ** Dept Animal Science, Universi ty'of Western Australia, Nedlands, W.A. 6009. 519 Animal Production in Australia MATERIALS AND METHODS Since the 'ram effect' is mainly applicable to the non-breeding season, two complementary experiments were carried out in 1981; one at Montpellier, France, in March, and the other at York, W.A., in September. Experiment 1 One hundred and five mature ewes of thebreedMerinos d'Arles, kept permanently indoors, were isolated from rams for a month and divided into three groups of 35. Group 1 received intravaginal sponges impregnated with 30 mg Fluorogestone Acetate for 12 days. Two vasectomised rams were introduced into the group two days before the sponges were withdrawn. Group 2 received the normal treatment for the flock at joining. Vasectomised males were left with the group for 15 days and were then replaced for the next month by intact rams. Group 3 received an intramuscular injection of 20 mg Progesterone in oil on the same day as they were introduced to vasectomised rams. Fifteen days later intact males were introduced and left for one month. In every case rams carried'sire-sine'harnesses and crayons (Radford et al. 1960). Sexual receptivity was estimated from marks on the rumps of the ewes. The three groups were so arranged that the introduction of rams for the first time was on 30th March - mid seasonal anoestrus in the Northern Hemisphere. Ovarian activity in the ewes was determined by laparoscopy, nine days after the introduction of rams and again 16 days later. Experiment 2 In this experiment the treatment with progesterone in Experiment 1 was expanded to include a range of doses,each in a single injection. One hundred and seventy-seven adult Merino ewes were isolated from males for at least a month and were introduced to rams fitted with'sire-sine'harnesses on 22nd September. At the same time ewes were allocated to five groups of approximately 35 ewes,each of which received 0, 5, 10, 15 and 20 mg progesterone in 2 ml oil. The level of spontaneous ovarian activity in the flock was estimated by examining the ovaries of 25 of the control ewes by laparoscopy on the day before rams were introduced. From day 13 after contact with rams until day 22 the ewes were examined twice daily for oestrus (0600 h and 1800 h). RESULTS Experiment 1 Table 1 shows that ewes primed with a course of progesterone before the introduction of the male (group 1) had a high level of both oestrus and ovulation. Without progestagen (group 2) ovulationms still high but only 20% of ewes displayed behavioural oestrus. A single injection of progesterone at the time of introduction of the males (group 3) did not influence the proportion of ewes displaying oestrus and ovulation was not significantly lower than the other two groups. In contrast, in the second cycle, most ewes of group 3 showed oestrus during a short period. Seventy-seven per cent of ewes were on heat over five days while in group 2, following the 'ram effect' only, oestrus was spread over about 10 days. Experiment 2 Laparoscopy of the control ewes revealed that about 20% of the flock was ovulating spontaneously. These ewes were probably incapable of responding to the introduction of rams. The distribution of oestrus in the five treatment groups is 520 Animal Production in Australia TABLE 1 Experiment 1: Effect of treatment with progestagen on the response of ewes to the 'ram effect' * ewes were mated at first cycles FIGURE 1. Experiment 2: Distribution of oestrus in ewes after teasing and treatment with a single injection of (a) 0, (b) 5 mg, (c) 10 mg, (d) 15 mg and (e) 20mgprogesteroneinoil. Figures in parenthesis are the proportions of ewes ovulating in response to teasing. 521 Animal Production in Australia shown in Figure 1. This shows that there was a progressive synchrony of oestrus as the dose increased from 0 to 20 mg. With no progesterone there were two peaks in the distribution which was very broad. At the other extreme 20 mg progesterone given at the time of introduction of the rams gave good synchrony of oestrus around day 19. Not only was oestrus better synchronised with high doses but it tended to take place later than at low doses of progesterone. DISCUSSION Short ovarian cycles caused by CL of short-term life spans can be overcome entirely with a single injection of progesterone. It is clear from the results of Experiment 2 that a dose of at least 20 mg is necessary to eliminate all short cycles. Whether lower doses are less effective because they fail to produce a sufficiently high concentration of progesterone, or a level of progesterone over a sufficiently long period is less clear. Certainly the amount of progesterone supplied in a single injection of 2 0 mg is insufficient to 'prime' ewes to exhibit behavioural oestrus. In contrast, long-term progesterone treatment, as in intravaginal sponges, combined with the 'ram effect' results in almost all ewes displaying oestrus. It is therefore likely that progesterone has two quite separate roles in control of reproduction in anoestrous ewes. Control over the presence of short cycles opens the way for the use of the 'ram effect' for synchronisation of oestrus. Isolation and then reintroduction of ewes and rams together with a single intramuscular injection of progesterone is neither expensive nor onerous and allows us to control oestrus in a high proportion of ewes in the flock. Controlled breeding using a complete hormone regime is not only more expensive but in many cases is associated with a significant fall in fertility at the synchronised oestrus (Robinson 1968). Since the synchronised oestrus using the 'ram effect' and progesterone is the second cycle it is not associated with exogenous hormones and normal fertility could be expected. Two major problems remain in controlling oestrus by this method. The first is that it can only be used on ewes which are in anoestrus and therefore susceptible to stimulation by rams. If only a few ewes are in anoestrus then it follows that synchrony will be poor. C. Oldham (pers. comm.) has shown that the proportion of the flock which is in anoestrus varies throughout the so-called non-breeding season but, under some circumstances, may reach 100%. The second problem is that if no ewes are cycling, the efficacy of the rams may not be as high as it is in flocks where the proportion of anoestrous ewes is less than 100% (Lindsay and Signoret 1980). These two reciprocal problems limit the theoretical degree of synchrony possible to about 70-80%. ACKNOWLEDGEMENTS We wish to thank Messieurs Prud'hon and Reboul for help in the French experiment and Mr. and Mrs. John Hewitt for the use of their sheep in the Australian experiment. Financial help was provided by the AMRC. REFERENCES COGNIE, Y., GAYERIE, F., OLDHAM, C.M., POULIN, N. and MAULEON, P. (1981). Proc. 32nd Eur. Ass. Anim. Prod. CORKE, D.G. (1980). Proc. Aust. Soc. Anim. Prod. 13: 81. HUNTER, G.L., BELONJE, P.C. and VAN NIEKERK, C.H. (1971). Agroanimalia 3: 133. LINDSAY, D.R. and SIGNORET, J.P. (1980). Proc. 9th Int. Congr. Anim. ReprTd. AI:83. OLDHAM, C.M., COGNIE, Y., POINDRON, P. and GAYERIE, F. (1980). Proc. 9th Int. Congr. Anim. Reprod. AI: 42. OLDHAM, C.M. and MARTIN, G.B. (1978). Anim. Reprod. Sci. 1: 291. RADFORD, N.M., WATSON, R.H. and WOOD, G.F. (1960). Aust. vet. J. 36: 57. ROBINSON, T.J. (1968). Proc. 6th Int. Congr. Anim. Reprod. AI: 1347. UNDERWOOD, E.J., SHIER, F,.L. and DAVENPORT, N. (1944). J. Agric. W.A. 11: 135. E 522