The comparative reproductive performance of ewes joined to one or three percent of rams.

Abstract

THE COMPARATIVE REPRODUCTIVE PERFORMANCE OF EWES JOINED TO ONE OR THREE PER CENT OF RAMS S. T. DAWE*, N. W. BENNETT*, F. B. DONNELLY*, B. D. FERGUSON*, J. P. RIVE*, B. C. ROBERTS* and B. I. TRIMMER* Summary In the three years 1967 to 69, the comparative reproductive performance of ewes joined to 1 or 3 per cent of rams was examined in 13 observations on commercial sheep-producing properties in New South Wales. Approximately 5200 ewes were involved. In each observation two flocks of 20 ewes were joined in the autumn, one with two rams (1 per cent) and the other with six rams (3 per cent). Saddle marks were recorded durin g a six-week joining period and, at the end of lambing, the number of dry ewes in each group was ascertained. Generally, the use of 3 per cent of rams increased the number of ewes mated by 1.4 per 100 ewes joined, and decreased the number of dry ewes by 2.4 per 100 ewes joined. Although significant statistically, these differences were small and of little practical importance. In one observation, however, the incidence of dry ewes in the 1 per cent and 3 per cent groups was 49.8 per cent and 12.5 per cent respectively. I. INTRODUCTION Little work has been carried out on the effects on flock reproductive performance of variation of the ram:ewe ratio at joining. Haughey ( 1959) concluded that one ram/ 100 ewes was sufficient provided joining paddocks were small and Edgar ( 1965) found no, differences from joining one, two or three rams/l00 ewes. Lightfoot and Smith ( 1968), h!owever, demonstrated large effects on fertility by varying the ram:ewe ratio from 1 to 4 per cent with young rams, but not with 3t toI 5 year old rams. To provide extensive information on the effects of ram percentage on flock fertility under a wide range of environments, a series of observations has been conducted in co-operation with commercial sheep producers in New South Wales. In each case the reproductive performance of ewes joined to 1 or 3 per cent of rams was examined. II. MATERIALS AND METHODS The location, year and numbers of ewes involved are shown in Table 1. Mature Merino ewes were used on all properties except Albury 2 and 3 (Polwarth * N.S.W. Department of Agriculture, New South Wales. 317 TABLE 1 ewes) and Parkes 1 (Border Leicester x Merino ewes). Mature Merino rams were used in all cases except Albury 1 (twobtooth Merinos), Albury 2 (two-tooth Polwarths) and Parkes 1 (mature Dorset Horns). Only rams producing semen of high density and motility (Morrant and Dun 1960) were used in the comparison. In each observation, approximately 400 ewes were allocated into two groups. In February or March, two rams were introduced into one group (1 per cent and six into the other (3 per cent). The two groups were joined separately in comparable paddocks for six weeks, during which: time the paddocks were alternated each week to minimise any nutritional differences. On all properties except those at 318 Parkes, rams were harnessed (Radford, Watson and Wood 1960) and ewes were inspected for saddle marks at two-week intervals. From the end of joining, the two groups were Tun as a single flock. At the end of lambing, each ewe was classified as 'wet' or 'dry' according to Dun ( 1963). Data from all properties over the three years were examined in an analysis of variance after angular transformation. Within individual observations, group data were compared by Chi square analysis. III. RESULTS AND DISCUSSION The results of joining and lambing are summarised in Table 1. Significant differences between treatments in individual observations are indicated. Mating data from West Wyalong and Finley 1 have been omitted because of discrepancies between per cent ewes not mated and per cent dry ewes. On West Wyalong, minima of 22.9 and 4.4 per cent of the ewes in the 1 per cent and 3 per cent groups respectively, lambed after being recorded as unmated. A similar situation existed on Finley 1 where 5.5 per cent of the 1 per cent group were implicated. On both these properties, particularly in the 1 per cent groups, all mated ewes were not adequately identified by the harnessed rams. Mattner and Braden (1967) and Lightfoot and Smith (1968) observed that individual ewes were served less frequently when the ram:ewe ratio was decreased. In the current observations, it was noted generally that saddle marks in the 1 per cent groups were of much lower intensity than in the 3 per cent groups, suggesting that individual ewes were served less frequently in the former groups. Mean differences between treatments (after exclusion of the data from West Wyalong and Finley 1) for per cent ewes mated in the first two weeks (6.8 per . cent) and per cent ewes not mated by the end of joining (1.4 per cent) were significant (P<O.Ol and P<O.O5 respectively). The reliability of these differences is questionable, however, as it is possible that small numbers of mated ewes may not have been identified as on West Wyalong and Finley 1. Despite this possibility, the differences were not large, particularly in regard to unmated ewes, and are of little practical significance. Th*ere was no consistent effect of ram percentage on the incidence of returns to service. (b) Lambing (a) Joining The percentage of dry ewes was significantly higher (P<O.Ol ) in the 1 per cent groups, but the interaction between ram percentage and property was also significant (P<O.Ol ). The only marked difference between treatments was on Finley 2 and, w&en this property was deleted from the analysis, the interaction was not significant. The effect of ram percentage, however, was still significant (P<O.Ol ) but the mean difference of 2.4 per cent in the incidence of dry ewes was of little practical importance. In relation to the rest of the data, the result on Finley 2 appears to have been atypical. It is evident that ram fertility in the 1 per cent group was inadequate as 65 per cent of those ewes served in the first four weeks in this group returned 319 to service compared with 25 per cent in the 3 per cent group. Whether the rams allocated to the 1 per cent group were initially less fertile than those in the 3 per cent group, or whether the problem was one common to both groups but accentuated by the lower ram percentage, cannot be deduced from the available data. Despite selection on semen characteristics it is possible that one or both of the rams in the 1 per cent group was of suboptimal fertility. Salamon and Robinson (1962) and Robinson et al. (1967) have recorded that rams producing semen of similar density and motility may vary in fertilising capacity. The result on Finley 2 may have been a chance effect or may be a real h.azard to be expected occasionally where only 1 per cent of rams are used, particularly where the number of ewes in the joining group -permits only a small number of rams to be used at such a percentage. Young rams were used on only two properties (Albury 1, Albury 2) and, in both! cases, differences in mating activity between treatments were significant. The only case in which treatment affected the number of ewes not mated was also one of these (Albury 2). It is possible that greater differences in flock reproductive performance might have been obtained if young rams had been used throughout the series (Lightfoot and Smith 1968). IV. ACKNOWLEDGMENTS Grateful acknowledgment is made of the co-operators - Messrs. R. Allworth., B. Colless, T. Cowper, R. Frogley, K. G. Hordern, K. Paterson-A. Scott, J. Simpson, R. Spinks and D. White - who so readily made available their sheep and facilities- Thanks are also due to Messrs. J. P. Drinan and P. D. Stevenson who supervised this work in the early stages. V. REFERENCES D UN, R. B. ( 1963). Aust. J. ex. Agric. Anim. Hus. 3: 228. E DGAR , D. G. ( 1965). Proc. Ruakura Frmrs' Conf. Week, p. 61. HAUGHEY, K. G. (1959). Sheepfmg. A., p. 17-26. LIGHTFOOT, R. J., and S MITH, J. A. C. ( 1968). Aust. J. agric. Res. 19: 1029. M ATTNER , P. E., and BRADEN, A. W. H. (1967). Aust. J. exp. Agric. Anim Hub. 7: 110. M ORRANT , A. J., and D UN, R. B. ( 1960). Aust. vet. J. 36: 1. RADFORD, H. M., W ATSON, R. H., and W OOD, G. F. (1960). Aust. vet. J. 36: 57. R OBINSON, T. J., S ALAMON , S., M OORE, N. W., and S MITH , J. F. ( 1967). 'The Control of S ALAMON, the Ovarian Cycle in the Sheep.' (Sydney University Press: Sydney.) S., and R OBINSON , T. J. ( 1962). Aust. J. agric. Res. 13: 52. 320