Effect of lupin grain supplementation on ovulation rate and plasma follicle stimulating hormone (FSH) concentration in maiden and mature Merino ewes.

Abstract

EFFECT OF LUPIN GRAIN SUPPLEMENTATION ON OVULATION RATE AND PLASMA FOLLICLE STIMULATING HORMONE (FSH) CONCENTRATION IN MAIDEN AND MATURE MERINO EWES F.D. BRIEN* , R.W. BAXTER*, J.K. FINDLAY and I.A. CUMMING* Summary on the ovaries were counted by laparoscopy at 12 days post coitus to determine ovulation rate. Effects of treatments on ovulation rate (OR) were analysed by a stepwise multiple regression programme. All independent variables were included in the final regression and-only those interactions significant at the five per cent level were not rejected. The independent variables investigated were : . . . . . . . . Cl) A pen experiment was undertaken in May to relate the effect of lupin grain supplementation to FSH levels in plasma. A number of ewes from the same flock used in the first experiment were injected with 125 pg of the prostaglandin analogue ICI 80996 on May 11. Seventeen ewes exhibited oestrus from May 12-15 and were individually penned in an animal house. After weighing the ewes were allocated at random in liveweight pairs to supplemented or unsupplemented groups. The supplemented ewes received 0.5 kg lupin grain/ewe/day, from May 11-30. Chopped hay, of similar origin to that fed in Experiment 1, was fed ad lib. to all ewes. Seven plasma samples (10 ml) were taken at hourly intervals each day from May 26-30, i.e. approximately 'Day 12-16 after mating. Aliquots (0.5 ml) of the plasma samples collected during one day for each ewe were pooled and the pooled samples were randomized within an assay for FSH (Salamonsen et _ al. 1973). The FSH concentration was related to the number of days be-fore the onset of oestrus (i.e. Day -6 to Day -1) which were determined either from mating records subsequent to blood sampling or from previous mating records. The mean oestrous cycle length was 17 days. III. RESULTS In the first experiment the mature ewes were 38 kg and the maiden ewes 30 kg at allotment. Both age groups were 5 kg heavier at the start of the mating period than at allotment. Supplemented subgroups were l-2 kg heavier during the mating period than the unsupplemented subgroups. Thirty one maiden and six mature ewes failed to mate, and of these 17 maiden and four mature ewes were from the unsupplemented groups. While all mature ewes ovulated, 13 maidens, of which 12 were from the unsupplemented groups, did not. Standard errors of regression coefficients are shown in parenthesis. interactions were rejected in the course of the analysis. All 238 In the pen experiment ten ewes were detected in oestrus in the two days following blood sampling. On Days -5, -4, -3, -2 and -1 of the oestrous cycle mean (*SD) plasma FSH concentration (ng/ml) from ewes in the supplemented 66 + 18, 59 + 30, 55 Itr 24, 38 & 14, and 43 =t ewes was 21, and in the unsupplemented group 48 f 24, 39 +, 17, 44 +, 21, 40 * 25, and 41 + 30 respectively. The difference in mean FSH level between Day -5 and the mean level on Days -2 and -1 was larger in the lupin supplemented group than in the unsupplemented group (25 * 10-v. 8 ,+ 18 ng/ml, t = 2.36, X0.05). IV. DISCUSSION Supplementation with lupin grain increased ovulation rates in maiden and mature ewes and the response in both age groups was of a similar magnitude. Numerous studies have related ovulation rate to liveweight parameters in mature ewes. There are few similar reports for maiden ewes and a lack of information relating these parameters in both mature and maiden ewes of similar genotypes. Over the common liveweight range at mating (30-35 kg) the mature ewes had higher ovulation rates than the maidens within both supplemented and unsupplemented treatment groups. Within the common liveweight range, mature ewes without supplementation, tended to have ovulation rates lower than maiden ewes which were supplemented. Coop (1966) has described both a static and dynamic liveweight component in the total flushing response and concluded that flushing could result in a 15020% increase in lambing percentage made up from a static component of S-10% and a dynamic component of 10%. When the responses reported in this paper were examined it was apparent that a flushing effect had probably occurred. The supplemented ewes were l-2 kg heavier at mating than the unsupplemented ewes within both the mature and maiden ewes. . The regression analysis indicated that this static effect would account for a 2-4% increase in ovulation rate. This relatively small increase in ovulation rate was probably a reflection of 239 the generally low live weights of all the ewes which put them in the low response area of the sigmoid liveweight-ovulation rate curve described by Edey (1968). The regression analysis described a dynamic response of 14%. Recognising that the conclusions of Coop were based on lambing results and were therefore probably an understatement of ovarian response, the dynamic response resulting from lupin grain supplementation reported in this paper must be described as comparable. The physiological significance of the higher FSH concentrations in the lupin supplemented ewes 5 days before oestrus compared to values 1-2 days before oestrus is not known but it may represent the means by which live weight or nutrition influences ovulation rate. There is some indirect evidence that FSH concentration at this time may be important in determining ovulation rate. Unilateral ovariectomy must be performed before Day 14 if compensation in ovulation rate by the remaining ovary is to be complete (Cumming and Findlay 1976) and treatment with an exogenous gonadotrophin increases ovulation rates in sheep when given on days 12-13 (Cumming and McDonald 1967). As Findlay and Cumming (1976) found no difference in the metabolic clearance rate of FSH of ewes with one and two ovulations, the relative increase in FSH was probably due to increased secretion by the pituitary gland. The endocrine mechanism responsible for this change in FSH secretion and the role of live weight and plane of nutrition in this mechanism now requires examination. ' V. ACKNOWLEDGEMENTS The authors wish to thank Mr. R, Jardine who assisted wifithe statistical analysis and Dr. R.A.S. Lawson and Mr. I. Davis who commented on the manuscript. The technical assistance of Mrs. G. Pruysers and Messrs. P. Langdon, S. McPhee, A. Makin and P. Weston and Misses S. Visser and P. Wilson is gratefully acknowledged. The financial assistance of the Australian Wool Corporation and Australian Extension Services Grant is gratefully acknowledged. VI. REFERENCES COOP, I.E. (1966). World Review of Animal Production, 4: 69. CUMMING, I.A., and FINDLAY, J.K. (1976). Journal of ReFroduction and Fertility (in press). CUMMING, I.A.I and MCDONALD, M.F. (1967). New Zealand Journal of Agricultural Research, 10: 226. EDEY, T-N. (1968). Proceedzgs of the Australian Society of Animal Production, 7: 188. FINDLAY, J.K., gd CUMMING, 1-A. (1976). Biology of Reproduction, (submitted for publication). LIGHTFOOT, R-J., and MARSHALL, T. (1974). Western Australian Journal of Agriculture, 15: 29. RIZZOLI, D-J., BGER, R.W., REEVE, J.L., and CUMMING, 1-A. (1976). Journal of Reproduction and Fertility (in press). SALAMONSEN, L.A., JONAS, H-A., BURGER, H-G., BUCKMASTER, J.M., CHAMLEY, W.A., CUMMING, I.A.', FINDLAY, J.K., and GODING, JR. (1973). Endocrinology, - 610. 93: 240