Abstract:
Proc. Aust. Soc. Anim. Prod. (I 974) 10; 265 THE EFFECT OF SHORT TERM FASTING IN EWES ON EARLY EMBRYONIC SURVIVAL M.A. de B. BLOCKEY*, I.A. CUMMING* and R.W. BAXTER* Summary Two experiments were conducted to examine the effects of short term fasting on early embryonic survival in 632 single ovulating and 364 twin ovulat ing ewes. In each experiment, ewes were fasted for 3 days from days 1 , 5, 8, 10 or 12 post coitus and embryo survival determined at day 22-29 post coitus. There was a reduction in the pregnancy rate in single ovulating ewes. In the first experiment this reduction (87 to 77%; 0.10, P>-0.05) wa,s confined to the ewes fasted during the first 10 days of pregnancy. I n the second experiment, the reduction in pregnancy rate was from 100 per cent in the control ewes to 87 per cent in the However , the pregnancy rate was higher (PxO.01) in the twin fasted ewes. It is concluded ovulating fasted ewes (92%) than in the controls (78%). that under practical farming conditions, three days fasting in early pregnancy would not significantly depress subsequent lambing percentage. I. INTRODUCTION Situations do arise when ewes in early pregnancy can be without feed for periods up to three days. This occurs when ewes are sold through Periods of undersaleyards or are yarded for shearing ox crutching. nutrition lasting for a week or more during the first three weeks of pregnancy can cause embryonic mortality (Edey 1966, 1970; Cumming 1972a). Van Niekerk, Belonje and Hunter (1968) suggested that short term fasting also caused embryonic death in ewes. In small numbers of ewes (5/group) fasted fox two to four days during the first two weeks of pregnancy, they found that 55% to 100% of embryos were degenerating when recovered on day 16 post coitum (p-c.). The two experiments reported in this paper were designed to examine the association between short term fasting and early embryonic death in single and twin ovulating ewes. II. Werribee. MATERIALS AND METHODS The experiments were carried out at The State Research Farm, Experiment 1 weight to one Groups 10 or In May, 1969, 589 mature Merino ewes were weighed (mean live33.5 kg) and allotted randomly within similar liveweight groupings Group A, the control group, was not fasted. of six treatment groups. B, C, D, E and F were fasted for 3 days beginning on days 1, 5, 8, 12 p-c., respectively (Table 1). Experiment 2 In May of the following year, 600 large-framed mature Border Leicester x Merino ewes were weighed (mean liveweight 57.5 kg) and * Department of Agriculture, Victoria, S.S. Cameron Laboratory, Werxibee, Victoria. 265 allotted, as in Experiment 1, to the control group U and similar treatment groups V, W, X, Y and 2. In early June, 1969, and late May, 1970, the ewes in Experiments 1 and 2 respectively, were joined with 18 entire Poll Dorset rams fitted with harnesses and marking crayons. On day 1 p.c. Group A and U ewes were placed in a second flock with two vasectomized rams fitted with harnesses. Ewes to be fasted were transported to a woolshed 1 km away and held in pens with water supplied. After fasting, they joined Group A or U ewes in the second flock where daily checks were made for returns to service. Ewes which returned to service underwent a laparotomy on the day of return to service and recent corpora albicantes (C.A.) were counted. Ewes not returning to service were slaughtered 22-29 days p.c. and the number of corpora lutea (CL) and embryos recorded. Embryos were assessed for viability. TABLE1 The percentage of single and twin ovulating ewes pregnant Blood samples were taken from the jugular vein of 105 and 120 ewes in Experiments 1 and 2 respectively for measurement of plasma glucose by the autoanalyser N methodology. Blood samples were taken from the jugular vein of ewes on one occasion prior to fasting, and the first, second or third day of fasting, or'on the first or second days after fasting. Non-esterified fatty acids (N.E.F.A.) concentrations were determined in the jugular plasma of four ewes of Group E and two from A from Day 9 to 13 p,. using the method of Annison (1960). Control group ewes were weighed twice weekly throughout both experiments. Mild winter conditions prevailed for the duration of the experiments (rainfall, 3.2-3.7 cm; mean daily maximum temperature, 13.813.5Oc; mean daily minimum temperature 4.506.6OC; in Experiments 1 and 2 respectively). III. RESULTS In the fasted ewes, concentration of plasma glucose gradually decreased as fasting progressed and rose to pre-fasting levels within one day of ewes returning to pasture (Figure 1). Plasma N.E.F.A. levels 266 remained high from 24 hr after the start of fasting until 24 hr after ewes returned to pasture (Figure 1). Ewes in the control groups A and U maintained body weight during the seven week experimental periods. In Experiment 1, 505 of the 589 ewes mated in the three weeks. There were 474 ewes with single ovulations, 14 with two ovulations. A further 17 were rejected because of ovarian and uterine adhesions, deaths or missing data. The percentage of single ovulating ewes pregnant at 22-29 days p.c. ranged from 87% in the control ewes (A) to 76% in the groups fasted from day 5 (C) or day 8 (D) p.c. (Table 1). There were no significant differences in pregnancy ratebetween any of the fasted groups and the controls (X 2 = 1.0). However, when B, C and D were pooled, their pregnancy 'rate t 77%) was lower (Xl2 = 3.43; O.lO> p' 0.05) than that of the controls (87%). The pregnancy rate in Groups E and F (85.5%) was similar to that of the controls. There were insufficient ewes with twin ovulations to carry out any meaningful analysis. In Experiment 2, 96 per cent of the 600 ewes mated in three weeks. Twenty-two ewes were rejected from the analysis because of missing data or abnormalities of the genital tract, and a further 29 ewes not included as 267 they had triple ovulations. Within ewes with single ovulations, the proportion of pregnant ewes was non-significantly lower in each of the fasted groups than in the control group (Table 1). However, when all five fasted groups were pooled, their pregnancy rate (87%) was lower _ (P <O-OS*) than in the control group (100%). Within the ewes with twin ovulations, there were no significant differences in pregnancy rate between any of the treated groups and the controls but, when data,from all five treated groups were pooled, their pregnancy rate (92%) was higher (Xl2 = 8.70; P x0.01) than that of the controls (78%). The 21-day non return rate for the fasted groups (pooled data) was 93.5% compared with 86.0% fox the control group. (al-day non return rate closely approximates fertilization rate in ewes - Blockey, Parr and Restall in press). In the ewes with twin ovulations, there was a lower proportion (not significant) of single pregnancies in the control group (12%) than in the pooled data for fasted groups (19%). IV. DISCUSSION Three days of fasting did mobilize fat reserves in pregnant ewes as indicated by the increased plasma N.E.F.A. and decreased plasma glucose levels in the ewes in both experiments. However, the effect of short term fasting on pregnancy rate was variable. Three days fasting was associated with an increased pregnancy rate in ewes with twin ovulations (92% for fasted groups v. 78% for control group). This could be a real effect of fasting. Undernutrition does increase circulating progesterone levels in early pregnancy (Cuxmning et al.' 1971) and the effect is more marked in twin ovulating than single ovulating ewes (Gumming 1972b). Progesterone levels were not related to embryonic survival of ewes in that experiment (Cumming et al. However, in one series of egg transfer experiments, Trounm- 1971). son and Moore (1973) found high plasma progesterone levels in three ewes with both embryos surviving compared to markedly lower progesterone levels in ewes losing both embryos.. Another more likely explanation for the difference in pregnancy rate is a difference in fertilization rate as reflected by the 210day non return rates (93.5% for fasted groups v. 86.0% for control group). This difference may have been induced by the experimental design in which the control group ewes were separated from fertile rams 24 to 48 hours after the onset of oestrus. Many twin ovulating ewes which remain in oestrus for significantly longer periods than single ovulating ewes (Blockey 1971) would still have been in oestrus at the time of separation. Fasting did not influence what is a most important practical source of ovum wastage in twin ovulators, the loss of one of two ova. The proportion of ewes with twin ovulations with a single pregnancy in the fasted groups (13025%) was within the range (8035%) reported by Edey (1966) and Gumming (1972a and c) fox well-fed ewes. It is concluded that short term fasting had no deleterious effect on the fertility of these twin ovulating Border Leicester x Merino ewes. Short term fasting did appear to cause embryonic mortality in single ovulating ewes. However, the reduction in pregnancy rate of the Merinos in Experiment 1 was small (from 87 to 77%) and the deleterious effect was confined to the first 10 days of pregnancy. Although fasting did reduce the pregnancy rate of single ovulators in Experiment 2, the pregnancy rate of the fasted groups was high (81.89%). The magnitude of the effect on ewes with single ovulations was small and would not be of practical importance if these ewes were joined with rams for two or three cycles. It is concluded that three days of fasting during mating would not significantly depress the lambing percentage. * Fisher's exact test. 268 V. ACKNOWLEDGEMENTS Thanks are due to Messxs A. Williams, A. Makin and R. Paxr for technical assistance, and to Dr R.H. Watson and the late Dr J.R. Goding Some statistical analysis was undertaken for advice and encouragement. by Mx R. Jardine, the plasma N.E.F.A. determinations by Mxs Meredith Drew, and the plasma glucose analyses by Dr J. Wilkinson of the Veterinary Financial assistance was Clinical Centre, University of Melbourne. provided by the Wool Research Trust Fund. VI. REFERENCES ANNISON, E.P. (1960). Aust. J. agxic. Res. 11: 58. M.V.Sc. Thesis, yniversity of Melbourne. BLOCKEY, M.A.- de B. (1971). Aust. J. BLOCKEY, M.A. de B., PARR, R.A. and RESTALL, B.J. (1974). p Agric. Anim. Husb. (In press). CUMMING, I?.* (1972a). Proc. Aust. Soc. Anim. Prod. 2: 199. CUMMING, 1-A. (1972b). Ph.D. Thesis, University of Melbourne. GUMMING, 1-A. (1972c). Proc. Aust. Soc. Anim. Prod. 4: 192. GUMMING, I-A., MOLE, B-J-# OBST, J., BLOCKEY, M-A. de B., WINFIELD, C.G. and GODING, J.R. (1971). J. Reprod. Fext. 22 : 146. EDEY, T-N. (1966). J. agric. Sci. 22: 287. EDEY, T.N. (1970). J. agxik. Sci. 22: 199. QUINLI VJW T.D.# MARTIN, C-A., TAYLOR, W.B., and CAIRNEY , 1-M. (1966). J. Reprod. Fert. &A: 379. Proc. Endocx. Soc. Aust. &g: 32. TROTUNSON, A.O.,and MOORE, N.W. (1973). V&AN NIEKERK, C-H., BELONJE, P.C. and HUNTER, G.L. (1968). 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