Synchronization of oestrus and ovulation in beef cows with progesterone releasing intravaginal devices (PRIDs) : effect of duration of treatment and of temporary calf removal.

Abstract

SYNCHRONIZATION OF OESTRUS AND OVULATION IN BEEF COWS WITH PROGESTERONE RELEASING INTRAVAGINAL DEVICES (PRIDs): EFFECT OF DURATION OF TREATMENT AND OF TEMPORARY CALF REMOVAL J.F. SMITH*, H.R. TERVIT* and P.G. GOOLD* SUMMARY Angus cows (355) were treated with either PRIDs + oestrogen for 10 or PRIDs alone for 14 days. At the time of PRID withdrawal they either remained with or were removed from their calves for a period of 56 h when they were inseminated. Following the 10 day treatment, more cows showed heat between PRID withdrawal and insemination (55% vs 47%) and conceived (44% vs 30%) than after the 14 day treatment. Temporary calf removal increased the proportion of cows showing heat (66% vs 40%) and conceiving (48 % vs 30%) compared to those that remained with their calves. INTRODUCTION The development of a simple and effective system of oestrous synchronization is an essential requirement for the increased use of genetically-superior sires and of artificial insemination in N.Z. beef herds. Because of the high level of anoestrus encountered at the start of the mating period, prostaglandins have not proved successful for large scale use on suckling beef cows (Smith 1977). Satisfactory results have been obtained, however, from the use of progesterone releasing intravaginal devices (PRID) (Smith 1978). The shortening of the duration of progesterone treatment from 21 days to about 10 days has resulted in higher and more consistent levels of fertility (Wiltbank et al. 1971; Sreenan 1975; Pelot et aZ. 1975), and the temporary weaning of calves for the period between end of progesterone treatment and insemination has increased the incidence of cows exhibiting oestrus and conceiving (Smith et al. 197939). The present study was conducted to determine the effects of duration of PRID treatment and temporary calf removal on the effectiveness of a synchronization programme with suckling beef cows. MATERIALS AND METHODS Mixed-age Angus cows (355) were used in the experiment which was conducted The cows were allocated to on the Crater Block Research Station near Rotorua. four treatment groups on the basis of age and date of calving. (i) Treatment 1 PRIDs inserted for a period of 10 days. A gelatine capsule containing 10 mg oestradiol benzoate was attached to the PRID at the time of insertion. (ii) Treatment 2 As for Treatment 1 and in addition the calves were temporarily removed from the cows for a period of 56 h between PRID withdrawal and insemination. PRIDs inserted for a period of 14 days without oestrogen (iii) Treatment 3 treatment. (iv) Treatment 4 As for Treatment 3 with the addition of temporary calf removal. The dates of PRID insertion were staggered so that PRID removal and insemination occurred in all groups at the same time. The occurrence of oestrus between PRID withdrawal and insemination was determined by the use of 'tail paint' (Macmillan and Curnow 1977) applied at *Ruakura Animal Research Station, Private Bag, Hamilton, N.Z. 309 Animal production in Australia the time of PRID withdrawal. All cows were given a single insemination with 1.0 ml of Hereford semen Inseminations diluted in 'Caprogen' (Shannon 1978) containing 10 x lo6 sperm. No further were performed 56 h after PRID withdrawal,by two inseminators. mating was conducted as all animals were destined for slaughter. All COWS were palpated per rectwn 60 days after insemination to determine pregnancy. RESULTS The data of incidence of oestrus and pregnancy rate are summarised in Table 1. TABLE 1 Effect of age, duration of treatment and temporary calf removal on the exhibition of oestrus and pregnancy rate in PRID-treated beef cows Incidence of Oestrus A total of 181 (51%) of the cows exhibited oestrus in the 56 h period The proportion of cows exhibiting between PRID withdrawal and insemination. Fewer (37%) of the 3 y-0. oestrus was influenced by the age of cow (P<O.OOl). Temporary calf or first calving cows showed heat than did the older cows (56%). removal increased (P<O.OOl) the incidence of oestrus compared to those cows that remained with their calves (66% vs 40%). Pregnancy Rate (i) Overall The overall pregnancy rate was 38% of the cows treated. This was influenced by age (P<O.Ol) with fewer 3 y-0. cows becoming pregnant (3 y-0. = 24% vs older = 42%) than older cows. There was a significant (P<O.Ol) effect of duration of treatment with more cows in the 10 day treatment groups becoming Animal Production in Australia pregnant (10 day = 44% vs 14 day = 30%). Temporary calf removal also increased (WO.001) th e pregnancy rate (without calves = 48% vs with calves = 30%). The pregnancy rate was markedly influenced by whether or not a cow exhibited oestrus between PRID withdrawal and insemination. Those that exhibited oestrus had a much higher (P<O.OOl) pregnancy rate (54%) than those which did not exhibit oestrus (20%). (ii) Oestrous cows The pregnancy rate of the oestrous cows was 54% overall and was similarly influenced by age (3 y.o. = 34% vs older = 59%; (P<O.Ol), duration of treatment (10 day = 63% vs 14 day = 43%; P<O.Ol) and temporary calf No effects of removal (without calves = 62% vs with calves = 45%; P<O.O5). age or treatment were found on the pregnancy rate of those cows not exhibiting oestrus. (iii) Inseminators There was no effect of inseminators on pregnancy rate. Interval from Calving to Treatment There were significant effects of the interval from calving to treatment on the proportion of cows exhibiting oestrus and on the pregnancy rate (Table 2). Those cows treated within 30 days of calving showed a lower incidence of oestrus (KO.05) and a lower pregnancy rate (P<O.OOl) than did cows treated later postThere was no significant effect of postpartum interval beyond 30 days. partum. TABLE 2 Effect of interval from calving to treatment on incidence of oestrus and pregnancy rate in PRID treated cows DISCUSSION The superiority of the shorter term (10 day) PRID treatment obtained in beef cows is similar to that obtained with short-term treatments with intravaginal Mawhinney sponges (Sreenan 1975) and progestogen implants (Pelot et al. 1975). and Roche (1978) have recently reported similar differences between short (9 day) and long (14 day) PRID treatment of dairy cows. The effectiveness of the short-term treatments is most likely associated with the higher levels of progesterone circulating at time of withdrawal (Smith et ail. 1979a). Temporary calf removal improved both the incidence of cows exhibiting Smith et al. (1979b) reported an increase in oestrus and the conception rate. the number of cows exhibiting oestrus but they did not cbserve any improvement in conception rates. The mechanism by which this operates is unclear except for the reduction of neural impulses as a result of the suckling stimulus but this is unlikely to be operating via a decrease in prolactin release (Smith et al. 1980). 311 Animal production in Australia The importance of inducing cows to exhibit oestrus between PRID withdrawal and insemination on pregnancy rates is highlighted in this experiment. The effects of various treatments on overall pregnancy rate cannot be explained simply in terms of increased numbers of cows exhibiting oestrus because within those cows that did exhibit oestrus, there were still significant effects of treatment on pregnancy rate. The effect of age observed in this experiment is most likely one of parity status with the well-documented depression in reproductive activity following the animal's first parturition. The need for a certain interval between calving and treatment before satisfactory results can be obtained is once again demonstrated in this trial. The lack of any significant improvement after 30 days postpartum however, indicates the ability of this treatient to induce oestrous behaviour and enable pregnancy to be obtained at a time when most beef cows run under these conditions could be considered anoestrus (Knight and Nicoll 1978). The use of the PRID inserted for a period of 10 days, augmented with oestrogen at the time of insertion together with temporary calf removal for the 56 h period between withdrawal and insemination,has proved a most satisfactory technique for the synchronization of oestrus in suckling beef cows under New Zealand conditions. ACKNOWLEDGEMENTS Mr T. Harvey and Mr A. Kivell for management of cows at the Crater Block. Mr M. Cooper and Mr G. Haszard for the inseminations. Mr L. McGowan for assistance with treatment and pregnancy diagnosis. New Zealand Dairy Board A.B. Centre for provision of semen and Abbott Laboratories for donation of the PRIDs. REFERENCES KNIGHT, T.W. and NICOLL, G.B. (1978). Proc. N.Z. Soc. Anim. Prod. 38:175. MACMILLAN, K.L. and CURNOW, R.J. (1977). N.Z. J. Exp. Agric. 5:357? MAWHINNEY, S. and ROCHE, J-F. (1978). 'Control of Reproductio; in the Cow.' Martinus Nijhoff: The Hague/Boston/London. PELOT, J., OLIVIER, J-P. and CHUPIN, D. (1975). Ann. Biol. Anim. Bioch. Biophys. 15:29. SHANN~(1~8). J. Reprod. Fert. 54:519. SMITH, J.F. (1977). Proc. N.Z. Soc. Azm. Prod. 37:120, SMITH, J.F. (1978). Proc. N.Z. Soc. Anim. Prod. 58:lOl. SMITH, J-F., FAIRCLOUGH, R.J. and PETERSON, A.J. (E79a). J. Reprod. Fert. 55: 359. SMITHTJ.F., PAYNE, E., TERVIT, H-R., McGOWAN, L.T., FAIRCLOUGH, R., KILGOUR, R. and GOOLD, P.G. (1980). J. Reprod. Fert. (in press.) SMITH, M.F., BURRELL, W.C., SHIPP, L-D., SPOROTT, L.R., SONGSTER, W.N. and WILTBANK, J.N. (1979b)w J. Anim, Sci. 48:1285. SREENAN, J-M. (1975). J. Reprod. Fert. 45:4% WILTBANK, J.N., STURGES, J.C., WIDEMAN, D., LE FEBER, D-G. and FAULKNER, L.C. J. Anim. Sci. E (1971). 33:600. 312