The effect of progestagen treatments and PMSG on reproductive activity of first calving beef cows.

Abstract

Proc. Aust, Soc, Anim. Prod, Vol. 18 THE EFFECT OF PROGESTAGEN TREATMENTS AND PMSG ON REPRODUCTIVE ACTIVITY OF FIRST-CALVING BEEP COWS G.J. SAWYER* first-calving cows including Angus x hundred and seventeen Two Friesian crossbreds, Wokalup multibreeds and Herefords were left untreated or treated with PRID coils for 12 days (Experiment l), at approximately 60 days after calving. In a second experiment treated cows received Syncro-Mate-B for nine days with 650 IU of PMSG at implant removal at a similar time after with observed calving. The treatments increased the proportion of cows cyclical ovarian activity by 20% (Experiment 1) and 50% or palpable more PRID treated cows conceived compared to (Experiment 2). Significantly the subsequent calving date and calving controls, but in both experiments distribution of treated cows was not affected. INTRODUCTION beef is a major determinant of profit from a Reproductive performance suckler enterprise and because early and lifetime productivity are positively associated (Morris 1980) benefits accrue from high fertility in young breeding cattle. First-calving cows often show persistent anoestrus because of the deficiency whilst lactating in an effects of suckling and energy quality varies seasonally. A environment where pasture quantity and first-calving cows postreliable method to induce oestrus and ovulation in advantage if the partum would facilitate early rebreeding, which would be an mating period is restricted or if the calving pattern must match nutrition available from pasture. ovulation been used to synchronise oestrus and Progestagens have commonly in cyclic cows (Roche 1976; Roche et al. 1981) and injections of progesterone with or without oestrogen have induced oestrus and ovulation in non-cyclic cows (Foote and Hunter 1964; Saiduddin et al. 1968; Brown et al. 1972). Intravaginal administration of progesterone (PRID) or norgestomet (SyncroMate-B) in an ear implant are convenient methods of dispensing progestagens, with the added advantage that they may stimulate cows in anoestrus to commence ovarian activity (Hoagland and Barnes 1984). Few have reports dealt specifically with the effects of these methods in lactating first-calved beef cows. This study investigated the return to cows using three reproductive activity of first-calving breed typesof differing lactational abilities, their response to progestagen treatment and their subsequent calving rate and distribution. WATERIALSANDMETBODS Two hundred and seventeen first-calved cows including Angus x Friesian crossbreds (n = 134), Herefords (n = 38) and Wokalup multibreeds (n = 45) which are a composite breed (Carrick and Robertson 1980), were used in two experiments conducted in autumn-winter of two years, Animals grazed annual pastures consisting of Trifoliutn subterraneum, Lolium spp and volunteer annual species on Wokalup Research Station and a private property near Donnybrook, in the high rainfall zone of Western Australia, They were stocked at 0.9 breeding cows per hectare and were fed supplementary meadow they calved, at approximately 5 kg/head/day during the -hay 8 immediately months of April, May and June. Animals which had not calved, had suffered * W.A. Department of Agriculture, PO Box 1231, Bunbury, W.A.. 6230. 348 Proc. Aust. Soc. Anim. Prod. Vol. 18 calving paralysis or had borne a still born calf (n=l5) were not included in the experiments. cows were run with harnessed and hormone-treated steers All first-calving were oestrous activity (Sawyer et al. 1986), o r to monitor cyclical palpated rectally to determine structures (follicles, corpus luteum) prior to groups treatment In Experiment 1, animals were allocated within paddock (Table 1) and observed cyclical activity to on the basis of calving date Controls (n = 76) left untreated; and treated with PRID coils two groups:(n = 79), (Bomac Laboratories, Australia) inserted at the start of joining for 12 days. All cows inserted with PRIDS were checked four days later and there -In Experiment 2 animals were allocated as in Experiment l:were no losses. Controls (n = 29) left untreated; and treated (n = 33) with an intramuscular same injection of 5 mg oestradiol valerate and 3 mg norgestomet given at the (Syncro-Mate-B - Intervet Australia Ltd, time as a norgestomet ear implant left in The implant was at the beginning of joining. Sydney, Australia) place for nine days and 650 IU of PMSG (Pregnecol serum gonadotrophin, Livestock Laboratories Pty Ltd, Australia) was injected at implant removal. rate) joined in early July to fertile, libido-tested bulls (6% cows were mating activity was recorded daily for the wearing chinball harnesses and In both first week after PRID or implant removal and thereafter twice weekly. PRID coil or Syncro-Mate-B experiments, between eight and 12 days after cows were palpated to the reproductive tracts of all implant removal, Animals were weighed and scored for determine palpable ovarian structures. East of Scotland College of Agriculture system) condition (O-5 point scale, The date of second calving was at four week intervals (Table 1). subsequently recorded. data were organised into contingency tables and analysed by ChiDiscrete Squared test. Analysis of variance and Student's t test were used on live and the interval from calving to oestrus or weight, condition score The calving distributions of control and treated firstconception, calvers were compared by the Kolmogorov-Smirnov two-sample test. Table 1 Live weight, condition, days since calving at allccation and change during joining in all first-calving cows weight RESULTS Less cows had shown cyclical oestrous or ovarian activity at the time of allocation to treatment in Experiment 2 compared to Experiment 1; the SOLincrease in activity in progestagen plus PMSG treated animals of Experiment 2 was significant (P<O.O05, Table 2) and the 20% increase in Experiment 1 was not. The trends observed in the timing of second conception and the interval from calving to second conception were different in the two experiments, but not significant in either case (Table 2). 349 Proc. Aust. Soc, Anim, Prod. Vol. 18 years more cows treated with either PRID coils or Syncro-Mate-B both In calved for a second time compared to controls. This effect was statistically Fifty percent of Syncrosignificant (P<O.O05, Table 2) only in Experiment 1. Mate-B treated cows calved in the first three weeks of the subsequnet season However, the trends for a later compared to 20% of controls in Experiment 2. Experiment 1 and an earlier date of calving after date of calving in 2 were not statistically significant (P>O.l, treatment in Experiment Kolmogorov-Smirnov test). Response to treatment did not differ with breed, live weight (range 284 - 496 kg) or the rate of weight gain in either experiment. Within treatment groups, response in teqns of an increase in cyclical ovarian activity or a reduction in the time from first calving to second conception, was not significantly affected by the time after calving at which treatment was imposed, or whether cows were already cycling before treatment. Table 2 Cyclical ovarian activity before and after treatment, calving to conception interval and subsequent calving percentage for all cows DISCUSSION both experiments cyclical ovarian activity increased in response In to progestagen treatment, though no significantly in Experiment 1. This increase was most pronounced when 650 IU of PMSG was administered after Though this resulted in 50% of cows calved in Syncro-Mate-B implant removal. the first three weeks of the subsequent calving period compared to 20% in the average calving to conception interval and the controls, subsequent calving distribution were not significantly affected. Our work was marked by generally high levels of fertility which resulted in an average time of conception of three to four weeks after joining commenced. In addition the calving to second conception interval was uniform as standard indicated by the error of the mean (Table 2) in both control and treated first-calvers. These results are similar to those of Peters (1982) where there was no overall effect of PRID treatment on the mean calving interval in 436 suckling beef cows. Unlike most previous work we commenced treatment at the start of joining with the aim of testing the ability of progestagen treatment to enhance fertility in the post-partum period and not simply synchronise animals already cycling. The focus was on late calving animals which could fail to conceive ina restricted joining period. Other work has shown an apparent advancement of the average date of conception because treated cattle were synchronised, while untreated cattle cycled randomly, and were mated, over the next 21 days. Because of the 350 Proc. Aust- Soc, Anim. Prod. Vol. 18 comparatively high cyclical activity of cows in Experiment 1 the progestagen treatment controlled, more than induced, oestrus and ovulation similar to the first year of Peters' (1982) work. In the current work PRID treatment did higher calving rate in Experiment 1, but this produce a significantly response could not be explained in terms of the time after calving when treatment was imposed or whether cows were cycling before treatment. In Experiment 2 the first-calvers were 0.5 units worse in condition and 60% had Syncro-Mate-B and PMSG treatment more no ovarian activity when palpated. 91% cyclical ovarian activity to which was similar in than doubled proportion (19% to 41%) to work reported by Munro and Moore (1985) with suckled beef cows. This encouraging response may be due to the progestagen treatment allowing accumulation of pituitary gonadotrophins or to an increase Hoagland in pituitary responsiveness to endogenous GnRH (Smith et al. 1983; and Barnes 1984). No measures of fertility or a response to treatment were influenced by live weight, condition or their rates of change at initiation of treatment. This is not surprising considering that 70% of cows were above target weights for these breeds for conception after first calving (Sawyer and Barker unpublished) and they all gained weight during joining, However, the low level of cyclical ovarian activity approximately 60 days post-partum in all Angus x Friesian cows of Experiment 2 may be due to the stress of a higher milk producing ability in this breed type especially when condition condition poorer than those of during joining is low (0.5 units of Experiment 1). In conclusion though few tangible benefits from progestagen treatment after first calving could be demonstrated overall in these herds, the results of Experiment 2 show that there may be a role for strategic use to induce oestrus and ovulation in selected animals, especially those in poorer condition. In a batch mating situation, a program which uses harnessed oestrogen-treated 1986) to assess which animals are cycling, and steers (Sawyer et al. then treatment with a progestagen plus PMSG on anoestrous first-calvers, could generate improved conception rates overall in young breeders, and subsequently in lifetime production. Strategic use should ensure that the benefits would far exceed costs of treatment. ACKNOWLEDGEMENTS I gratefully acknowledge the assistance given me by Mayberry, Mr M, Sumors, Mr G, Stephens, Mr R. Morris and Mr J-S. Fry, Crendon Farms, Donnybrook. REFERENCES BROWN, J-G., PETERSON, D.W. and FOOTE, W-D. (1972). J, Anim. Sci. 35:362, CARRICK, M-J. and ROBERTSON, D.E. (1980). Proc. Aust. Soc. Anim. Prod, 13:505. HOAGLAND, T.A. and BARNES, M.A. (1984). Theriogenology 22:247. MORRIS, CA. (1980). Anim. Breed. Abstr. 48:655. MUNRO, R-K. and MOORE, N.W. (1985). Aust. Vet, J. 62:228. PETERS, A-R. (1982). Vet. Rec. 110:515. ROCHE, J-F. (1976). Wld. Rev. Anim, Prod, 12:79. 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