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A note on oestrous response toprogesterone treatment in NewZealand romney ewesI. A. Cumming a b & M. F. Mcdonald aa Sheep Husbandry Department , Massey University ,Palmerston Northb S. S. Cameron Animal Research Laboratory ,Werribee, Victoria , AustraliaPublished online: 12 Jan 2012.

To cite this article: I. A. Cumming & M. F. Mcdonald (1967) A note onoestrous response to progesterone treatment in New Zealand romneyewes, New Zealand Journal of Agricultural Research, 10:2, 316-318, DOI:10.1080/00288233.1967.10425139

To link to this article: http://dx.doi.org/10.1080/00288233.1967.10425139

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316

A NOTE ON. OESTROUS RESPONSE TO PROGESTERONE TREATMENT IN NEW ZEALAND

ROMNEY EWES

By 1. A. CUMMING*t AND M. F. McDONALD*

(Received 21 December /966)

ABSTRACT

Daily injections of iOmg of progesterone into 319 Romney ewes for 13~ 15 days just before the onset of the normal breeding season induced ovulation in all animals. Oestrus also occurred in 65% of the sheep.

Most ewes studied returned to oestrus about 16 days after the in-duced ovulation and regular cycles were initiated.

INTRODUCTION Synchronisation of oestrus in ewes following treatment with

progesterone or its analogues has been reviewed by Lamond (1964). With New Zealand Romney ewes, treatments during the breeding season are effective in synchronising oestrous cycles (Clarke, Roberts. Carter, and Kirton 1966) but less successful in the induction of breeding during the anoestrous season (Raeside and Lamond 1956; McDonald 1961). The results of treatments just before commencement of the normal breeding season are of interest in view of attempts to advance the time of mating or to ensure one or more oestrous cycles before mating at the usual time for a breed within a district.

MATERIALS AND METHODS

Four- to six-year-old Romney ewes drawn from flocks of Massey University (Groups A and B) and from a commercial property in the same district (Groups C and D) were used during February-April in either 1964 or 1965. Ewes were identified by ear tags and numbers branded on their sides. The animals grazed predominantly ryegrass-white clover pasture and were managed to maintain constant body-weight. Liveweights were recorded weekly (1964) or fortnightly (1965) .

Treatments with progesterone were commenced over a 12-day period from approximately 18 February in both years. Progesterone was given as 13-15 daily i.m. injections (at 9 a.m.) each of 10 mg in 1 ml arachis oil. Vasectomised rams fitted with Sire Sine harnesses * Sheep Husbandry Department, Massey University, Palmerston North. t Present address: S. S. Cameron Animal Research Laboratory, Werribee,

Victoria, Australia.

N.Z. Jl agric. Res. (1967), 10: 316~8

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I. A. CUMMING AND M. F. McDoNALD 317

were with all ewes from a week before treatment until after oestrus or "silent" oestrus had occurred. Observations for mating marks were made daily during progesterone treatment and each 12 hours following cessation of the injections.

RESULTS AND DISCUSSION

The numbers of ewes treated and the incidence of oestrus within 6 days of the final injection of progesterone are shown in Table 1. As it was suspected that ovulation might have occurred in the ewes not experiencing oestrus, laparotomies were conducted on two ewes estimated to be about 5 days after the possible "silent" oestrus. In each animal there was one corpus luteum which from its appearance suggested it to be the result of an ovulation approximately 3 days earlier. In the remainder of the sheep. laparotomies performed (in connection with other experiments) about 22 days after progesterone treatment revealed regressing corpora lutea consistent with ovulation some 19 days earlier. Thus, while the oestrous response to progesterone given at this period just before the start of the normal breeding season (e.g. Goot 1949) was low, nevertheless the effect of the hormone was sufficient to induce ovulation in nearly all animals examined. The reason for the failure of oestrus to occur in a high proportion of ewes in spite of what was thought to be adequate progesterone priming (i.e. 10 mg daily for 13-15 days) is not clear. Further studies involving treatment of ewes with higher daily doses of progesterone are indicated. Never-theless these results with progesterone alone are very much better than those achieved with Romney ewes treated during deep anoestrus (Raeside and Lamond 1956; McDonald 1961).

The occurrence of oestrus after progesterone in ewes in groups C and D (each of 50 ewes) was 48% and 68% respectively (p < 0.05). These sheep were obtained from a commercial flock two months before study in 1964, and were selected for differences in average liveweight (group C: 118 -+- 7.2 lb; group D: 97 :t:: 4.6 lb). The remaining 58 ewes in 1964 (group A) and all in 1965 (group B) were animals

TABLE 1. OestrollS response in Romney ewes fol/owing progesterolle trca/ment

Season Number of Observation Percentage <?f ~wesl Bodyweight (lb)

ewes treated wlthm (M a + S E) I

the season ! e n - .. ,

,

1964 158 Oestrus 62.0 I 110.2 ± 0.12 I

"Silent" oestrus 38.0 , 114.1 ± 0.22

1965 161 Oestrus 67.7 123.8 ± 0.13

"Silent" oestrus 32.3 124.6 ± 0.34

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318 Oestrous response to progesterone

allocated to the study without any restnctIOn as to liveweight. The pooled data for bodyweights of all ewes as presented in Table 1 show that within each season the mean weights of ewes in oestrus were less than those of animals with "silent" oestrus. Analysis of variance revealed the differences were not statistically significant.

The interval from last progesterone injection until onset of oestrus varied from 48 to 144 hours (mean 80 hours) and is similar to that reported for other breeds (Lamond 1964). There was a weak relation-ship between the liveweight of the ewe and the interval to oestrus after treatment (r = 0.38; p < 0.01).

Observations for oestrous behaviour and ovulation were made on 160 of the ewes over several weeks following treatment, and oestrous cycles commenced in 97% of the sheep. For ewes which exhibited oestrus soon after progesterone, the length of first cycle was 16.5 days. Thus it is clear that induction of ovulation in Romney ewes just before the start of the breeding season will be followed by regular cyclic breeding activity.

REFERENCES CLARKE, 1. N.; ROBERTS, E. M.; CARTER, A. H.; KIRTON, A. H. 1966:

Hormonal synchronization of oestrus in Romney ewes during the breeding season. Proc. N.Z. Soc. Anim. Prod. 26: 107-21.

GOOT, H. 1949: Studies on some New Zealand Romney Marsh stud flocks. III. Tupping season. N.Z. I. Sci. Technol. 30A: 330-44.

LAMOND, D. R. 1964: Synchronization of ovarian cycles in sheep and cattle. Anim. Breed. A bstr. 32: 269-85.

McDoNALD, M. F. 1961: Studies of the response of the anoestrous ewe treated with progesterone and pregnant mare serum. I. agric. Sci. Camb. 56: 397-406.

RAESIDE, J. 1.; LAMOND, D. R. 1956: Effects of progesterone and pregnant mare serum (PMS) administration in the anoestrous ewe. r. Oestrus, ovarian changes, and gonadotrophic potency of the pituitary gland. Aust. I. agric. Res. 7: 591--600.

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