34
NEW ZEALAND VETERINARY JOURNAl
Sir,-Following synchronisation of oestrus in ewes with a synthetic prostaglandin (PG; ICI 80996) there has been premature regression of corpora lutea (CL's) in some animals()) and a return to oestrus within 4 -1 days. The cause and incidence of this phenomenon is unknown. In a comparison of various methods of synchronisation, breeding-season II) observations were made on the timing and incidence of these short returns and the fertility of ewes to matings at this oestrus and at any subsequent oestrus. Eighty ewes were treated with two injections of 125 mcg PG, 10 days apart. Harnessed vasectomised rams ran with ewes immediately after the first injection of PG and, 2 days after recording of oestrus, ewes were placed with other vasectomised rams with a different coloured crayon in the mating harness to record any recurrent oestrus within the next 6 days. Following the second injection of PG entire rams were joined with ewes in a similar sequence. If a recurrent oestrus was recorded within 1 days of a preceding oestrus, after either the first or second injection ofPG, a laparotomy was carried out within 2 days. The age ofCL's was estimated on the basis of size and colour ll, and follicular activity noted. Ewes were run with entire rams for 23 - 29 days after the second PG. After the first injection of PG two ewes were again marked by vasectomised rams, one at 2 and the other at 4 days after the synchronised, or first recorded, oestrus. The ewe re-marked after 2 days had one CL 3 -4 days old, coinciding with ovulation at the first recorded oestrus. This animal was not mated at all following the second PG or in the subsequent mating period. The other ewe had not ovulated after the first PG injection and still had not ovulated at the time of laparotomy. After the second PG in jection this ewe did not synchronise but showed oestrus II days later and conceived normally. After the second PG injection a further 1 ewes returned 4-1 days after the synchronised oestrus. There appeared to be CL's of two different ages present on the ovaries of six of these ewes. The other ewe, which returned 4 days after the previous recorded oestrus, had not ovulated at either oestrus, but had a pre ovulatory follicle and conceived to mating at the timeofthe short return. In the six ewes, evidence of early regression ofCL's that were not fully developed was apparent, as they were small and pale pink in comparision with the more recent small red haemorrhagic CL's which appeared to correspond with the recurrent oestrus. Of five of these ewes present at lambing, three were barren and two apparently conceived to the ovulation at the time of the short return. Conception rates of ewes synchronised with PG's were con siderably lower than in control ewes II, and the occurrence ofthe short returns contributed to this result. The premature regres sion of CL's and apparent subsequent infertility in some ewes needs further definition but may occur when oestrus in ewes is controlled by PG's. A. J. Allison Invermay Agricultural Research Centre Mosgiel
13th December 1977
References (l) Allison. A. J. and Kelly. R. W. (1978): Synchrotlisalion of_aDd renility ill sheep lRIIled
with ptogestag_impregnated int,avaginal spooges and subcutaneous implanls, and prostaglandins with or without Pregnant Mare's Serum. N.Z. J. DF. Res. (submitted). (2) Restall. B. J. (1964): The growth and retrogression or the corpus luteum iIItbe ewe. AIISI. J. ~xp.
Agrit. Anim. Hush.• 4: 274.
(lITeMt. H. R.; Allison.A.I.; Smitb.l. f.; Harvey. T. M.and Havik.P.G.(1976): Egtransfers
.n exotIC sb«p. Prot:. N.Z. Soc. Anim. Prod. 16: 67.
NEW ZEALAND VETERINARY JOURNAl
Sir,-Following synchronisation of oestrus in ewes with a synthetic prostaglandin (PG; ICI 80996) there has been premature regression of corpora lutea (CL's) in some animals()) and a return to oestrus within 4 -1 days. The cause and incidence of this phenomenon is unknown. In a comparison of various methods of synchronisation, breeding-season II) observations were made on the timing and incidence of these short returns and the fertility of ewes to matings at this oestrus and at any subsequent oestrus. Eighty ewes were treated with two injections of 125 mcg PG, 10 days apart. Harnessed vasectomised rams ran with ewes immediately after the first injection of PG and, 2 days after recording of oestrus, ewes were placed with other vasectomised rams with a different coloured crayon in the mating harness to record any recurrent oestrus within the next 6 days. Following the second injection of PG entire rams were joined with ewes in a similar sequence. If a recurrent oestrus was recorded within 1 days of a preceding oestrus, after either the first or second injection ofPG, a laparotomy was carried out within 2 days. The age ofCL's was estimated on the basis of size and colour ll, and follicular activity noted. Ewes were run with entire rams for 23 - 29 days after the second PG. After the first injection of PG two ewes were again marked by vasectomised rams, one at 2 and the other at 4 days after the synchronised, or first recorded, oestrus. The ewe re-marked after 2 days had one CL 3 -4 days old, coinciding with ovulation at the first recorded oestrus. This animal was not mated at all following the second PG or in the subsequent mating period. The other ewe had not ovulated after the first PG injection and still had not ovulated at the time of laparotomy. After the second PG in jection this ewe did not synchronise but showed oestrus II days later and conceived normally. After the second PG injection a further 1 ewes returned 4-1 days after the synchronised oestrus. There appeared to be CL's of two different ages present on the ovaries of six of these ewes. The other ewe, which returned 4 days after the previous recorded oestrus, had not ovulated at either oestrus, but had a pre ovulatory follicle and conceived to mating at the timeofthe short return. In the six ewes, evidence of early regression ofCL's that were not fully developed was apparent, as they were small and pale pink in comparision with the more recent small red haemorrhagic CL's which appeared to correspond with the recurrent oestrus. Of five of these ewes present at lambing, three were barren and two apparently conceived to the ovulation at the time of the short return. Conception rates of ewes synchronised with PG's were con siderably lower than in control ewes II, and the occurrence ofthe short returns contributed to this result. The premature regres sion of CL's and apparent subsequent infertility in some ewes needs further definition but may occur when oestrus in ewes is controlled by PG's. A. J. Allison Invermay Agricultural Research Centre Mosgiel
13th December 1977
References (l) Allison. A. J. and Kelly. R. W. (1978): Synchrotlisalion of_aDd renility ill sheep lRIIled
with ptogestag_impregnated int,avaginal spooges and subcutaneous implanls, and prostaglandins with or without Pregnant Mare's Serum. N.Z. J. DF. Res. (submitted). (2) Restall. B. J. (1964): The growth and retrogression or the corpus luteum iIItbe ewe. AIISI. J. ~xp.
Agrit. Anim. Hush.• 4: 274.
(lITeMt. H. R.; Allison.A.I.; Smitb.l. f.; Harvey. T. M.and Havik.P.G.(1976): Egtransfers
.n exotIC sb«p. Prot:. N.Z. Soc. Anim. Prod. 16: 67.
