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THE RELATIONSHIP BETWEEN NUMBERS OF SPERMATOZOA INSEMINATED AND FERTILIZATION RATE OF OVA IN EWES TREATED WITH FLUORO-PROGESTAGEN INTRAVAGINAL SPONGES IN SUMMER AND AUTUMN

Summary.: Two experiments were conducted, during December and March, designed primarily to determine the oestrous response and fertilization rate following the insemination of varying numbers of spermatozoa in ewes treated with intravaginal sponges impregnated with Cronolone, a synthetic progestagen. The main results were:

1. Incidence of oestrus: December; (a) treated ewes, 45·7%; (b) untreated teased ewes, 47·5%; (c) untreated non-teased ewes, 30·0%; March; (d) treated ewes, 94·8% (a versus b, NS; a versus c, P < 0·01; a versus d, P < 0·001).
   
2. Peak incidence of oestrus after withdrawal of sponges: December, 72 hr; March, 48 hr (P < 0·001).
   
3. Overall percentage of ewes which yielded fertilized ova: December, 64·3; March, 83·2 (P < 0·001).
   
4. Numbers of spermatozoa and fertilization in treated ewes: December, linear increase in percentage of ewes fertilized, with increasing sperm numbers, from 44·0% (300 x 10⁶ spermatozoa) to 76·0% (1500 x 10⁶ spermatozoa); March, no effect of numbers of spermatozoa, with 83·2% ova fertilized (100 to 1500x 10⁶ spermatozoa).
   
5. Number of spermatozoa and fertilization in untreated versus treated ewes: December (300x 10⁶ spermatozoa); untreated, 43·3%, treated 44·0% (NS); March (100 to 1500x 10⁶ spermatozoa); untreated 78·8%, treated 83·2% (NS).
   
6. Effect of breed of ram on percentage of treated ewes fertilized in December: Merino, 75·6%, Border Leicester, 47·5% (P < 0·001). Similar differences were observed in untreated ewes.
   
7. In both December and March, 21·4% of fertilized ova showed unequal cleavage or anuclear fragmentation.
   

1. 8. The estimated mean numbers of spermatozoa recovered from the Fallopian tubes of progestagen-treated and untreated ewes 24 hr after the insemination of 300 x 10⁶ spermatozoa were 807 and 5019 (P < 0·001).