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P. J. BURFENING and J. L. VAN HORN

Induction of fertile oestrus during the anoestrous season in mature lactating and dry ewes is possible with the proper sequence of hormone treatments. Wagner (1964) found 0·5 or 1·0 mg of 6-chloro-6-dehydro-17α acetoxyprogesterone (CAP) per head per day in the feed for 16 days and 1000 i.u. pregnant mare's serum gonadotrophin (pmsg) injected 36 hr and 18 days later to be effective in producing fertile matings. The best regimen resulted in 77% of the treated ewes lambing. Hansel (1964) observed that treating lactating Western White-faced ewes with 750 i.u. of pmsg on Days 1 and 15 and feeding 60 mg of 6-methyl-17-acetoxyprogesterone (MAP) daily from Days 7 to 14 resulted in 65% of the treated ewes lambing. Hulet & Foote (1967), testing various combinations of CAP, MAP and pmsg on dry and

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P. J. BURFENING and L. C. ULBERG

Summary.

Following a preliminary experiment, split ejaculates of rabbit semen, incubated for 3 hr at 38° or 40° C, were examined and inseminated separately into the uterine horns of rabbits mated 4 hr previously to vasectomized males. Eggs were recovered and examined for evidence of fertilization 30 hr post coitum. Following return of the eggs to the oviduct their survival was estimated by counting the implantation sites at 9 days post coitum. There was no evidence of any effect of treatment temperature on fertilizing capacity of semen, but embryonic survival rate was higher (75%) in horns inseminated with semen incubated at 38 ° C than in those inseminated with semen incubated at 40° C (53%). Neither fertilization rate nor embryonic survival rate was significantly correlated with semen quality.

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H. Cardenas, J. G. Berardinelli, P. J. Burfening and R. Adair

The objective of this study was to determine whether gross or histomorphological components of the testes, capacity and dissociation constants (K d) of testicular oLH and hCG receptors, and gonadotrophin-stimulated testosterone secretion in vitro differed among Rambouillet rams from lines selected for low or high female reproductive rate and from rams of a random-bred control line. Lines had been selected for approximately 20 years. Data were collected from 22-month-old rams during the late breeding season. Rams among lines did not differ (P > 0.05) in gross testicular characteristics or most histomorphological characteristics. However, the percentage volume of interstitial vascular tissue was greater (P < 0.05) for rams from lines selected for low female reproductive rate than for rams from lines selected for high female reproductive rate. Receptor sites per Leydig cell and binding capacities of oLH and hCG receptors per testis, per gram of parenchyma, and per milligram of membrane protein did not differ (P > 0.05) among lines. The K d values for oLH and hCG receptors did not differ (P > 0.05) among lines; however, receptor sites per Leydig cell, capacities of testicular parenchyma to bind gonadotrophin and K d values were higher (P < 0.05) for oLH than for hCG receptors. Total oLH- and hCG-stimulated testosterone secretion in vitro did not differ (P < 0.05) among lines. In conclusion, selection for or against reproductive rate in Rambouillet ewes has not altered gross or most histomorphometric characteristics of the testes of male offspring, with the exception that selection against reproductive rate increased the proportion of testicular volume occupied by vascular tissue within the interstitium. Furthermore, selection has not altered total oLH- and hCG-stimulated testosterone secretion in vitro or the affinity and capacity of oLH and hCG receptors of the testes of male offspring.