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L. Selwood and F. McCallum

Summary. Twenty-six female brown marsupial mice in a laboratory colony were mated at intervals ranging from 1 to 20 days between coitus and ovulation. The numbers of corpora lutea and normal embryos were counted.

A multiple regression model examined the parabolic relationship between the proportion of normal embryos and the time from coitus to ovulation. The proportion of normal embryos increased until a mean of 9·5 days and decreased thereafter. This relationship was independent of the year of breeding and the number of corpora lutea. After survival of spermatozoa for up to 13 days in the female reproductive tract, the fertility levels of females was 88–92%. Low fertility levels after 13 days appeared to be due to a decrease in the number of spermatozoa.

Reproductive tracts from 7 females killed after insemination and examined histologically showed many spermatozoa in the isthmus of the oviduct and the uterus at 5 days post coitum; spermatozoa confined to the isthmus between 6 and 13 days; and few spermatozoa in the isthmus at 14 days after copulation.

A comparison between the fertility levels in the females which had been inseminated once and a further 17 females which had been inseminated 2 or 3 times suggested that spermatozoa from 2nd and 3rd inseminations can contribute spermatozoa for fertilization. In these females fertility levels did not decline with time after the first mating.

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C. Lindsay, H. J. Staines, P. McCormick, C. McCallum, F. Choulani and G. J. Wishart

Semen collected from 3-year-old male Houbara bustards contained large proportions (6–40%) of spermatozoa with large nuclei. In these spermatozoa, the length of the nucleus was up to twice the mean length of the nucleus in normal spermatozoa. The lengths of the acrosome, midpiece and flagella were all normally distributed, but the length of the nucleus formed a bimodal distribution. The proportion of spermatozoa with large nuclei varied among males, but not among different semen samples collected from the same male throughout the breeding season. The proportion of motile spermatozoa with large nuclei was half that of normal spermatozoa, but their velocity was significantly greater. After insemination into females, spermatozoa with large nuclei were observed in the outer perivitelline layer of eggs laid, indicating that they were stored and transported within the oviduct and reached the egg at about the time of fertilization. Furthermore, there was no difference in the ability to produce viable progeny in females that were mated with males producing greater proportions of spermatozoa with large nuclei compared with those producing 'normal' spermatozoa. Thus, the abnormal spermatozoa did not appear to impede fertility. There were no signs of triploidy in the males that produced spermatozoa with large nuclei, or in their progeny, as demonstrated by the size of erythrocytes. Therefore, it appears that the spermatozoa with large nuclei were the result of aberrant spermatogenesis.