On some Factors controlling Fertility in Domestic Animals

Abstract

After a consideration of the ways in which the fertility of domestic animals is controlled some of the factors which limit it have been investigated. Various circumstances control the number of ova shed at each heat period. Data are presented which show that the low fertility of young as compared with adult sows is due to the fact that not so many ova are shed at each period.Counts have been made of the number of corpora lutea present in the ovaries and number of foetuses present in the uteri of pregnant rabbits and pigs. The results show that many more ova are shed at the heat period than young are produced at birth. Some ova possibly may be lost but many after fertilization atrophy at some period of their development and undergo absorption in utero.While the occurrence of atrophic foetuses only causes reduced fertility in animals which have many young at birth yet their occurrence in animals producing only one young would give rise to sterility so that the problem of the cause of the atrophy becomes an important one.Investigation points to the conclusion that the atrophy is not bacterial in origin since frequently healthy and atrophic foetuses lie side by side in the uterus. Moreover no bacteria could be found either in the foetus or foetal membranes.Evidence is given to show that nutrition cannot be the cause of the atrophy although it may affect to a certain extent the size of the young.No conclusion has yet been arrived at as to the cause of the atrophy, and the several possibilities suggested are still under investigation.