U.S. Department of Agriculture: Agricultural Research Service, Lincoln, Nebraska
Date of this Version
1983
Abstract
The major advances over the past 25 yr in male reproductive physiology of cattle, sheep, swine and horses are reviewed. Those findings which have allowed efficient culling of subfertile males and exploitation of the reproductive capacity of genetically superior sires are emphasized.
Hormones secreted by the male gonad early in gestation induce regression of potentially female structures and development of the male reproductive tract. Compartmentalization of the testis and formation of the bloodtestis barrier during prepubertal development permit the steroidogenic and gametogenic activities of the adult testes to proceed normally. The role of the central nervous system, hypothalamus and anterior pituitary in regulation of the endocrine and exocrine functions of the testes are discussed in view of the physiological constraints and reproductive requirements of the domestic male. The relationships among testes size, the efficiency of spermatogenesis and daily spermatozoal production are discussed. Ignorance about epididymal function and the physiology of spermatozoal maturation are mentioned. Successful techniques have been developed and applied to the extension and preservation of genetically superior bovine sperm, but similar success and exploitation has not been achieved in other species. A better understanding of the biochemical and biophysical differences among sperm from domesticated animals should enable development of procedures for successful extension and cryopreservation of sperm from the boar, ram and stallion. This would allow producers to make more efficient use of genetically superior sires.
Artificial insemination of beef cattle and sheep is likely to increase, but not to the extent achieved for dairy cattle or swine. Most sheep and beef cattle probably will continue to be bred by natural mating under conditions which maximize the utilization of forage but which make difficult, or preclude, application of high technology management practices. Sires used for natural mating routinely will undergo a breeding soundness examination. By the year 2,000, spermatozoal motility, velocity and concentration probably will be measured by dipping a fiber optic probe into a semen sample. However, visual examination of semen quality still will require a phase contrast microscope. Insemination of frozen semen enriched in sperm bearing either the X- or the Y-chromosome, with at least 80% offspring of the desired sex, is likely within the next 20 yr. Application of sexed semen in commercial dairy herds will be common, but its impact on other species of livestock may be marginal.
An expanded array of options for management of sires will be available to the livestock producer in the next decade. The greatest impact of those technologies will be on dairy cattle and swine. Future sires may be conceived as a result of planned matings accomplished by artificial insemination followed by sexing and splitting of embryos, transfer of desirable embryos to appropriate recipients, and possible manipulation of reproductive development before or after birth. A better understanding of factors controlling sexual behavior should enhance the usefulness of sires used for natural matings or in artificial insemination centers. Manipulation of the seasonal pattern in sperm production of rams and stallions also will be commonplace.
Comments
Published in Journal of Animal Science (1983) 57:2, 380-403