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The Effect of Sex on the Development of the Pig

IV. Histological and Endocrinological Studies of the Boar¹

University of Minnesota

Abstract

1. The sexual development of boars of lines of inbred swine has been studied by the assay of urinary 17-ketosteroids at various ages, and by the measurement of the rate of testicular growth and seminiferous development.
   
2. Differences among lines were found in the amount of male hormones (17-ketosteroids) excreted in the urine and in the rate of increase in the weight of testes, numbers of spermatogonial cells, and numbers of primary spermatocytes. Differences were also found in the diameters of the interstitial cells.
   
3. Sexual desire of boars, as a line characteristic, was found to have considerable relationship to the excretion of 17-ketosteroids by the line.
   
4. The various lines were found to illustrate the independent occurrence of factors usually associated with sexual development: age of appearance of ranting, degree of sex drive, development of secondary sex characteristics, and growth of seminiferous elements. Possible causes of these line differences were discussed.
   
5. Although it is possible to develop a line of swine which possesses both early sexual development and rapid, economical gains, breeders are still confronted with the problem of selecting individuals and trying to estimate the effects of the gonads on bodily growth and type.
   
6. When studying problems dealing with sexual maturity in boars, differences in the genetic constitution of the animals, in season of farrow, and in the season of the year in which the data are collected should be considered.
   

¹ Paper No. 2157, Scientific Journal Series of the Minnesota Agricultural Experiment Station, University Farm, St. Paul, Minn. This study was conducted with animals produced in cooperation with the Regional Swine Breeding Laboratory, Ames, Iowa, Bureau of Animal Industry, U.S. Department of Agriculture.