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The Effect of Sex on the Development of the Pig. I. Differences in Growth between Boars and Barrows by Lines of Breeding¹

University of Minnesota

Abstract

A total of 86 boar-barrow pairs were measured every four weeks from eight weeks until 24 weeks old or 220 pounds in weight.

Nineteen of the pairs were Minn. No. 1 hogs (an inbred line being developed from a Landrace-Tamworth crossbred foundation), and the other 67 pairs belonged to six different inbred lines of Poland China hogs.

No significant differences were found between the inbred Poland China lines in their response to the presence and absence of testes, but the Poland China and Minn. No. 1 hogs differed significantly. The Minn. No. 1 hogs showed both earlier and greater sex differences than the Poland China hogs.

Both the Minn. No. 1 and Poland China boars differed from their barrow mates. Each of these differences was small (especially for the Poland Chinas), so small that it is questionable if the eye could detect each difference if taken independently. It appears that the differences tend to accentuate one another.

It appears that the testes first accelerate increased weight but that at puberty some other factor enters in and has a depressing effect.

¹ Paper No. 1941, Scientific Journal Series of the Minnesota Agricultural Experiment Station in cooperation with the Regional Swine Breeding Laboratory, Ames, Iowa, Bureau of Animal Industry, U. S. Department of Agriculture.