Interrelationships of porcine X and Y chromosomes with pituitary gonadotropins and testicular size

Endocrine and testicular responses to unilateral castration on 1, 10, 56, o r 112 days of age were characterized in 132 Chinese Meishan (MS) x White co mposite (WC) crossbred boars in which testicular size associates with a qua ntitative trait locus (QTL) on X chromosome. At 220 days of age, testicles of boars unilaterally castrated on Day I or 10 weighed more and had greater total daily sperm production (DSP) than one testicle of bilaterally intact boars (P < 0.05); compensation did not double these two responses. Boars w ith MS alleles at the X chromosome QTL had smaller testicles, darker colore d parenchyma, and lower total DSP than boars with WC alleles (P < 0.05). Th e MS alleles engendered greater (P < 0.05) plasma FSH and LH during puberty than WC alleles. Plasma FSH increased (P < 0.05) within 48 h of unilateral castration on Days 1, 10, and 56. Subsequent increases occurred earlier du ring puberty (P < 0.05) after unilateral castration at younger ages than af ter unilateral castration at older ages. Pubertal increases in plasma FSH a nd LH were greater (P < 0.05) in boars with MS alleles than in those with W C alleles for the X chromosome QTL. Breed of Y chromosome had no effect on testicular traits, FSH, testosterone, or estrone. For LH, boars with an MS Y chromosome had greater (P < 0.01) plasma LH across all ages than boars wi th a WC Y chromosome. We conclude that a gene or groups of genes that resid e on the porcine X chromosome regulate testicular development and pubertal gonadotropin concentrations.