Date of this Version
Body, testis, and epididymis weights were recorded and homogenization-resistant sperm nuclei were counted to determine daily sperm production and the number of sperm stored within the cauda epididymis (CAUDASP) in 145 boars of a control line (C) and 128 boars of a line selected for increased predicted weight of testis (TS) at 150 d of age. Random samples of boars were evaluated at five ages between 70 and 450 d in Generation 8 and 15 ages between 70 and 296 d in Generation 9. Data were analyzed using an animal model that included the fixed effect of line and the linear, quadratic, and cubic effects of age. Variance components were estimated using a DFREML algorithm. Boars of the TS and C line did not differ in body weight (P > .05) in Generation 8. In Generation 9, boars of line TS were heavier between 118 and 198 d of age (P < . 00l ) ; thereafter, body weights of the lines were similar (P > .05). The increase in organ weights for the testes and epididymides between 70 and 160 d of age were greater (P < .01) for boars of line TS in each generation, and differences between the lines in testis weights established around puberty were maintained at 450 d of age. Daily sperm production and CAUDASP increased more rapidly at younger ages and plateaued at greater values (P < .05) in boars of line TS. At ages less than 200 d, boars of line TS produced more sperm per gram of parenchyma than control boars. Selection for greater predicted weight of paired testes resulted in increased body weight at younger ages, increased daily sperm cell production at all ages, and larger numbers of sperm stored in the cauda epididymis of young boars.