Variation in Penis Development in Ram Lambs

Abstract

At birth the glans penis and processus urethra of the ram lamb are adhered to the preputial mucosa, the urethral process lying in a groove on the wall of the prepuce. The adhesions gradually break down as the lamb grows older so that the prepuce can be everted and the penis exposed. The developmental process can be divided in five fairly well defined stages which were scored as follows: (1) infantile condition, (2) urethral process free, (3) tip of glans penis free, (4) free to bottom of glans penis or slightly below and (5) adult condition. The stage of development was scored at weaning time, at ages of 91 to 155 days, in 1250 ram lambs born in 1951. Although developmental scores of 3 and 5 were found in lambs 91 and 103 days old respectively, the organs of a number of the oldest lambs examined were still in an infantile condition. There were significant breed differences in development; 278 Columbias and 359 Targhees, both weaned at an average age of 115 days, had mean scores of 2.45 and 2.37, respectively, while 613 Rambouillets, weaned at an average age of 125 days, had a mean score of only 1.87. Corresponding standard deviations for the three breeds were 1.32, 1.20 and 1.09. The coefficients of variation were higher in inbreds than in outbreds of the same breed in Columbias and Rambouillets but not in Targhees. Simple correlation coefficients of penis scores with other weanling traits were: age, 0.092**; inbreeding, −0.086*; weight, 0.440**; condition, −0.270**; staple length, 0.175**; and index, 0.308**. Lambs born and raised as singles and lambs born as twins but raised as singles had average penis scores of 2.30 and 2.32, respectively, while lambs born and raised as twins had an average score of 1.88. Lambs out of ewes 4 to 7 years old had slightly lower average scores than lambs out of 2- and 3-year-old ewes probably because a higher proportion of them were twins. Lambs from 8- and 9-year-old ewes had much lower scores than lambs from younger ewes. Heritability estimates obtained from half-sib correlations were quite variable for the various breeding groups. The estimate for Rambouillets was considerably higher than the estimate for Columbias and Targhees. An experiment conducted in 1952 indicates that the developmental process is under the control of the testis hormone. Development was arrested by castration and by the administration of the synthetic estrogenic hormone, dienestrol. Results of administering testosterone propionate to intact animals were inconclusive.