Testicular development in Dorper, DOhne Merino and crossbred rams

Abstract

Testicular development from 3 to 14 months of age was examined in Dorper (DD), Dohne Merino (DM) and crossbred (Meatmaster; MM) rams. Testicular measurements included testis volume (TV), diameter (TD), length (TL) and scrotal circumference (SC). Soth TD and SC were highly repeatable and positively correlated with live body mass and other testicular measurements. Soth SC and TD showed significant breed differences (P<O,05) from 3 to 10 months of age which disappeared later on. Non-linear equations were fitted for testicular measurements on age for each breed group. Testicular growth pattems are more similar in the mutton breed types (DD and MM) and differfrom dual-purpose DM. This difference probably indicate earlier puberty in the DD and MM breeds. In an attempt to accountfor body size differences, a SC : live body mass ratio is recommended as a practical selection criterion. A more rapid decrease in this ratio is indicated in the DD and MM breeds compared to the DM, probably because of later puberty in the latter. Individual ratios within and between breed groups varied from 0,378 to 0,948 em/kg.

 Testisontwikkeling is tussen 3 en 14-maande-ouderdom in Dorper (DD), Dohnemerino (DM) en kruisings (Vleismeester; MM) ondersoek. Testismates hetvolume (TV), deursnee (TD),lengte (TL) en skrotumomtrek (SC) ingesluit. Seide TD en SC is hoogs herhaalbaar en positief met Iiggaamsmassa en ander testismaatstawwe gekorreleer. Seide SC en TD het betekenisvol (P<0,05) tussen rasse vanaf 3-tot 10-maande ouderdom verskil, waama geen betekenisvolheid aangetoon is nie. Nie-lineere vergelykings vir testismates op ouderdom is vir elke ras gepas. Die patroon van testisgroei stem meer ooreen tussen die vleistipes (DD en MM) en verskil van die dubbeldoel-DM. Hierdie verskil is moontlik die gevolg van vroeer puberteit by die DD en MM. In 'n poging om die effek van verskille in liggaamsgrootte te oorkom is 'n SC : lewendemassa-verhouding as 'n moontlike praktiese seleksiemaatstaf aanbeveel. 'n Vinniger afname in hierdieverhouding is in die DD en MM in vergelyking met die DM aangedui, waarskynli k as gevolg van later pUberteit in die geval van laasgenoemde. Individuele verhoudings binne en tussen groepe het vanaf 0,378 tot 0,948 em/kg gevarieer.

Keywords: Testicular development, repeatability, Dorper, Dohne Merino, crossbred, rams