Puberty and ovulation rate of Romanov, Dorper, and their crosses during the first breeding season

Abstract

Six Dorper (D), 21 Romanov (R), 50 3/4D x 1/4R, 53 1/2D x 1/2R, and 46 1/4D x 3/4R ewe lambs, born over a six-week period in October/November 1989, were teased twice daily from weaning during 1990 until they showed no further signs of oestrus. Ovulation rate was determined laparoscopically three to four days after the cessation of oestrus. Age of the dam had a significant (P < 0.01) effect on mass and age at first oestrus, but had no significant effect on ovulation rate of the ewe lambs. Dorper ewe lambs were the heaviest and oldest at the end of the breeding season, but none completed three oestrous cycles. Fifty per cent of the 3/4D X 1/4R, 66% of the 1/2D X 1/2R, 74% of the 1/4D X 3/4R, and 71% of the Romanov genotypes completed three oestrous cycles. Genotype had a significant (P < 0.01) effect on age and mass at first oestrus and also on ovulation rate. An increase in the percentage Romanov genes resulted in a decrease in ewe mass and an increase in ovulation rate. The mean age of ewe lambs over the first three oestrous cycles decreased up to the 1/2D X 1/2R genotype, but increased again with a further accruement of Romanov genes.

Ses Dorper(D)-, 21 Romanov(R)-, 50 3/4D X 1/4R-, 53 1/2D X 1/2R-, en 46 1/4D X 3/4R-ooilammers, gebore oor 'n periode van ses weke in Oktober/November 1989, is tweemaal daagliks gedurende 1990 gekoggel totdat geen teken meer van estrusaktiwiteit waargeneem is nie. Drie tot vier dae later is ovulasietempo van die ooie wat estrus vertoon het, laparoskopies bepaal. Ouderdom van die moeder het 'n betekenisvolle (P < 0.01) invloed op massa en ouderdom by eerste estrus van die lammers gehad. maar nie op ovulasietempo nie. Dorperlammerooie was die swaarste en die oudste aan die einde van die teelseisoen, maar geen Dorperooi het drie estrussiklusse voltooi nie. Drie estrussiklusse is wel deur 50% van die 3/4D X 1/4R-, 66% van die 1/2D X 1/2R-, 74% van die 1/4D X 3/4R- en 71% van die Romanov-genotipes voltooi. Genotipe het 'n betekenisvolle (P < 0.01) invloed op ouderdom en massa by eerste estrus, en op ovulasietempo gehad. 'n Verhoging in die persentasie Romanovgene het gelei tot 'n verlaging in ooimassa en 'n toename in ovulasietempo. Die gemiddelde ouderdom van ooilammers oor die eerste drie estrussiklusse het afgeneem tot by die 1/2D X 1/2R-genotipe, waama dit weer toegeneem het met 'n verdere toename in Romanov-gene.

Keywords: Crosses, Dorper, ovulation rate, puberty, Romanov.