PROMOTING ACCESS TO AFRICAN RESEARCH

South African Journal of Animal Science

Log in or Register to get access to full text downloads.

Remember me or Register



The repeatability of reproduction rate in the Tygerboek Merino Dock

S.W.P. Cloete, H.J. Heydenrych

Abstract


The repeatability of reproduction rate at 2 years or up to 3 years of age was investigated by regression methods considering subsequent reproduction averaged over a number of lambing opportunities or within sUbsequent age groups. Results from the study suggested multiple birth rate at 2 years of age to be more repeatable than conception rate. SUbsequent differences in lambs born/ewe mated (Lb/Em), derived from an initial difference of one lamb at 2 years of age, were approximately twice as large between one and two lambs born (0,20) than between no and one lamb born (0,11). The culling of all the barren ewes at 2 years of age would not improve Lb/Em in the current flock sUbstantially, whereas the proportion of ewes bearing multiples at 2 years was too low to supply replacement requirements. Differences in the subsequent rearing performance of ewes rearing no or one lamb or one or two lambs at 2 years of age were apprOXimately of the same magnitude (0,15 and 0,17). The culling of all the ewes rearing no lambs at 2 years was associated with moderate gains in rearing performance in the current flock. The subsequent reproduction of ewes barren up to 3 years was considerably lower than in ewes conceiving at least once. Expected gains in the current flock by cUlling the former ewes are limited by the small proportion of ewes in this category (0,03). Comparable results were obtained for ewes rearing no lambs up to 3 years of age. Ewes bearing or rearing at least one set of twins were more productive in subsequent years than their contemporaries. The utilization of modern techniques to accelerate gains in reproduction rate in the current flock and in future generations by techniques such as superovulation, embryo transfer and the manipulation of the fecundity threshold are discussed.

Die herhaalbaarheid van reproduksietempo op 2-jaar-, of tot op 3-jaar-ouderdom, is met regressiemetodes ondersoek met gemiddelde latere reproduksie oor 'n aantal lamgeleenthede of binne ouderdomsgroepe as afhanklike veranderlikes. VerkreEi resultate dui op 'n hoEir herhaalbaarheid vir meerlinggeboortes as vir besetting. Latere verskille in lammers gebore/ooi gepaar (Lb/Em) wat ooreenstem met 'n aanvanklike verskil van een lam op 2 jaar, was ongeveer dubbel so groot vir die verskil tussen een en twee lammers (0,20) as vir die verskil tussen geen en een lam (0,11). Die uitskot van aile droEi oole op 2-jaar-ouderdom sou nie Lb/Em In die huidige kudde noemenswaardig verhoog nie, terwyl die proporsle oole met tweelinge op 2 jaar te laag is om vervangingsbehoeftes te bevredig. Verskille in die latere speenpersentasle van ooie wat op 2 jaar geen of een lam of een of twee lammers gespeen het, was naastenby ewe groot (0,15 en 0,17). Die ultskot van ooie wat op 2 jaar geen lammers gespeen het nie, sou speenpersentasie in die huidige kudde tot 'n mate verhoog. Die daaropvolgende reproduksietempo van ooie wat tot op 3 jaar nie beset geraak het nie, was laer as by ooie wat minstenseen keer beset geraak het. Vordering In die huidlge kudde word egter beperk deur die lae proporsle ooie in hierdle kategorie (0,03). Vergelykbare resultate is verkry vir oole wat tot op 3 jaar geen lammers gespeen het nie. Oole wat minstens een tweeling gehad of gespeen het, was meer produktief in latere jare as hulle tydgenote. Die gebruik van moderne tegnieke soos superovulasie, embrio-oorplasing en die manipulasie van die drumpel vir meerlinggeboortes om vordering In die huidige kudde te versnel, word bespreek.

Keywords: Repeatability, reproduction rate, Merino sheep




AJOL African Journals Online