Reproductive performance of commercial Merino, Dohne Merino and SA Mutton Merino flocks in the Southern Cape

Abstract

Data of 23 189 Merino ewes (8 farms), 7692 Dohne Merino ewes (3 farms) and 2399 SA Mutton Merino ewes (1 farm) were recorded for the 1988-1991 lambing seasons. The udders of ewes present at lamb marking were inspected to differentiate between barren (unlambed), lambed and lost (lambed ewes suckling no progeny), and wet (lambed and suckling ≥ 1 lamb) ewes, using the 'wet and dry' technique. The lambs present at lamb marking were counted, and information regarding number of ewes mated and managerial inputs was recorded. The mean number of lambs marked as a percentage of ewes joined (Lm/Ej) was 87.7% for Merino flocks, ranging between 62.8-103.3%. Figures for Dohne Merino flocks were found to be similar, ranging between 75.6-113.2% Lm/Ej, with a mean of 92.6%, while Lm/Ej was 112.7% in the SA Mutton Merino flock. Between 72.2% (Merino) and 80.4% (SA Mutton Merino) of joined ewes suckled ≥ 1 lamb at lamb marking. Mean fecundity (estimated number of lambs born as a percentage of ewes lambed) was estimated at 121.6% for Merino ewes, 122.7% for Dohne Merino ewes and 140.2% for SA Mutton Merino ewes. Significant (P ≤ 0.05) differences in Lm/Ej occurred between Merino and Dohne Merino ewes stocked on different farms. It was attempted to relate these differences to managerial practices (flock size at mating, mating period, percentage of rams, the use of vasectomized rams, the use of ultrasonic scanning, and management at lambing). Increasing flock sizes tended to be associated with a decline in Lm/Ej. Reproductive efficiency within flocks was independent of the other managerial practices. Ewes which failed to suckle ≥ 1 lamb to lamb marking during 1988 -1990 were ear notched (marked). The mean levels of reproductive failure in marked ewes (groups with < 40 marked ewes were excluded) were compared with those of contemporaries without a history of reproductive failure within lambing years and farms. In 15 groups of Merino ewes where this procedure was followed, the number of ewes dry (the total of the unlambed and lambed and lost categories) as a percentage of ewes present at lamb marking (Ed/Epm) was 33.7% compared to 24.2% for the 15 groups of contemporaries of these ewes (P ≤ 0.05). In four groups of Dohne Merino ewes, Ed/Epm was 32.8% for marked ewes and 21.5% for their contemporaries (P = 0.06). It was concluded that there was scope for the improvement of the reproductive efficiency of local woolled sheep flocks. Selection against reproductive failure by using the simple 'wet and dry' technique appears to be a low-input method for the improvement of reproductive performance in commercial sheep flocks, at least in the current flock. Results from the literature suggest that such selection will also benefit future generations.

Data aangaande 23 189 Merino-ooie (8 plase), 7692 Dohne Merino-ooie (3 plase) en 2399 SA Vleismerino-ooie (1 plaas) is tydens die 1988-1991 lamseisoene aangeteken. Die uiers van ooie is by merk van lammers ondersoek om tussen onvrugbare (nie gelam), gelam en alle nageslag verloor (wel gelam, maar laat geen lammers suip nie) en produktiewe (gelam en laat suip ≥ 1 nageslag) ooie te onderskei, deur die eenvoudige 'soog en droog'-tegniek te gebruik. Die aantal lammers beskikbaar by merk is getel, en inligting oor aantal ooie gepaar en bestuursinsette is aangeteken. Die gemiddelde aantal lammers gemerk as 'n persentasie van ooie gepaar (Lm/Ej) was 87.7% vir Merinokuddes, met variasie tussen 62.8% en 103.3%. Ooreenstemmende syfers vir Dohne Merinokuddes het tussen 75.6 en 113.2% Lm/Ej gevarieer, met 'n gemiddelde van 92.6%, terwyl Lm/Ej vir die SA Vleismerinokudde 112.7% was. Tussen 72.2% (Merino) en 80.4% (SA Vleismerino) van gepaarde ooie het by merk ≥ 1 lam laat suip. Gemiddelde fekunditeit (beraamde aantal lammers gebore as persentasie van ooie gelam) is op 121.6% vir Merino's, 122.7% vir Dohne Merino's en 140.2% vir SA Vleismerino's beraam. Betekenisvolle (P ≤ 0.05) verskille in Lm/Ej het tussen Merino- en Dohne Merino-ooie op verskillende plase voorgekom. Daar is gepoog om dié verskille met bestuursinsette op verskillende plase (kuddegrootte by paar, lengte van paring, die persentasie ramme, die gebruik van koggelramme, die gebruik van ultraklankskandering en lambestuur) in verband te bring. 'n Toename in kuddegrootte het geneig om tot 'n afname in Lm/Ej te lei. Reproduksiedoeltreffendheid binne kuddes was onafhanklik van die ander bestuursinsette. Ooie wat geen lammers laat suip het gedurende 1988-1990 nie, is met oorknippe gemerk. Die gemiddelde peile van reproduksie-mislukking in gemerkte ooie (groepe met <40 gemerkte ooie is uitgesluit) is vergelyk met dié van tydgenote sonder 'n geskiedenis van reproduksieverliese binne jare en plase. In 15 groepe van Merino-ooie waar hierdie prosedure gevolg is, was die gemiddelde aantal 'ooie droog as persentasie van ooie teenwoordig by merk' (Ed/Epm) 33.7%, in vergelyking met 24.2% vir 15 groepe tydgenote van dié ooie (P ≤ 0.05). In vier groepe Dohne Merino-ooie in vergelyking met hul tydgenote was die ooreenstemmende syfers vir Ed/Epm onderskeidelik 32.8% en 21.5% (P = 0.06). Dit blyk dus dat daar ruimte vir die verdere verbetering van reproduksie in plaaslike wolskaapkuddes is. Seleksie teen reproduksie-mislukking deur gebruik te maak van die eenvoudige 'soog en droog'- tegniek blyk 'n lae-insetmetode vir die verbetering van reproduksie in kommersiële skaapkuddes te wees. Volgens resultate uit die literatuur sal sodanige seleksie ook toekomstige generasies bevoordeel.

Keywords: Management, reapeted failure, reproductive performance, sheep