Browsing by Author "Cloete, J. J. E."
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- ItemProduction of five Merino type lines in a terminal crossbreeding system with Dormer or Suffolk sires(South African Society for Animal Science, 2003) Cloete, S. W. P. (Schalk Willem Petrus van der Merwe); Cloete, J. J. E.; Durand, A.; Hoffman, L. C.This study details the production performance of ewes and lambs that originated from a terminal crossbreeding experiment that involved five Merino type dam lines and two terminal crossbreeding sire lines from 1999 to 2002. Ewe lines were SA Mutton Merino (SAMM), SAMM rams crossed to Merino ewes (SAMM cross), Dohne Merino, as well as specialist Merino lines selected for clean fleece weight (FW+) and for an increased reproduction rate (Rep+). Dormer and Suffolk rams were used as sire breeds on these ewes. Data include 777 birth and 605 weaning records of lambs and 562 production year records of ewes. At birth the progeny of SAMM ewes were heavier than those of the other ewe lines, while FW+ ewes produced smaller lambs at birth than SAMM cross and Rep+ ewes. Lamb survival was not significantly affected by ewe line or sire breed. The progeny of the dual-purpose ewe lines (SAMM, SAMM cross and Dohne Merino) were heavier than those of Merino ewes (FW+ and Rep+) at weaning. No sire breed difference was found for birth or weaning weight. The joining weights of dual-purpose ewe lines were higher than those of Merinos. Although considerable variation was found between ewe lines in terms of lamb output (number or weight of lamb weaned per ewe joined), the only significant difference was for weight of lamb weaned between SAMM cross and FW+ Merino ewes. Means for weight of lamb weaned per joining (in kg) were 37.3 for SAMM ewes, 39.6 for SAMM cross ewes, 35.5 for Dohne Merino ewes, 28.9 for FW+ ewes and 34.6 for Rep+ ewes. No differences in ewe reproduction were found between ewes joined to Dormer or Suffolk rams. The clean wool production of SAMM ewes amounted to 46% of that recorded in FW+ ewes. Corresponding percentages were 68% for SAMM cross ewes, 74% for Dohne Merino ewes and 90% for Rep+ ewes. The wool of SAMM ewes was slightly coarser in diameter than those of SAMM cross and FW+ ewes, which in turn was coarser than those of Rep+ and Dohne Merino ewes. The economic viability of crossbreeding programs involving the respective ewe lines would depend on the ratio between the prices of wool and lamb. No conclusive advantage could be demonstrated in favour of any of the sire breeds.
- ItemRelative performance and efficiency of five Merino and Merino-type dam lines in a terminal crossbreeding system with Dormer or Suffolk sires(South African Society for Animal Science, 2004) Cloete, S. W. P. (Schalk Willem Petrus van der Merwe); Cloete, J. J. E.; Herselman, M. J.; Hoffman, L. C.ABSTRACT: The production performance of ewes was assessed in a terminal crossbreeding experiment involving five Merino and Merino-type dam lines and two terminal crossbreeding sire breeds. Dam lines were SA Mutton Merino (SAMM), SAMM rams crossed to Merino ewes (SAMM cross), Dohne Merino, as well as specialist Merino lines selected for clean fleece weight (FW+) and for an increased reproduction (Rep+). Dormer and Suffolk rams were used as sires. Dual-purpose ewes were heavier than Merinos on average and at the ultimate joining at 3.5 years. Average clean fleece weight for SAMM ewes was approximately half that of Merino ewes while clean fleece weights for Dohne and SAMM cross ewes were intermediate. Differences between progeny in slaughter age, marketing weight, dressing percentage and carcass weight could largely be attributed to the comparison of purebred Merino lines with dual-purpose lines. The slaughter age of lambs from the two Merino lines was between 14 and 21% higher than that of the dual-purpose lines. Lambs from purebred SA Mutton Merino (SAMM) dams also outperformed lambs from SAMM cross ewes for slaughter age, slaughter weight and carcass weight. Considerable variation was found between dam lines for reproduction parameters, but few significant differences were found. Lamb output, defined as total weight of lamb slaughtered per joining, averaged 42.7 kg for SAMM ewes, 44.2 kg for SAMM cross ewes, 39.3 kg for Dohne ewes, 32.9 kg for FW+ Merino ewes and 42.0 kg for Rep+ Merino ewes, but differences between lines only tended to be significant. Sire breed did not affect lamb performance or ewe productivity markedly. An economic simulation indicated large differences in gross income per small stock unit between dam lines, warranting further research on the efficiency of terminal Merino-type dam lines.
- ItemSlaughter traits of Merino sheep divergently selected for multiple rearing ability(South African Society for Animal Science, 2004) Cloete, J. J. E.; Cloete, S. W. P. (Schalk Willem Petrus van der Merwe); Hoffman, L. C.; Fourie, J. E.ABSTRACT: Carcass data of 114 19-month-old Merino sheep descended from two lines that were divergently selected for maternal multiple rearing ability (H and L lines, respectively) were used. In study A only ram progeny of the same age were slaughtered, while ewes and rams of the respective selection lines were included in study B. Study A: Mean slaughter weight of H line rams was 12% heavier than that of L line contemporaries. A corresponding difference of 13% was found for carcass weight. Carcass component weights, body measurements, retail cut weights and eye-muscle areas were higher in the H line than in the L line, barring a few exceptions. Adjustment for the higher slaughter weight resulted in most of the line differences being eliminated, but the difference in the loin retail cut remained in favour of the H line. Study B: Mean slaughter and carcass weights of H line animals were respectively 7% and 11% heavier than that of L line contemporaries. Adjustment for the higher slaughter weights of H line animals resulted in most of the differences in the retail cut weight being eliminated, but the hindquarters of H line animals remained heavier than that of L line contemporaries. Line did not affect the moisture, protein, lipid or ash content of the M. longissimus dorsi toracis in study B. The effect of gender on the retail cut weights and proximate analysis was consistent with results from the literature. Selection for multiple rearing ability did not result in any unfavourable responses in retail cut weights or meat chemical properties. Carcasses in the H line, in fact, yielded better in the highly priced loin and hindquarters areas, independently of slaughter weight.