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Studies on the genetic parameter estimates and trends to reduce reproductive wastage in the Tygerhoek Merino sheep resource flock
Thesis (MScAgric)--Stellenbosch University, 2024.
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Stellenbosch : Stellenbosch University
2025
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| _version_ | 1867613796981276672 |
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| access_status_str | Open Access |
| author | Meijboom, Samuel Mendel |
| author2 | Cloete, Schalk |
| author_browse | Cloete, Schalk Meijboom, Samuel Mendel |
| author_facet | Cloete, Schalk Meijboom, Samuel Mendel |
| author_sort | Meijboom, Samuel Mendel |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (MScAgric)--Stellenbosch University, 2024. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/131831 |
| institution | Stellenbosch University (South Africa) |
| last_indexed | 2026-06-10T12:41:50.126Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2025 |
| publishDateRange | 2025 |
| publishDateSort | 2025 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/131831 Studies on the genetic parameter estimates and trends to reduce reproductive wastage in the Tygerhoek Merino sheep resource flock Meijboom, Samuel Mendel Cloete, Schalk Nel, Cornelius Dzama, Kennedy Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Sciences. Tygerhoek Merino sheep -- Breeding Merino sheep -- Effect of temperature on Merino sheep -- Effect of stress on Conception Merino sheep -- Reproduction Merino sheep -- Productivity -- South Africa Wool -- Quality Lambs -- Growth UCTD Thesis (MScAgric)--Stellenbosch University, 2024. ENGLISH ABSTRACT: Reproductive wastage has been and continues to be a major constraint to production in the South African small stock industry. Reproductive wastage is a large contributor to income loss and raises welfare concerns for the sheep industry worldwide. This study evaluated different methods to minimize reproductive wastage by estimating phenotypic and genetic parameters, as well as analyzing genetic trends for ewe reproduction and lamb survival in a well recorded Merino resource flock. Furthermore, the study also considered the effect of the ambient environment on ewe conception to curb reproductive wastage. The Tygerhoek Merino resource flock has detailed records for ewe reproduction and lamb survival trait complexes. The research farm is also close to an official weather station, which allows for long-term climate data to construct a temperature-humidity index (THI) as a descriptor of the ambient environment. This placed the flock in a unique position to allow for a comprehensive analysis on strategies to minimize reproductive wastage. The first aim of the study was to conduct an extensive analysis on the composite trait; number of lambs weaned (NLW) and its individual components (conception (CON), ewe rearing ability (ERA) and litter size (LS)). The genetic relationships of NLW with the components were examined and yielded no unfavorable correlations. It also suggested that component traits (CON, ERA and LS) should be emphasized to increase reproductive efficiency instead of only focusing on NLW. The study then focused on the effect of the ambient environment on CON. Heat stress has had a negative effect on CON in dairy cattle, however, similar studies have not been repeated in sheep. Hence, this study aimed at being one of the first studies to consider the THI and its effect on CON in Merino ewes. Increased levels of heat stress, as reflected by an increased THI, exhibited a clear negative effect of heat and a more prominent effect of accumulative heat on the CON of ewes. Apart from ewe reproduction, another comprehensive genetic analysis was conducted on the early stages of lamb survival. This analysis considered the traits lamb survival at birth and survival until 3 days of age. The aim of this was to minimize reproductive wastage by targeting survival as a trait of the lamb, rather than the more common approach of concentrating on ewe reproductive traits. The thesis conformed with previous literature by reporting low heritability estimates for both ewe reproduction and lamb survival traits. However, despite low heritability estimates, genetic gain can be achieved over numerous generations. It is recommended that reproductive efficiency must be included in selection objectives and, where possible, the early stages of lamb survival must also be considered to minimize reproductive wastage. Derived genetic trends reflected slow change (<0.2% of the overall mean per annum), generally in the desired direction. These results were expected as the experimental protocol followed precluded directed selection for reproduction or lamb survival. These results conformed to previous studies suggesting that reproductive efficiency and lamb survival can be increased while still maintaining a high standard of wool production. It also identified keyways to minimize reproductive wastage through concentrating on traits of the ewe as well as of the lamb. AFRIKAANSE OPSOMMING: Reproduksieverliese is ‘n belangrike beperking vir produksie in die Suid-Afrikaanse kleinveebedryf. Dit lei tot verliese aan inkomste en is wêreldwyd ‘n belangrike bron van kommer aangaande die welsyn van skape. Hierdie studie het verskeie metodes om reproduksieverliese te beperk ondersoek, deur fenotipiese en genetiese parameters, sowel as genetiese tendense, in ‘n goed aangetekende Merinokudde te ontleed. Die studie het verder die invloed van klimaat op die besetting van ooie ondersoek om so reproduksieverliese te beperk. Die Tygerhoek Merinohulpbronkudde het detail-inligting van die reproduksie van ooie en die oorlewing van lammers beskikbaar. Die navorsingsplaas is verder na aan ‘n amptelike weerstasie, waarvan lantermyndata gebruik kon word on ‘n temperatuur-humiditeitsindeks (THI) as ‘n beskrywing van die omgewing te gebruik. Die kudde was dus in ‘n unieke situasie deurdat ‘n omvattende ontleding van strategieë vir die vermindering van reproduksieverliese moontlik was. Die eerste mikpunt van die studie was om on uitgebreide ontleding van die saamgestelde eienskap; aantal lammers gespeen per ooi gepaar (NLW) en die individuele komponente daarvan, nl. besetting (CON), ooigrootmaakvermoë en werpselgrootte, te doen. Die genetiese verwantskappe van NLW met die komponente is ondersoek, en het op geen ongunstige korrelasies gedui nie. Dit het ook gedui daarop dat komponente beklemtoon kon word om reproduksie te verbeter, in stede daarvan om slegs op NLW te fokus. Die studie het verder die effek van klimaat op CON ondersoek. Hittestres en die incloed daarvan is voorheen by melkbeeste ondersoek, maar soorgelyke studies is nog nie met skape herhaal nie. Hierdie studie mik dus om een van die eerste studies te wees wat THI in ag neem om die effek daarvan op CON by Merino-ooie te ondersoek. Hoër vlakke van hittestres, soos deur ‘n verhoogde THI weerspieel, het ‘n duidelike negatiewe effek op CON uitgeoefen. Benewens vir reproduksie, is nog ‘n omvattende genetiese ondersoek na vroeë lamoorlewing geloods. Die oogmerk was om reproduksieverliese te voorkom deur oorlewing as ‘n eienskap van die lam te ontleed, in stede van om die meer algemene benadering om dit as ‘n ooieienskap te beskou, te volg. Hierdie tesis het, in ooreenstemming met die literatuur, lae ooreflikheidsvlakke vir ooireproduksie sowel as lamoorlewing beraam. Daar word egter verwag dat genetiese vordering moontlik is, ten spyte van die lae oorerflikheidsberamings. Daar word voorgestel dat reproduksiedoeltreffendheid in seleksiedoelwitte ingesluit moet word. Waar moontlik, moet lamoorlewing ook geteiken word om reproduksieverliese te verlaag. Behaalde genetiese tendense het op stadige verandering (<0.2% van die algehele gemiddelde per jaar) gedui, deurgaans in die verlangde rigting. Hierdie resultate is verwag, siende dat die eksperimentele protokol seleksie vir reproduksie-eienskappe en lamoorlewing uitgesluit het. Hierdie resultate stem ooreen met vorige studies dat lamoorlwing verbeter kan word sonder om woleienskappe prys te gee. Dit het ook op wyses gedui om reproduksieverliese te verminder deur op eienskappe van die lam sowel as die ooi te fokus. Masters 2025-04-01T07:08:33Z 2025-04-01T07:08:33Z 2024-12 Thesis https://scholar.sun.ac.za/handle/10019.1/131831 Stellenbosch University vii, 76 pages : illustrations application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Tygerhoek Merino sheep -- Breeding Merino sheep -- Effect of temperature on Merino sheep -- Effect of stress on Conception Merino sheep -- Reproduction Merino sheep -- Productivity -- South Africa Wool -- Quality Lambs -- Growth UCTD Meijboom, Samuel Mendel Studies on the genetic parameter estimates and trends to reduce reproductive wastage in the Tygerhoek Merino sheep resource flock |
| title | Studies on the genetic parameter estimates and trends to reduce reproductive wastage in the Tygerhoek Merino sheep resource flock |
| title_full | Studies on the genetic parameter estimates and trends to reduce reproductive wastage in the Tygerhoek Merino sheep resource flock |
| title_fullStr | Studies on the genetic parameter estimates and trends to reduce reproductive wastage in the Tygerhoek Merino sheep resource flock |
| title_full_unstemmed | Studies on the genetic parameter estimates and trends to reduce reproductive wastage in the Tygerhoek Merino sheep resource flock |
| title_short | Studies on the genetic parameter estimates and trends to reduce reproductive wastage in the Tygerhoek Merino sheep resource flock |
| title_sort | studies on the genetic parameter estimates and trends to reduce reproductive wastage in the tygerhoek merino sheep resource flock |
| topic | Tygerhoek Merino sheep -- Breeding Merino sheep -- Effect of temperature on Merino sheep -- Effect of stress on Conception Merino sheep -- Reproduction Merino sheep -- Productivity -- South Africa Wool -- Quality Lambs -- Growth UCTD |
| url | https://scholar.sun.ac.za/handle/10019.1/131831 |
| work_keys_str_mv | AT meijboomsamuelmendel studiesonthegeneticparameterestimatesandtrendstoreducereproductivewastageinthetygerhoekmerinosheepresourceflock |