Thesis (Ph. D.)--University of Hong Kong, 2008. / Also available in print.

Master of Science / Department of Animal Sciences and Industry / Twig T. Marston / One hundred ninety-three crossbred steers from two herds were used to determine the association of leptin gene polymorphisms and effects of feedlot management of lean and fat steers on carcass performance. Steers were sorted into FAT and LEAN groups by ultrasound backfat at weaning and randomly assigned to a finishing phase. Steers were assigned to a backgrounding phase (BACK) and were fed a forage-based diet for 90 days or directly entered a feedlot phase (FEED). Genotypes were determined by IGENITY® (Atlanta, GA) for a panel of nine single nucleotide polymorphisms (SNP) in the leptin gene (UASMS1, UASMS2, C963T, E2FB, A1457G, and A252T), leptin receptor (T945M), growth hormone receptor (G200A), and fat metabolism enzyme (K232A). Initial backfat (BF) means for the FAT and LEAN group were 3.4 mm and 1.8 mm, respectively. Mean on-test weight was heavier for FAT (306.5 kg) than LEAN (292.9 kg). Age-adjusted hot carcass weights (HCWT) were heavier for LEAN/BACK when compared to FAT/FEED and FAT/BACK (P<0.05). Dressing percent for the FAT/FEED group tended to be higher (P<0.10) over all groups except LEAN/BACK. Steers that went directly to the feedlot had higher marbling scores than backgrounded groups. FAT/FEED had higher 12th rib BF than the other contemporaries. None of the SNPs were useful for predicting ultrasound BF at weaning. Some association was detected with UASMS2 and HCWT (P<0.10) resulting in an 11 kg difference between genotype CC and CT (P<0.05). Five of the leptin polymorphisms (UASMS1, UASMS2, A1457G, C963T, and E2FB) were associated with adjusted carcass BF (P=0.01, 0.06, 0.01, 0.01, and 0.01, respectively) and calculated yield grade (P<0.01). A252T was associated with REA, and genotype TT was larger than AA and AT (P<0.05). This study suggests that segregation by initial fatness estimates and feedlot management strategies has the opportunity to increase HCWT by 35 kg. Sorting cattle upon feedlot entry by ultrasound BF and segregation using genetic markers are useful tools that can assist in the estimation of carcass composition in the live animal. With additional research, the possibility exists to incorporate genetic markers into feedlot selection to assist in marketing decisions.

Darbo tikslas: Nustatyti nerujojančių ir neapsivaisinančių paršavedžių leptino geno (LEP) polimorfizmą ir leptino koncentraciją kraujyje bei įvertinti jų įtaką lytinį ciklą reguliuojantiems veiksniams. Darbo uždaviniai: 1. Nustatyti normalių (NP) ir nerujojančių bei neapsivaisinančių (NNP) paršavedžių leptino geno įvairovę. 2. Nustatyti leptino geno polimorfizmo (LEP) įtaką paršavedžių lašinių storiui po paršelių atjunkymo. 3. Įvertinti leptino geno polimorfizmo įtaką gimstančių paršelių gyvybingumui bei išsaugojimui. 4. Nustatyti leptino geno polimorfizmo įtaką paršavedžių brokavimo priežasčiai. 5. Nustatyti ir palyginti leptino koncentraciją skirtingų leptino genotipų paršavedžių kraujyje. 6. Įvertinti ir palyginti leptino geno polimorfizmo įtaką paršavedžių kraujo biocheminiams rodikliams. 7. Įvertinti dėl nerujojimo arba neapsivaisinimo išbrokuotų paršavedžių kiaušidžių funkcinę būklę atsižvelgiant į leptino geno polimorfizmą. 8. Nustatyti leptino geno polimorfizmo įtaką NNP paršavedžių gonadotropinių ir lytinių hormonų sekrecijai. 9. Nustatyti leptino geno polimorfizmo įtaką kiaušidžių morfologijai. 10. Nustatyti leptino koncentracijos kraujyje įtaką kiaušidžių morfologijai. Mokslinis darbo naujumas: Pirmą kartą buvo nustatytas leptino (LEP) geno polimorfizmas neapsivaisinančioms ir nerujojančioms (NNP) paršavedėms ir nustatyta šio geno įtaka šių paršavedžių reprodukcinių savybių sutrikimo pasireiškimui. Įvertinta leptino (LEP) geno polimorfizmo ir leptino koncentracijos... [toliau žr. visą tekstą] / The aim of the study: Define anoestrous repeat-breading sows’ leptin gene (LEP) polymorphism and leptin concentration in blood as well as evaluate its influence to the factors regulating oestrus cycle. Goalsof the study: 1. Define a diversity of leptin gene in normal sows (NS) and in anoestrous repeat-breading sows (NNS). 2. Define an influence of leptin gene (LEP) polymorphism to sows’ fat thickness after weaning. 3. Evaluate the influence of leptin gene polymorphism to newborn piglet viability and survival. 4. Define causal relationship of leptin gene polymorphism on sows culling rate. 5. Define and compare leptin concentration in blood of different leptin genotypes sows. 6. Evaluate and compare the influence of leptin gene polymorphism on sows’ blood biochemical parameters. 7. Evaluate the functional ovarian status of sows, culled due to anoestrous or failure to conceive, considering leptin gene polymorphism. 8. Define an influence of leptin gene polymorphism to secretion of NNS sows’ gonadotropin hormones and sex hormones. 9. Define an influence of leptin gene polymorphism on ovarian morphology. 10. Define an influence of leptin concentration in blood on ovarian morphology. Research novelty: For the first time leptin gene (LEP) polymorphism was determined for non-conceiving and anoestrous sows (NNS) as well as the influence of this gene on reproductive disorders in sows. We also assessed the effect of leptin gene (LEP) polymorphism and leptin concentration on NNS sows’... [to full text]