Browsing by Author "Davids, Annelin Henriehetta"
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- ItemEstimation of genetic distances and heterosis in three ostrich (Struthio camelus) breeds for the improvement of productivity(Stellenbosch : University of Stellenbosch, 2011-03) Davids, Annelin Henriehetta; Cloete, Schalk W. P.; Dzama, Kennedy; University of Stellenbosch. Faculty of AgriSciences. Dept. of Animal Sciences.ENGLISH ABSTRACT: A study was conducted to characterize the three ostrich breeds available as genetic resource in South Africa, namely the South African Black (SAB), Zimbabwean Blue (ZB) and the Kenyan Redneck (KR), and their respective crosses. Growth, slaughter traits and reproduction of these ostriches were recorded at Oudtshoorn Research Farm in the Western Cape of South Africa. Individual non-linear regressions (Gompertz) were fitted to the data of 390 purebred and 41 crossbred ostriches, using the SAS NLIN function. Heterosis was estimated for each parameter of the Gompertz model. The estimated adult weight (Aparameter) of the ZB (147 kg) and the KR breeds (148 kg) were higher than that of the SAB breed (129 kg). The overall growth rate (B-parameter) of the ZB breed (0.0075) and the SAB breed (0.0080) was lower than that of the KR (0.0150). The age at maximum weight gain (C-parameter) was higher for the ZB breed (226 days) compared to the SAB (198 days) and the KR (194 days). Heterosis for the A-parameter was estimated at -6.2% and at -12% for the C-parameter. The slaughter traits studied were slaughter weight (SLW), carcass weight (CW), dressing percentage (DP), fan fillet weight (FFW), pH0, pH24, drip loss % (DL%), cooking loss % (CL%), tenderness and meat colour traits. Differences were observed between the means for SLW of the SAB (86.5 kg) and ZB (93.9 kg). Mean DP of the KR breed (52.5%) was increased relative to the low DP of their SAB contemporaries (48.8%). The sire lines (ZB and KR) and crosses were heavier than the SAB (dam line), whereas the crosses resembled the dam line for meat quality traits. Means for pH24 also differed, with higher values for the sire lines (ZB – 6.36; KR – 6.4) relative to the SAB (5.85). The instrumental b* colour value also differed between the SAB (9.4) and KR (6.9). Records used for assessing the reproduction and body measurements of purebred and crossbred dams were 428 in total. Traits analyzed were, total egg production (TEP), the number of fertile eggs, number dead in shell chicks, hatchability and chick production (CP), the time to lay, live weight, front chest circumferences as well as tail circumference. The ZB and KR were heavier in live weight and of larger body measurements than the SAB, whereas the SAB exhibited superior reproduction performance in comparison with the ZB and KR breeds. Derived heterosis estimates amounted to 2.2% for tail circumference, 12% for TEP, 12% for hatchability and 19% for CP. Genetic variation between and within the breeds were determined utilizing 19 microsatellite markers. Significant molecular genetic differences were observed between the three breeds. The SAB and ZB (Fst = 0.10 and Nei = 0.49) were genetically most similar, whereas the genetic distance between the KR and ZB breeds were furthest (Fst = 0.13 and Nei = 0.61). The SAB breed exhibited the highest heterozygosity within its population and the ZB the lowest heterozygosity. These results contribute to a better understanding of the utilization of the distinct ostrich breeds for commercial production.