Browsing by Author "Fair, M. D."

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    Nitrogen retention response to the abomasal infusion of amino acids in South African Mutton Merino lambs
    (South African Society for Animal Science, 2002) Ferreira, A. V.; Van der Merwe, H. J.; Fair, M. D.
    The nitrogen (N) retention response to the abomasal infusion of amino acids in South African Mutton Merino ram lambs fed a standard finishing diet was investigated. The basal diet consisted of (g/kg air dry weight): 300 lucerne, 80 wheat straw, 561.5 maize meal, 35 molasses meal, 10 urea, 5 salt, 7.5 ammonium chloride, 1.0 vitamin/mineral premix and 0.29 taurotec®. Twenty-eight lambs (ca. 38 kg live weight) were randomly allocated to four treatments consisting of different abomasal infusion rates of an amino acid mixture, formulated to contain essential amino acids in the same ratio as that of the whole empty body. The mixture consisted of (g/kg): 119.7 arginine, 154.9 histidine, 22.1 isoleucine, 106.5 leucine, 91.5 lysine, 146.9 methionine, 105.6 phenylalanine, 133.8 threonine and 118.7 valine. The mixture was infused at levels of (g/d): 0.00, 38.27, 51.02 or 63.78. Glycine was used to balance the various mixtures on an iso-nitrogenous basis. Infusion of 51.02 g/d of the essential amino acid mixture resulted in a significant increase in N retention, expressed as a percentage of N intake, compared to the control group which received the test diet and glycine (Phase 1). The omission of histidine, methionine or threonine from the infusate (Phase 2) had no significant decrease in N retention or plasma amino acid concentrations compared to the infusion of the mixture of nine essential amino acids.
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    Parameter estimates for reproductive output and product quality traits of ostrich females within breeding seasons
    (South African Society for Animal Science, 2011) Fair, M. D.; Van Wyk, J. B.; Cloete, S. W. P. (Schalk Willem Petrus van der Merwe)
    Data involving monthly records of egg production (EP), chick production (CP), hatchability (H), mean egg weight (MEW) and mean day-old chick weight (MCW) were analysed using REML procedures. All traits were treated as hen traits. Egg production of young birds increased to reach a peak of approximately 4 to 5 eggs per month relatively late in the breeding season (September to December). Older hens reached a higher peak of 6 to 9 eggs per month earlier in the breeding season (August to September). There was a secondary peak in older birds from November to December. All birds except 2-year olds exhibited evidence of a slump of production during October. Chick production, MEW, MCW and H followed similar trends. The random effects of direct additive genetic, permanent environment (PE), temporary environment (TE - unique hen-year combinations) and service sire (SS) were estimated from the data. Heritability estimates of the direct additive genetic effect (h2a) of the hen were 0.04 for EP, 0.05 for CP, 0.44 for MEW, 0.67 for MCW and 0.02 for H. The estimates of permanent environment (c2pe) as a ratio of phenotypic variance for the four traits (MCW did not exhibit a significant c2pe effect) were 0.08, 0.08, 0.09 and 0.11, respectively. The effect of service sire as a ratio (c2ss) was significant but relatively low for all traits, ranging from 0.04 for MEW and MCW to 0.06 for CP. Monthly EP and CP were highly correlated at all levels, ranging from 0.74 for the TE correlation to unity (1.00) for the genetic correlation. Egg production was favourably correlated with H at a genetic level (0.98). The genetic correlations of EP and CP with MEW and MCW were variable and in some cases antagonistic as is often found in poultry. The genetic correlations of H with MEW and MCW were positive (0.52 and 0.47, respectively). As expected, the genetic correlation of MEW and MCW was very high at 0.94. The results indicate that selection for improved reproduction (reproductive output and product quality traits) in ostriches is possible. Selection is unlikely to be complicated by unfavourable correlations with H, MEW and MCW.
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    Pedigree analysis of an ostrich breeding flock
    (South African Society for Animal Science, 2012) Fair, M. D.; Van Wyk, J. B.; Cloete, S. W. P. (Schalk Willem Petrus van der Merwe)
    Pedigree records, maintained from 1978 to 2005 at the Oudtshoorn Research Farm, South Africa, of 40 074 birds of a pair-breeding ostrich flock were used to estimate the effective number of founders (fe), the effective number of ancestors (fa), the effective population size and the effective genome equivalents (fg) under random mating, to assess the genetic variability present in the population. The average level of completeness of the pedigrees was high (99.3%) in the first generation, and the average level of inbreeding (F), calculated from the pedigrees, was 0.51%. The reference population was defined as the 39 784 birds hatched from 1990 to 2005. The estimated measures of variability were fg = 47.3, fe = 59 and fa = 58, with an fe/fa ratio of 1.02. The numbers of ancestors responsible for 100%, 50% and 20% of the genes in the reference population were 254, 21 and 6, respectively. The largest individual contribution to the population hatched from 1990 to 2005 was from a male that was responsible for 4.85% of the genetic variability. The generation interval for the four selection pathways – calculated as the average age of parents when offspring that were kept for reproduction were born – were sire to son (7.74 ± 4.92), sire to daughter (7.77 ± 5.13), dam to son (7.50 ± 4.29) and dam to daughter (7.90 ± 4.92). The average generation interval of the reference population was 7.72 ± 4.79 years. The linear regressions of mean annual individual rate of inbreeding on year of birth for the two distinct periods 1995–2002 and 2003–2005 were 0.08% and -0.07% per year, respectively. The estimate of effective population size (Ne), computed via the increase in the individual rate of inbreeding, was 112.7. Estimates of Neusing the alternative methods of tracing the numbers of generations were 73.6, 177.4 and 95.3 for complete, maximum and equivalent complete generations. The results of this study indicated that the population under study was at an acceptable level of genetic variability.