title: Genetic trends for objectively measured and subjectively assessed traits in a Dorper sheep flock.
abstract: Genetic trends were constructed to monitor the genetic change for subjectively assessed and objectively measured traits using data emanating from complete records from the National Small Stock Improvement Scheme database and performance records accumulated by a single breeder over a period of 24 years. The objectively measured production traits considered were weaning weight, post-weaning weight (PWW), yearling weight, average daily weight gain to weaning (ADGW), average daily weight gain during post-weaning phase (ADGPW) and average daily weight gain up to yearling age. The subjectively assessed traits (scored on a five-point scale) were conformation, fat distribution, size, type and colour. Direct genetic trends for live weight and growth traits (with the exception of ADGPW) were positive. All the objectively measured traits where maternal effects were significant, except PWW, registered small declines in maternal breeding values. The fastest genetic progress was attained by ADGW, which amounted to 0.29 % of the overall phenotypic mean per annum. Conformation and type exhibited positive but slow increments in direct breeding values at an equivalent annual rate amounting to 0.12 and 0.09 % of the overall phenotypic mean, respectively. Size demonstrated a negative genetic trend of -0.14 % of the overall phenotypic mean per annum. Genetic trends for fat distribution and colour were negligible. It was concluded that breeders should focus more on the performance recording of objective traits as they are likely to respond favourably to selection pressure.
authors.affiliation: Department of Animal Sciences, University of Stellenbosch, Private Bag X1, Matieland, 7602, South Africa. oliverzish@gmail.com
authors.forename: Oliver Tendayi
authors.initials: OT
authors.lastname: Zishiri
authors.forename: Schalk Willem
authors.initials: SW
authors.lastname: Cloete
authors.forename: Johannes Jacobus
authors.initials: JJ
authors.lastname: Olivier
authors.forename: Kennedy
authors.initials: K
authors.lastname: Dzama
mesh_terms: D000818:Animals; D001835:Body Weight; D001947:Breeding; D014644:Genetic Variation; D008957:Models, Genetic; D010641:Phenotype; D012641:Selection, Genetic; D034561:Sheep, Domestic / Q000235:genetics* / Q000254:growth & development*; D013019:South Africa; D015430:Weight Gain