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Accueil du site → Doctorat → États-Unis → 1984 → Simulation of genetic and environmental interaction of sheep production in northern Kenya

Texas A and M University (1984)

Simulation of genetic and environmental interaction of sheep production in northern Kenya

Blackburn, Harvey David

Titre : Simulation of genetic and environmental interaction of sheep production in northern Kenya

Auteur : Blackburn, Harvey David

Université de soutenance : Texas A and M University, USA

Grade : Doctor of Philosophy (PhD) 1984

A mathematical model, programmed in FORTRAN IV, was developed to simulate flocks of sheep on an individual animal basis. Simulations can be performed for any breed where specified breed parameters are potential mature size (WMA), potential peak daily milk production (GMLKL), maturing rate, ovulation rate, seasonality of breeding and wool growth. The nutritional environment is defined by crude protein content, dry matter digestibility and availability of forages. Managerial options are flexible to allow simulation of a wide range of production scenarios. The Integrated Project in Arid Lands (IPAL) collected production data on a flock of Somali Blackhead sheep located in northern Kenya. These data were used for model validation. Simulations were performed for this area for 9 genotypic combinations with WMAs of 30, 35, and 45 kg and GMLKLs of .90, 1.30 and 1.75 kg. Four years were simulated in which 2 nutritional environments were simulated ; base year, drought year, recovery years 1 and 2 which were a resumption of forage parameters used in the base year. For reproductive rate, offtake of meat and milk per ewe, and flock production efficiency, sheep with a WMA of 30 were not as productive as 35 and 45 WMA sheep. The stress of a high level of milk production causes the 30/1.75 and 35/1.75 not to recover from the drought. The 35/1.75 and 45/1.75 were the most productive genotypes tests, illustrating the necessity of matching WMA and GMLKL to enhance efficiency. Genotypes were ranked for flock efficiency for protein, energy, weight sold and dairy milk offtake. The 45/1.75 ranked first or second, and 35/1.30 ranked from first to third except for weight sold. The 35/1.75, 30/1.75 and 45/.90 always ranked the lowest. The simulations performed are being utilized by IPAL for planning the next phase of their project. Simulated results on body size and milk production level led IPAL to investigate the use of larger sheep. Before these simulations, testing a new genotype was not planned. Furthermore, simulations indicate a controlled breeding season may be counterproductive ; therefore IPAL is reevaluating controlled breeding as a possible practice to increase sheep productivity

Mots clés : Sheep / Computer-based modeling / Breeding of animals / Northern Kenya

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