A52-75-2007E.pdf - AgroMedia International Inc

Genetics6Analysis of inbreeding and its relationship with functionallongevity in canadian dairy cattleCorresponding AuthorSewalem, A.AAFC Dairy and Swine Researchand Development CentreCollaboratorsKistemaker, G.J.Canadian Dairy NetworkMiglior, F.AAFC Dairy and Swine Researchand Development CentreVan Doormaal, B.J.Canadian Dairy NetworkJournal of Dairy Science (2006) Vol. 89 p. 2210-2216.Inbreeding refers to the mating of animals that are genetically more closelyrelated than the average members of a population. Inbreeding increasesthe probability that the genes determining a given characteristic are identicalin both mates. The inbreeding coefficient (IC) is an estimate of thatprobability. Currently, the average IC for Canadian Holsteins is in the 5.5-6.0% range; for other Canadian dairy breeds the figure is between 2.4 and7.1%. Inbreeding decreases genetic variance in the population, reducingthe potential for genetic improvement. Many studies have demonstratedthat inbreeding decreases both productive and reproductive performancebut few have examined its effect on cow longevity, defined as the numberof days from first calving to permanent removal from recording dueto death, culling or other reasons. This study examined the effect of inbreedingon risk of being culled for cows in the Canadian dairy herd. Forall breeds, there was a trend toward reduced longevity as IC increased.Although little effect on longevity was observed when IC was less than12.5%, risk of earlier culling increased when IC was greater than 12.5%.7Optimal random regression models for milk production in dairycattleCorresponding AuthorYang, R.Q.Shanghai Jiaotong UniversityCollaboratorsLiu, Y.X.Shanghai Jiaotong UniversityZhang, J.Shanghai Jiaotong UniversitySchaeffer, L.R.University of GuelphZhang, W.L.Shanghai Supercomputer CenterJournal of Dairy Science (2006) Vol. 89 p. 2233-2235.Production traits are influenced by both genetics and environment. Toquantify these separate influences, statistical techniques are used to findmathematical equations that account for variation in raw production datain terms of these and other factors. The choice of equations can affect theresulting estimates of genetic and environmental effects. This paper describesthe methods and results of a search for an equation that wouldfacilitate a ‘best-fit’ to lactation data from first lactation Canadian Holsteins.The authors conclude that the equation currently used in Canada was themost satisfactory of those tested.58 Highlights in Canadian Dairy Cattle Research - 2007