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Unformatted text preview: Control of Genetic Defects in Cattle Important Concepts • All breeds have genetic defects • The genes controlling genetic defects are almost always recessive • Dominant genes responsible for genetic defects are nearly always immediately removed from the population • Defective recessive genes are nearly always spread throughout a breed by the extensive use of superior sires that are heterozygous for the defective gene • Artificial insemination allows individual beef and dairy bulls to sire over 100,000 progeny • DNA testing greatly assists in the control of genetic defects Genetic Defects of Dairy Cattle • Bovine leucocyte adhesion deficiency (BLAD) was a major concern to the Holstein breed in the early „9 0s. • Weaver syndrome similarly impacted the Brown Swiss breed somewhat earlier. • Both of these recessive defects are homozygous lethal, yet result in calves that appear normal at birth. Bovine Leucocyte Adhesion Deficiency in Holstein Cattle • BLAD became widespread in the breed through the use of popular heterozygous sires • The fact that homozygous calves appear normal at birth delayed the discovery of the problem • About 14% of the sires in AI studs were found to be heterozygous for BLAD Bovine Leucocyte Adhesion Deficiency in Holstein Cattle • Affected animals die because of extreme susceptibility to infections caused by an inability of white blood cells (leucocytes) to pass from the bloodstream into infected tissue. • This inability is due to the lack of membrane protein called CD18. The Spread of BLAD Osborndale Ivanhoe Pennstate Ivanhoe Star Carlin-M Ivanhoe Bell - BL Emprise Bell Elton - BL Control of BLAD in Holsteins • Cause: a mis-sense mutation in the CD18 gene • All bulls prior to entering AI studs are tested for BLAD • Few, if any, positive bulls are progeny tested • Since nearly all sires used in the future will be free of BLAD, the gene frequency will be reduced by 50% per generation Other Defects of Holstein Cattle • Syndactylism (mulefoot) - Chromosome 15 – Affected animals survive but do not perform well (“Wayne” sired over 60,000 calves) –also in Angus cattle • Protoporphyria (pink tooth) – Accumulation of porphyrins in the teeth and bones due to a lack of an enzyme needed to degrade them – Is also a concern in Limousin cattle Other Defects of Holstein Cattle • DUMPS – Deficiency of Uridine Monophosphate Synthase • Autosomal recessive • Homozygotes die early...
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This note was uploaded on 07/16/2011 for the course ANS 3384 taught by Professor Olson during the Spring '09 term at University of Florida.

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