Ans3384gencattle

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

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...
View Full Document

Ask a homework question - tutors are online