Applied genetics in cattle breeding

List quantitative traits that are inherited

Measured traits:

• milk yield

• m. growth rate

What factors influence the phenotype of an animal?

• genotype

• environment

What is required for genetic improvement of a trait in a population?

variability between animals of the population we want to improve

• influenced by genetics & environment

Outline heritability

Estimates how easily a trait can be improved through genetic selection

• high heritability = greater genetic influence on offspring through genetic selection

Outline phenotypic correlation

measures direction & strength of association between observed phenotypes e.g. milk yield / protein, live weight / fat depth

Outline the genetic correlation

Direction & strength of association between genetic merit for two traits

• pleiotrophy —> genes affecting more than one trait

• closely linked genes affecting two traits

What are some other traits of interest?

• Feed efficiency / dry matter intakes

• Greenhouse gas emissions

• Immune response

• bTB resistance

• Lameness

Outline breeding values

the additive genetic merit of an animal

• 2x the expected deviation in progeny performance from the population mean

  • predicted from animal’s own performance & performance of relatives

  • comparisons of performance of animals that have been treated in similar way

• +ve, zero or -ve

  • genetically above/ below mean?

  • expressed in same units as performance

Outline predicting breeding

Influenced by

• own performance

• parents performance

• progeny performance

Requires access to extensive records for reliability

What are genomic estimated breeding values?

estimated breeding values without performance records but using SNPs (single nucleotide polymorphisms)

Outline the genetics of bovine leucocyte adhesion deficiency

• single point mutation (A to G) on CD18 gene

• autosomal recessive

What is bovine leucocyte adhesion deficiency?

• impaired expression of beta-2 integrin of leukocyte adhesion molecule of neutros

  • fewer neutros get into tissue to fight infection

List clinical signs of bovine leucocyte adhesion deficiency

• ulcers on oral mucosa, gingivitis/periodontitis

• chronic pneumonia

• recurrent/chronic D+

• die due to infectious complications <1yo

  • no tx

Outline the genetics of complex vertebral malformation (CVM)

• Autosomal recessive

• mutation of sugar transporter in golgi apparatus

  • abnormal protein glycosylation of chondroitin sulphate

What is complex vertebral malformation

• cardiac abnormalities

• mis-shapen and fused vertebrae around cervico-thoracic junction

• symmetrical arthrogryposis of limbs

• 50% have cardiac abnormalities

Describe the Holstein Haplotype for Cholesterol Def

• Heterozygous animals have reduced cholesterol

• Homozygotes have no cholesterol & survive only a few months

List genes tested for a bull's proof

• bovine leucocyte adhesion deficiency

• complex vertebral malformation

• fertility haplotypes

• holstein haplotype for cholesterol deficiency

• Production traits

• conformation traits

List conformation traits you may breed for

• Foot angle

• rear legs

  • rear/ side view

• udder depth

• udder support and fore attachment

• teat placement and length

• rear udder width and height

• rump angle and width

• strength: chest width, body depth and bone quality

List factors of a lifetime index

• calving ability

• efficiency (FCR)

• Production

  • milk yield

  • muscle mass %

  • fat %

• survival

• udder health

• leg health

What is the difference between direct and maternal calving rates?

1. Direct calving traits reflect how easily a calf is born — influenced by calf size, shape, and growth rate.

2. Maternal calving traits reflect how easily a cow gives birth — influenced by pelvic size, uterine tone, and maternal behaviour.

Outline genomic evaluation

• genetic test —> SNP chip

  • DNA analysis

• Best for selection of young bulls

  • useful for natural servicing farms

• Genomic Evaluation breeding values (GEBVs)

• Higher reliability

What are the relabilities over time for traditional & genomic evaluations for bulls, depending ont heir age?