Genetics and Genetic Disorders

In

Beef Cattle

Discussion

Update Items

● Genetics vs Environment● Genetics Refresher● Currently Recognized Disorders● Genetic Testing● Implications for Purebred's● Implications for Commerical

Genetic vs Environmental

● Environmental– Crooked-calf

● Lupine plant● Manganese deficiency

– Hairless calves● Iodine deficiency

– Two-headed calves● Embryonic

development

– Prolapse

● Genetic– Prolapse– Curly calf syndrome

● Angus, Red Angus, Charolais

– Hypotrichosis● Hairless, Hereford

Genetic Refresher

Cattle = 60 chromosomesGametes (sex cells)

30 chromosomes female30 chromosomes male

Genetic Refresher

Changes to DNASubstitution – incorrect pairing

Insertion – extra nucleotideDeletion – missing nucleotide

Frame Shift – enough changes in base pairs to alter amino acid coding

Genetic Refresher

Genetic Refresher

Genetic Refresher

WHAT IF I DON'T WANT ANY CARRIERS?

HOW CAN I DETERMINE

BB from Bb

WITHOUT MATING?

GENETIC TESTING

● PCR – polymerase chain reaction● SNP's (snips) – single nucleotide

polymorphisms● PCR – florescent tags {B = red, b = yellow)● GeneChip

– Looks a many,many base pairs for multiple animals in a single scan

– 50,000k and 100,000k chips

GENETIC TESTING

● Methods like PCR and Chips for detecting differences in oligonucleotide sequences and SNPs has made genetic testing more practical and less expensive.

● Detection

– Parentage testing

– Simple recessive traits (remove carriers from population)● Increase knowledge of complex traits and underlying

mechanisms

– Susceptibility to BRD

– Feed efficiency

Genetic Disorders

● Affect many breeds

● Prone to come about through line breeding (a form of inbreeding to increase the proportion of genes from a common ancestor).

● Angus probably gets most attention because of size of registry.

● Genetic disorders are often simple recessive

– Few genes

– Those that express the disorder usually don't make it into production

Genetic Disorders

● Concerns– How many carriers are out there?– How many calves are born with the disorder?– What does it mean if we have a large number of

carriers but a low proportion of expression?

Developmental Duplication

● Latest genetic disorder in Angus– Recognized in Australia– Calves born with extra limbs

● Remember this can be caused by embryo environment

– Work of Jonathan Beever (U of Ill.) genetist found commonality in genes associated with calves compared to normal calves.

Developmental Duplication(polymelia)

● Genetic testing indicates 3% US sires are carriers and a breed wide frequency of 6%.

Concern with carriers

● Dd x Dd = 25% chance of dd.– Rare occurrence of developmental duplication– Embryonic death high among dd?

● Increased PPI● Increased conception to herd sire vs AI sire

– Complication● Incomplete penetrance

– Animals that are dd but are not exhibit duplication.

Purebred Implications

● Discovery of dd animals that are expressing duplication

– Is the situation more difficult than first thought?

● Proactive to eliminate carriers from the breed (example known lethals like AM a.k.a. curly calf)

– Possible carriers flagged (ancestry)

– Required testing (sells)

– Required testing (registration)

– Optional testing (remove pending condition from registry)

● What about carrier bulls destined for commercial herds?

This animal has one or more ancestors known to carry a mutation that can result in calveswith a genetic condition known as Developmental Duplication (DD). Avoidance of mating

carrier animals is an essential component of managing the incidence of genetic conditions asis the strategic use of DNA testing. AAA Statement of Certificate until confirmed by testing.

Commercial Implications

● Little crossbreeding– Greater risk of developing female base herd with

carriers

● High degree of crossbreeding– Reduced risk of developing female base herd with

carriers

● Y1 calfcrop from: 1 bull [+-] x 25 cows [++]

– - = simple undesirable trait

– Kept 8 replacement heifers● 4 [++] and 4[+-]

● Y3 calfcrop from: 1 bull x 17 cows [++], 4 [++],4 [+-]

– 0.25 {chance of --} x 4 = 1

– Herd level odds of negative result 1:24

● Y1 calfcrop from: 1 bull [+-] x 25 cows [++]

– - = simple undesirable trait

– Kept 8 replacement heifers● 4 [++] and 4[+-]

● Y3 calfcrop from: 1 bull [+-] x 17 cows [++], 4 [++],4 [+-]

– 0.25 {chance of --} x 4 = 1

– Herd level odds of negative result 1:24Probability of being a carrier = (0.5)n where n = number of generations between offspring and carrier ancestor - does not factor in number of animals for herd level probability

Commercial Breeders

● Crossbreeding helps avert risk.● Breeders that maintain a high percentage of

certain breeds should familiarize themselves with recognized disorders and try to purchase free genotypes (> 50% cattle sold are black).

Currently Recognized

● 12 genetic abnormalities– 5 non-lethal, 7 lethal– 11 have gene tests

UNL Publication G2055

Testing

● Companies (order forms and testing online)

– GeneSeek (Neogen subsidiary)– Igenity– Zoetis (used to be Pfizer)

● Cost

– Most $24/condition– Some discount samples > 50 ($2.00)