Equine Genetics and Breeding - Texas A&M University - ANSC 201 - Schobert

Phenotype

genetics + environment

female tail line goal

consistent production of winners of females for first 3 generations which leads to quality performers will continue to come from this line

mares effects on phenotypes

uterine environment, milk production, temperament

broodmare temperament

H2= .25-.20, important bc female passes behavioral characteristics to offspring

genetic progress

the increase in favorable genes in the population

genetic progress per year

(accuracy X selection intensity X genetic standard deviation) / generation interval

accuracy of selection

correlation between predicted genetic value and true genetic value

how can the accuracy of predicting true genetic value be increased?

using many progeny records

selection pressure

increasing the frequency of positive genes within a population

genetic progress decreases as the number of traits selected for increases

true

generation interval

average time between birth of animals and birth of the replacement

generation interval for cattle

3-5 years

generation interval for sheep

2-4 years

generational interval for swine

1.5-2 years

generational interval for horses

10 years

horse generation interval characteristics

long reproductive life, replacement rates are low, results in slower genetic progress

conformation and physiological parameters

conformation is highly heritable, heritability of stride length is high

environmental effects

feed and hay, cattle, facility/arena, judges, trainers

mating systems

inbreeding, inbreeding depression, linebreeding,outcrossing,crossbreeding

inbreeding

started with king ranch old sorrel, inbreeding coefficient of more than 10%

what horse was foundation of king ranch quarter horse breeding program?

old sorrel

Solis x panda

Wimpy-P

inbreeding depression

expression of recessive genes for individual characteristics

what can inbreeding depression cause?

Hereditary equine regional dermal asthenia (HERDA)

what is HERDA?

genetic skin disease characterized by hyperextensible elastic skin, severe dermatologic lesions, scarring along back and whithers

How is HERDA inherited?

autosomal recessive trait, 28.3% of cutting horses carry recessive gene

what horse can be traced back to HERDA?

poco bueno

Line breeding

mild form of inbreeding used to maintain high relationship to an outstanding individual

goals of linebreeding

Minimize inbreeding = F < .10 and Maximize relationship = R > .25

outcrossing

mating animals with same breed without a close genetic relationship, breeding population is not closed, minimize level of inbreeding in offspring

what horse was claimed to be the perfect outcross?

DeRenzo - halter horse

Crossbreeding

heterosis, half-arabian, quarter horse and thoroughbred cross

heterosis

hybrid vigor, enhances specific traits

heritability estimates for racing time INCREASES as the length of the race DECREASES

false

longer races allow for greater jockey effects

true

longer distances do not require difference genetic lines

false

speed index (SI)

measures horses relative speed under certain conditions, developed to compare horses and races run at different tracks

SI 70

above average

SI 80

good

SI 90

very good

SI 100+

excellent

genetic change

expected difference in progeny based upon sire and dams superiority

Genetic change equation

(sire SI - breed avg)+(dam SI - breed avg)/2 x h2 (speed) + 75 (BA)

what does BA stand for

breed average = 75

what does h2 stand for

speed

Haplotype

group of genes in organism that are inherited together from single parent

genotype

genetic makeup of an organism

autosomal dominant

A pattern of inheritance in which an affected individual has one copy of a mutant gene and one normal gene on a pair of autosomal chromosomes.

autosomal recessive trait

one of several ways that a trait, disorder, or disease can be passed down through families

autosomal recessive

two copies of an abnormal gene must be present in order for the disease or trait to develop

hyperkalemic periodic paralysis (HYPP)

muscular disease caused by known genetic mutation with autosomal dominant mode of inheritance, affected horses have muscle tremors, weakness, paralysis, AUTOSOMAL DOMINANT

polysaccharide storage myopathy(PSSM)

abnormal accumulation of glycogen (form of sugar in muscle), causes episodes of muscle stiffness and pain after exercise (Tying up), AUTOSOMAL DOMINANT

hereditary equine regional dermal asthenia (HERDA)

degenerative skin disease, AUTOSOMAL RECESSIVE

glycogen branching enzyme deficiency (GBED)

found primarily in quarter horses, inability to correctly store glycogen (fatal to foals), AUTOSOMAL RECESSIVE TRAIT

malignant hyperthermia (MH)

affected horses are triggered by halogenated anesthetics, succinylcholine, stress or excitement, can induce hyper metabolic state which causes muscle contractions, elevated temp, irregular heart beat, AUTOSOMAL DOMINANT

SNP genotyping

measurement of genetic variations of single nucleotide polymorphisms between members of species

performance records for race horse industry

sire and dam that produce and or are stakes winners or champions - claiming, allowance, stakes

racing phenotype

sprinter - <6f, middle distance - 7-8 f, strayers -> 8f

racing genotype

• C/C - Sprinters

• C/T - Middle distance

• T/T - Long distance

Mean Best Racing Distance - Highest grade or most valuable race

C/C - 6f, C/T - 9f, T/T - 10.5 f

Myostatin gene (MSTN)

associated with muscle hypertrophy

muscle mass to body weight ratio

high - 55%

gene mapping

elite group race winning horses are genotyped, association between MSTN sequence and racing phenotype

most race horses have a time

true

environmental effects on phenotype for racing

jockey, training, track, competition

horses are effected by level of competition, can cause horses to run faster or slower

true