Genetic Influences on Growth, Meat Quality and Muscle myopathy

Question 1

Why breed for Beef Tenderness?

Answer 1

Tenderness is the most important factor determining consumer satisfaction

Difficult factor to control at processing:
chill rate: the meat in the beef carcass does not fall below 10 degrees within 10 hours postmortem to avoid cold induced toughening
Temperament: animal reaction to an unfamiliar or challenging situation
Stress: pre-slaughter stress depletes muscle glycogen, resulting beef with a higher pH, darker colour, firm and dry

Question 2

What are the available tools for beef tenderness at present?

Answer 2

Traditional selection and breeding (time consuming and costly, only to known about sire and dam performance)

Aging (wet and dry) - post mortem proteolytic enzymes (to increase tenderness and taste, expensive process)

Calpastatin and calpain activities to beef tenderness (calpain enzyme naturally breaks down the muscle fibers in beed during the post mortem aging process)

Protein turnover

Question 3

What is commercially available?

Answer 3

Genomics technologies allowed researchers to identify DNA markers associated with different beef production traits including beed tenderness

Question 4

Gene contributing to genetic variation of muscling

Answer 4

Myostatin
A negative regulator of myogenisis
Suppresses myoblast proliferation and myogenic differentiation
TGF-B regulates at the terminal differentiation level, blocking the differentiation of myoblasts
Myostatin inhibits myogenic differentiation by inhibiting the expression of the myogenic transcription factor MyoD and myogenin
Controls the muscle fiber number
The function of myostatin in highly conserved among mammals
Mutation causes “double muscling” in cattle, sheep, mice, humans, dogs, pigs
Autosomal recessive, bovine chromosomes 2
Typical cattle breeds of DM: Belgian blue, Charolais, Piedmontese
There are 9 variants of the mutation identified in cattle that occur in differing levels in different breeds

Question 5

Double Muscle

Answer 5

D = normal functioning myostatin gene
d = one of the mutated variants form of the gene

Calves can be:
DD = Regular muscle with two normally functioning genes for myostatin (Normal)
Dd = some double muscle characteristics (heterozygous carrier) –> increase muscling without calving difficulties; useful under rangeland management to increase muscle mass without calving problems
dd = extreme DM characteristics (homozygous)

Question 6

The super cow

Answer 6

20% more muscle

Reproductive issues:
late puberty
poor reproductibe tract development
calving difficulty

extent of double muscling varies with polymorphism

Question 7

Impact of double muscling

Answer 7

Increase muscle mass of about 20% due to hyperplasia and a lesser extent of hypertrophy

Collagen reduced in amount and has a lower proportion of stable, non-reducible, collagen cross links

the bone mass tends to be around 10% less than that of normal cattle

having a higher percentage of PUFA 6% higher

higher dressing 65-70% this is due to:
increase muscle mass
reduced body fat, bone mass and smaller internal organs

Question 8

Myostatin F94L varient

Answer 8

Many different mutations have been identified in the bovine myostatin gene

one of the mutations in the bovine myostatin gene is a cytosine (C) to adenine (A) transversion in exon 1, causing amino acid substitution of leucine of phenylalanine

associated with increased loin muscle area and increased mono-unsaturated fatty acids

Question 9

The Callipyge sheep

Answer 9

Greek for “beautiful buttocks”

Ram named soil gold - solid gold sired lambs that had significant hypertrophy of muscles in the hind leg and loin

trait only occurs in lambs that inherit that callipyge mutation from the sire

only known example of polar-over dominance

lambs born with 2 copies of the mutation appear normal

Question 10

Callipyge sheep study

Answer 10

Callipyge lambs appeared normal at birth

At 7kg live weight were similar between phenotypes

selective muscular hypertrophy of callipyge lambs develops during the postnatal growth period

Question 11

Effect of temperament on Live weight and beet quality

Answer 11

As the temperament score increased:
- Average daily gain decreased significantly
- The incidence of dark cutting (DFD) in beef increased significantly
- Meat toughness increased significantly

Question 12

Selection for muscling: Pigs

Answer 12

selection based on growth rate, carcass leanness and visual appraisal: inadvertent selected for poor meat processing and eating quality

Halothane gene is the RYR1 gene which encoding the calcium release channel is the skeletal muscle sarcoplasmic reticulum called ryanodine receptor

mutations appeared with these selections in two major genes referred to as halothane (HAL) and rendement napole (RN)

Same result: pale, sold and exudative pork (PSE pork)

Question 13

Causes of PSE in pork

Answer 13

Genetics (halothane gene and rendement napole gene)

Environment

Question 14

Halothane Gene

Answer 14

Makes pigs more stress susceptible and causes porcine stress syndrome

The animals typically responded to stressors by developing a condition known as malignant hyperthermia

Question 15

Rendement napole gene

Answer 15

causes higher incidence of glycolysis

Question 16

Porcine stress syndrome (PSS)

Answer 16

genetic defect in the ryanodine receptor of SR

mutation lead ryanodine receptor hypersensitive and releases excessive calcium from SR into muscle severe muscle contraction

Heritability low (recessive gene”nn”)
Heavily Muscled pigs
Halothane causes muscle ridgity

Question 17

Pale, soft, and exudative pork

Answer 17

Pale - because myofibrillar protein and myoglobin dentures leads to greater degree of reflection of light

Soft - because the water escaped from muscle ells to equalize osmotic pressure and accumulates between the myofibrils tearing the connective tissue

Exudative - because as muscles are cut these is excessive loss of water from ECM area

Question 18

Why are post-mortem muscle pH and temperature important?

Answer 18

low pH at high muscle temperature denatures muscle proteins

Denatured muscle proteins release water from their structures

Denatured muscle proteins release water from their structures

Denatured muscle proteins determine meat colour, water holding capacity and eating quality

water leaks from muscle cells -> produces drip

Question 19

minimizing PSE pork

Answer 19

rapid chilling of carcass sides - slow down anaerobic glycolysis and reduce the temperature to pH ratio

Minimizing stress

Question 20

White stripping (Myopathies in Broiler meat)

Answer 20

parallel white stripes on the surface of the pectoralis major muscle

Question 21

Woody breast (Myopathies in Broiler meat)

Answer 21

accumulation of connective tissue fibers and fat cells in the pectoralis minor muscle

Question 22

Spaghetti meat (Myopathies in Broiler meat)

Answer 22

appearing like splitting of muscle bundles, which seam to be associated with fast growing and heavier birds