Growth, Composition and Meat Quality

ANSC 590 ANIMAL GROWTH AND DEVELOPMENT

USDA GRADING

Quality versus Yield Definition(s)- provide uniform standards

Table 12.1 Factors Affecting Quality Grades

Kind, Class and Grade Maturity (Figure 12.2) Marbling relationship to palatability

Poultry (Table 12.2) Yield/Cutability (Table 12.3)

Yield Grade Relationships

Fat, muscle and bone relationshipsFigure 12.14

Regression models versus short-cut calculations

Anatomical measurements for compositional traits

Ex. Pork percent muscle, Beef yield grade

Conversion of Muscle to Meat

Ante-mortem versus post-mortem conditions of the animal

Steps:StunningExsanguinationAerobic to anaerobic conditionGlycogenolysis

Conversion of Muscle to Meat

ATP to ADP , thus energy expended Pyruvate converted to Lactate and

ultimately lactic acid Progressive reduction in pH Deviations of normal post-mortem

metabolismDark cutters, PSE, etc.

Meat Tenderness

Little can be gained by improvement of animal growth if the resulting quality of the endproduct is undesirable to the consumer

Connective Tissue- collagenAs animals mature crosslinkages increase

resulting in more stability, yet tougher and stronger collagen bonds thus decreases solubility and reduces gelatinization

Meat Tenderness

Myofibrillar Protein InteractionsDegree of overlapping structures within

actinomyosin formation resulting in varying sarcomere length

Proteolytic activity Calpain enzyme system are responsible for

destruction of myofibrils

Quality versus Quantity

Figure 12.23 Sex/gender variations within growth and

development-biological maturity Intact males have:

Less fat as well as less firmness of fat Increased protein, myoglobin, red color, yields Increased off-odors due to increased steroid metabolism

synthesized by the gonads, stored in the salivary glands, released by the saliva ingested and deposited in the fatty tissue

Skatole is a fat-soluble cmpd from tryptophan metabolism in the hind gut esp. in swine and is correlated to the off-odor

Absence of Fat

Cold shortening possibility Age

Negative relationship with increased ageExcept with feedlot cattle

PSS in pork

Rendement Napole Gene Acid meat Responsible for glycolytic potential index AMPK- adenosine monophosphate-activated protein

kinase which is responsible for synthesizing glycogen If this ability is lost and glycogen is accumulated at a

higher rate this produces more lactate and ultimately results in more acid meat upon rigor mortis completion

PSS pork

Halothane Gene Extremely lean pigs Incapable of handling stress Malignant hypothermia along with cyanotic (blue),

lethargic, increased respiration, and increased core body temp

Characterized by a severe reaction when exposed to halothane gas

Positive pigs possess a mutated calcium release channel located in the SR. This is known as ryanodine receptor

PSS pork

Halothane cont. Increased metabolism is a result of increased

ctyoplasmic calcium in early postmortem. This stimulates increases in glycogen phosphorylase which speeds up glycogen breakdown.

This increased rate of metabolism then increases the rate of pH decline when carcass temps are elevated

This ultimately reduces the water holding capacity

Double Muscling

Muscular hypertrophy- increase fiber size Increase yield and gains Decreased quality and reprod effic. Less connective tissue Increased cold shortening effect

NUTRITION

Delayed feedlot gains will decrease tenderness Shorter periods of feeding high energy will

results in lower quality aspects Connective Tissue concentration remains

constant with increased growth rates Due to increased proteases Lacks excessive cross-linking More soluble collagen matrices Do not remove high energy too long before slaughter

this may result in Dark Cutters

Repartitioning Agents and Hormone Implants Table 12.7 and 12.8 Somatotropin Beta-agonists Hormones- estrogen, progesterone, testosterone Effects on tenderness Table 12.9 Effects on sensory perceptions Table 12.10