Growth and body composition of animals
19 important questions on Growth and body composition of animals
Draw the sigmoidal growth curve
- Relationship between weight of an animal & its age (S-curve)
- Food for maintenance of existing tissue & growth of new tissues
- Growth is fastest at maximum point
- Growth is most efficient as limited energy is used for maintenance
- Occurs at 30% mature weight
The rate of growth can be described in two different ways:
- divide increase in weight over a particular time by length of that period
- average growth rate = w2-w1 / t2-t1
Relative growth rate
- increase in weight over a time period divided by initial weight
- Relative growth rate = w2-w1 / w1
Certain tissues, organs or parts of the body grow faster than others. Explain by drawing the growth curves
- Head; Brain; Cannon; Kidney fat
- Neck; Bone; Tibia-Fibular; Intermuscular fat
- Thorax; Muscle; Femur; Subcutaneous fat
- Loin; Fat; Pelvis; Intramuscular fat
A - Early maturing animal or animal on high plane of nutrition
B - Late maturing animal or animals of low plane of nutrition
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Growth of tissue consist of two processes
- Number of cells increase by cell division
- Hyperplasia
- Most occurs before birth
- 30-40 cel divisions take place during gestation compared to 2-4 post-natally
- Cells increase in size
- Hypertrophy
- After birth tissue mass increases with little change in number of cells (cels hypertrophy)
Is the fibre size similar in larger animal species?
double muscled animals have more & larger fibres in muscles than normal animals = pronounced muscling when mature
- lack myostatin (which inhibit differentiation & growth of myoblasts before birth
What are the four major deports [fat growth]
- Subcutaneous
- Perinephric
- Omental
- Inter- & intramuscular fat
How is growth controlled
- e.g. Insulin, growth hormone (somatotrophin), insulin-like growth factors & epidermal growth factor
- sex hormones (oestrogen & androgens)
- important factors limiting potential growth is stimulation of immune system by environmental factors
- leptin (mainly produced in adipose tissue
- controls food intake, energy expenditure & body weight
Carcass yield (opbrengst) =
- weight of carcass to weight of live animal = important measurement of meat yield
- killing-out% = dressing %
- killing-out% = (carcass weight/live weight) x 100
- carcass weighted immediately after preparation & before cooling
- cooling = moisture loss
- hot vs cold carcass weight
Killing-out% differs in different species
- Sheep & cattle have bigger guts
- Pig carcasses - include skin, feed & head
What is conformation? [carcass conformation]
- Conformation --> carcass shape
- Reflect proportion of muscle to bone
- Good conformation = appearance of thicker more defined muscles
- higher price
- joints & steaks of better appearance
- at same level of fatness these carcasses yield more lean meat
- modern breeds selected for better carcass conformation
- High muscle/bone ratio = good carcass conformation
How does castration influence the muscle development of male animals?
- older animals tend to be fatter
- fat deposited mainly from onset of puberty
- daarin cattle breeds have carcasses with more muscle & less fat than beed
- male animals are
- leaner than females
- grow to larger mature size
What are the two main edible components of an animal's carcass
- Muscle (lean)
- Adipose tissue (fat)
animal tissue: protein & chemical fat associated with w
- Muscle contain about 75% water & 20% protein
- Adipose tissue contains only 30% water
Discuss the difference in meat quality between a Texel lamb on a high plane of nutrition versus one on a low plane of nutrition if they were both slaughtered at the same chronological age
food place a role - the energy of the food
What happens when animals get older & heavier?
muscle:bone ratio
- higher ratio better = more saleable lean meat & better carcass conformation
What are the growth-promoting steroids? (5)
- Androgens - actions like mal sex hormone testosterone
- Oestrogens - actions like female sex hormone oestradiol
- Progestagens - act like female hormone progesterone
- Trenbolone acetate - synthesis androgen that promotes growth by decreasing protein degradation in muscles
- Zeranol - synthetic oestrogen that promotes growth by decreasing protein degradation
sex hormones important in fatness & growth control
females tend to respond beter to androgens and males to oestrogens
What are beta2-agonists & how are they used to manipulate meat quality?
Called so because act on cells via beta-receptors cell0membrane
may produce meat darker & duller in colour & tougher after cooking
use not permitted in EU
The use of porcine & bovine somatotrophin (PST & BST)
- Giving frequent growth hormones (somatotrophin) to pigs in decreases carcass fat and increases muscle development
- Somatotrophin can be produced by bacteria using recombinant DNA techniques to insert appropriate genes
- naturally occurring may be more acceptable to consumers than beta-adrenergic agonists
- Not currently permitted in EU
Why do we classify & grade carcasses?
- To describe carcasses & allocate to categories based on criteria like fatness & conformation
- Classification schemes should be differentiated from grading schemes
- classification: objectively describes carcass in terms of estimated yield & weight
- grading: assigns a yield & weight class/values (for pricing purposes)
- Description of carcasses in classification schemes enables buy & sell unseen
- Facilitates carcass going to appropriate use
Explain how the (S)EUROP classification system works, i.e. What do the letters stand for? Also, mention which class would be considered more valuable
- S = superior - >60% lean meat
- E = excellent - 55 - 60%
- U = very good - 50-55%
- R = good - 45-50%
- O = average - 40-45%
- P = poor - <40%
S has highest % of lean meat, this is better & most valuable
P has lowest % of lean meat
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