Factors Influencing the Development and Growth of Muscle of Meat Animals
Shubha Singh* and Bhawana
Ph.D. Scholar, LLR University of Veterinary and Animal Sciences, Hisar, Haryana, 125001
*Corresponding author: drshubha.singh06@gmail.com
Introduction
The increasing pressure of world population and need to raise living standards has made the production of more and better meat. The sequence of development of various muscles in the body reflects their relative importance in serving the animal’s needs. Thus, the early development of the muscles of the distal limbs confers the mobility required to forage for food; and the development of the jaw muscles promotes effective mastication of the food secured. Muscle growth is controlled by many factors like Genetic Factor, physiological age, nutritional Factor and hormones & hormones like materials.
- Genetic factor: –
Animals of given breeds grow and develop in characteristic manners and produce carcasses with distinctive characteristics that are peculiar to breed. E.g., Duroc pigs and Augus cattle are known for their tendency to deposit intramuscular fat. A major difference between dairy and beef breeds is the distribution of various fat depots, dairy type animals tend to have higher proportions of subcutaneous fat than beef type animals. Mature size also is a breed characteristic, e.g., Southdown sheep are smaller than suffolk sheep. In meat animals, Phenotypic variations are due to genotype, environment, or to an interaction of both. Genotype provide necessary potential for growth and development; the environment will tend to maximize or minimize the realization of this potential. Occasionally, mutations occur in genes that encode for specific factors that control animal or muscle growth traits. Various genes identified by DNA isolation technique which control muscle growth. Eg Myostatin gene for Double muscling, Callipyge gene.
- Myostatin gene for double muscling:-
It is present in cattle that results in thick, bulging muscles. Double muscled animal has the same number of muscles as normal animals but have nearly twice as many muscle fibres, which results in an exaggerated muscle hypertrophy. Coupled with nearly twice the muscle fibres, double muscle animals have a lower proportion of red fibres and a higher proportion of white fibres than normal animals.
- Callipyge gene in sheep: –
It causes enlarged muscle development in hind legs and loin area of lambs. It causes greatly exaggerated hypertrophy (as much as more than 40% more than normal) in specific muscles of loin and hind legs and less hypertrophy of muscles of forelimbs. These muscles have less fat compare to normal muscle.
At cellular level, muscle of callipyge lambs has greater protein to DNA ratio, more white muscle fibres & greater fibre diameter. This phenotype is caused by point mutation in telomeric end of ovine chromosome 18 which show polar over dominance.
- Physiological age: –
Physiological age refers to stage of development of an animal that can be described by identifiable stages of body development or function, such as body weight, body composition or onset of puberty. All animals within species or breeds or among sexes do not grow, develop, fatten, or mature at the same chronological age. Animals may attain physiological age at different chronological ages and may be described as being early or late maturing. Thus, at a given chronological age, animals form an early maturing breed would be physiologically older than animals from late maturing breed.
- Nutritional factor: –
It is possible to control the rate at which different tissues and parts of body grow and develop by altering the nutritional level of animals at critical times. Eg. When pig is maintained on high level of nutrition during first several weeks of postnatal growth, the growth rate of bone, muscle and fat is greater than pigs on a low level of nutrition. Animal full fed high concentrate diets usually produces more carcass fat & less efficient in converting feed to lean meat than are animals fed slightly below Ad libitum energy intake.
- Protein: –
An adequate amount & supply of protein is required in animal diet for growth & maintenance of tissue. Growth rate in monogastric animals are reduced by an inadequate total amount of protein. In ruminant animals, amount & quality of dietary protein are less critical than in monogastric. If animal consume surplus of protein, the excess is broken down & uses as energy or stored as fat.
- Fat:-
Dietary fats are used by the animal for energy & certain fatty acids are essential for growth. They also may be assimilated and deposited as body fat. All meat animals are able to synthesize fatty acids in the liver or adipose tissue from carbohydrate and proteins & fat is deposited is characteristic of species. Fat in diet of monogastric animal may be assimilated & deposited in relatively unchanged form whereas dietary fat consumed by ruminants undergo degradation & resynthesis of more saturated fat by rumen bacteria before assimilation and deposition.
- Hormones and hormone – like materials
Hormones are substances secreted into body fluids by ductless endocrine glands. They act as regulators of chemical reactions involved in growth process, maintenance of tissues & other physiological process. E.g., somatotropin produces lean tissue growth throughout the animal. It promotes the release of insulin like growth factor (IGF) from liver which is responsible for protein synthesis associated with somatotropins. Such hormones induced protein accretion partitions the utilization of nutrients towards lean tissue growth & away from fat deposition. Epinephrine & norepinephrine in reference to muscle tissue assist in mobilization of glycogen to provide energy however their effects influence muscle protein & lipid metabolism also. Hormones of testes & ovary play an important role in growth & development of body. Males usually grow faster & have carcasses that are more muscular & less fat than females. Androgens stimulate growth in muscle by increasing protein synthesis, particularly muscles of forequarter of males especially those in neck & crest region shows greater development than in females. Androgens also stimulate deposition of bone salts causing increase bone growth as compare to females. Estrogens have little or no effects on skeletal muscle protein synthesis. Synthetic estrogens with synthetic progesterone are effective in increasing cracass leanness of growing wethers steers by stimulating muscle growth and suppressing fat deposition.
