Scientific Farm Animal Production
Quiz 18 :
Growth and Development
The prenatal life includes three phases known as sex cells, embryo and the fetus. Embryological development starts with the spherical mass of cells differentiating into specific cell types and eventually developing into organs. The endoderm forms digestive tract, lungs and bladder. The mesoderm produces skeleton, skeletal muscle and the connective tissue. The ectoderm produces skin, hair, brain and spinal cord. The growth and development and differentiation mainly involve the process of protein synthesis that are directed by DNA chains of chromosomes and organizes the developing embryo. Therefore, the nucleus is the activity center for different types of cells to direct the growth and development process. The fetus undergoes noticeable changes in shape and form during the prenatal growth and development. In early prenatal period, the head much larger than the body and later the body and limbs grow faster than other parts. The tissue growth is sequential and determined by the physiological importance. It begins with the development of central nervous system and progresses to the development of internal organs, bones, tendons, muscles, intermuscular fat and subcutaneous fat. In the first two-thirds of prenatal period, increase in muscle weight is due to hyperplagia or increase in number of muscle fibers. In the later 7 months of pregnancy and in post natal period, development is due to hypertrophy or increase in the size of muscle fibers that contribute to the muscle growth. The content of water in the fetal muscles reduces with the fetal age and declines in postnatal growth as well. The relative size of fetus changes during gestation period resulting in largest increase in weight occurs during the last trimester of the pregnancy.
Development of chick is different from development of mammals because there is no physiological connection with its mother. The development of the chick takes place outside the hen's body. Therefore, the embryonic development in chicks is more rapid than in the farm animals. The fertile or nonfertile egg contains a germ spot known as blastoderm. Blastoderm is the site of development of chick embryo in the fertile egg when it is properly incubated. Controlled environment must be maintained in order to incubate the fertile eggs and to produce live chicks. The controlled environment should include the temperature in the range of 99.5 to 100°F, relative humidity in the range of 60 to 75% and the turning of the egg for every 1 to 8 hours and providing adequate oxygen supply. Post fertilization the blastoderm divides to form two cells after 3 hours. The cell division takes place till the maturity except in the holding period before the incubation of eggs. Four growth membranes are observed in the chick embryo. The allantois is a membrane that enables the embryo to breath. It takes the oxygen through the pores of the shell and supplies the oxygen to the blood of the embryo. Allantois removes the carbon dioxide and also receives the excretions from kidneys. It absorbs the albumin that serves as the food for the embryo and calcium from the shell for the use of embryo. The amnion is a membrane filled with colorless fluid and provides protection from mechanical shop. The yolk sac is a layer of tissue growth produced over the surface of the yolk. This tissue contains special cells to digest and absorb the yolk material for developing embryo. The chorion is the membrane surrounding the amnion and yolk sac. During the development of the embryo, several phenomenal changes take place rapidly and sometimes within hours.
The muscle tissue is of three types known as skeletal, smooth and cardiac. Skeletal muscle is the biggest component of meat animal products. Smooth muscle is located in digestive, reproductive and urinary organs. Heart is composed of cardiac muscle. The muscles of poultry are known as dark meat (legs and thighs) and white meat breast and wings. Dark meat is produced from muscles containing high amounts of myoglobin that helps the transport of oxygen to muscles. Dark meat muscles require more oxygen because of their high work capacity. Muscle converts the chemical energy into mechanical energy and performance of muscle depends on power, strength and endurance. Power of the muscle is determined by the amount of work that can be done in a fixed period of time. Therefore, the power is the resultant of speed and strength of muscle contraction. Strength of the muscle depends on the muscle size and larger muscles have greater contractible force. Endurance is the length of the time required by a muscle to work without fatigue. Endurance depends on the nutrient storage capacity of muscle. The three components of muscle performance are improved in a working horse through effective training program. Skeletal muscle fibers are differentiated into fast twitch and slow twitch fibers. The fast twitch fibers occur predominantly in sprinters and jumpers. Fast twitch fibers have significant power and are efficient in managing the anaerobic activity for short periods of time. This is because they have less capillary supply than the slow twitch fibers. The fast twitch fiber is also known as white fibers. Slow twitch fibers are known as red fibers and rich in capillary supply. Therefore, they are well suited for aerobic supply of nutrients and endurance activity. The slow twitch fibers have small diameter than the fast twitch fibers and contain more myoglobin to increase the oxygen diffusion.