ANP 303- Growth and Development

There is no single definition for growth. Growth may simply be defined as an increase in size. It could be an increase in weight of an animal or any part of the animal as it approaches mature body size. Growth is an increase in body height, length, girth and weight that occurs when a healthy young animal is given adequate food, water and shelter. It is a fundamental characteristic of all living organisms. Growth can be more specifically defined as a normal process of increase in size, produced by accretion of tissues similar in constitution to that of the original tissue or organ. This increase in size is accomplished by any of these processes: • Hypertrophy – an enlargement of cells • Hyperplasia – an increase in the number of cells • Accretion – an increase in the quantity of non-cellular material Growth can be considered in two aspects in animal production. Firstly, true growth, which comprises an increase in the structural tissues such as muscle, bone and vital organs. Secondly, fattening, which comprises an increase in deposition of fat or adipose tissue (where fat is stored). Growth usually involves increase in size and development. Growth, in terms of increase in size, can occur without development but development cannot occur without growth. Development is a gradual progression from a lower to a higher stage of complexity as well as gradual expansion in size. This increase in complexity involves differentiation and specialization for increased functionality. Differentiation is the process by which cells and organs become unique and acquire completely individual characteristics such as simple cells of the embryo diversifying into muscle cells or brain cells or cells of different organs. Differentiation also involves morphogenesis, which involves the organization of various dividing cells into specific organs. Differentiated cells undergo maturation, which is when they become fully developed. Fully mature tissues have attained their highest stage of complexity. The end of growth and development is senescence, when individual tissues and organs are no longer maintained in their mature form but begin to degenerate without complete replacement or repair (Forrest et al., 1975). The growth of animals commercially exploited in animal production can be divided into two phases, prenatal and postnatal. Animals had started growing before being born, and thereafter continue to grow until slaughter or period where products are harvested.