Growth, development and growth manipulation in goats.

A thorough understanding of growth and development in goats and the factors that affect these processes is important, because it affects the efficiency of production and it has a direct bearing on product quality. Although the use of growth promotants or molecules that change the efficiency of growth are not generally employed in goats, other more natural pathways exist to manipulate growth and development. These approaches do not detract from product quality and provide the opportunity to produce meat, milk, fibre, leather and related products that meet the demands of consumers for more environmentally friendly and natural production systems. Growth and development in goats occur in a similar way compared with other land-living mammals, and these processes are directly dependent on influences in the external and internal environment. There is great significance in the way in which the growth and developmental processes have evolved in goats to ensure the propagation of this unique species. There are obvious advantages in ensuring a minimum size at birth in terms of survival value, while the size of the birth canal limits excessive size at birth. The skeletal size of goats is rather variable due to the effects of natural selection and adaptation of the various breeds or types of goat to different ecological regions in the world. Goats are subdivided into three categories based on frame size, namely, dwarf breeds, small breeds and large breeds. Embryological development includes organogenesis, skeletal growth and development, myogenesis and adipose tissue synthesis and deposition. The growth and development of fatty tissue in goats occur at a lower rate and to a lower extent compared with sheep. Accumulation of abdominal fat occurs at an earlier stage compared with subcutaneous fat in all genders. Growth is a chronological process and its inevitable consequence is an enlargement in size and ageing. Ageing is associated with an increasing inability to sustain the functional integrity of cells, organs and systems. Animal growth is the consequence of complex interactions between the genetic potential of the animal and several hormones, the nutrient supply and the environment. This complexity is beneficial in terms of manipulating growth and development because it provides the possibility for many different ways of manipulating growth. The most significant means of manipulating growth and development in goats include genetic selection, castration and intensive fattening. Selection pressure on different production characteristics has resulted in the development of different types of goat for different purposes. The effects of nutrition on the growth and development of goats are well documented. These effects are sometimes described as 'production system' effects and include 'intensive' feeding and conditioning, or 'extensive' grazing. Certain goat genotypes respond better to feeding or feed supplementation, and this ability differs mainly between the dairy and meat types of goat. Conditioning of goats has a marked effect on body composition. Consumer preferences for goat carcasses differ among countries and this makes it difficult to implement universally acceptable grading or classification systems, as well as standard carcass cuts. In addition, the variation in subcutaneous fat thickness between goats of different ages, sex and types is extremely limited, which makes it difficult to use fat thickness for purposes of carcass classification or grading.