Agriculture Reference
In-Depth Information
composition of goat meat. A brief informative coverage of
potential goat meat products is also presented in this
chapter.
most does may kid at 1 year of age. Some producers do
not breed does during their fi rst year, but prefer to allow
the female to grow to maturity without the nutritional
demands of pregnancy on the body, which may infl uence
growth rate. It is advisable to allow the doe to be at 60-
75% of her adult weight before breeding. When an animal
reaches the highest degree of complexity in the body, it is
considered to be mature. In a practical sense, livestock and
avian species are considered to have reached maturity
when a maximum body weight that remains stable without
excess fat deposition has been achieved.
GROWTH STAGES
General Growth Changes
Growth may be defi ned as an increase in weight until a
mature size has been reached, and maintenance is the con-
stancy in weight or other measurement of growth. Growth
is a function of the life cycle of each animal that begins
with embryo fertilization and ends with death. Growth and
development may be separated into two distinct processes:
growth attributes and developmental changes.
Any increase in body weight, size, shape, form, compo-
sition, or structure over time may be considered to be
growth. Cells are the basic unit of growth, and develop-
ment is an increase in complexity of the body components
that comprise the body. Usually weight is an overriding
factor in determination of growth because it is more easily
measured than the other body changes. Development or
complexity occurs when there is a differential rate of
change or distinguishing of characteristics of specifi c body
components. In the early stages of life cycles, it may be
more diffi cult to separate changes due to growth and
changes in complexity.
Chemical components are compounds that constitute all
matter. The major chemical components in the animal
body are known as nutrients and are water, lipid, protein,
ash (minerals), carbohydrates, and vitamins. Physical com-
ponents are the tissues and organs composed of cells.
Physical components of the body are often generally clas-
sifi ed as lean, fat, bone, digestive, and neural.
The different organs and tissues grow and develop at
different rates. Chronological or calendar age is measured
as the number of days after parturition (birth); the physio-
logical age is used as a guide to the relative development
of the body at a given age compared with the development
at a mature age. Cell types are specialized for specifi c func-
tions or purposes, and the process of differentiation is the
specifi c time when a cell or groups of cells has character-
istics distinct from those of other cells or groups of cells.
Ontogeny is the progression of an individual through its
life cycle. Prenatal is the time before parturition, and post-
natal is from parturition to death. Puberty is the stage in
the growth and development cycle when an animal is able
to sexually reproduce offspring. Male goats often reach
puberty at 4-8 months; female goats reach puberty in 7-10
months. The age at puberty varies between breeds, although
Prenatal Growth
Prenatal growth occurs in three main phases:
1. The ovum phase is from fertilization to implantation on
the uterine wall and is characterized by cell division
through proliferative mitosis to form a zygote.
2. The embryonic phase is from implantation to tissue
differentiation. After implantation, the blastocyst dif-
ferentiates into the inner cell mass and the embryonic
disk. The fl attened plate of embryonic disk cells of the
morula differentiates into the primary germ layers. The
outer germ layer that surrounds the amnionic cavity is
the ectoderm. The primitive streak becomes the noto-
chord and rolls into a neural tube that differentiates into
the brain, spinal cord, nerve, and epithelial structures.
The middle germ layer, the mesoderm, forms somites
on the sides of the neural tube that will develop into the
circulatory system, mesenchyme (connective tissue and
bones), and myotome muscle plates (muscles). The
inner germ layer that lined the yolk sac, the endoderm,
will differentiate into the digestive system and glands.
3. The fetal phase of prenatal growth is from differen-
tiation to parturition. During this phase, tissues
and organs are further differentiated, and the fetus
size increases through rapid hypertrophy of cells.
The greatest prenatal weight gains are in this phase
and are affected by the nutritional and disease status of
the doe.
Postnatal Growth
The factors that affect postnatal growth and development
are genetic potential and the infl uence of environment and
nutrition to allow the animal to reach its genetic potential.
The different body components have relative size changes
during postnatal growth and development. The head is
proportionately larger than other body parts at birth, so
early postnatal growth is for size and shape of the body
before the limbs begin to lengthen. The pattern of postnatal
