Unit Summary

Mammary gland development commences embryonically and continues post-natal even during
lactation. The mammary gland begins developing in utero at approximately 30 d gestation in
dairy cattle. Puberty in females may be attained when the heifers have gained 35-45% of their
mature body weight but the breeding should be allowed when the female has gained 55% of
adult body weight. When a pregnant cow is dried off, there is some stimulation of udder
growth, so a complete loss of alveoli cells does not occur. It is important that cows are dry for
their last two months of pregnancy. Lactogenesis is manifested by a process of differentiation
of mammary cells, an increase in the blood uptake of precursor molecules, an increase in the
enzymatic activity responsible for the synthesis of the components of milk, in this way the
mammary cells acquire the capacity to synthesis and secretion of milk. The synthesis of milk
components is a process that requires energy, the two main sources of energy are glucose and
acetate, these molecules are degraded by various metabolic pathways to produce adenosine
triphosphate (ATP). The ejection reflex in the cow is induced by mechanical stimuli such as
touching or massaging the nipples of the mammary glands that activate pressure-sensitive
receptors in the dermis of the nipple, also by visual or auditory stimuli such as presentation and
bellowing of he calf, udder washing or milker presence. There are many factors may alter milk
composition, but the mechanism involved may be indirect with the direct cause of the
compositional change being the total amount of milk produced. Of these factors are the
environmental factors such as feeding, and overall management and genetic factors are the
most important ones.