Scientific Farm Animal Production
Quiz 19 :
The mammary gland is an exocrine gland producing the external secretion of milk which is transported through a series of ducts. Cow contains four separate mammary glands terminating into four teats. Sheep and goats have two mammary glands with two teats. A mare contains four mammary glands terminating into two teats. Sows contain 6 to 20 mammary glands that are arranged in two rows along the abdomen and each terminates into a teat. The secretary tissue of a mammary gland consists of millions of grape like structures known as alveoli. Each alveolus is supplied with the blood separately. The milk constituents are obtained by the epithelial cells lining the alveolus. The milk is selected with lumen of alveolus and travels through the ducts into large collection area called gland cistern. When the milk is letdown during the process of milking it is forced into teat system and exits through streak canal exterior to the teat. The mammary gland mainly serves two functions. It provides the nutrition to offspring and also serves as a source of passive immunity to the offspring. Milk supply comes from mainly by the dairy cows into a less extent from goats and sheep. Milk supply from water buffalo, yak, reindeer, camels, donkeys and sows is also used in some countries.
Daily average milk production is not dependent on the number of teats. For example, sows contain 6 to 20 mammary glands arranged in two rows along the abdomen and each gland possesses a teat. Of these many mammary glands only 10 to 14 are functional therefore, teat number in swine is not related to litter size or litter weaning weight. The dairy cow produces 55lbs of milk per day. The beef cow produces 15lbs, a doe or goat produces 7lbs of milk per day. A ewe is capable of producing 3lbs of milk while a mare can produce 27lbs of milk and a sow is known to produce 13lbs of milk per day.
Lactation is initiated by the hormones such as growth hormone, adrenal corticoids and prolactin. When the parturition nears, the levels of estrogen and progesterone hormones decrease while the concentration of growth hormone, adrenal corticoids and prolactin becomes effective. During the milking or nursing the milk in the gland cistern is removed. A large amount of milk remains in the alveoli and is forced into ducts by the contractions of myoepethelial cells. The cells contract by the activity of oxytocin hormone secreted by posterior pituitary gland. Suckling reflects the release of oxytocin along with other stimuli such as nudging the udder with suckling calf head to initiate the milk secretion. The milk letdown is associated with feeding the cows or washing the udder. The oxytocin is inhibited by pain, loud noise and various other stressful stimuli.