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Chapter 15: Lactation. Chapter overview: Chapter 15 reviews the anatomy and physiology of lactation, including: comparative anatomy of mammary system of various mammals growth and development of the mammary system physiology of milk production and release. Lactation :.

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chapter 15 lactation
Chapter 15: Lactation
  • Chapter overview:
    • Chapter 15 reviews the anatomy and physiology of lactation, including:
      • comparative anatomy of mammary system of various mammals
      • growth and development of the mammary system
      • physiology of milk production and release
  • Lactation may be defined as milk production
  • A part of the definition of a mammalian species is the ability to produce milk
  • Mammary glands produce the milk
  • Mamma - a Latin word which means breast
  • Milk production is an endocrine and exocrine function
mammary system comparative anatomy
Mammary System: Comparative Anatomy
  • Bovine - four glands in the inguinal area; each teat serves one gland
  • Ovine and caprine - two glands in the inguinal area; each teat serves one gland
  • Equine - four glands formed into two units in the inguinal area; each teat serves two glands
mammary system comparative anatomy4
Mammary System: Comparative Anatomy
  • Porcine - multiple glands from pectoral to inguinal area, arranged in two rows; each teat serves two glands
  • Canine and feline - multiple glands from pectoral to inguinal area, arranged in two rows: each teat has up to 10 streak canals
structures of the mammary gland
Structures of the Mammary Gland:
  • Alveolar cell- basic cell producing milk in the mammary gland
  • Alveolus - microscopic unit made up of alveolar cells with an open lumen for collection of secreted milk
  • Myoepithelial cell- muscle-like cell surrounding the alveolus; contracts to express milk from the alveolar lumen
structures of the mammary gland6
Structures of the Mammary Gland:
  • Collecting duct - tubules formed into a network from fine ducts leaving each alveolus to ever enlarging branches that terminate in the udder cistern
  • Udder cistern - small collecting area for milk above the teat
  • Teat cistern - open collecting area in the teat
structures of the mammary gland7
Structures of the Mammary Gland:
  • Teat - the terminal structure of the mammary system from which milk will be nursed or drawn by machine
  • Streak canal - exit from the teat surrounded by a sphincter muscle to maintain closure until nursing or milking
  • Udder - term applied to the entire system
manufacture of milk
Manufacture of Milk:
  • Milk is manufactured in the mammary gland by a combination of screening components from the blood and by construction of components from precursors
    • Blood brings components via the pudic arteries
    • Blood carries away the byproducts via the pudic and subcutaneous abdominal veins
    • Lymph system carries away escaped plasma
mammary development
Mammary Development:
  • Present at birth in mammals:
    • Teats
    • Streak canals
    • Teat and gland cisterns
    • Rudimentary collecting ducts
mammary development10
Mammary Development:
  • Impact of puberty and cycling
    • Extension of duct development
  • Impact of pregnancy
    • Development of alveolar system
    • Generally visual evidence of growth
    • At parturition the mammary system of most farm mammals is fully developed for the subsequent lactation period; swine continue development until peak lactation
the dry period
The “Dry Period”:
  • The “dry period” is a period of nonlactation between subsequent lactations
  • A dry period is necessary for optimum lifetime production
  • Between lactations the mammary gland proceeds through a revitalization process of involution, alveolar regeneration, and return to lactation at the next parturition
hormonal impact on lactation
Hormonal Impact on Lactation:
  • Prolactin - initiates lactogenesis (lactation); source: anterior pituitary
  • Somatotropin - influences growth rate of the glands and level of milk secretion; source: anterior pituitary
  • Thyroid hormones - influences milk production by regulating rate of metabolic processes; source: thyroid gland
hormonal impact on lactation13
Hormonal Impact on Lactation:
  • Parathyroid hormone - regulates blood calcium and phosphorus; related to “milk fever”; source: parathyroid glands
  • Adrenal hormones - small amounts necessary for normal milk production; large amounts during stress are counter-productive; source: adrenal glands
hormonal impact on lactation14
Hormonal Impact on Lactation:
  • Oxytocin - causes contraction of myoepithelial cells for milk letdown; source: posterior pituitary
  • Placental lactogens - hormones with prolactin and growth hormone-like activities; source: placenta
  • Insulin - moves glucose across membranes for milk synthesis; source: pancreas
milk synthesis
Milk Synthesis:
  • Water, vitamins and minerals - screened from arterial blood
  • Lactose - manufactured in the alveolar cell
  • Protein - 90 percent is manufactured in the alveolar cells; some passage from blood; critical exception: immunoglobulins in colostrum are transported from dam’s blood
  • Fat - 75 percent is manufactured in alveolar cell
milk letdown
Milk “Letdown”:
  • Milk letdown is the evacuation of milk from the alveolar lumen to the duct system
    • Nerves receive stimuli at the teat end or nipple
    • Stimuli is received in the posterior pituitary
    • Oxytocin is released from pituitary into blood
    • Blood circulation brings oxytocin to mammary tissue
    • Targets are the myoepithelial cells that contract
normal cessation of production
Normal Cessation of Production:
  • As a lactation cycle proceeds, alveolar cells are lost normally
  • Eventually an animal ceases milk production due to degree of loss of secretory cells
  • “Drying off” and involution can be enhanced by cessation of milking or nursing and reduction of caloric intake
factors impacting milk production
Factors Impacting Milk Production:
  • Inheritance - genetic selection for increased production is effective
  • Stage of lactation - cows “peak” about 45 days into lactation, then decline until dry
  • Frequency of milking - more milk is harvested with more frequent milking
factors impacting milk production19
Factors Impacting Milk Production:
  • Pregnancy - late pregnancy fetal demands reduce production, but pregnancy is required for normal initiation of lactation
  • Age - production increases as animals reach maturity, but decreases as older animals begin to physically decline
  • Estrus - production is generally reduced during estrus
factors impacting milk production20
Factors Impacting Milk Production:
  • Dry period - lack of a dry period will reduce production in subsequent lactation
  • Body condition - over or under conditioned animals may have reduced production
  • Environment - high temperature and humidity reduce milk production; extreme cold stress reduces milk production
factors impacting milk production21
Factors Impacting Milk Production:
  • Feed - well balanced diets are critical to maximum production and proportion of some components in milk
  • Proper preparation at milking time and lack of stress - critical to milk letdown and complete removal of milk