Lactation

  • Lactation is the process of producing milk, occurs in all mammalian species

  • Lactogenesis

    • Stage I Lactogenesis

      • Immunoglobulin uptake occurs and colostrum is formed, much of this is prior to parturition

    • Stage II Lactogenesis

      • Copious milk secretion begins, and during the next few days colostrum production is shut down and milk of normal composition is produced

  • Anatomy

    • Alveoli

      • milk secreting structure

    • Lobe

      • contains several alveoli

    • Duct

      • pathway that carries milk

    • Gland cistern

      • collection point where milk pools

    • Teat Cistern

      • Perfect swallow for neonate

    • Sphincter Muscle

      • closes the mammary gland off from the outside world and bacteria

    • Streak/Teat Canal

      • last canal that milk flows through to leave the body

  • Mammary Gland Development

    • Mammogenesis: development of the mammary gland

      • Birth to Puberty

        • Duct growth and little alveolar growth

      • Puberty to Pregnancy

        • Duct System becomes branched - estrogen

        • Alveoli and lobe development- progesterone

      • Pregnancy to Parturition

        • Final growth and development

        • Lactogenesis - initiation of milk secretion

          • Oxytocin

          • Prolactin

          • Estrogen

          • Progesterone

  • Endocrine Control of Lactation

    • Progesterone

      • Initiates milk synthesis

    • Placental lactogen

      • Produced by placenta to stimulate mammary gland development

    • Prolactin

      • Released just prior to parturition, works synergistically with other hormones to initiate and maintain lactation

    • Oxytocin

      • Stimulates milk let-down

    • At time of parturition

      • Prolactin, oxytocin, and glucocorticoids reach peak levels to bring mammary glands into full production

  • Release of the teat sphincter can lead to an increased risk of mastitis because it remains open for 15 - 60 minutes making the teat canal susceptible to entry by microorganisms

  • Milk Letdown

    • 2 forms of milk secretion

      • Passive Milk Removal

        • negative and/or positive pressure; i.e. suckling by calf

      • Milk ejection reflex

        • Milk is forced out of the mammary gland by contractions of the myoepithelial cells

      • Triggers

        • Sight, smell, sound, touch of neonate

  • Factors that affect milk production

    • Although females begin producing milk immediately after giving birth, milk production does not peak for several days to weeks after parturition

    • Generally, sows reach peak production 18-22 days after farrowing and cows reach their peak production at 50 to 70 days postcalving

    • The mammary gland undergoes a gradual involution, decreasing in weight, volume, and productivity as lactation progresses

    • Factors:

      • Feed and management

      • Stress

      • Mastitis

      • Milk demand

    • Milk Demand + Growth Rate + Environment = Milk Composition