Lactation

• the process of producing milk following parturition • the defining feature of mammals • provides nourishment of neonatal offspring

• secreted by cells contained in the mammary gland • a balanced ration • contains: water, protein, carbohydrate, fat, vitamins, and minerals

protein (3.2% in cow milk) -casine (80%) (cheese) and whey (20%) carbohydrates (4.5%) in cow milk) -lactose (glucose and galactose) fat (3.5% in cow milk) -triglycerides (butter) minerals (Ca, P) vitamins (all vitamins) -vik k is low, commercial milk D fortified

primary structure responsible for milk production = alveoli huge blood supply required for delivery of -glucose (lactose synthesis) -amino acids (protein synthesis) -acetate and long chain fatty acids (milk fat)

specialized muscle cells respond to oxytocin contract (a bit) to eject milk into ducts called "milk let down" -more correctly "milk ejection"

linked together by tight junctions absorb nutrients from blood (e.g. glucose and AA) synthesize milk components (e.g. lactose, casein and milk fat) secrete products into alveolar lumen milk is stored into alveolar lumen until milk letdown

mammogenesis lactogenesis galactopoiesis (stage 3 lactogenesis) mammary involution

development of the mammary gland

final differentiation of mammary epithelial cell ability to produce milk STAGE 1: immunoglobulin uptake, colostrum STAGE 2: milk secretion begins

stage 3 lactogenesis production and maintenance of milk production

following cessation of lactation

first milk concentrated nutrient supply high in immunoglobulins (antibodies) antibody transfer to neonate (very important in some species) -passive transfer

(of immunoglobulins) extremely important in cow, mare, pig to provide early immunity to disease less important in human, dog, rodent -importance depends on ability of antibodies to cross placenta to fetus colostrum must be delivered in 1st day of life or antibodies won’t be absorbed intact

bovine somatotropin aka bGH bovine growth hormone results in 10-15% inc. in milk production -cow inc. feed intake to meet demand -thus extra milk is not free but is on top of maintenance requirements already being paid for

often associated w/ neg energy balance -mobilization of body reserves (fat) -loss of body weight metabolic disease - ketosis mammary infection - mastitis parturition paresis - milk fever -due to low levels blood Ca -results in compromised ability of muscles to contract -muscle weakness