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The Mammary Gland :glass_of_milk: (Colostrum (Lipids (Particularly Vitamin…
The Mammary Gland :glass_of_milk:
Anatomical Aspect Of The Mammary Gland
The Milk-Secreting Cells Of The Mammary Gland Develop Through Proliferation Of Epithelium Into Hollow Structures Called Alveoli
Embryonic ectoderm form the mammary ridge, and the develop to form mammary bud.
Milk secreting cells from the primary mammary cord epithelial cells, form the hollow circular structures-" alveoli"( functioning unit parenchyma).
Nipple connect internal milk-secreting system to external surface.
Male nipple do not have developing mammary cord to form glandular tissue.
Most Of The Milk That Accumulates Before Suckling Or Milking Is Stored In The Alveoli, Even Though Animals Have Enlarged Milk- Storage Areas Called Cisterns.
Duct system connect the alveoli to nipple to pass milk.
Cattle,goat, sheep have 1 final duct per gland.
Mare and sow have 2 main ducts per gland.
Cow and Doe(goat) have cisterns- specialised area for holding milk.
Mammary gland develop in pairs.
Goat, horse, sheep- 1 pair mammary gland
Cattle - 2 pairs mammary gland.
Sow and Bitch= 7-9 pairs mammary gland.
Cattle, goat , horse, sheeps = mammary gland are closely apposed to each other to form "udder".
A Suspensory System Involving The Udder Of The Cow Allows The Animal To Carry A Large Amount Of Milk.
Median suspensory ligament (between mammary glands), composed of elastic connective tissue.
Suspensory system hold the udder to store heavy weight of milk.
Lateral suspensory ligament ( non elastic), originates from prepubic and subpubic ligament.
Milk Removal
Efficient Milk Removal Requires The Release Of Oxytocin, Which Causes Contraction Of Muscle Cells That Surround The Alveoli (Myoepithelial Cells), And Movement Of Milk Into The Ducts And Cisterns.
Myoepithelial cell respond to oxytocin and contract to force the milk out.
Suckling stimulation release oxytocin from neurohypophysis.
Auditory, visual , olfactory sensory stimuli for oxytocin release too.
Oxytocin release through Ferguso reflex.
Ferguso reflex = cervix stimulation by blowing air into the vagina to induce oxytocin release.
Oxytocin initiate passive part of lactogenesis → release prolactin.
Control Of Mammogenesis
Initial Development Of The Mammary Gland Is Programmed By Embryonic Mesenchyme
Development of mammary gland control by genetic and endocrine system.
Fetal administer exogenous hormone to mother - activate mammary gland secretion.
Proliferation Of The Mammary Duct System Begins At Puberty, With Ducts Under The Control Of Estrogens, GH, Adrenal Steriods, And Alveoli Under The Control Of Progesterone And Prolactin.
Mammary gland develop at puberty but inactive until pregnancy happen.
Estrogen, GH, adrenal steriods = proliferations of duct system.
Progesterone ,prolactin = proliferation of alveoli
Udder develop in middle gestation and begin to secrete milk at the latter gestation, (↑[prolactin])= form colostrum.
Many alveoli → lobules → lobes
Colostrum
Prepartum Milk Secretion ( Without Removal) Results In The Formation Of Colostrum.
Milk formed before parturition - "colostrum".
Colostrum represent lactogenesis activity.
Progesterone & estrogen ( prolactin inhibitor) being removed before parturition.
The Ingestion Of Colostrum Is Important Because Of The Passive Immunity It Confers Through The Presence Of High Concentrations Of Immunoglobulins.
Provide nutrient, temporary passive immunity to the youngs.
Contain IgA produced by B-lymphocyte plasma cell when mother exposed to microorangisms.
neonate receive immunity against pathogens experienced by mother.
The Time Immunoglobulins Can Be Absorbed Through The Neonatal Gut Is Limited To The First 24 to 36 Hours of Life.
Neonates have limited time ( 24-36 hours) to absorb immunoglobulin protein from colostrum.
Colostrum contain antimicrobial factors ( lysozyme, lactoferrin lactoperoxidase).
Lipids (Particularly Vitamin A) And Proteins (Caseins And Albumin) Are High In Concentration In Colostrum, Carbohydrate (Lactose) Are Low.
High in Vitamin A.
Placental transfer of Vitamin A is low for calves, piglets at birth, but can be compensate by colostrum ingestion.
Casein and albumin high in colostrum.
[lactose]↓, inhibited by progesterone.
Lactogenesis
Prolactin, Inhibited By Dopamine And Stimulated By Vasoactive Intestinal Peptide(VIP), Is The Most Important Hormone Involved In The Process Of Milk Synthesis, Or Lactogenesis, GH Is Also Important For Lactogenesis
Prolactin promotes milk secretion ( lactogenesis).
Prolactin can be released by suckling stimulus.
Sensory stimuli send impulse to hypothalamus to synthesis dopamine is blocked, in contrast, paraventricular nucleus produve VIP ( prolactin stimulator).
GH also promote lactogenesis.
The Release Of Fat Into Milk From The Alveolar Cell Involves Constriction Of The Plasma Membrane Around The Fat Droplet; Fats Are Dispersed In Milk In Droplet Form.
Alveolar cells synthesize fats, protein sad carbohydrates→extrudes into alveolar lumen.
Fat droplets accumulates at basal cytoplasm, then move to apex → form droplets.
Fat droplets ( contain a portion of cytoplasm ) disperse in milk.
Milk Proteins And Lactose Are Released From Alveolar Cells By The Process Of Exocytosis.
Milk protein ( casein) synthesized on endoplasmic reticulum and phosphorylated and packed by Golgi apparatus.
Lactose also synthesized the same way.
Milk protein and lactose transported out by exocytosis.
Composition Of Milk
Fats Are The Most Important Energy Source In Milk.
Milk fats = monoglycerides, diglycerides, triglycerides, free fatty acids, phospholipids and steriods.
Triglycerides is the main component.
Marine mammals milk has high fat content to insulate heat loss of the young.
Domestic animal less milk fat.
Lactose,Composed Of Glucose And Galactose, Is The Main Carbohydrate Of Mammalian Milk.
Lactose is the main carbohydrate.
Glucose + galactose = lactose
α-lactalbumin + galactosyl trnasferase = Lactose synthetase
Lactose synthesis is suspended by progesterone ( inhibit α-lactalbumin fomation ) until parturition.
Prolactin is lactose synthetase stimulator.
Animal need lactase in jejunum to digest lactose, some adult do not have lactase - cause diarrhea.
The Main Proteins In Milk Are Called Caseins And Are Found In Curd.
Main milk protein is caseins.
Casein can be removed as curd from milk through " curdling or coagulation ".
When albumins and globulins remain in milk = "whey".
First Nursing
Carbohydrate Stores Are Good In Neonates Born As Singles Or Twins,Whereas Carbohydrate Stores Are Low In Neonates Born In Litter; Consequently The Former Can Stand A Longer Interval To First Suckling Than Can The Latter.
Cattle, horse, sheep, goat neonates have to stand suckle and locate the mammary gland, thus the neonate require enough carbohydrates supply to do so. ( nurse in 2 hour interval).
Cat, dog, pigs - the young immediately nestled toward mammary gland and suckling in less than 30 minutes after birth. (nurse in 1 hour interval).
If suckling delay, neonates suffer from hypoglycemia, which lead to bowel stasis and neonatal sepsis.
Rabbit nurse their young 24 hour intervals.
Diseases Associated With The Mammary Gland
The Main Disease That Affect The Mammary Gland Directly Are Mastitis ( Prevalent In Dairy Cattle And Dogs) And Neoplasia ( Prevalent In Intact Dogs And Cats)
Mastitis = inflammation of gland.
mastitis caused by injury to teat canal from repeated strecthing during milking, easily exposed to microorganism , lead to infection.
Connective Tissue form in udder, swollen, limits the duct and alveoli to proliferate, decrease milk production.
Mastitis treatment = antiinflammatory and antibacterial agent.
Neoplasia = mammary tumour when mammae exposed to estrogen and progesterone.
Neoplasia treatment = ovariectomy before puberty to reduce risk.
The Main Conditions That Involve The Mammary Gland Indirectly Are passive Transfer Of colostrum (Mare) And Hypocalcemia Caused By The Transient Drain Of Calcium That Occurs With Initiation Of Lactation ( Dairy Cattle) Or During The Prenatal Period (Dog).
Immunological disease, transfer of RBC agglutinating antibody to the fetus through milk.
Fetal RBC pass into maternal system , and form antibody against fetal RBCs ( foreign to mother ).
RBC agglutinating antibody concentrate in colostrum.
Foals undergo hemolytic crisis and can die if not treated.
treatment = muzzle the foal for the 48 hours after birth, feed on frozen colostrum.
same as neonatal isoerythrolysis in kitten.
Hypocalcemia = lack of calcium due draining of maternal Ca2+ to form milk.Animal tend to become weak and unable to stand.
Ca2+ administer can recover in 10-20 minutes.
Lactation Cycle
Milk Production Peaks At 1 Month Postpartum In Dairy Cattle, Followed By A Slow Decline In Production; Milking Usually Stops At 305 Days Of Lactation So That The Animal Can Prepare The Mammary Gland For The Next Lactation.
Cow " dried up" after 305 days lactation period.
Lactation cycle is change colostrum to normal milk.
Dairy cow is forced to stop lactating to prepare for next lactation.
Back pressure of milk in alveoli gradually inhibit milk secretion by alveolar epithelial cells.
Alveolar cell regress, small duct regress = "involution".
Involution happen to replace the regressed alveoli and duct.
Lactation Can Be Induced By Hormone Administration ( Estrogen And Progesterone ) And Enhanced By GH And Increased Photoperiod Exposure.
" Induction of lactation" apply to those animals with high-lactation record but poor reproductive performance.
Estrogen + Progesterone = induce alveolar development to produce milk.
GH enhance lactation by absorb and direct nutrient to milk synthesis system.
Negative energy balance, GH mobilize body fat to form milk.
Positive energy balance, GH show no effect on body fat metabolism.
GH decrease energy balance in cow, can be compensate by increase feed consumption.
Thyroid hormone use to increase lactation in cow.
Dog, gynecomastia ( enlarged mammary) is profound hypothyroidism→ TRH increase → prolactin increase.
Long photoperiod increase cow lactation by increase prolactin synthesis.
Low dose of oxytocin and metaclopramide ( dopamine D-2 receptor antagonist) → improve bitch lactation.
Queens sensitive to photoperiod (expose to dark), melatonin ↑, prolactin ↑.
Clinical Correlations
Pregnant Mare That Does Not Have Sufficient Milk Or Udder Development.
Clinical examination
A mare is pregnant, and current under vaccination and deworming, the mare is in good body condition and the foal is viable. The mare was fed with hay and fescue. Fescue contain endophytic fungus,
Neotyphodium coemophialum
, produce alkaloid toxins that are dopaminergic and inhibit prolactin. The mare has limited udder development.
Treatment
Domperidone administration to inhibit the dopaminergic effects.If domperidone is started 5 to 10 days before parturition to allow enough time for the mare to develop sufficient milk.
Neonatal Isoerythrolysis
Clinical Examination
A mare that have foaled 3 times. The mare is normal and in good body condition. The last 2 foal died within 2-4 days after birth. The mare had colostrum and milk. Suspect neonatal isoerythrolysis as the foals are healthy right after birth, and weakened after consuming colostrum. The mare exposed to RBCs of fetus during pregnancy or the stallion RBCs. The RBCs are foreign to the mare, and develop antibody against the fetus RBCs if the the foal inherited same blood type as the father. The antibodies cannot pass through placenta but concentrated in colostrum. Once the foal suckle the colostrum,it acquire the antibodies that will react to its own RBCs. The foal develops type II hypersensitivity reaction.
Treatment
Muzzle the foal after birth and feed the foal with frozen colostrum from other mare for the first 1-2 days to prevent absorption of the antibodies from the mother. If the foal already consumed the colostrum from mother, immediate blood transfussion are required for the foal survival.