Introduction to Animal Science

LactationAGR Vet Science

1-3-2012

Lactation

Definition of Lactation The process of producing milk. Occurs specifically in the mammalian

species. Milk is the food source for the

nourishment of the young. Calcium and Phosphorus Protein Carbohydrates & Fat Vitamins and Minerals

Milk Produced and secreted by the

mammary glands of the female. A liquid containing these major

constituents Water (88%) Triglycerides (Fat) (3.5 – 9.6%) Lactose (4 -5%) Protein (3 – 6%) Refer to Table 12-1 on page 260 in text

Discussion of the udder and mammary gland is like the

chicken and egg discussion, where do we start first?

Mammary Gland A milk secreting structure consisting of:

Teats (storage and delivery) Duct system Lobes of a secretory system

A modified sweat gland (sudoriferous gland) of the exocrine system

All a part of the total called the udder.

Mammary Gland Development

Prenatal – Anatomical structures are present.

Birth to puberty – Structural growth is influenced by somatotropin (growth) hormone. Hormone produced for each species is similar to each other.

Puberty – onset of progesterone and estradiol hormones stimulate the growth of the mammary gland at a rate greater that prepuberty.

Development Cont’d During gestation,

progesterone stimulates the lobule-alveolar development.

The lobule-alveolar are responsible for milk synthesis.

The Mammary Gland

Another View of the Mammary Duct

An Udder

A complex organ made up of: A supportive system A secretory system made up of

epithelial cells (lubule – alveolar) A duct system for the storage and

conveyance of milk Blood, lymph and nervous systems

Supportive System

Anatomy and Physiology of the Udder

Anatomically, the udder hangs from the pelvis

Physiologically Supported by the median suspensory

ligament and the lateral suspensory ligaments on each side.

Connective tissue attaches the udder to the abdominal wall.

Connective membranes divide the udder into quarters or halves depending on species.

Teat Structure

Anatomy and Physiology of the Teat

Exterior portion or visible structure attached to the duct system of the mammary gland.

Limited storage capacity. Physiologically

Smooth muscle surrounded by skin (epidermal layer of tissue).

Circular muscle form a sphlincter at the base with a teat canal for milk flow or a wax barrier.

Hormonal Activities Before, At and Immediately After Parturition

Related to Mammary Activity and Lactation

Prolactin Released from the anterior pituitary gland Initiates and maintains lactation

Progesterone and estrogen Decreases abruptly at parturition Lactogenesis begins with decrease

Oxytocin Released by the posterior pituitary gland Responsible for milk letdown from the

ducts of the udder

Circulatory System Related to the Mammary

Gland

The primary aorta and the cranial epigastric artery provide blood from the heart to the arteries which provide to the udder and its milk producing components. External iliac artery External pudic or mammary artery Subcutaneous abdominal artery Perineal artery

Circulation from Udder to Heart

While arteries carry blood from the heart, veins carry blood back to the heart from the udder. Vena cava External iliac vein External pudic vein Subcutaneous abdominal vein

100 Days & 106 Days of Gestation

Milk Production or Lactogenesis

Colostrum produced Stage I lactogenesis Specialized milk produced in the early days

following parturition to provide extra nutrients and immunology to the newborn offspring.

Contains immunoglobulins produced by the mother’s immune system. Antibodies are specific to mother.

Easily absorbed into the digestive tract for 2-3 days after birth.

Contains higher levels of milk proteins and lipids. Contains higher levels of Vit. A & D as well as iron

(note exception in swine)

Feeding Orphans Colostrum

Use frozen colostrum from your farm

Old ice cube trays work well. Use oesapageal feeding

tubes to get young animals too weak to feed on their own.

Never feed young unless standing.

Allow them to “chew” down the tube, thus avoiding the wind pipe and drowning or causeing lung infections.

Mares’ Waxing

Lactogenesis Stage II The primary structures of the gland are the

alveoli. Milk is secreted by the secretory cells that

surround the outside of the lumen. The alveoli are spherical and are capable of

storing milk. The secretory cells are housed in the alveoli

and contain the necessary enzymes to produce the components of the milk.

Practices to Encourage Oxytocin Production & Milk

Letdown

Wash and massage the udder prior the milking with dairy cows.

Maintain are routine in the milk shed. Play music to drown out unusual or

startling sounds. Play recorded sounds of sow’s nursing

to encourage other sow’s to letdown milk.

Function of the Secretory Cells

To absorb the necessary precursors (nutrients) from the bloodstream.

To transform the nutrients into the lactate, fat, and protein of the milk.

To transfer the newly synthesized milk into the lumen of the alveolus.

To absorb minerals and vitamins from the bloodstream and are combined with the synthesized prior to discharge from the alveolus.

Activities of the Alveoli Contains the milk produced by the

secretory cells. Arranged in lobules and drainage is

through a complex ductwork system. The ducts terminate at the teats into a

gland cistern. From the gland cistern, milk leaves the

udder through the streak canal of teat with relaxation of the sphincter of the teat.

Another View of the Mammary Duct

Milk Letdown Cont’d

Oxytocin from the pituitary gland acts on the specialized muscle cells called myoepithelial cells, which surround the secretory cells, causing them to contract.

Contraction squeezes the lumen of the alveolus. With milk discharge, the alveoli deflate allowing space for more milk to be produced.

Another View of the Mammary Duct

Preventing Udder Infections

Infections of the udder are called mastitis. Reduce the incidence of mastitis by:

Maintain clean bedding for the female to lay on. Clean udders prior to milking. When using a milking machine, use automatic

teat cup releases. Avoid excessive energy immediately after

parturition causing excess milk to be released. Remove excess colostrum if necessary. Select females according to udder design.

Desirable Udders to Select For

With sows, select females with distinct separation of teats and their “quarters”.

Note the top picture and compare it to the lower one. Which one will you select for?

Ailments Associated with Mastitis

Metritis – uterine infections following parturition caused by bacteria moving up the female tract during parturition. Assisting at parturition using unsanitary instruments or hands and arms can lead to infections.

Agalactia – milk failure due to udder infections or the inability to letdown milk from the udder.

Udder Placements Inguinal – cattle,

sheep, horses, pigs, dogs, cats, goats

Abdominal – pigs, dogs, cats

Pectoral (Thoracic) – pigs, dogs, cats, humans

Udder Attachments Cont’d

Lactation Curve Info

Basic curve

Dairy Cow Milk Curve and Persistence

Lactation Curve Info

Basic curve Persistence of lactation over time

Dairy Cow Milk Curve and Persistence

Lactation Curve Info

Basic curve Persistence of lactation over time Effect of multiple births

Milk Production Rates of Twin Lambs (x) vs Single Lambs (o)

Lactation Curve Info

Basic curve Persistence of lactation over time Effect of multiple births Differences between species

Lactation Curve Info

Basic curve Persistence of lactation over time Effect of multiple births Differences between species Differences within species with

different functions

Milk Involution Gradual decrease

in weight, volume, and productivity of milk from the udder.

Major Components of Milk

Carbohydrates – lactose Protein Lipids Calcium

Lactose Synthesized in secretory cells by combining

glucose with galactose. Glucose must come from the body of the cow

through the bloodstream. Propionic acid (VFA) is converted to glucose

by the liver. Acetic and Butyric are used to make milk fat

or simply oxidized and used as an energy source by the animal.

Lactose Cont’d

A disaccharide which must be broken down in the s. intestine.

The enzyme, lactase, is responsible for the breakdown.

Protein Primary protein in milk is casein. Casein makes up 80% of all the protein in milk. Casein proteins contain a negative charge due

to the phosphate ions held in association with the casein. Ca++ from the bloodstream combines with the casein protein and the phosphate.

Other milk serum proteins: Lactoglobulin, lactalbumin and immunoglobulins. Approximately 18% of the total protein present in milk.

Protein Cont’d Immunoglobulins in the colostrum

provides high levels of protein for the newborns.

Provide passive immunity since the immunoglobulins are absorbed directly into the s. intestine. Closure of the gut usually occurs within the first 24 hours.

Milk content containing colostrum returns to normal in 3-4 days following parturition.

Lipids Percentage and chemical makeup of fats in

milk vary between species. Primary lipids are:

Triglycerides Cholesterol Phospholipids

Fatty acids which make up triglycerides vary in length and degree of saturation. Fatty acids extracted from blood-borne

lipoproteins Produced by the mammary gland

Lipids Cont’d

Mammary gland produces mostly saturated fats as a result unsaturated fats being saturated in the s. intestine. These are packaged into lipoproteins.

The precursor to the fatty acids synthesis in the mammary gland is acetic acid (VFA). It comes from the rumination of roughages in the rumen.

Calcium Present in the milk because of its positive ionic

charge combines with the negatively charged protein ion.

High producing females of milk may undergo lower levels of calcium in the blood stream when high levels of protein are needed to be produced during periods of high milk production.

Milk fever or parturient paresis occurs as a result of the above.

BST – Bovine Somatotropin

Approved by the FDA in 1985. Somatotropin is a natural growth hormone

responsible for milk production and produced and released from the pituitary gland.

Naturally increases milk production. Synthetically produced BST increase production

an additional 10-20% with improved presistence. Safe for human consumption of the milk because

it is a protein and if present in the milk it would naturally be broken down in the human stomach.

Monsanto product originally observed at Cornell U.