Lactation, growth and development

what’s lactation?

milk production

what gland produces milk?

milk gland

what types of activities is milk production?

endocrine activity (hormone secretion),

exocrine activity (ducts for body secretion),

what do exocrine glands have?

ducts to carry their secretions to specific locations

what are examples of exocrine glands?

1. salivary glands whose ducts carry saliva to the mouth,

2. pancreas whose glands carry pancreatic fluids to the duodenum

what’s the duodenum?

the 1st section of the small intestine

how many independent glands does a cow, sheep and pig have?

cow - 4,

sheep - 2,

pig - 12 to 18,

what does each independent gland have and produce?

their own blood supply and they each produce their own milk

what’s a gland?

an independent area that produces milk

what’s each gland liked to?

a teat

what’s the udder supported by?

a system of strong, flexible ligaments, which include the medial suspensory ligament and the lateral suspensory ligament

where is the medial suspensory ligament found?

it runs down the centre of the udder

what causes the udder of some cows, often older cows, to drag on the floor?

the ligaments in the glands of older cows become weakened

what does the streak canal do?

keeps milk in the udder and bacteria out

what does the teat cistern contain?

30 to 45ml of milk

what’s the teat cistern separated from?

the canal by folds of tissue called Furstenberg’s rosettes

what is the gland cistern?

the open collection area within the teat

how much milk can the gland cistern hold?

up to 400ml

what’s the gland cistern connected to?

branched of the milk glands

what are epithelia cells/alveoli?

cells which produce milk within the mammary glands

how many alveoli are there per inch of tissue?

1 million

what is the alveolus?

a microscopic unit made up of epithelial cells.

it has an open lumen for milk to collect after being secreted.

how big is the alveolus?

0.1-0.3mm

what are myoepithelial cells?

muscle-like cells surrounding the alveolus

what happens when myoepithelial cells contract?

they release milk from alveoli

what can interfere with milk production (how)?

stress

it can block oxytocin production

what’s mastitis?

the inflammation of the mammary gland and udder tissue

what does mastitis usually occur as?

an immune response to bacterial invasion of the teat canal by a variety of bacterial sources.

what can cause mastitis?

• bacteria,

• pathogens,

• mechanical, chemical or thermal injury of the udder

what levels of lactose are present in milk?

they remain constant at about 4.8%

why do lactose levels remain constant?

because it’s an osmoregulator

what is the main osmoregulator of milk volume?

lactose

what’s lactose made up of?

one glucose molecule and one galactose molecule

what are the protein and fat levels in milk like?

they vary depending on breed, diet etc

what’s the typical % of protein in milk?

3.3%

what’s the typical fat % in milk?

4%

what can milks with higher fat contents be used for?

cheese production and more premium products, not just milk to drink

what’s associated with low fat levels in milk?

high levels of fatty acids

what’s mammogenesis?

the initial development of the mammary gland. it begins in the embryo and extends beyond the initiation of lactation

what’s lactogenesis?

the establishment of milk secretion post calving/lambing etc

what’s galactogenesis?

the continued production of milk by the mammary glands

what does progesterone do?

promotes the development of the alveoli and prevents the secretion of milk

what does prolactin do?

promotes the development of the secretory epithelium to promote milk secretion

what does oxytocin do?

stimulates milk let down

what do growth hormones impact?

milk production levels

what’s present in milk?

feedback inhibitor of lactation (FIL)

when is there more FIL?

when there’s more milk in the udder

what does FIL do?

inhibits milk production and internal physical pressure

what is involution?

alveoli cells are naturally lost over time

what is the dry period?

the time between the halting of lactation and the subsequent calving

what happens during the cessation of milk production?

the udder can repair - new alveoli cells are created,

there’s the natural removal of pathogens

how long is the cessation of milk production usually in cattle?

60 days

what is premium paid for?

higher levels of protein and fat in milk

what type of hormone is prolactin, where is it synthesised and secreted by?

proetin hormone that’s synthesised and secreted by lactotropes in the adenohypophysis

what’s the release of prolactin primarily regulated by?

a humoral inhibitory factor from the hypothalamus (believed to be catecholamine dopamine)

what happens when there isn’t this inhibitory factor?

there’s a continuous and relatively high rate of prolactin release

what happens to blood levels of prolactin late in gestation?

they gradually increase

when is there an abrupt increase in blood levels of prolactin?

at the time of parturition

what else happens during late gestation?

prolactin receptors in the mammary glands also increase under the influence of rising oestrogen

what does prolactin promote?

the anatomic and functional development of the secretory epithelium of mammary glands to promote milk secretion, so the abrupt increase at parturition is key for lactogenesis

what produce intracellular enzymes necessary for milk secretion?

secretory cells lining alveoli, under the influence of prolactin

what’s enhanced by glucocorticoids?

the functional development of alveolar secretory cells

what are the 4 types of bones?

1. flat bones,

2. long bones,

3. short bones.

4. irregular shaped bones,

what’s the function of bones?

• support the body,

• protecting the body’s organs,

• frame for muscles - ensuring movement is possible,

• mineral storage,

• production of red and white blood cells,

what can rickets be caused by?

a deficiency in Ca, P and vitamin D

what is vitamin D essential for?

the absorption of Ca and P from the gut

what does rickets lead to?

mis-shaped and fragile bones as the young animal grows

what is osteomalacia?

‘soft bones’ which is similar to rickets but affects mature animals

what are the 3 types of muscles?

1. skeletal,

2. cardiac,

3. smooth,

what do muscles do?

convert chemical energy into mechanical energy

is skeletal muscle…

• voluntary?

• striated fibres (visible)?

• organs?

• yes,

• yes,

• connected to bones,

is cardiac muscle…

• voluntary?

• striated fibres (visible)?

• organs?

• no,

• yes,

• present in the heart,

is smooth muscle…

• voluntary?

• striated fibres (visible)?

• organs?

• no,

• no,

• present in the lungs, stomach, liver etc

what influences muscle yield on a carcass?

genetics, nutrition and health

what is skeletal muscles? (so what is muscle growth a key component for?)

meat

key component of livestock production

what’s the role of body’s fat tissues?

• inslation,

• energy store,

• protect organs

where is white fat present?

in mature animals

where is brown fat present?

within young/newborn animals

what are qualities of brown fat?

• large blood supply,

• important method of keeping young animals warm,

what determines value?

levels of fat on a carcass

what’s fat within the body mainly made into?

triglycerides

where are triglycerides formed?

in the liver during positive energy balance

what’s glycerol usually made from?

glucose

where do fatty acids come from?

they can be absorbed immediately from the digestive system or made from glucose

what’s a triglyceride made of?

3 fatty acids and glycerol

what does a negative energy balance lead to?

poor fertility, health and metabolic disease