partus & lactation

7/27/2019 Partus & Lactation

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Metabolic load


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Sudden metabolic load placed on mother as

compared to providing nutrients to fetuses

Tend to focus on the mammary gland

Lactation requires the integrated and

orchestrated activities of most of the organs

and tissues in the body.

Recall that the mammary gland evolved

after all the endocrine organs haddeveloped.


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Metabolic adaptations associated with

onset of lactation

Milk synthesis

-increased used of nutrients

mammary gland

- energy budget 2-3X in some species,larger than any other time in life cycle.


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onset of lactation (cont.)

Intake and digestion

-increased food and water consumption

-hypertrophy of digestive tract

-increased capacity for nutrient absorption

central nervous system most important,

but other factors will be listed-all segments of digestive tract


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onset of lactation (cont.)

Lipid metabolism

-Increased lipolysis

-decreased lipogenesis

adipose tissue

- major difference among species

- seals stay on land, eat nothing

- body fat stores massively mobilized

- litter bearers rats, mice

- food intake about 300%

- woman + 25% max.


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Metabolic adaptations associated

with onset of lactation (cont.)

Glucose metabolism

-increased gluconeogenesis, increasedglycogenolysis

liverenlarges in some species and health ofthis organ is vital to whole animal heath status.


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Protein metabolism

-mobilization of protein reserves

muscle and other body tissues


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Mineral metabolism

-increased absorption and mobilization of

reserves- Ca, P, Mg

gut, bone, kidney, liver

- downer cow syndrome, milk fever, muscleweakness

- hormonal control- PTH, CT, E2


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Water metabolism

-increased absorption and expansion of

plasma volume

gut, kidney, central nervous system


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Appetite Regulation

1. Palatability - important primaryconstraint

2. Physical capacity - distension of rumen or

stomach

3. Chemical signals - blood glucose levels

- fatty acids (NEFA in bloodstream)

- rumen function- intake during mobilization

obesity - NEFA


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4. Hormonal Signals

- insulin

- cholecystokinin satiety signals

- gastrin

- opiates -- stimulate feeding

- endorphins

Appetite Regulation (cont.)


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A previous world record cow >19 gal/day


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Important factors on milk yield

1. Genetics- species and breed differences.

2. Nutrition- nutrient availability.

Diet formulation- milk composition

3. Age- growth requirements limit nutrients

for milk production in 1st or 2nd parity vs.

older mature animal.


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4. Pregnancy- nutrition of fetus in latepregnancy milk yield due to energy demand.Also pregnancy hormones have an effect onappetite.

5. Environment- cold & heat stress- watermetabolism, maintenance requirements (fig.)

6. Disease- ketosis- incomplete oxidation of fattyacids when glucose is lacking.

--mastitis- inflammation reducesmammary secretion.

Important factors on milk yield-2


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Lactation delays reproduction

Effects of negative energy balance during high milkyield- inhibits reproduction- expect poorest

reproduction in highest producing females. TABLE

NEB (undernutr i tion in ear ly lactation) suppresses LH

pulse generator resulting in delay of ovarian

cycles. FIGURE

Mobilization of body reserves is related to delayed

ovarian activity. How does LH neuroendocrinesystem monitor body composition? LEPTIN??


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Milk Yield Kg Conception Rate %

8640 38.5

Spring and Fall 39.0Summer 55.0

Winter 17.0


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High milk production

Negative energy balance-

Mobilization of body reserves

LH pulses

Delay of ovarian cyclesLower fertility due

to fewer cycles

Lactation and reproduction


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Lactation delays reproduction

Effects of negative energy balance during high milkyield- inhibits reproduction- expect poorest

reproduction in highest producing females.TABLE

NEB (undernutr i tion in ear ly lactation) suppresses LH

pulse generator resulting in delay of ovarian

cycles. FIGURE

Mobilization of body reserves is related to delayed

ovarian activity. How does LH neuroendocrinesystem monitor body composition? LEPTIN??


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Lactation delays reproduction-2

Energy costs of lactation-- low glucoseand insulin?

Effects ofsuckling stimulus- overlapping

effects on the ovarian control system- LHsecretion is depressed.

Most important mechanism may be

opiate inhibition of LH.


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Suckling PRL via opiate pathway(endorphins)

LH prolonged interval to ovulation Lactational anovulation leads into seasonal

anestrous in some species.

Overall combination of energy andmetabolic demands coupled with sucklingresults in reduced reproductive capability.

Lactation delays reproduction-3


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Darwin, 1859 and 1868

hard living retards the period at

which animals conceive amount of food affects the fertility

it is difficult to fatten a cow that is

lactating

partus & lactation

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