Slide Set 1: Biological Functions of Lactation Flashcards
What are the key charactestics of mammals?
- 4000 species
- Most of mammals are viviparous and possess hair
- The only vertebrates to have a mammary gland
- Feeding young by secretion from the mother
What are the animals that carry the mammalian characteristics but they are not mammals?
- piscus fish (produces milk from their skin, they don’t produce regular milk but it is more like a mucous substance to feed their young)
- pigeon, flamingo, emperor penguins
Pigeons secrete ___ milk
crop
What is crop?
Crop is a tissue between esophagus adn the top of the stomach. The main function of this region is to store food but 2 days before hatching the function of this tissue becomes producing milk.
What is the hormone that controls milk synthesis?
Prolactin
Prolactin is the msot important hormone for milk production in pigeons, rabbits, humand but NOT for _____
cows
What is the origin of the crop milk?
crop sloughed epithelial cells
What is the compostion of crop milk like?
Protein = 60% Fat = 30-35% CHO = 1-3%
No casein
No lactose
Baby pigeons are called
squabs
What determines the volume of milk?
High lactose means more diluted milk, lactose is responsible for the volume of the milk
How long does the laction lasts in pigeons?
10 days
What are the 2 subclasses of mammals?
Protheria (no placenta)
Theria (placenta)
What is the order of protehria?
monotemata (egg-laying mammals)
What are the 2 infa-classes of theria?
- metatheria (marsupials)
- eutheria (true placentals)
What are the key characteristics of metatherians?
- viviparous
- very immature young
- poorly developped placenta
- long lactation
What are the key characteristics of monotremes?
- Only two species still exist (Australia)
- Egg laying mammals (oviparous) - no placenta
- No placenta & mammary glands have no teats
- Young very immature and rely totally on milk
What are the two monotremes that still exist?
- Echidna (Spiny anteater)
- Duckbill platypus
What are the key characteristics of Echidna’s eggs?
- Eggs laid ~30 days after ovulation (single egg)
- Eggs incubated inside a pouch (10 days)
- Hatched young & very immature
How and when is echidna born?
After 10 days, young pierces egg shell with egg tooth
What are the key characteristics of a newborn echidna?
– 1⁄2 inch long
– Hind legs buds, front legs and toes well formed with tiny transparent claws for gripping the pouch hair
What are the key characteristics in lactation of echidna?
- Milk oozes into a depression within the pouch
* Suckling period for the young ~ 200 d
Explain the life cycle of a young echidna
- Carried in the pouch for ~ 53 days
- Suckles its mother once every 5 days
- May drink up to 20% of its body weight in milk daily
- Grows fast (from 0.5 g to 200 g in 2 months )
- When spines begin to appear, young is placed in a nursing burrow
- Leaves the burrow ~ 5 months and is weaned 4 weeks later
- Becomes independent ~ 1 year
What are the key characteristics of Duckbill platypus’ eggs?
• Lays 2 eggs 15 d after mating
• Eggs incubated in a burrow and
hatched in 10 to 14 d
• Hatched young are very immature
What are the key characteristics in lactation of duckbill platypus?
- Suckling period for the young ~100 d
- Milk oozes into stiff hairs in the abdomen
- Young suckles milk off stiff mammary hair on abdomen
- Young can take up to 20% of its body weight in 2 hours
What are the key characteristics of the mammary gland of duckbill platypus?
- Mammary glands are located on each side of the midline of the abdominal wall
- 100-150 separate glands composed of simple branched convoluted tubes
What are the key characteristics of Marsupials (Metatheria) in terms of young bearing, birth, mammary gland and lactation period?
☛ Viviparous & have short gestation period (3-6 weeks)
☛ Give birth to very immature young
☛ Mammary gland more developed than in monotremes
☛ Mammary glands have teats (up to 20)
☛ Long suckling period (50-550days)
What is so unique about Marsupial lactation?
- Drastic changes in milk composition over lactation period
early lactation vs late lactation - Asynchronous lactation
What are the features of the early lactation milk in marsupials?
☛ Early lactation (parturition to 200 days):
☛ Simple milk high in carbohydrates (mainly oligosaccharides) and low protein and fat
What are the features of the late lactation milk in marsupials?
☛ Late lactation 200 to 330 days):
☛ Complex milk low in carbohydrates and high in fat
What is asynchronous lactation?
☛ Adjacent mammary gland produce milk of different composition
☛ Some glands can be lactating while other are regressing
Explain the sexual maturity and breeding in Tammar Wallaby (marsupial)
- The female reaches sexual maturity at approximately 9 months of age.
- Males become sexually mature at 2 years of age.
- Female can be constantly pregnant from 1st pregnancy until death
- Strict seasonal patterns of breeding, young are born between January and March.
Explain the gestation of tammar wallaby
- Female wallabies give birth to young (joey) but lack a true placenta. Therefore young are very immature at birth.
- The female kangaroo can support three offspring, each at a different stage of development
- Gestation lasts between 25-28 days.
- Young weighs between 350-400mg at birth (0.01% of mother’s body weight).
Explain how tammar wallaby can raise 3 offspring at one time
– Joey #1: lactation (outside pouch, ~1.5 years)
– Joey #2: lactation (inside pouch, ~9 months)
– Joey #3: held in embryonic diapause
What is the first sign of birth in tammar wallaby?
- First sign of the female about to give birth is the cleaning of the pouch.
- Birth posture is also very specific.
What happens after the birth of tammar wallaby?
- Once the neonate is born it takes about 15 seconds before it starts climbing to the pouch.
- Duration of the climb is 2-3 minutes.
How does tammar wallaby climb inside the pouch?
• Hair extending from the cloaca to the pouch grows upwards to facilitate the climb to the neonate.
What happens to the mother tammar wallaby once she gives birth?
• After giving birth the female mates again, however this embryo will remain dormant until the joey begins to leave the pouch.
How is the pouch maintained for Joey?
- Once the joey is in the pouch, the mother ensures that it is clean.
- She removes the brown waxy substance being secreted but she is also ingesting the feces and the urine of the joey.
- The waxy substance will be recycled back into milk for the nursing.
What is the life inside the pouch like for Joey? What is the timeline is like?
- Once inside the pouch, the neonate attaches to one of the 4 teats.
- Once the teat is inside the joey’s mouth it expands locking it firmly into place.
- Whichever teat it chooses will continue to develop.
- The remaining teats will undergo involution and/or produce milk with different composition.
- The joey then remains attached to this specific teat for 100 days.
- After this period the joey should weigh 100g.
- At 180 days the joey is now able to pull its head out of the pouch and starts to nibble on grass.
- At 190 days the joey begins to leave the pouch for short periods of time.
What is the overview of a timeline of joey from day 70 to 350?
- 70-day old joey (still in the pouch)
- 150-day old joey (still in the pouch), eyes open at day 140, under hair visible
- 200-day old joey (stay outside the pouch, but still nurse for few weeks), able to stand and urinate at day 160, thermoregulation at day 180
- At 250 days the joey leaves the pouch permanently.
- It can return to suckle from a protruding teat.
- Milk yield peaks at day 240
- The decline in frequency of suckling coincides with a 2nd joey being born.
- Between 300-350 the joey ceases to suckle completely
What are the key characteristics of Eutherians?
☛ 95% of mammals, viviparous and more diverse
☛ Young develop and grow in utero (True placenta)
☛ Mammary glands have teats
☛Young are born more mature than the marsupials
Evaluate eutherians in terms of gestation, neonate weight and lactation
☛ Gestation: 22 d (shrew) to 660 d (African elephant)
☛ Neonate weight: 7 g (shrew) to 5 tons (whales)
☛ Lactation (nursing): 5 d (fur seal) to 900 d (orangutan)
Compare metatherians and eutherians
Metatherians
• Rely more on lactation
• Gestation represents only
12% of the time between conception and weaning
• Paternal invest at birth smaller than eutherians
• Total maternal invest
similar to eutherians
Eutherians
• Rely more on gestation
• Gestation represents > 50% of time between conception and weaning
• Paternal invest at birth larger than marsupials
• Total maternal invest
similar to marsupials
What are the similarities between metatheria and monotremata
- milk composition changes significantly during lactation
- simple milk during early lactation
- nutrient-dense milk later in lactation
What is the 2 major roles of lactation?
☛ Milk production is only one function of lactation
☛ Parent offspring bond is a vital function of lactation
What are the benefits of lactation?
- Defense against predators
- Educational opportunity
- Social facilitation
What are the other roles of lactation?
- fertility control
- thermoregulation
- nutrition
- immunological functions
- physical protection
- protection, learnt skills
What is reproductive investment?
Time between conception & weaning
Reproductive investment of mammals include:
- Pregnancy
- Lactation
- As a general role, lactation occupies ~50% (40-60%) of time between conception and weaning (fairly constant among mammals)
- The role does not apply for mammals with very short or very long lactation (e.g. in marsupials 75-95%)
What is the relationship between lactation and reproduction
- Physiology of lactation is closely linked to physiology of reproduction
- the female cannot produce milk without being pregnant and giving birth
- the way the hormones are controlled in reproduction the same way the hormones are controlled in lactation
What does lactation strategy mean?
Lactation strategies represent different adaptive solutions to different problems
What are different lactation strategies?
☛ Litter size ☛ Degree of young development at birth ☛ Length of gestation ☛ Length of lactation ☛ Growth rate of the young ☛ Kind and extent of parental care ☛ The fraction of total growth contributed to milk
Differences in lactational strategies are reflected on:
☛ Milk quantity
☛ Milk composition
☛ Frequency and duration of suckling
☛ Time until weaning
How does litter size affect lactation strategy?
☛ Varies by species from 1 to 20
☛ Large litters are usually altricial while small litters are either precocial or altricial
☛ Demand on mother for nutrition is higher for large litter size
How does length of lactation affect the lactation strategy?
☛ Range from 4-5 d (hooded seals) to 900 d (chimpanzees)
☛ ~50% of lactations range from 30-135 d
☛ Lactations are longer for prototherians (av. 150 d) & metatherians (av. 120 d) than for eutherians (av. 50 d)
☛ Lactation lengths are longest for eutherians
☛ Short lactations (< 10 d) are rare but long lactations (> 500 d) are common in large-bodied mammals
What is the relationship between the length of lactation and the adult female mass?
☛ Positive correlation.
☛ Exceptions include: earless seal, baleen whale
☛ Possible justification for long lactation in some mammals:
A- Marsupials: Very immature young
B- Primates: Extensive psychosocial development
C- Bats: Extensive neuromuscular co-ordination required for food acquisition in flight
Which mammals have short lactation period?
Earless seal & baleen whale
Which mammals have long lactation period?
Marsupials, primates, bats
Which mammals have intermediate lactation period?
Other eutherians
What are the types of nursing habits? Give examples
A- Animals nursing on demand: marsupials, primates, perissodactyls (odd-toed), some artiodactyls (even-toed)
B- Animals nursing on schedule: rodents, many carnivores, many artiodactyls
C- Others: seals (harp and hooded seals), bears, whales
What does nursing on demand mean?
also known as feeding “on cue” and “baby-led” feeding—-is about responding flexibly to your baby’s hunger cues. It means initiating feedings when the baby requests them, and continuing each feeding session until the baby is satisfied.
What does nursing on schedule mean?
the mother determines the time of the milk ejection (herbivores)
Compare the nutrient content in milks of nursing on demand and nursing on schedule
☛ Animals nurse on demand tend to produce milk with lower nutrient content than those nurse on schedule
Compare the solids concentrations in milks of nursing on demand and nursing on schedule
Other (higher fat) > Nursing on schedule > Nursing on demand (carbohydrates and ash constitutes > 50 of
milk total solids)
What type of young nurses on demand?
Precocial young tend to nurse on demand
What type of young nurse on schedule?
Nest-building animals nurse on schedule
What are the types of young?
- Altricial young
- Precocial young
What are the key characteristics of altricial young?
• Very immature young
• Born after short gestation (not all the time)
• Born in large litters
• Nurse on schedule or on demand
• Include marsupials, monotremes & some eutherians
ex: dog, cat, lions, rats, mice
What are the key characteristics of precocial young?
• Mature young • Born after long gestation (not all the time) • Nurse on demand (some exceptions) • Born in small litters • Include some eutherians
What are the two other classifications of eutherians?
- Monotocous eutherians
- Polytocous eutherians
What are the key characteristics of monotocous eutherians?
☛ Give birth to precocial young
☛ Small offspring relative to adult mass
☛ Gestation & lactation are not concurrent
☛ Young are furred, mobile, but they remain with their mothers for long periods
☛ Young eat solid food early in lactation
What are the key characteristics of polytocous eutherians?
☛ Give birth to altricial or semi-altricial young
☛ Litter mass relative to adult mass can be small or large
☛ Gestation & lactation are commonly concurrent
☛ Young eat solid food usually late in lactation
What is the caloric value of milk in terms of macronutrients?
Fat 9.11 kcal/g
Protein 5.86 kcal/g
Carbohydrates (lactose) 3.95 kcal/g
☛ Due to incomplete digestion & absorption, the following values (metabolic values) are used
Fat = 9, protein 4 and carbohydrates 4 kcal/g
True/False
Ash (minerals) has no caloric value
true
Give examples of comparison of the caloric energy content of milk in different mammals
fur seal > dolphin > Echidna > bat > red kangaroo > human > cow > donkey
What does caloric value of milk reflect?
☛ The low caloric content of primate and ungulate milk may reflect the alternative functions (social & protective) of lactation in these mammals
What does high caloric value of milk indicate?
☛ Milk with high caloric value (e.g. seals, whales) may have a thermo-regulatory function for altricial young who are unable to regulate their body temp.
Milk energy transfer from the mother to young depends:
1- Maternal body weight
2- Energy requirement of young (related to litter size)
Strong relationship exists between energy secreted in milk (peak lactation) & maternal body wt
What are the two equations that show the relationship between the energy secreted in milk and the maternal body weight?
E = 175 Wm0.81 (species with large litter) E = 83 Wm0.73 (species with single young) E = milk energy output (kcal/d)
What is the equation that shows the amount of energy secreted in milk is directly proportional to the litter size and the maternal body wt?
Energy milk output (kcal/d) = 225nWm0.83
n = # of young
Wm = maternal body wt.
What is the location of the mammary gland?
Ventral and lateral to the midline of the abdomen
What is Simple vs Complex Mammary gland?
Simple gland: Milk empties through a single opening or orifice at the surface.
Complex gland: May have multiple openings, each draining a functionally separate simple gland.
