L12: Energy for reproduction

Energy (and nutrients) for reproduction is required for:

• sperm

• eggs (mammals and birds)

• fetal development

• reproductive organs (testes, ovaries, uterus, mammary gland)

• milk production

• heat production for egg incubation

• territorial establishment/defense

• courtship

• nest/burrow construction

• searching for and acquiring food for young

Males – energy/nutrient demands

a) Testicular growth

• minimal energy and protein requirements

b) Sperm production

• minimal energy and protein requirements

Females – energy/nutrient demands

a) Ovary/oviduct growth

• minimal energy and protein requirements

b) Fetal development (gestation)

c) Mammary gland development

d) Milk production (lactation)

DEE of fetal development (gestation) mammals =

2.9 x BMR

Which animals product milk

all mammals (placental, marsupial, monotreme)

DEE of lactating mammals =

5.5 x BMR

Colostrum

The first milk produced during each lactation

• Typically, rich in immunoglobulins

• Provides passive immunity to the neonate

How is colostrum transferred through passive immunity

Maternal immunity can be passed to the fetus in colostrum only for as long as the GIT is permeable to Ig absorption

• Ungulates = upwards of 36 hours

• Marsupials = upwards of 200 days

Taurine in colostrum

• essential AA for felids, critical during neonatal stages

• very high levels in felid colostrum > 5 days

Nutrient concentration in rhinos vs seals

Water: Dilute (90%) in rhinos, concentrated (40%) in seals

Protein: Low (<2%) in rhinos, high (>10%) in seals

Fat: Low (<2%) in rhinos, high (>40%) in seals

Sugar (soluble CHO): high (>5%) in rhinos, low (<1%) in seals

Milk in seals

Fat/protein/energy concentrated milk

• maternal diet is primarily protein (e.g. fish)

• may compensate for rapid rates of heat loss

• accommodates extremely short lactation

• may be adaptive for breeding/birthing on unstable pack ice

Lactation in hooded seals

4-day lactation (pup can grow upwards of 30 kg

Milk in marsupials

• Milk production and composition changes between periods

• Period 1 = young are confined to the pouch

• Period 2 = you can leave the pouch

Milk composition in marsupials (Period 1 vs. Period 2)

Types of milk intake by neonates

Hiders

• mother returns to hidden neonate periodically to nurse

• young nurse infrequently, but drink lots each time

Followers

• young follows mother around and is constantly nursing

• young nurse frequently, drink small amounts each time

Nutrient requirements for egg production in birds depends on:

1. Clutch size

• varies with age, food availability; younger and less food lay fewer

2. Egg size

• varies with age, food availability, and is inversely proportionate to body weight; younger and less food lay smaller eggs, and smaller birds lay larger eggs relative to BW

3. Egg composition

• varies with stage of development at hatching: altricial vs precocial

Altricial species and examples

• young show marked delay in becoming independent

• young hatched/born naked (and afraid), blind, immobile

• e.g. robins, crows, rats, mice, humans)

Precocial species

• young show high degree of independence from birth/hatch

• young born/hatched with plumage/pelage, well-sighted, mobile

• e.g. chickens, ducks, deer)

Egg composition in precocial species

Yolk size is larger

• Yolk = ~40% of egg weight for precocial species

• Yolk = ~20% of egg weight for altricial species

Egg production in precocial birds

Precocial birds tend to lay fewer, larger eggs than altricial ones

• 1 egg = ~150% of BMR for precocial species

• 1 egg = ~30% of BMR for altricial species

To meet energy/nutrient requirements for egg laying in birds, it requires:

• fat deposition prior to egg laying

• mobilizing body fat and protein (lean mass) when laying

• increase food intake

• diet shift to nutrient-rich foods (e.g. insects)

Incubation and its purpose

Maternal/paternal heat is needed to:

• initiate embryonic development in the egg

• ensure development continues appropriately

Amount of heat required for incubation depends on:

• clutch size

• nest insulation

• body weight of adult

• ambient air temperature

Incubation affect on parents

• adult incubating eggs has less time to feed

• both parents may share the incubation (other brings food)

• one parent may do all the incubating (rely on fat stores)

Lactation in birds

Eesophageal/crop secretions fed to hatchlings

• sloughed epithelial cells (rich in fat/protein)

• may be fed as only source of food for first 3-5 days

• gradually mixed with solid food over 3-4 weeks

Energy for reproduction in reptiles and amphibians is required for:

• Energy required for reproductive behaviours (e.g. courtship or nesting) and egg, follicle, and sperm development

• Most reptiles breed seasonally, so they need to build up energy stores prior to reproduction

• Especially important: many female reptile (including viviparous and oviparous) species will reduce food intake during certain periods of reproduction

Reproductive costs for female reptiles

1. Survival

• Can be reduced due to behavioural changes: more basking

• Increased basking associated with higher predation risk but may be needed due to increased body mass, temperature for embryonic development, compensation for reduced motility

• Can also include reduced motility overall and energy depletion of reserves

2. Energy Allocation

• Can be “expensive” for the animal especially if food intake is reduced

• In most reptiles fecundity is body size dependent

• Energy allocated to reproduction rather than growth may depress fecundity during later reproductive seasons

Reproduction classification in reptiles and amphibians

Viviparous

• birth of live young developed within the body of the parent

Oviparous

• young are hatched from eggs