Reproduction and Pregnancy

Question 1

How do health and nutrition relate to reproduction?

Answer 1

1. Only healthy animals reproduce
2. Optimum reproduction requires optimum nutrition

Question 2

How are body growth and puberty related?

Answer 2

Body growth is prioritized before puberty, so puberty is only reached after a certain stage of growth.

Body size is more important than age, and well fed animals grow faster and reach puberty earlier.

Puberty is also impacted by other factors like seasons, exposure to males, etc.

Question 3

Describe the prioritization and nutrient partitioning leading to puberty.

Answer 3

1. body growth
2. increase in fat reserves
3. puberty

Question 4

After puberty, when do females become pregant?

Answer 4

Females delay pregnancy until after they have accumulated sufficient energy reserves to sustain pregnancy and lactation in the face of food shortage

Females will be infertile if energy stores are low, and will only be fertile once these reserves build back up

Question 5

What is the most costly stage of reproduction?

Answer 5

Lactation, especially for smaller mammals bearing litters of multiple offspring

Question 6

What are the consequences of reproduction with insufficient energy?

Answer 6

High energy demand coupled with low energy supply could prove fatal

Question 7

What are capital breeders?

Answer 7

Capital breeders are animals that rely on body stores for a large portion of nutrients for reproduction (pregnancy and lactation)

ex. some whales and seals do not consume any food during lactation - all comes from fat stores

Question 8

What are income breeders?

Answer 8

Income breeders rely more heavily on consuming food for reproduction (pregnancy and lactation)

ex. Mice eat 50% of their body weight during lactation to meet their requirements; they simply cannot have enough fat stores to meet this demand; lactating mice who run out of food will eat their pups to get nutrients to keep the other pups alive

Question 9

What is needed for optimum reproduction?

Answer 9

All nutrients in adequate supply

Question 10

What determines nutritional issues of reproduction?

Answer 10

The level of inadequacy determines the effect, from minimal interference to sterility.

ex. sheep
1. nutrition in early pregnancy affects embryo survival
2. feeding in late pregnancy affects lamb birthweight
3. feeding in lactation affects milk production and lamb growth
4. nutrition affects bodyweight recovery of the dam before mating
5. nutritional condition at mating affects number of eggs shed

Question 11

What limits the reproductive rate?

Answer 11

food supply

Question 12

What is most important to have an adequate supply of?

Answer 12

Energy; its availability is signaled by leptin

Question 13

How is reproduction regulated?

Answer 13

It is regulated by the brain through GnRH and its stimulation of LH and FSH. The brain then integrates the signals to determine reproduction.

Question 14

What is the function of GnRH?

Answer 14

It stimulates the pituitary gland to produce LH and FSH.

Question 15

What does LH do?

Answer 15

Stimulates hormone production

Question 16

What does FSH do?

Answer 16

Stimulates production of gametes

Question 17

How is leptin involved in reproduction?

Answer 17

Leptin is the main signal that communicates body mass or adipose reserves to the brain to regulate the reproductive system.

Leptin increases production of GnRH, which increases production of LH and FSH. This in term causes higher fertility, sperm count, and advances puberty.

Obese mice (ob/ob) lack leptin and are infertile.

Leptin is a product of adipocytes, and increases with fat reserves and metabolic status. It decreases appetite and increase metabolic rate through brain receptors.

Leptin receptors are in the ovary, uterus, testis, hypothalamus, and anterior pituitary.

Question 18

Why has their traditionally been a negative correlation between milk yield and reproduction in dairy cows?

Answer 18

High production in early lactation causes negative energy balance and body fat loss - this delays estrous cycles and lowers fertility.

This has recently been reversed by genetic selection and estrous synchronization.

Question 19

Where are the nutrients required for pregnancy going?

Answer 19

1. nutrients required by uterus, placenta, and fetus
2. mammary requirement (may be significant in some species)

Question 20

What do the metabolic and nutritional impact of pregnancy on the dam depend on?

Answer 20

1. ratio of fetal weight to maternal weight
2. gestation length

Question 21

How do energy requirements change during pregnancy?

Answer 21

Requirements change over the course of pregnancy and accelerate in the last trimester.

Uterus and placenta have a major demand in the first two trimesters, and nutrient for the fetus increases dramatically in the last trimester.

Question 22

Why do sheep experience pregnancy toxemia and cattle don’t?

Answer 22

The fetus in a pregnant sheep takes up a higher percent of the body weight of the mother.

Question 23

What is the general trend of dam body weight and gestational length?

Answer 23

This is generally a linear relationship, but some animals fall off the curve.

Question 24

Describe the nutrient recommendations by stage of pregnancy.

Answer 24

1. During early pregnancy serious under and overfeeding can cause increased embryo mortality (high protein means higher blood ammonia, which can cause pregnancy complications). Pregnancy loss is common in the first 28 days and may be sensitive to nutrition.

Recommendation: feed at or a little above maintenance for about a month after breeding.

2. Well-conditioned animals can afford to lose weight through mid pregnancy if they are well fed during late pregnancy.
3. Avoid overfeeding because early/mid pregnant animals synthesize and deposit fat very efficiently.

Question 25

What happens if a dam is short of nutrients during gestation?

Answer 25

She will prioritize supporting the fetus over other tissues. Maternal tissues decreases in an underfed state.

ex. Sheep gain body fat in early pregnancy and then lose it during late pregnancy (make it available) when fetal requirements are very high.

Question 26

Describe the effects of utero undernutrition.

Answer 26

Decreases weight, increases age at first conception, and decreases litter size

increases obesity and insulin resistance (thrifty phenotype)

Question 27

What are nutritional epigenetics?

Answer 27

When the maternal diet changes DNA methylation, which changes the animal

Question 28

Provide an example of nutritional epigenetics

Answer 28

Agouti mice (yellow mice) do not have properly methylated DNA, and have a higher risk of cancer, obesity, and a reduced lifespan.

If an agouti dam’s diet is supplemented with methyl-donating substances (methionine, choline, folate, B12, betaine, etc.), they produce an agouti methylated mouse. These mice have lower risks of cancer, diabetes, obesity, and a prolonged lifespan.

Question 29

What is a thrifty phenotype?

Answer 29

Epigenetic programming for more body reserves in utero

Question 30

Describe fetal programming or the Barker Hypothesis.

Answer 30

Obesity, cancer, heart disease, allergies, and other diseases have been linked to conditions experienced in utero, especially the mother’s nutrition