Nutritional Effects on Reproduction

Question 1

When is primordial follicle number determined and what influences it?

Answer 1

Prenatally, influenced by nutrition

Question 2

When should a heifer fed on moderate nutrition reach puberty?

Answer 2

9-11 months

Question 3

Why can fat covering the testes be a problem?

Answer 3

Decreases cooling

Question 4

How are sex hormones synthesised?

Answer 4

Cholesterol -> pregnenolone -> progesterone -> testosterone -> oestradiol

Question 5

What metabolic hormones can have an effect on reproduction?

Answer 5

Insulin – direct action on antral follicle growth and steroid production
IGF – enhances ovarian action of gonadotrophins (IGF I) & directly effects follicle growth and steroidogenesis (IGF I & II)
Leptin – at physiological levels, inhibits oestradiol secretion and increases folliculogenesis

Question 6

How does nutrition affect ovulation?

Answer 6

Via reproductive hormones (LH)

Question 7

What nutritional problems can cause pregnancy loss in the cow?

Answer 7

Deficiencies in vitamin A, selenium, phosphorus & copper, negative energy balance, high intake of rumen-degradable protein, ingestion of dietary oestrogens/anti-oestrogens

Question 8

How does chronic undernutrition during early gestation affect the placenta weight?

Answer 8

Reduces placental weight in early gestation but increases its weight when measured at term

Question 9

What problems relating to nutrition occur around parturition?

Answer 9

Dystocia (fat cows) & milk fever

Question 10

What is flushing?

Answer 10

Moving ewes onto fresh good pasture or supplementary feed 2 weeks prior to start of tupping, usually results in an increased fecundity

Question 11

How does selenium deficiency affect females?

Answer 11

Increases incidence of retained placenta, cystic ovaries & endometritis, high embryo mortality, decreased conception rates, birth of premature, weak or dead calves

Question 12

What is the effect of dietary molybdenum and iron on plasma copper concentrations in heifers?

Answer 12

Plasma copper reduced for both iron fed and molybdenum fed heifers, but only molybdenum fed are showing clinical symptoms

Question 13

What other effects does molybdenum have on the heifer?

Answer 13

Increases age of puberty, decreases peak LH concentration & decreases conception rate

Question 14

What are the clinical symptoms of copper deficiency?

Answer 14

Delay of puberty, failure to display oestrus, irregular oestrus and ultimately anoestrus, reduces conception rates, reduced peak ovulatory LH, reduced feed intake and conversion efficiency, hair pigmentation and texture, reduced energy utilisation, swayback

Question 15

What is the actual cause of a copper deficiency?

Answer 15

Thiomolybdate toxicity

Question 16

What have thiomolybdates also been found to cause?

Answer 16

Gross alterations in pathology and function of pituitary, ovarian somatic cell effects (decreased steroidogenesis), reduced postovulatory progesterone (reduced MRP)

Question 17

Why does reduced progesterone increase pregnancy failure?

Answer 17

Decreased progesterone -> decreased interferon tau -> decreased MRP -> increased pregnancy failure

Question 18

How does zinc deficiency affect males?

Answer 18

Essential for spermatogenesis

Deficiency gives decreased libido and testicular size

Question 19

How does zinc deficiency affect females?

Answer 19

Mild deficiency decreases number born, birth weight and leads to increased pregnancy toxaemia
Severe deficiency in early pregnancy leads to teratogenic effects

Question 20

What are the reproductive symptoms of iodine deficiency?

Answer 20

Lowered conception rates, irregular oestrus & ultimately anoestrus, retained placenta, abortions, still births & birth of weak and/or hairless calves, cystic ovaries, in male decreased libido and semen quality

Question 21

What are the last trimester effects of iodine deficiency?

Answer 21

Abnormal brain development, thyroid hormones produce lung surfactants – decreased newborn viability, increased post natal susceptibility to hypothermia