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Nutrition and reproduction – the sheep model. Stewart M. Rhind. Why are nutrition-reproduction relationships important?. Wild animals – exploiting food resources to the full – e.g. clutch size in birds - more food means = more eggs = more young reared.

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Nutrition and reproduction – the sheep model

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Nutrition and reproduction the sheep model l.jpg

Nutrition and reproduction – the sheep model

Stewart M. Rhind


Why are nutrition reproduction relationships important l.jpg

Why are nutrition-reproduction relationships important?

  • Wild animals – exploiting food resources to the full – e.g. clutch size in birds - more food means = more eggs = more young reared.

  • Domestic animals –More offspring = more money!


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Why sheep?

  • Economically important

  • Much is known of their physiology

  • Reproductive performance is closely related to nutrition in some breeds

  • Can be used to investigate underlying mechanisms


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A few basic facts

  • Ewes typically breed once per year, in the autumn and produce 1 to 4 lambs

  • Ewes (and females of many other species) are “designed” to gain and lose large fat reserves

  • The fat reserves have to “speak to” the ovaries!


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When and how does nutrition determine reproduction?

  • Number of eggs produced.

  • Number of embryos that survive.

  • Reproductive performance can be adjusted at EVERY stage

    - during gestation

    - before gestation

    - before the mother is born!


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Reproductive rate is matched to nutritional resources


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When does nutrition determine lambing rate?

  • During gestation – loss of embryos


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Embryonic loss

Nutrition effects :

  • Undernutrition during first month of gestation can increase embryo death rate

  • Overnutrition during first month of gestation can increase embryo death rate


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Embryonic loss

Other causes of increased loss:

  • Parity (higher in first)

  • Simultaneous lactation

  • Heat and cold stress

  • High ovulation rate (breed or hormonal treatment)


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When does nutrition determine lambing rate?

  • During gestation – loss of embryos

  • Days, weeks, months and years before mating – ovulation rate


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Short term intake effects and medium term body condition effects are NOT expressed through the same physiological mechanisms


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Body condition

Numbers of large, potentially ovulatory, ovarian follicles at 48h before ovulation :

High body condition (HBC) 4

Low body condition (LBC) 2


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Numbers of large, potentially ovulatory, ovarian follicles at 48h before ovulation :

NOT affected by level of food intake

…..and so …..

Intake


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Hypothetical ewe

HBC HI 4 LF4 ovulated

HBC LI 4 LF3 ovulated

LBC HI 2 LF 2 ovulated

LBC LI 2 LF 1 ovulated


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If there is only one large follicle present, it doesn’t matter how good the premating nutrition is, there cannot be more than one ovulation!


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How is the rate of feed intake signalled to the ovary in the ewe?


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Probably by the LH pulse frequency during the 3 days before ovulation – high intake = more frequent pulses- low intake = less frequent pulses


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BUT this difference in LH pulse frequency operates against a background of different nutrient and hormone signals within the follicle (leptin? )


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When does nutrition determine lambing rate?

  • During gestation – loss of embryos

  • Days, weeks, months and years before mating – ovulation rate

  • Before the ewe is born

  • ……before the ewe is conceived (?!)


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Effects of fetal nutrition on adult reproductive performance.


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It’s NOT About…

  • Contemporary body condition

    - thin animals produce fewer offspring (sheep) or breed later (postpartum cattle)

  • Pre-mating nutrition

    - higher feed intakes before mating results in more offspring


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It is certain that the significance of correct nutrition in child-bearing does not begin in pregnancy itself or even in the adult female before pregnancy. It looms large as soon as a female child is born and indeed in its uterine life.

Edward Mellanby (1933) Lancet ii, 1131-1137


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WHEN?

  • using this to illustrate the diversity of mechanisms through which nutrition can operate

  • same fundamental mechanisms may operate to control reproduction in the adult animal


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Late Pregnancy / Lactation

  • 100 days 100 days PostProportions :

  • before birth after birth -weaning Single/ Twin

  • __________________________________________________

  • No supplement Supplement Normal0.43 / 0.54

  • Supplement No supplement Normal0.46 / 0.57

  • No supplement No supplement Normal 0.57 / 0.43

  • __________________________________________________

  • Gunn et al. (1995)


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Mid-pregnancy

  • Effects on gonad structure and function

  • (Rae et al. (2001, 2002)


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Early Pregnancy (0 - 11 days)


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Associated Ontogeny


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HOW?


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How?

  • Nutrient delivery


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Nutrient delivery

Maternal Undernutrition

Maternal Overnutrition

Normal Placenta

Small Placenta

Litter “Runt”

All affect reproductive development


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How?

  • Nutrient delivery

  • Endocrine signals


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Endocrine signals

Maternal Undernutrition

Maternal Overnutrition

Normal Placenta

Small Placenta

All change with nutritional state

All directly affect gonad function

All present and active in brain


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Other Candidates

  • Growth hormone

  • Cortisol

  • Glucagon

  • Prolactin

  • Ghrelin

  • Progesterone

  • Etc.


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What Evidence Is There That…

  • early life nutrition can alter profiles of these hormones

  • the hormones can affect reproductive development


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  • Gallaher et al. (1998) – early fetal undernutrition altered profiles of IGF-1, IGFBP-3 and responses to ACTH, later

  • Rae et al (2002) – undernutrition reduced T3 concentrations in fetus and ewe.

  • Augustin et al. (2003) – exposure of bovine blastocysts to insulin increased cell number and cleavage rate and decreased the number of apoptotic bodies


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How?

  • Nutrient delivery

  • Endocrine signals

  • Structure and physiology


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Structure and Physiology

Type 2 follicles /mm2 - 110d fetus


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How?

  • Nutrient delivery

  • Endocrine signals

  • Structure and physiology

  • Reproductive behaviour


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Reproductive Behaviour Effects?

  • Normal:

  • Offspring of undernourished ewes:

• Demasculinisation of some non- reproductive behaviours

• By extrapolation - reduced sexual capacity?


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How?

  • Nutrient delivery

  • Endocrine signals

  • Structure and physiology

  • Reproductive behaviour

  • Cellular level effects


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Effects At Cellular Level

  • Effects can be expressed on very early embryos


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Effects At Cellular Level

  • Effects can be expressed on veryearly embryos

  • Modified expression of multiple genes


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Effects At Cellular Level

  • Effects can be expressed on veryearly embryos

  • Modified expression of multiple genes

  • DNA methylation altered by nutrition


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Effects At Cellular Level

Gene

Nutrition

Methylation 1

Methylation 2

F1 Gene expression altered

Gene expression altered

F2 Gene expression unaltered

Gene expression altered

F3 Gene expression unaltered

Gene expression altered


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Transgenerational effects mean that the reproductive performance of animals is determined before they are conceived!


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Additional effects

  • Reproductive function

  • Altered thyroid function


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Additional effects

  • Reproductive function

  • Altered thyroid function

  • Increased cardiovascular disease


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Additional effects

  • Reproductive function

  • Altered thyroid function

  • Increased cardiovascular disease

  • Altered neuroendocrine development


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Male offspring more nervous


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Additional effects

  • Reproductive function

  • Altered thyroid function

  • Increased cardiovascular disease

  • Altered neuroendocrine development

  • Impaired glucose tolerance / diabetes


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Impaired tolerance in late adult life


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Conclusions

  • In female sheep, nutrition of both the fetus and adult can influence reproductive performance

  • Many different physiological mechanisms are involved

  • Effects may be exerted at one time and expressed at another


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