Sep 20, 2017 - ewes during husbandry procedures during mid-pregnancy (pregnancy day 85-95) or dur- ing late-pregnancy ...... Veterinary and animal sciences have also made use of this technology to ...... In 'Refresher course on sheep.
UNIVERSITY OF NEW ENGLAND
The effects of mild prenatal stress during mid- and late-pregnancy, on lamb vigour traits.
A Dissertation submitted by
Lea Labeur, MSc For the award of Doctor of Philosophy September 2017
Certification of Dissertation I certify that the ideas, experimental work, results, analyses, software and conclusions reported in this dissertation are entirely my own effort, except where otherwise acknowledged. I also certify that the work is original and has not been previously submitted for any other award, except where otherwise acknowledged.
20/09/2017 Signature of Candidate
Date
ENDORSEMENT
21/09/2017
Signature of Supervisor/s
Date
21/09/2017
Signature of Supervisor/s
Date
21/09/2017
Signature of Supervisor/s
Date
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This thesis is dedicated to Marie-Louise, Odette and Yvan Whom I know would have been very proud to see me complete this work and would have loved to see me thrive doing what I love.
« Le simple travail ne suffit pas pour finir ce qu'on entreprend, c'est de l'assiduité du travail que dépend la réussite » Ménandre ; Fragments - IVe s. av. J.-C.
« Work alone is not is not enough to complete what we began, it is from the assiduity and commitment of work that success depends »Menandre ; Fragments - 4hc. b. J.-C.
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Acknowledgements Looking back from the end of this adventure, I am not going to pretend that the journey was smooth and easy, and that it was not frustrating at times but I can genuinely say that it was fun and that I had a blast, and if I went back in time I would probably do it again. This is obviously all thanks to my great support system and all the people around who sometimes even helped me without realising it. There are so many people I would like to thank and I would probably need another full book to thank everyone. A massive thank you to my supervisors: Sabine Schmoelzl, Alison Small and Geoff Hinch. Your support, critique, encouragement, guidance, valuable time and passion were instrumental for the completion of this work. Special mention also to your patience and understanding with my English flaws and writing skills (or sometimes the lack of). Ali without your kindness and your encouragements I would have probably never undertaken this challenge which gave me a chance to come back to Australia on top of doing something I love.
I would like also to thank all the people who provided me with technical support, valuable input and practical help, to actually complete my experiments despite the long hours and lambing always falling outside of expected dates. So to Uppy, Heather, Jodie, Deno, Jim, Dom, Brad and Danila, all the French minions: Aurelie, Etienne, Mathilde, Marie, Domitile, Alexandre, Francois, Aymeric, Guillaume, Elodie, Morgane, Maxime, Laury and Diane and the farm staff at Chiswick a massive thank you, without you I doubt I would have survived the long lambings! Your welcome, work ethics and atmosphere provided a work environment in which it was a pleasure to work every single day.
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Surrounding yourself with great people is probably the only way to ensure the successful and enjoyable completion of a PhD. Danila and Lauren, your support, friendship and answers to my multiple questions helped greatly. Gillian, thank you for being my Aussie mum and ensuring I was always fed with home cooked hearty meals. To my Blues family just ‘Merci’! You guys (and girls) were the back bone of my support system, always there to take my mind out, provide entertainment and help me embrace my Australian adventure.
Lastly, but not least, none of this could have been achieved without the support of my family. Mum and Dad, you never doubted me and did everything in your power to ensure I was doing my PhD in the best conditions possible. You always being present when I needed some support, in spite of the distance and time difference, made a great difference. Final thank you goes to my lovely younger sister Emma who went through my thesis for editing and final read proof in a few hours, shortly before submission.
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Abstract Shearing during pregnancy has been shown to increase lamb birthweight but the underlying mechanisms remain unknown. This thesis aims to examine the effects of prenatal husbandry-like and cold stressors during mid- (pregnancy day 85-95) and late-pregnancy (pregnancy day 120-130) on lamb vigour traits. The long-term effects of prenatal mild stress on lamb vigour traits were assessed using lamb growth and body dimensions, neonatal behaviour and reactivity after a cold challenge and the lambs thermoregulatory abilities when exposed to cold. Maternal glucose response to the stressors and lamb metabolic responses were also examined. It was hypothesized that increased birthweights were a result of a maternal stress response to the husbandry-like stressors involved with shearing, particularly handling, and/or the subsequent cold exposure of shearing. It was also hypothesized that this maternal stress response would impact on lamb vigour traits such as behaviour and thermoregulation. This thesis examined the effects of a range of mild stressors commonly experienced by ewes during husbandry procedures during mid-pregnancy (pregnancy day 85-95) or during late-pregnancy (pregnancy day 120-130) such as yarding, handling, shearing, transport as well as cold exposure. The effects of these stressors on lamb vigour traits were assessed using a separation test for reactivity, before and after a 1 hr separation and cold challenge and thermal imaging during the cold challenge to determine the ability of the lamb to maintain body surface temperature. Shearing during mid-pregnancy increased lamb body dimensions and weight at birth while other stressors did not, which suggests that the causal mechanisms are something other than psychological and cold stress. Cold exposure during both mid- and latepregnancy (cold exposure and/or cold exposure resulting from shearing) negatively imvii
pacted the reactivity levels of newborn lambs by increasing their latency to bleat, stand and return to ewe during a separation test. Cold exposure combined with acute stressors in keeping with husbandry procedures resulted in improved body surface temperature maintenance in newborn lambs when exposed to cold. The presence of effects of mild stressors for both stages of pregnancy on all three lamb vigour traits tested, suggests a number of alternate mechanisms are triggered by maternal-pregnancy stress impacting foetal development. Understanding how to modulate these effects could allow flock management to be modified to improve lamb survival.
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Table of content Certification of Dissertation ............................................................................................... iii Acknowledgements .............................................................................................................. v Abstract ..............................................................................................................................vii List of Figures .................................................................................................................... xv List of Tables .................................................................................................................... xxi Chapter 1:
General Introduction ...................................................................................... 1
The following review will focus particularly on lamb factors involved in adaptation to the environment by the neonatal lamb and will investigate current knowledge on the effects of prenatal stress on this adaptability. .................................................................................. 2 Chapter 2: 2.1
Literature Review........................................................................................... 3
Lamb survival ...................................................................................................... 4
2.1.1
Timing of lamb losses .................................................................................... 4
2.1.2
Causes of death .............................................................................................. 4
2.1.2.1
Dystocia, Birth Injury and Still birth ...................................................... 5
2.1.2.2
Starvation and mismothering .................................................................. 6
2.1.2.3
Exposure ................................................................................................. 7
2.1.3
Factors contributing to lamb survival ............................................................ 7
2.1.3.1
Ewe factors ............................................................................................. 8
2.1.3.2
Lamb risk factors .................................................................................. 12
2.2 2.2.1
Adapting to a new environment during lambing ............................................... 16 Cold resistance in newborn lambs ............................................................... 16 ix
2.2.1.1
The transition to the outside environment at birth. ............................... 16
2.2.1.2
Environmental conditions impact the cold resistance in neonates ....... 17
2.2.2
Thermoregulation in neonates: BAT localisation and hormonal regulation 19
2.2.3
Assessing thermogenesis ............................................................................. 21
2.2.3.1
Methods to induce and assess cold stress ............................................. 21
2.2.3.2
Assessing heat production in newborn lambs....................................... 23
2.3
Prenatal stress and foetal development. ............................................................. 26
2.3.1
Stress, stress response .................................................................................. 26
2.3.2
Effects of prenatal stress .............................................................................. 28
2.3.2.1
Hormonal and physiological changes impact on foetal development .. 28
2.3.2.2
Effects of chronic stress ........................................................................ 31
2.3.3
The effects of stressors during management practices on lamb vigour traits ……………………………………………………………………………..31
2.3.3.1
Shearing during pregnancy ................................................................... 32
2.3.3.2
The effects of prenatal cold stress on lambs ......................................... 37
2.3.3.3
The impact of other stressors during pregnancy on lambs: isolation,
yarding and transport ............................................................................................. 38 Chapter 3:
Impact of prenatal stress on ewe metabolism and lamb birthweight and body
dimensions.... ..................................................................................................................... 41 3.1
Introduction ........................................................................................................ 45
3.2
Material and methods ......................................................................................... 47
3.2.1
Experimental animals and design ................................................................ 48 x
3.2.2
Housing ........................................................................................................ 49
3.2.3
Ewe Stress Treatments ................................................................................. 50
3.2.4
Lambing ....................................................................................................... 53
3.2.5
Blood glucose levels .................................................................................... 53
3.2.6
Statistical analysis ........................................................................................ 54
3.3
Results ................................................................................................................ 55
3.3.1
Blood and plasma glucose in ewes .............................................................. 55
3.3.2
Lamb birthweight ......................................................................................... 58
3.3.3
Girth circumference ..................................................................................... 59
3.3.4
Crown-Rump length..................................................................................... 60
3.3.5
Lambs blood and plasma glucose and lactate .............................................. 61
3.4
Discussion .......................................................................................................... 61
Chapter 4:
Impact of mid- and late-pregnancy prenatal stress on lamb neonatal
reactivity and vigour. ......................................................................................................... 69 4.1
Introduction ........................................................................................................ 73
4.2
Material and methods ......................................................................................... 75
4.2.1
Experimental animals and design ................................................................ 76
4.2.2
Housing ........................................................................................................ 77
4.2.3
Treatments.................................................................................................... 79
4.2.4
Lambing ....................................................................................................... 80
4.2.4.1
Cold challenge ...................................................................................... 80
4.2.4.2
Blood samples....................................................................................... 82 xi
4.2.4.3 4.2.5 4.3
Behaviour test ....................................................................................... 82
Statistical analysis ........................................................................................ 84 Results ................................................................................................................ 85
4.3.1
Behaviour ..................................................................................................... 85
4.3.2
Lambs blood glucose and lactate ................................................................. 89
4.3.2.1
Experiment 1- GLUCOSE .................................................................... 89
4.3.2.2
Experiment 1 – LACTATE .................................................................. 90
4.3.2.3
Experiment 2 - GLUCOSE ................................................................... 90
4.3.2.4
Experiment 2 - LACTATE .................................................................. 90
4.3.2.5
Experiment 3 - GLUCOSE ................................................................... 90
4.3.2.6
Experiment 3 - LACTATE ................................................................... 91
4.4
Discussion .......................................................................................................... 91
Chapter 5:
Impact of prenatal stress on lamb neonatal ability to maintain body surface
temperature in cold conditions ......................................................................................... 103 5.1
Introduction ...................................................................................................... 107
5.2
Material and methods ....................................................................................... 108
5.2.1
Experimental animals................................................................................. 109
5.2.2
Housing ...................................................................................................... 110
5.2.3
Treatments.................................................................................................. 111
5.2.4
Lambing ..................................................................................................... 113
5.2.4.1
Cold challenge .................................................................................... 113
5.2.4.2
Thermograms analysis ........................................................................ 115 xii
5.2.5
Statistical analysis ...................................................................................... 116
5.3
Results .............................................................................................................. 117
5.4
Discussion ........................................................................................................ 123
Chapter 6:
Infrared thermal imaging as a method to evaluate heat loss in newborn
lambs………. ................................................................................................................... 131 6.1
Introduction ...................................................................................................... 135
6.2
Materials and methods ..................................................................................... 136
6.2.1
Animals and Treatment .............................................................................. 136
6.2.2
Lambs measurements ................................................................................. 137
6.2.3
Image analysis ............................................................................................ 139
6.2.4
Statistical analysis ...................................................................................... 140
6.3
Results .............................................................................................................. 142
6.3.1
Rectal temperature ..................................................................................... 142
6.3.2
Thermal imaging ........................................................................................ 143
6.4
Discussion ........................................................................................................ 145
Chapter 7:
General Discussion and Conclusion .......................................................... 153
REFERENCES ................................................................................................................ 161
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List of Figures Figure 2.1 Factors contributing to lamb survival (adapted from Gautier and Corbière (2011)).................................................................................................................................. 8 Figure 2.2 Heat production of lambs over ambient temperature depending on environmental conditions (adapted from Martin (1999)) .................................................. 18 Figure 3.1 Maternal plasma glucose levels at (baseline D0 (full bar) and after stress D7 (striped bar) of ewes either shorn at mid or late pregnancy (MID-S& LATE-S) or sham shorn at mid or late-pregnancy (MID-C & LATE-C). Asterisk denote tendency (0.05≤P
