Equine reproductive physiology, breeding and stud management

385 Pages·2008·8.92 MB·English

by  Davies Morel, M. C. G. (Eds.)

Equine Reproductive Physiology, Breeding
and Stud Management, 3rd Edition
To Mum and Dad
Equine Reproductive Physiology,
Breeding and Stud Management,
3rd Edition
Mina C.G. Davies Morel
Institute of Rural Studies
University of Wales, Aberystwyth
UK
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A catalogue record for this book is available from the British Library, London, UK.
Library of Congress Cataloging-in-Publication Data
Davies Morel, Mina C.G.
Equine reproductive physiology, breeding, and stud management/M.C.G. Davies Morel – 3rd ed.
p. cm.
Includes bibliographical references and index.
ISBN 978-1-84593-450-7 (alk. paper)
1. Horses – Reproductive. 2. Horses – Breeding. I. Title.
SF768.2.H67D39 2008
636.1'082–dc22
2008008422
ISBN-13: 978 1 84593 450 7
Typeset by SPi, Pondicherry, India.
Printed and bound in the UK by Cambridge University Press, Cambridge.
Contents
1. The Reproductive Anatomy of the Mare 1
2. The Reproductive Anatomy of the Stallion 15
3. Control of Reproduction in the Mare 28
4. Control of Reproduction in the Stallion 40
5. The Anatomy and Physiology of Pregnancy in the Mare 46
6. Endocrine Control of Pregnancy in the Mare 64
7. The Physical Process of Parturition 69
8. The Endocrine Control of Parturition 77
9. The Anatomy and Physiology of Lactation 82
10. Control of Lactation in the Mare 93
11. Selection of the Mare and Stallion for Breeding 95
12. Preparation of the Mare and Stallion for Covering 117
13. Mating Management 134
14. Management of the Pregnant Mare 155
15. Management of the Mare at Parturition 169
16. Management of the Lactating Mare and Young Foal 185
17. Weaning and Management of Young Stock 213
18. Stallion Management 225
19. Infertility 237
20. Artifi cial Insemination 266
21. Embryo Transfer in the Mare 294
Bibliograhy 307
Index 359
Contents v
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1
The Reproductive Anatomy
of the Mare
1.1. Introduction this area is regularly swabbed in mares prior to
covering, and, indeed, in the Thoroughbred indus-
This chapter details the anatomy and function of the
try such swabbing is compulsory (McAllister and
mare’s reproductive system. Further accounts may
Sack, 1990; Ginther, 1992; Horse Race Betting
be found in other texts, such as Ashdown and Done
Levy Board, 2008). Within the walls of the vulva
(1987), Frandson and Spurgen (1992), Ginther
lies the vulva constrictor muscle, running along
(1992), Kainer (1993), Dyce et al. (1996), Bone
either side of the length of the vulval lips. This
(1998), Senger (1999), Bergfelt (2000), Hafez and
muscle acts to maintain the vulval seal and to
Hafez (2000) and Le Blare et al. (2004). The repro-
invert and expose the clitoral area during oestrus,
ductive tract of the mare may be considered as a Y-
known as winking (Ashdown and Done, 1987;
shaped tubular organ with a series of constrictions
Kainer, 1993).
along its length. The perineum, vulva, vagina and
cervix can be considered as the outer protective
structures, providing protection for the inner, more 1.3. The Perineum
delicate structures, the uterus, Fallopian tubes and
The perineum is a rather loosely defined area in the
ovaries, which are responsible for fertilization and
mare, but includes the outer vulva and adjacent
embryo development. Figure 1.1, taken after slaugh-
skin along with the anus and the surrounding area.
ter, shows the reproductive structures of the mare,
In the mare, the conformation of this area is of
and Figs 1.2 and 1.3 illustrate these diagrammati-
clinical importance, due to its role in the protection
cally. Each of these structures will be dealt with in
of the genital tract from the entrance of air. Mal-
turn in the following account.
conformation in this area predisposes the mare to a
condition known as pneumovagina or vaginal
wind-sucking, in which air is sucked in and out of
1.2. The Vulva
the vagina through the open vulva. Along with this
The vulva (Fig. 1.4) is the external area of the mare’s
reproductive system, protecting the entrance to the
vagina. The outer area is pigmented skin with
the normal sebaceous and sweat glands along with the
nerve and blood supply normally associated with
the skin of the mare. The inner area is lined by
mucous membrane and is continuous with the
vagina. The upper limit (the dorsal commissure) is
situated approximately 7 cm below the anus. Below
the entrance to the vagina, in the lower part of the
vulva (the ventral commissure), lie the clitoris and
the three clitoral sinuses (ventral, medial and lat-
eral; Fig. 1.5). These sinuses are of importance in
the mare as they provide an ideal environment for
the harbouring of many venereal disease (VD) bac-
teria, such as Taylorella equigenitalis (causal agent
for contagious equine metritis (CEM)), Klebsiella Fig. 1.1. The mare’s reproductive tract after slaughter
pneumoniae and Pseudomonas aeroginosa. Hence, and dissection (see also Fig. 1.3).
©M.C.G. Davies Morel 2008. Equine Reproductive Physiology, Breeding 1
and Stud Management, 3rd edn (M.C.G. Davies Morel)
sacral
vertebra
kidney rectum
anus
broad ligaments cervix
uterine body vagina
Infundibulum vulva
ovary clitoris
Fallopian tube
uterine horn
Fig. 1.2. A lateral view (from the side) of the mare’s reproductive tract.
fallopian tube
uterine horn
ovary
endometrial folds
broad ligaments
uterine body
cervix
bladder
vagina
urethra
vulva
Fig. 1.3. The mare’s reproductive tract: a diagrammatic representation of Fig. 1.1.
2 Chapter 1
Fig. 1.5. The vulva of the mare showing the ventral
Fig. 1.4. The vulval area of the mare: in this instance,
commissure within which lie the clitoris and clitoral
the conformation of the perineal area is poor with the
sinuses on either side.
anus sunken cranially, opening up the vulva to faecal
contamination.
passage of air also go bacteria, which bombard the There are three seals within the tract: the vulval
cervix, exposing it to unacceptably high levels of seal, the vestibular or vaginal seal and the cervix;
contamination, which it is often unable to cope these are illustrated in Fig. 1.6.
with, especially during oestrus when it is less com- The perineal area plus the vulva constrictor mus-
petent. Passage of bacteria into the higher, more cle in the walls of the vulva form the vulval seal.
susceptible parts of the mare’s tract may result in The vestibular seal is formed by the natural col-
bacterial infections, such as CEM, and other VDs lapsing and apposition of the walls of the posterior
leading to endometritis (uterine infection). Chapter vagina, where it sits above the floor of the pelvic
19 (this volume) gives further details on the causes girdle plus the hymen, if still present. The tight
of VD infection in the mare, all of which adversely muscle ring within the cervix forms the cervical
affect fertilization rates (Ginther, 1992; Easley, seal. This series of seals is affected by the confor-
1993; Kainer, 1993). mation of an individual and also by the stage of the
oestrous cycle (Figs 1.7 and 1.9).
The ideal conformation is achieved if 80% of
1.3.1. Protection of the genital tract
the vulva lies below the pelvic floor. A simple test
Adequate protection of the genital tract is essential can be performed to assess this. If a sterile plastic
to prevent the adverse effects of pneumovagina. tube is inserted through the vulva into the vagina
Reproductive Anatomy of the Mare 3