Havemeyer Foundati<strong>on</strong> M<strong>on</strong>ograph Series No. 3collecti<strong>on</strong>, transfer procedures and maintenance <str<strong>on</strong>g>of</str<strong>on</strong>g><str<strong>on</strong>g>the</str<strong>on</strong>g> corpus luteum. Equine vet. J. Suppl. 3, 25-33.Behrens, C., Aurich, J.E., Klug, E. Naumann, H. andHoppen, H.O. (1993) Inhibiti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> g<strong>on</strong>a-dotrophinrelease in mares during <str<strong>on</strong>g>the</str<strong>on</strong>g> luteal phase <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g>oestrous cycle by endogenous opioids. J. reprod.Fert. 3, 509-514.Granström, E. and Kindahl, H. (1982)Radioimmunoassay <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> major plasma metabolite<str<strong>on</strong>g>of</str<strong>on</strong>g> PGF 2a , 15-keto-13,14-dihydro-PGF 2α. MethodsEnzymol. 86, 320-339.H<str<strong>on</strong>g>of</str<strong>on</strong>g>fmann, B., Schams, D., Gimenez, T., Ender, M.L.,Herrmann, C.H. and Karg, H. (1973) Changes <str<strong>on</strong>g>of</str<strong>on</strong>g>progester<strong>on</strong>e, total oestrogens, corticosteroids,prolactin and LH in bovine peripheral plasmaaround parturiti<strong>on</strong> with special reference to <str<strong>on</strong>g>the</str<strong>on</strong>g>effect <str<strong>on</strong>g>of</str<strong>on</strong>g> exogenous corticoids and a prolactininhibitior, respectively. Acta endocrinol. 73, 385-395.Hurtgen, J.P. and Ganjam, V.K. (1979) The effect <str<strong>on</strong>g>of</str<strong>on</strong>g>intrauterine and cervical manipulati<strong>on</strong> <strong>on</strong> <str<strong>on</strong>g>the</str<strong>on</strong>g> equineoestrous cycle and horm<strong>on</strong>e pr<str<strong>on</strong>g>of</str<strong>on</strong>g>iles. J. reprod. Fert.Suppl. 27, 191-197.Kask, K., Odensvik, K. and Kindahl, H. (1997)Prostaglandin F release associated with an embryotransfer procedure in <str<strong>on</strong>g>the</str<strong>on</strong>g> mare. Equine vet. J. 29,286-289.Wilde, M.H., Dinger, J.E., Hoagland, T.A., Graves-Hoagland, R.L. and Woody, C.O. (1989) The effects<str<strong>on</strong>g>of</str<strong>on</strong>g> cervical dilatati<strong>on</strong> <strong>on</strong> plasma PGFM,progester<strong>on</strong>e and <str<strong>on</strong>g>the</str<strong>on</strong>g> durati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> luteal functi<strong>on</strong> indiestrous mares. Theriogenol. 32, 675-681.73
Equine Embryo TransferTHE INFLUENCES OF MATERNAL SIZE, AGE ANDPARITY ON PLACENTAL AND FETAL DEVELOPMENTIN THE HORSES. Wilsher and W. R. AllenEquine Fertility Unit, Mertoun Paddocks, Woodditt<strong>on</strong> Road, Newmarket, Suffolk CB8 9BH, UKClear evidence that maternal size, and henceuterine size, pr<str<strong>on</strong>g>of</str<strong>on</strong>g>oundly effects <str<strong>on</strong>g>the</str<strong>on</strong>g> birthweight <str<strong>on</strong>g>of</str<strong>on</strong>g><str<strong>on</strong>g>the</str<strong>on</strong>g> foal was dem<strong>on</strong>strated by Walt<strong>on</strong> andHamm<strong>on</strong>d (1938) in <str<strong>on</strong>g>the</str<strong>on</strong>g>ir classical experiment <str<strong>on</strong>g>of</str<strong>on</strong>g>between breed inseminati<strong>on</strong>s in Shetland p<strong>on</strong>iesand Shire horses. Tischner and Klimszak (1989)also showed <str<strong>on</strong>g>the</str<strong>on</strong>g> effect <str<strong>on</strong>g>of</str<strong>on</strong>g> intrauterine envir<strong>on</strong>ment<strong>on</strong> <str<strong>on</strong>g>the</str<strong>on</strong>g> development <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> fetus in horses bytransferring p<strong>on</strong>y embryos to larger draft mares andcomparing <str<strong>on</strong>g>the</str<strong>on</strong>g> birth size and subsequentdevelopment <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> foals with sex-matched siblingsborn from <str<strong>on</strong>g>the</str<strong>on</strong>g>ir natural p<strong>on</strong>y mo<str<strong>on</strong>g>the</str<strong>on</strong>g>rs. In bo<str<strong>on</strong>g>the</str<strong>on</strong>g>xperiments <str<strong>on</strong>g>the</str<strong>on</strong>g> size differences between <str<strong>on</strong>g>the</str<strong>on</strong>g> foalsat birth persisted into adulthood. It is hardlysurprising that uterine size effects <str<strong>on</strong>g>the</str<strong>on</strong>g> size <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g>foal so dramatically since <str<strong>on</strong>g>the</str<strong>on</strong>g> diffuse, n<strong>on</strong>-invasive,epi<str<strong>on</strong>g>the</str<strong>on</strong>g>liochorial equine placenta establishes a closemicrovillous interdigitati<strong>on</strong> with <str<strong>on</strong>g>the</str<strong>on</strong>g> entireendometrial surface <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> maternal uterus.Endometrosis may compromise <str<strong>on</strong>g>the</str<strong>on</strong>g> uterineenvir<strong>on</strong>ment during pregnancy and Bracher et al.(1996) showed a close relati<strong>on</strong>ship between <str<strong>on</strong>g>the</str<strong>on</strong>g>health <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> endometrium and <str<strong>on</strong>g>the</str<strong>on</strong>g> normality anddensity <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> microcotyled<strong>on</strong>s per area <str<strong>on</strong>g>of</str<strong>on</strong>g> placentaduring <str<strong>on</strong>g>the</str<strong>on</strong>g> first two thirds <str<strong>on</strong>g>of</str<strong>on</strong>g> gestati<strong>on</strong>. Thec<strong>on</strong>diti<strong>on</strong> appears to be associated more with agethan parity and Ricketts and Al<strong>on</strong>so (1991)showed that aged maiden mares developendometrosis, without <str<strong>on</strong>g>the</str<strong>on</strong>g> endometrium havingsuffered <str<strong>on</strong>g>the</str<strong>on</strong>g> challenges <str<strong>on</strong>g>of</str<strong>on</strong>g> semen, infecti<strong>on</strong>,pregnancy or parturiti<strong>on</strong>. Parity is also associatedwith foal birthweight and Hintz et al. (1979)observed that Thoroughbred mares < 7 years <str<strong>on</strong>g>of</str<strong>on</strong>g>age had lighter foals with smaller cann<strong>on</strong> b<strong>on</strong>esthan mares 7–11 years old. Fur<str<strong>on</strong>g>the</str<strong>on</strong>g>rmore, <str<strong>on</strong>g>the</str<strong>on</strong>g>sedifferences persisted until at least 510 days <str<strong>on</strong>g>of</str<strong>on</strong>g> age.Barr<strong>on</strong> (1995) surveyed racetrack performance <str<strong>on</strong>g>of</str<strong>on</strong>g>Thoroughbreds and c<strong>on</strong>cluded that foals born fromparous mares aged 7–11 years were moresuccessful than those from maiden mares or olderanimals. Similarly, Finocchio (1996) reported thatthat third foals were most likely to become Stakeswinners, followed closely by foals produced inparities 5, 2 and 4, in that order.In <str<strong>on</strong>g>the</str<strong>on</strong>g> present experiment <str<strong>on</strong>g>the</str<strong>on</strong>g> effects <str<strong>on</strong>g>of</str<strong>on</strong>g>maternal size, age and parity <strong>on</strong> <str<strong>on</strong>g>the</str<strong>on</strong>g> gross andmicroscopic development <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> placenta and <strong>on</strong>foal birthweight were investigated. Normal termplacentae were recovered at sp<strong>on</strong>taneous thirdstage labour from 2 cohorts <str<strong>on</strong>g>of</str<strong>on</strong>g> mares and, afterweighing <str<strong>on</strong>g>the</str<strong>on</strong>g> allantochori<strong>on</strong> and measuring itsgross area and volume, stereological techniqueswere applied to 10 biopsies selected randomlyfrom all parts <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> allantochori<strong>on</strong> to measure <str<strong>on</strong>g>the</str<strong>on</strong>g>microscopic surface area <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> microcotyled<strong>on</strong>s.The microscopic fetomaternal c<strong>on</strong>tact per unitvolume <str<strong>on</strong>g>of</str<strong>on</strong>g> chori<strong>on</strong> (surface density <str<strong>on</strong>g>of</str<strong>on</strong>g>microcotyled<strong>on</strong>s) and, by multiplicati<strong>on</strong> with <str<strong>on</strong>g>the</str<strong>on</strong>g>gross volume <str<strong>on</strong>g>of</str<strong>on</strong>g> chori<strong>on</strong>; <str<strong>on</strong>g>the</str<strong>on</strong>g> total area <str<strong>on</strong>g>of</str<strong>on</strong>g>fetomaternal c<strong>on</strong>tact across <str<strong>on</strong>g>the</str<strong>on</strong>g> entire placenta,were recorded.In <str<strong>on</strong>g>the</str<strong>on</strong>g> first cohort <str<strong>on</strong>g>of</str<strong>on</strong>g> mares between-breedembryo transfer was used to create 8Thoroughbred-in-P<strong>on</strong>y (Tb-in-P) pregnancies inwhich <str<strong>on</strong>g>the</str<strong>on</strong>g> genetically larger Thoroughbred fetusexperienced cramping and nutriti<strong>on</strong>al deprivati<strong>on</strong>in utero, 7 P-in-Tb pregnancies in which <str<strong>on</strong>g>the</str<strong>on</strong>g>smaller P<strong>on</strong>y fetus was exposed to nutriti<strong>on</strong>alexcess in utero, with 7 normal Tb-in-Tb and 7 P-in-P pregnancies as c<strong>on</strong>trols. Str<strong>on</strong>g positivecorrelati<strong>on</strong>s were dem<strong>on</strong>strated between maternalweight and foal birthweight and betweenbirthweight and both <str<strong>on</strong>g>the</str<strong>on</strong>g> weight and gross area <str<strong>on</strong>g>of</str<strong>on</strong>g><str<strong>on</strong>g>the</str<strong>on</strong>g> placenta. Unexpectedly, surface density <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g>microcotyled<strong>on</strong>s, which was also was positivelycorrelated with foal birthweight, was <str<strong>on</strong>g>the</str<strong>on</strong>g> highest in74
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