The effects of maternal age and parity on placental and fetal development in the mare.

REASONS FOR PERFORMING STUDY The normality of equine placentation is essential for fetal health and development. Substantial information exists on the gross morphological status of the placenta but few studies have addressed the problem of degenerative lesions that interfere with placental morphology and placental efficiency. HYPOTHESIS Degenerative changes in the endometrium with increasing age and parity are reflected in the morphology and density of the placental microcotyledons. OBJECTIVE To assess placental efficiency on the basis of foal birthweight as a function of total microscopic area of fetomaternal contact. METHODS Stereology was used to examine the placentae of 84 Thoroughbred mares grouped on the basis of age and parity. Placental efficiency, assessed by expressing foal birthweight as a function of total microscopic area of fetomaternal contact, was also determined. RESULTS Mare age and parity influenced the development of the microcotyledons and microcotyledon surface density (Sv) was lowest in aged multiparous mares, presumably due to degenerative changes in their endometrium. However, primiparous mares also showed significantly lower Sv values than young multiparous mares, despite the virginal endometrium of the former group. This apparent 'priming' effect of a first pregnancy on microcotyledonary Sv was illustrated further by 11 maiden mares followed in 2 successive pregnancies. They all showed significant increases in Sv values in their second parity, with equivalent improvements in foal birthweight. CONCLUSIONS Foal birthweight is a reflection of the balance between fetomaternal contact and placental efficiency. Increases in fetomaternal contact are correlated to reductions in placental efficiency, which may reflect the ability of the placenta to modify its exchange capabilities. POTENTIAL RELEVANCE Further work is needed to elucidate how such changes in microcotyledon morphology and efficiency are brought about.

[1]  P D Rossdale,et al.  Influence of maternal size on placental, fetal and postnatal growth in the horse. I. Development in utero. , 2002, Reproduction.

[2]  A. Fowden,et al.  Scanning electron microscopy of the microcotyledonary placenta of the horse (Equus caballus) in the latter half of gestation. , 2000, Placenta.

[3]  S. Suire,et al.  Immunolocalization of a novel protein (P19) in the endometrium of fertile and subfertile mares. , 2000, Journal of reproduction and fertility. Supplement.

[4]  M. Wilson,et al.  Novel insight into the control of litter size in pigs, using placental efficiency as a selection tool. , 1999, Journal of animal science.

[5]  R. Stolla,et al.  Equine uterine blood flow during pregnancy , 1999 .

[6]  J. M. Ellis,et al.  Accuracy of different methods of estimating the weight of horses , 1998, Veterinary Record.

[7]  M. Wilson,et al.  Development of Meishan and Yorkshire littermate conceptuses in either a Meishan or Yorkshire uterine environment to day 90 of gestation and to term. , 1998, Biology of reproduction.

[8]  M. Symonds,et al.  Influence of maternal bodyweight on size, conformation and survival of newborn lambs. , 1997, Reproduction, fertility, and development.

[9]  W. Allen,et al.  Influence of chronic degenerative endometritis (endometrosis) on placental development in the mare. , 1996, Equine veterinary journal.

[10]  H. Rodríguez-Martínez,et al.  Ultrastructure of the secretory endometrium during oestrus in young maiden and foaled mares. , 1995, Equine veterinary journal.

[11]  L. Amet,et al.  Identification of the horse epidermal growth factor (EGF) coding sequence and its use in monitoring EGF gene expression in the endometrium of the pregnant mare. , 1994, Journal of molecular endocrinology.

[12]  P. Rossdale.  Equine Endometritis: John P. Hughes International Workshop , 1993 .

[13]  W. Allen.  Proceedings of the John P. Hughes International Workshop on Equine Endometritis. Davis, California, August 1992. , 1993, Equine veterinary journal.

[14]  E. Carnevale,et al.  Relationships of age to uterine function and reproductive efficiency in mares. , 1992, Theriogenology.

[15]  Mayhew Tm,et al.  The new stereological methods for interpreting functional morphology from slices of cells and organs , 1991, Experimental physiology.

[16]  S. Ricketts,et al.  The effect of age and parity on the development of equine chronic endometrial disease. , 1991, Equine veterinary journal.

[17]  C. Cottrill,et al.  The placenta as a determinant of fetal well-being in normal and abnormal equine pregnancies. , 1991, Journal of reproduction and fertility. Supplement.

[18]  E. Pivalizza,et al.  Placentae of light for dates infants born to underweight mothers at term: a morphometric study. , 1990, Placenta.

[19]  H. W. Mossman,et al.  Types of Eutherian Placentation , 1987 .

[20]  L M Cruz-Orive,et al.  Estimation of surface area from vertical sections , 1986, Journal of microscopy.

[21]  F. Bazer,et al.  Adaptations to reduction of endometrial surface available for placental development in sheep. , 1984, Journal of reproduction and fertility.

[22]  Steven Dh.  Placentation in the mare. , 1982 .

[23]  J. Robinson,et al.  Studies on reproduction in prolific ewes:7. Variability in the growth of individual foetuses in relation to intra-uterine factors , 1981, The Journal of Agricultural Science.

[24]  D. Brooks.  The interaction of α-chlorohydrin with glycerol kinase , 1979 .

[25]  L. D. Van Vleck,et al.  Growth rate of thoroughbreds, effect of age of dam, year and month of birth, and sex of foal. , 1979, Journal of animal science.

[26]  D. H. Steven,et al.  Studies on the equine placenta II. Ultrastructure of the placental barrier. , 1976, Journal of reproduction and fertility.

[27]  D. H. Steven,et al.  Ultrastructural development of the equine placenta. , 1975, Journal of reproduction and fertility. Supplement.

[28]  P. Sharp,et al.  Seasonal changes in plasma LH levels in domestic ducks. , 1975, Journal of reproduction and fertility.

[29]  D. H. Steven,et al.  STUDIES ON THE EQUINE PLACENTA , 1974 .

[30]  L. Jeffcott,et al.  Twinning as a cause of foetal and neonatal loss in the thoroughbred mare. , 1973, Journal of comparative pathology.

[31]  K. Jayant.  Birth weight and survival: a hospital survey repeated after 15 years , 1966, Annals of human genetics.

[32]  J. C. Mccarthy.  Genetic and environmental control of foetal and placental growth in the mouse , 1965 .

[33]  P. L. Broadhurst,et al.  Parity as a determinant of birth weight in the rhesus monkey. , 1965, Folia primatologica; international journal of primatology.

[34]  C. T. Blunn,et al.  Some Factors Affecting Gestation Length and Birth Weight of Beef Cattle , 1952 .

[35]  L. Penrose,et al.  Birth weight and gestation time in relation to maternal age, parity and infant survival. , 1952, Annals of eugenics.