Chivas

Reprod. Nutr. Dev. 46 (2006) 367–378 c INRA, EDP Sciences, 2006 DOI: 10.1051/rnd:2006018

367

Review

The effect of undernutrition on the establishment of pregnancy in the ewe
José-Alfonso Aa *, Cecilia Sa,b , Fernando Fa , Ana Mb
Animal Production and Food Science, Faculty of Veterinary Medicine, Miguel Servet, 177. 50013 Zaragoza, Spain b Biochemistry, Faculty ofVeterinary Medicine, Lasplaces 1550, Montevideo 11600, Uruguay
a

Abstract – The relationship between nutrition and reproduction in sheep has been the subject of research in several international groups. This review will particularly focus on the effects of undernutrition on the potential causes of reproductive failure including abnormalities of the ovum or the embryo, luteal inadequacy and failureof the supply of progesterone to the uterus, or the mechanisms involved in maternal recognition of pregnancy. The level of nutrition and peripheral progesterone concentrations are inversely related, and increased rates of embryo loss, associated with higher progesterone concentrations in ewes with low levels of nutrition have been reported. Undernutrition may act through changes in thedistribution of progesterone in the endometrium. Thus, lower endometrial levels on day 5 of the cycle in ewes fed half of their maintenance requirements have been observed, providing a link between the known role of progesterone in embryo survival by the modulation of uterine function and the higher embryo losses found in undernourished ewes. The evidence of an effect of maternal nutrition on IFNτ secretionfrom the conceptus and of PGF2α production from the uterus is presented. Moreover, undernutrition provokes a reduction in the sensitivity of the endometrium to progesterone that may affect embryo survival. Finally, a state of undernutrition induces changes in the endometrial sensitivity to steroid hormones at early stages of pregnancy that could adversely alter uterine environment to the detrimentof embryo survival. sheep / nutrition / reproduction / progesterone / embryo

1. INTRODUCTION The relationship between nutrition and reproduction in sheep has been the aim of research of several international groups from the sixties, and has been reviewed on several occasions [1–6]. Many groups have furthered knowledge of the mechanisms by which nutrition modifies the reproductive performance ofthe flocks, from the classical concept of the “static” and “dynamic” effect of liveweight on litter size described by Coop [7] in Australia, to the introduc* Corresponding author: alf@unizar.es

tion of the body condition (BC) score [8] and its link with changes in ovulation rate and fertility [9]. The techniques for the measurement of hormone levels (RIA, ELISA), together with laparoscopic andultrasonography routines, to characterize follicular changes and ovulation rate, have been incorporated into these studies and have improved the understanding of the underlying mechanisms that determine reproductive performance. Biochemistry and molecular biology are now providing answers to many of the questions arisen during the last 40 years.

Article published by EDP Sciences and available athttp://www.edpsciences.org/rnd or http://dx.doi.org/10.1051/rnd:2006018

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J.-A. Abecia et al.

Whilst early investigations focused on the effects of nutrition on the hypothalamic-pituitary axis, more recent studies have tested the hypothesis that nutritional signals (e.g. metabolic hormones) exert a direct effect at the ovarian level. Less research has been performed on the effect ofundernutrition on the uterine environment that plays a major role in determining the success of the embryo in the maintenance of pregnancy. The present review will focus its attention on the effect of undernutrition on the mechanism of establishment of pregnancy, which is essential to the survival of the embryo. The potential causes of wastage include abnormalities of the ovum or the embryo, luteal...