Faecal Oestrogens and Progesterone Metabolites in Mares of Different Breeds During the Last Trimester of Pregnancy

• Published in: Reproduction in Domestic Animals
• Main Authors: Palme, R, Entenfellner, U, Hoi, H, Möstl, E
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2001
• Subjects: Iceland
• Online Access: http://dx.doi.org/10.1046/j.1439-0531.2001.00302.x; http://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1046%2Fj.1439-0531.2001.00302.x; https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1439-0531.2001.00302.x

Non‐invasive pregnancy diagnosis in mares by measuring faecal oestrogens has been performed over years with great accuracy. However, results have indicated breed‐related differences in the amount of excreted steroids during late pregnancy. Therefore faecal samples were collected during the last 4 months of pregnancy of Thoroughbred (n=10), New Forest pony (n=9), Shetland pony (n=10) and Iceland pony mares (n=11). Concentrations of oestrogens, 20α‐hydroxy‐ and 20‐oxopregnanes were measured using enzyme immunoassays. Breed differences concerning both levels (though significant only in case of oestrogens) and time course of measured steroids were observed. There was a highly significant time effect (p < 0.00001) and an interaction between time and breeds (p < 0.02) for all steroids measured, suggesting that the time effect differs for different breeds. Oestrogen concentrations showed a decrease towards parturition, whereas in 20α‐hydroxy‐ and 20‐oxopregnane levels a pronounced increase was found 2 and 1 months, respectively, before parturition. A breed effect was only significant (p=0.001) when comparing oestrogen concentrations and was mainly due to Iceland ponies, which had the lowest concentrations especially during the last 2 months of pregnancy. An almost significant (p=0.06) breed effect was found for 20‐oxopregnanes. In Iceland mares an additional increase in faecal pregnane content was already observed earlier, reaching maximum levels before the 60th day ante‐partum (a.p.), followed by a decrease until the 30th day a.p. The ratio of 20‐oxopregnanes to oestrogens in the samples was significantly higher (p < 0.006) in Iceland ponies in comparison with any other breed throughout all months before parturition. The breed differences observed in the amounts of oestrogens and/or progestagens present during late pregnancy may demonstrate micro‐evolutionary changes in the endocrine system of a species.