EN
The aim of the study was to assess strongylus invasions in mares during the first three months of pregnancy. Studies were carried out on 11 mares naturally infected with strongyles and divided into 3 groups: I - mares following 1-2 deliveries, II - 3-6 deliveries, and III - 9-10 deliveries. Each group was additionally subdivided into 2 subgroups: A included mares which had bred mare foals and B - mares which had bred stallion foals. Samples of excrement were collected during the following periods: 7 days before delivery and next at weekly intervals up to day 63, and then every two weeks up to day 115 following the delivery date. The intensity of strongyles invasions in the mares was directly related to the postnatal period, number of deliveries and even the sex of the foals. Analyzing the course of the strongyles invasion indicated that the greatest number of eggs were contained in the excrement on day 21 post delivery in the all the groups of mares breeding mare foals whereas a significant decrease in the amount of eggs was noted in mares breeding stallion foals on that day, and it only significantly increased on day 28. During the following gestations the intensity of the strongyles invasion was reduced up to day 42 in group A of the mares and day 49 in group B. A gradual increase in the number of eggs was observed up until day 77 e.g. there were 1000 eggs in group A on day 115 following delivery, and 796 in group B. Hormones produced in the estrus period and early pregnancy seem to affect the progress of Strongylidae invasions in mares.