The outcome of the first stages of pregnancy on mares' bloodstream thyroid hormones

摘要

The objective of this study was to compare in detail the total and free iodothyronines' pattern of mares from the first ovulation of the year over an extended period of 12 weeks. A total of 20 mares were used in the study. The mares were classified into two groups: mares mated at the ovulation (n = 10) used as observational group and mares unmated at the ovulation (n =10) used as control group. Serum total and free triiodothyronine (T-3, fT(3)) and thyroxine (T-4, fT(4)) levels were measured in baseline conditions at the first ovulation of year and once a week until 12 weeks Jater. For the experimental group, the first week of postovulation mating was considered as the first week of gestation. One-way analysis of variance showed a significant effect of time over 12 weeks for T-3 (F = 2.44; P = 0.007) in pregnant mares, with the higher levels at the seventh and 12th weeks (P 0.05) than baseline values, and for fT(3) (F = 2.36; P = 0.009), with the higher levels at the 11th week (P 0.05) than baseline values. Two-way analysis of variance showed a significant pregnancy effect compared with nonpregnancy stage for T3 (F = 15.82; P = 0.009), with the higher levels at the seventh and 12th weeks (P 0.05) of pregnancy than that in nonpregnant values. Thus, it appears that, under similar environment, management and nutritional regime, the first trimester of pregnancy plays a dynamic role on the thyroid patterns by their anabolic activity; therefore, significant effects of time points on the T-3 and tT3 concentrations probably may contribute to the control of early embryonic growth and development, before the onset of fetal thyroid activity. Considerable additional research, outwith the aim of this study, will be required to elucidate the mechanisms by which gestational age affects the physiological thyroid function in mares and/or fetus ratio in the first pregnancy stage. (C) 2016 Elsevier Inc. All rights reserved.