*4.5. Statistical Analysis*

Plasma concentrations of ZEN (see Figure 1), α-ZEL (see Figure 1), and ZON (see Figure 2) as well as E2 (see Figure 3) and T (see Figure 4) levels in the blood plasma of the examined gilts were presented as arithmetic means (*x*) and SD (±). Statistical calculations were performed using the Statistica application (Statsoft Inc., Tulsa, OK, USA). Due to the applied ZEN dose and the length of application, arithmetic means were compared by one-way analysis of variance for systems with repeatable measurements. The homogeneity of variances in the compared groups (required in analyses of variance) was verified by the Brown–Forsythe test. Differences between groups were analyzed by Tukey's honestly significant difference test (*p* < 0.05 or *p* < 0.01).

**Author Contributions:** Developed the concept of the article, reviewed the literature, and wrote the article, Ł.Z.; reviewed the literature and prepared the manuscript for submission, M.T.G.; performed laboratory tests, M.G., S.L.-Z. and M.D.; critically revised the paper, M.T.G. All authors have read and agreed to the published version of ˙ the manuscript.

**Funding:** The experiment was supported by research grant N N311 608938 from the National Science Centre Poland. The project was financially co-supported by the Minister of Science and Higher 613 Education under the program entitled "Regional Initiative of Excellence" for the years 2019-2022, 614 Project No. 010/RID/2018/19, amount of funding PLN 12,000,000.

**Conflicts of Interest:** The authors declare no conflict of interest.
