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The aim of this study was to examine the influence of individual characteristics of female dogs (Canis familiaris) of the Bull Terrier breed on the dynamics of progesterone levels in their blood throughout the estrous cycle. The experiment involved 25 clinically healthy female dogs divided into three age groups: young (1.4 years), middle-aged (4.8 years), and older dogs (8.6 years). The health status of the animals was assessed through clinical examinations and laboratory analyses, including the determination of reproductive status using folliculometry, vaginal cytology, and blood progesterone level analysis. Blood samples were collected from the jugular vein during key periods of the estrous cycle and analyzed using an enzyme-linked immunosorbent assay (“Progesterone – ELISA,” HEMA, Ukraine). Additionally, the impact of body condition (evaluated using the BCS scale) and temperament (assessed using the C-BARQ questionnaire) on hormonal status was investigated. To this end, 12 groups of female dogs were formed according to behavioral characteristics (aggression, fear and anxiety, excitability, learning ability, and obedience). All experimental procedures complied with the requirements of the Ukrainian Law “On the Protection of Animals from Cruelty” and the principles of the European Convention for the Protection of Vertebrate Animals Used for Experimental and Scientific Purposes. The results of two-factor ANOVA revealed that, regardless of age, body weight, or temperament, the stage of the estrous cycle was the determining factor influencing blood progesterone levels (F=79.8–173.0; P<0.001). Among individual characteristics, body weight had the greatest impact (F=16.3; P<0.001), while age differences showed a statistically significant but less pronounced effect (F=3.65; P<0.05). The temperament of female dogs also significantly affected progesterone levels, particularly in terms of aggression (F=10.68; P<0.001), fear and anxiety (F=9.21; P<0.001), and excitability (F=7.6; P<0.001). In contrast, learning ability and obedience did not show a significant effect on hormonal status (F=0.91; P=0.41). Analysis of interaction effects revealed a significant relationship between body weight, behavioral characteristics (aggression, fear), and the stage of the estrous cycle (F=2.24–2.92; P<0.005–0.001). This indicates that individual physiological and behavioral traits influence the endocrine regulation of reproductive function in female dogs. The findings expand the understanding of regulatory mechanisms in the estrous cycle of dogs and emphasize the need to consider individual characteristics when planning veterinary interventions and breeding programs.

 

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