Cortisol as a marker of physiological stress in Bos taurus sires

The endocrine mechanism in animal stress has not yet been fully elucidated. Social stress due to hierarchy in the herd increases the production of cortisol, catecholamines, can affect sexual behavior and fertility, and reduce productivity. Despite the enormous importance of the problem for breeding enterprises involved in the production and cryopreservation of sperm of farm animals for commercial and scientific purposes, there are no special studies to investigate the connection of the qualitative and quantitative parameters of the ejaculate and its fertilizing ability with the post-ejaculatory cortisol level. In the presented work, we revealed for the first time that the effectiveness of artificial insemination is directly proportional to the concentration of blood cortisol in stud bulls after ejaculation. In young stud bulls, stress associated with blood sampling dominated; in adult bulls, sexual arousal suppressed stress caused by this veterinary manipulation. For the first time, we find out the dependence of the fertilizing capability of the bull sperm on the post-ejaculation blood cortisol level. We assessed the pattern of post-ejaculation cortisol concentration in 11 Holstein bulls of foreign selection aged 29-71 months (holding JSC GCV, a subsidiary breeding enterprise of JSC Uralplemtsentr, Sverdlovsk region, 2018-2021) which are exploited according to approved technology and determined the fertilizing rate of the cryopreserved resulting sperm as influenced by the blood cortisol level. In both young and adult animals, there was a significant positive dynamics of cortisol in response to blood sampling. The average blood cortisol concentration in young sires (n = 6) under stress from this regular manipulation increased evenly and reached 70.8; 91.1 and 144.7 nmol/l on the days of three consecutive doublet collections of semen after 4-5-day intervals. In bulls (n = 5) older than 4 years, the peak concentration of cortisol (172.5 nmol/l) occurred in the second semen collection, and by the third collection, there was a slight decrease in the cortisol level, by 5 %. As post-ejaculation blood cortisol increases, the number of spermatozoa per ejaculate increases. In young bulls, after three consecutive double collections of semen at 4-5 day intervals, 4.0, 5.5 and 6.2 billion spermatozoa per ejaculation were obtained, in sires over 4-year old, 6.6, 7.3 and 7.5 billion sperm. The sperm from sires with the highest post-ejaculation levels of cortisol released into the bloodstream (162-216 nmol/l) exhibited the best fertilizing rate, 59-60 % (p function show_eabstract() { $('#eabstract1').hide(); $('#eabstract2').show(); $('#eabstract_expand').hide(); }