Association assessment of hair cortisol levels with productive performance and meat qualities in Hereford bulls

Hormones play a crucial role in regulating a variety of physiological processes in farm animals, including metabolism, productive (dairy, meat) and reproductive traits. In this work, for the first time, we detected the association of the cortisol concentration in hair with the productive traits of steers and the qualitative characteristics of beef, including amino acid, fatty acid and mineral composition. The aim of the study was to evaluate the effect of cortisol concentration in hair as related to the productive and slaughter traits of Hereford bulls, as well as the qualitative characteristics of beef. The research was carried out in 2024 in OOO Agrosakmara and OOO Orenbiv of the Orenburg Province on 18-month-old Hereford bulls (n = 55). Animals were divided into 3 groups according by the cortisol concentration in the hair: group I - up to the 25th percentile (n = 15); group II - in the range of 25-75th percentiles (n = 25); group III - above the 75th percentile (n = 15). The choice of these percentile intervals were previously assessed. Hair samples from the upper part of the withers were taken using a clipper for farm animals, followed by an adjustment of the proximal part in length corresponding to the 15-18-month growth period. Cortisol was extraction using a Constractional Vapor rotary evaporator (Xi'an Heb Biotechnology Co., Ltd., China) and isopropanol and methanol reagents (HPLC grade) as described for humans and monkeys. The concentration of the hormone in hair samples was determined by enzyme immunoassay (an Infinite F200 PRO microplate analyzer, Tecan, Austria) using a cortisol assay kit (OOO Olvex Diagnosticum, Russia). The bulls aged 18 months was slaughtered (OOO Orenbiv, Orenburg Province), The carcasses were assessment by category, class and subclass (State Standard 34120-2017, M., 2018), and after 24 h at 2-4 °С, minced meat and the longissimus dorsi muscle at the 9-11th ribs were sampled from the left half. Estimated parameters in the samples were moisture and dry matter, protein, fat, ash energy value, pH, moisture capacity, amino acid, fatty acid and elemental compositions. The observed range of cortisol concentration in the hair of group I calves varied from 4.39 to 5.28 ng/g, in group II from 5.46 to 9.42 ng/g, in group III from 9.51 to 11.09 ng/g. The bulls of group I surpassed (р ≤ 0.05) their peers of groups II and III in live weight at the age of 15 months by 3.2 and 5.7%, at 18 months by 4.7% and 7.0 %, in the average daily gain from 15 to 18 months by 11.5 and 13.1 %, in the weight of a hot carcass by 5.0 and 8.2 %, in slaughter weight by 4.6 and 7.0%, but were inferior in terms of internal fat weight by 4.5 and 15.3 %, respectively. Group I bulls produced more flesh by 5.25 and 8.47%, and more muscle tissue by 5.3 and 8.84 %, with a decrease in bone weight by 3.20 and 5.94 % and in tendons and ligaments by 4.58 and 7.06 % compared to groups II and III, respectively. As the cortisol concentration in the hair increased, the amount of arginine, phenylalanine, histidine, leucine+isoleucine, methionine, valine, alanine, glycine and tryptophan. High cortisol concentration in the hair was associated with high levels of palmitic, myristic and less linoleic and linolenic fatty acids in the lipids of the longissimus dorsi muscle. The longissimus dorsi muscle of group I bulls was characterized by a high content of essential elements (Ca, Mg, Cu, I, Se, Zn) and less amounts of conditionally essential and toxic elements (Ni, As, Pb). Thus, the cortisol level estimated by its concentration in the hair of Hereford bulls is associated with productive performance, slaughter traits, and quality parameters of beef, namely amino acid, fatty acid and mineral compositions.