Simple SummaryThe persistent demands for better understanding of the relationship between endocrine adaptation, BW, and productive performances from the perspective of both farmers and the market values of the beef carcass underline that further research on this main topic may be of great interest. In intensive beef production systems, the increase in the prices of feed ingredients has led to changes in the feed formulations, and agri-food wastes can be valorised by incorporating them in diet formulations. In this context, the use of olive cake, a by-product of the olive oil industry, in the formulation of animal feed has been linked with positive effects on the quality of final products, but no previous studies have been conducted to evaluate the thyroid and adrenocortical response to a diet supplemented with olive cake in young growing Limousine beef calves. The present study reveals that the inclusion of olive cake at levels of 10% or 15% in grower/finisher beef diet formulations does not have a detrimental effect on maintaining the physiological thyroid and adrenocortical hormones’ concentrations.AbstractAgro-industrial by-products incorporated into livestock feed formulations can positively impact feed costs and promote a circular bio-economy. Italy produces significant amounts of olive cake (OC), a by-product of olive oil extraction, with the potential for incorporation into bovine diets. However, information on its effects on endocrine responses in growing beef calves is lacking. Forty-eight Limousines randomly allocated to dietary treatment (control or 10%-OC or 15%-OC inclusion) were segregated according to sex and body weight. Serum concentrations of TSH, thyroid hormones, and cortisol were measured on day 0, day 56, and at the end of the trial on day 147. Circulating TSH, total (T3, T4) and free (fT3, fT4) iodothyronines, and cortisol concentrations were all within the normal physiological ranges, with no significant effect imparted by diet. However, the diet × time interaction was significant for T3. The cortisol, T3, T4, and fT4registered on day 147 were higher than those of day 56, and cortisol was higher in heifers than bulls. Final body weight was positively correlated with TSH and T3and negatively with cortisol concentration. These findings suggest that the inclusion of OC at levels up to 15% in growing/finishing beef diets had no adverse effects on the calves’ thyroid and cortical status.