Monitoring of the physiological and behavioural stress response of Holstein bulls following group mixing

Holstein bulls destined for beef production which are unfamiliar with each other are routinely mixed prior to marketing. This practice constitutes a stressful event which affects both animal welfare and meat quality. We questioned whether mixing 34 days before marketing could induce a stress response that would affect the animal performance and pH of meat. For the experiment, 22 Holstein bulls (at a mean age of 7.35±0.07 months and mean weight of 285.5±90 kg) were raised in groups of three and were mixed 34 days prior to marketing to form two groups (n1=13, n2=9). The daily rumination and activity of the bulls were monitored for 20 days before and 33 days post mixing (DPM) and bulls were weighed 1 day before mixing (DBM), 3 and 33 days DPM. Plasma concentrations of non-esterified fatty acid (NEFA), and anti-oxidative capacity in bulls were measured pre- and post-mixing (PM). After slaughter, pH measurements were taken at the m. longissimus thoracis et lumborum (LTL) 24 h after the carcasses were chilled. The results demonstrated that mixing had significantly decreased the calves’ weight gain by 6.2±2 kg at 3 DPM. Daily rumination decreased twofold 24 h PM (P