This study examined whether combining Azomite (a volcanic clay) with zilpaterol hydrochloride enhanced productive performance, dietary net energy utilisation, carcass traits, meat primal cuts, and visceral mass in finishing lambs. Twenty-four Pelibuey × Katahdin intact male lambs (38 ± 2.64 kg) were fed high-energy total mixed diets supplemented with 6 mg zilpaterol/kg diet (ZH), 0.75% Azomite (AZO), or 0.75% Azomite + 6 mg zilpaterol/kg diet (ZH+AZO). The trial lasted 34 days and zilpaterol was withdrawn three days before slaughter. Contrary to our hypothesis, ZH+AZO and ZH lambs had very similar responses for all measured variables. Compared with ZH and ZH+AZO, AZO lambs had a 16.7% lower average daily gain and 5.5% lower dietary net energy utilisation, without affecting dry matter intake. The expected-to-observed dietary net energy ratio was 2% higher than expected in AZO lambs, representing a 6% smaller increase than that seen in ZH and ZH+AZO lambs. Compared to ZH and ZH+AZO lambs, carcass weight (6.15%), dressing percentage (3.77%), and Longissimus muscle area (12%) were lower in AZO lambs, whereas kidney-pelvic fat percentage was higher (20%). Lambs in the AZO group had a lower percentage of lean in the shoulder tissue and a lower lean-to-fat ratio than ZH and ZH+AZO lambs. Similarly, leg yield (as a percentage of the cold carcass weight) was 6.4% lower and visceral fat was 13% higher in AZO lambs. The effects of zilpaterol supplementation were not improved by combining it with Azomite; therefore, combining Azomite with zilpaterol during the last finishing phase of lamb rearing offers no productive advantage.

(Submitted 20 March 2026; Accepted 07 August 2026; Published 24 August 2026)