What Happens When Cows Get This Feed Additive? Scientists Explain

Scientists wanted to know exactly how a drug called lubabegron makes cattle grow bigger. This drug got approved for cutting ammonia fumes from feedlots. But nobody fully understood the biological steps behind the muscle changes it creates.

The research team worked with 32 Angus-influenced steers. Each animal weighed around 524 kilograms at the start. The scientists split them into two equal groups. One group ate normal feed. The other group received feed mixed with lubabegron for 63 days. Both sets of steers had received hormone implants when they arrived at the facility, 58 days before the experiment began.

The results were striking. Steers on lubabegron ended up weighing 637 kilograms on average. The control group reached only 612 kilograms. The treated animals ate more feed and turned it into weight more efficiently. Their carcasses weighed about 18.5 kilograms more overall. Yet measurements like ribeye size, fat thickness around the 12th rib, and marbling scores stayed identical between groups.

When researchers examined the actual muscle tissue, they found important differences. Longissimus muscle from lubabegron-treated steers contained more protein and less fat. But here is the catch: meat tenderness suffered. Warner-Bratzler shear force tests showed the lubabegron steaks were noticeably tougher at both 2 days and 14 days after slaughter. Blood tests revealed elevated levels of creatinine, total protein, bilirubin, and cholesterol in treated animals.

By day 56, genetic analysis uncovered 643 genes behaving differently between groups. The lubabegron-treated muscles showed increased activity in genes controlling muscle formation, sugar breakdown, and fast-twitch fibers. Fat-related genes became less active. The mTOR signaling pathway, crucial for building muscle protein, showed significantly higher activation levels in treated steers.

Since lubabegron primarily targets β3-adrenergic receptors, the team checked whether this receptor pathway explained the changes. Evidence pointed the other way. β3-AR gene expression in muscle tissue was extremely low and missing entirely in over 40% of samples. Downstream signaling markers showed no meaningful differences between groups. This suggests the mTOR pathway, not the β3-AR route, drives the muscle-building effects.

For cattle producers, lubabegron offers a way to produce leaner beef. For consumers, that might mean sacrificing some tenderness. The study reveals how complex biological systems respond to feed additives, showing that single drugs can trigger multiple interconnected pathways simultaneously.