Differences in the Relationship Between Tibia Breaking Strength and Ash in Two Fast-Growing Commercial Strains of Broiler

Leg problems are one of the biggest welfare and financial challenges in chicken farming. When researchers want to check how strong a chicken’s bones are, they typically use one of two tests: they either physically snap the bone to measure how much force it takes to break (breaking strength), or they burn the bone in a furnace and weigh what is left to find out how much mineral it contains (bone ash). It is generally assumed that these two tests give similar information — that a bone with more mineral will also be harder to break. But is that actually true across all breeds of chicken? To find out, we looked at bone data from over 5,700 broiler chickens across two popular commercial breeds, measured at 21 days and again at 42 days (roughly market age). We found that the two breeds started out quite differently — Breed A had stronger and more mineralized bones at 21 days — but by 42 days the gap had largely closed. More importantly, we found that the relationship between the two tests was not the same in both breeds. In Breed B at 42 days, knowing how much mineral was in the bone told us almost nothing about how strong it was. In other words, the two tests were giving completely different answers by market age in that breed. This matters because researchers and farmers often rely on just one of these tests to judge bone health. Our results show that using only one test — especially without knowing which breed is being assessed and how old the birds are — can lead to misleading conclusions. To get a full and accurate picture of leg health in broiler chickens, both tests should be used together.