26 Bone Growth and Calcium Metabolism

26.1 Introduction

Bone is important for meat animal production in several ways.
  1. Longitudinal growth of muscles accounts for much of the meat we produce. The longitudinal growth of muscles is limited by the longitudinal growth of bone.  When we select animals to produce more meat, we often increase the length of their bones.  Thus, frame size (the maximum size of the adult skeleton) is related to efficient meat production.
  2. Bones store calcium.  Bone calcium is used for milk production and the formation of egg shells in poultry.
  3. When we grade beef, we need to know the approximate age of the animal. If the head remained on the commercial beef carcass, we might get this information from the state of the dentition. Without this, we use the degree of ossification of the carcass.  The general principle is bones are first formed from cartilage - then progressively ossified. Thus, the extent of ossification tells us the approximate age of the animal.

26.2 Cartilage

26.3 Bone

In the section of bone shown above, the marrow cavity is at the top, the calcified matrix is stained red, and the periostium runs acroos the bottom.


The prenatal formation of bone is initiated by either of two basically different processes, either intramembranous or endochondral ossification. Intramembramous ossification is typical of the bones forming the vault of the skull, and occurs when sheets of connective tissue produce osteoblasts which then initiate centres of ossification. Endochondral ossification is more common, and is the process by which cartilagenous models become ossified to form the bones of a commercial meat carcass.


26.4 Bone calcium

26.5 Control of bone growth

How do bones adapt to patterns of use?

One hypothesis is loads frequently placed on a region of bone cause the transduction of mechanical energy to electrical energy by a piezoelectric effect. In a frequently loaded and negatively charged region, growth is stimulated.  In electrical fields, osteoclasts migrate towards the positive electrode while osteoblasts migrate towards the negative electrode. In an unloaded and positively charged region, resorption is stimulated.

Why do bones from older animals have more knobs and wrinkles?

Because most farm animals are slaughtered in a fairly immature condition, the relationship between muscles and the bony processes  they pull on may not be immediately obvious. But knobs and wrinkles on bone surfaces become more conspicuous with age, and they are readily seen in the carcasses of old bulls. One possible relationship between muscle activity and bone growth may be muscle contraction - by stopping or slowing the venous blood flow, it may stimulate bone growth. Alternatively, by pulling on the periosteum, the effect of muscle activity may be mediated by connective tissue. The importance of local factors is seen in bone transplants, where growth of the transplant almost immediately becomes regulated by the new local conditions.

SOME HISTORY. In the early 1950s, attempts were made to use measurements of isolated carcass bones such as the cannon bone to predict the muscle to bone ratios of carcasses. Although the method worked satisfactorily when applied to a wide range of dissimilar carcasses, it was of little practical value when applied to more uniform commercial carcasses. Muscle to bone ratios improve as animals grow older or fatter, since longitudinal bone growth slows down in older animals and muscles start to accumulate appreciable amounts of intramuscular fat. Animal age is the dominant factor that determines muscle to bone ratios.  

Some years ago, the desire to produce small compact animals with bulging muscles favoured the survival of dwarf animals with impaired longitudinal bone growth. Although mildly affected animals looked very muscular, severely affected animals became increasingly common and were poorly suited for beef production. Dwarfism from impaired longitudinal growth of bones is a recessive trait that affects males more strongly than females.

Further information

Structure and Development of Meat Animals and Poultry.  Pages 96-106.