Bone fractures in first-calving dairy heifers

Under nutrition

A growth check during skeletal development causes changes in how bone is laid down. During periods of reduced nutrition/feed shortage, less bone is laid down around the growth plates. These areas become spongy and may serve as weak points in bone strength.

This seems reasonable, but studies have revealed cases are not isolated to only stunted heifers and can occur in well grown heifers with normal length bones. Bone is constantly remodeling itself and changes as the animal grows, so the outward appearance of a well-grown heifer does not give a true reflection of bone density and strength. Another study concentrating on feeding different amounts during the first 4 months of life could not replicate this condition, but concluded changes developing in the humerus are relatively recent and most likely occur during the winter prior to calving.

Lactation

Bone is a major storage site for calcium and calving signals a rapid mobilization of calcium from bone to meet the physiological demands of lactation. Bone loss is also greatest in an animal’s 1st lactation, so this is probably why we see this occurring in heifers around calving time.

Genetics or environmental influences

Although the majority of cases seem to appear in the South Island, it appears there are seasonal and geographical variation among cases. There isn’t a breed or genetic worth association, affecting 49% Friesian, 49% Kiwi Cross, and 2% Jersey. Feeding of fodder beet was assumed to play a role since low phosphorous levels in beet may affect calcium-phosphorous metabolism. But not all heifers on fodder beet had fractures and not all animals with fractures were fed on fodder beet. Aside from this finding, we still recommend supplementing heifers with phosphorus if grazing on fodder beet.

With the jury still out, these research findings suggest this condition is likely influenced by a number of factors and there is not one sole contributing cause. Despite a lack of answers though, herds that have experienced shoulder fractures in first calving heifers have been able to reduce the number of cows affected in subsequent seasons after supplementing with copper.

Copper deficiency

The role of copper in bone formation is still not fully understood but copper does play a role in cross-linkage of collagen molecules which provides strength to bones. We know that adequate copper levels are important for overall bone health as there are a number of other conditions which occur due to low copper levels eg. swayback, osteochondrosis dissecans, enzootic ataxia.

How should I monitor copper levels?

Copper levels can be determined using blood testing or liver biopsies. Blood testing, while cheaper and a whole lot easier to collect, will only give an indication of circulating copper levels in the blood and do not give an estimation of liver reserves until they become very low.

Liver biopsies are the most accurate measurement of copper sufficiency. More specifically, if there is sufficient storage of copper in the liver, then it is assumed there will be sufficient copper available for normal maintenance.

How many animals to test?

If blood testing, preferably 10 animals to get a good representation across the mob/herd with a high level of confidence (90%). To estimate liver concentrations with some confidence (80%), at least 14 samples are required.

Liver biopsies can be taken at the slaughter plant if more convenient, but remember this condition mostly affects first calving heifers so unless you are culling a lot of heifers sampling on-farm may be necessary. Taking samples before winter is recommended to give an indication of whether levels are deficient, marginal or adequate and to guide supplementation pre-calving.

Should we sample blood or liver?

Choosing which to sample let’s use a water tank and water pipe analogy. Think of the liver, the storage organ for copper as the water tank, the storage area for water. Then think of the pipework attached to the storage area/organ - the blood circulating through the body and the water reticulating through the pipes. The storage area tops up what is removed from the pipes/body.

Therefore, if we take a sample from the storage area, then we have an accurate assessment of what future reserves are available - “sufficiency”. But, if we sample from the pipes, then we can only estimate what is currently available and cannot predict when it will likely run out.

Consequently, and depending on the reason for sampling, if we want to determine if there are sufficient copper reserves to get through winter pre-calving, then liver biopsy is preferred. If we want to determine if current copper supplementation is adequate, then blood sampling is more cost effective. Also, if a couple of animals in a mob have low serum copper, then it likely the copper levels in livers of all animals in the group will be low.

Animal welfare is important

This is an extremely painful condition. Fractures occur in heifers spontaneously and result in very severe spiral fractures with bone fragments pushed into overlying muscle. All heifers with humeral fractures also had evidence of active or healed rib fractures. Therefore, overall bone health is likely to be affected.