STOCK BONE INJURIES
Broken shoulders in heifers Words by: Penny Back
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esearch at Massey University is investigating heifers who have had broken shoulder bones and need to be put down, with considerable economic and potentially genetic loss. While some farmers may not have seen the condition, many others have or know someone who has encountered it - with losses reported of 2-25% of first-lactation heifers in some herds since it first arose in 2008. A ‘broken shoulder’ is a spontaneous humeral fracture, which occurs with no warning and requires euthanasia of the animal as the fracture can not heal, Massey University senior lecturer in dairy production Penny Back says. The humeral fracture is a complete spiral fracture caused by osteoporosis and a decrease in cortical bone thickness (the wall of the bone) , as shown in post mortem examinations of the broken humerus bone. This means the animal has a similar
bone length to an unaffected animal but the bone has a reduced diameter and mass (density). This reduced diameter and mass results in a weaker bone which is important as the humerus is a bone under huge strain due to muscles in the shoulder. The ‘broken shoulder’ condition is commonly seen in two-year-old, first lactation heifers from later pregnancy to several months after calving but has also been seen in older animals. This indicates that the condition may be caused by multiple factors, which all contribute to weak bones. Preliminary work indicates periods of inadequate calf and heifer nutrition (and in some cases copper deficiency) impacts bone growth and development. Combine this with improving genetics for milk production, which increases the draw of calcium from bone in early lactation, increasing the likelihood of fractures. Preliminary investigations of the project have shown not a lot is known about the effect of some of the factors, like the amount of feed, different feed
Dairy Exporter | www.nzfarmlife.co.nz | August 2020
Above: Gross image of an affected humerus. In most cases, a spiral fracture is observed, extending from beneath the humeral head (blue star) to end above the humeral condyles (yellow star).
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