Mastitis around Calving Time

Trace Mineral Nutrition Can Play a Role in Prevention

Calving time brings a variety of problems, not the least of which is mastitis. Having taken care to use appropriate dry cow therapy, cull chronic cases, and take all other measures to limit mastitis, it is disappointing to experience a rash of cases at the start of the season. Is there anything more we can do to reduce the problem?

The body’s first line of defence against bacterial invaders is the immune system. Its only when white cell defences are overwhelmed that bacteria can multiply and establish a clinically evident infection. This suggests that cows need to have their immune system functioning as well as possible as their udders prepare for lactation.

Ironically, during the last few weeks of gestation as preparation for calving progresses, the competence of the immune system actually falls and does not return to normal until a few weeks after calving. During this time, there is generally a drop in the level of white blood cells. This is a natural phenomenon and reflects hormonal changes that initiate the birthing process. (Corticosteroids such as cortisone are well known to depress the immune system, yet this is what we use to induce calving.)

In the face of this natural (or induced) depression of the immune system, cows then need whatever defence mechanisms they have, to be functioning as effectively as possible. Many of the biochemical processes by which white cells combat bacteria are dependent on or catalysed by enzymes that use zinc or copper as co-factors. Thus it is reasonable to assume that zinc and copper levels should be optimal for cows as they approach calving, to ensure that defence systems can operate optimally.

In fact, a number of trials, including some in New Zealand, have demonstrated that supplementation with bioavailable forms of zinc and copper can reduce the incidence of mastitis in cows and result in significantly lower SCC’s over the lactation period. This has been observed in cows that were not “deficient” in zinc or copper. They were measured by comparison with non-supplemented controls in the same herd.

Some trials measured the difference between cows fed zinc sulphate or an organic zinc in the form of zinc amino acid complex. It is interesting that there was an average 33% reduction in SCC’s in the zinc amino acid groups compared to the inorganic zinc groups. It seems it is the nature or bioavailability of the zinc type used that makes the difference.

Under our predominantly seasonal calving and pasture grazing conditions, there is an additional justification to supplement with bioavailable copper and zinc prior to calving and during early lactation. In the final months of gestation, the demand of both the foetus and its dam for copper and zinc increases. There is also high demand up to the period of peak milk production and mating. Unfortunately, pasture surveys have shown that it is just at this time that grass levels of these minerals are at their lowest.

It is now common for dairy farmers in many countries to supplement regularly with organic zinc and copper to maintain their herds’ health and production. But such supplementation should not be regarded as a panacea for poor management practices. Fine tuning of trace element requirements to minimise mastitis and SCC’s is only worthwhile if all other measures to combat mastitis have been properly implemented.

Overseas, there has been evidence that supplemental selenium at above “adequate” requirements, can also reduce the incidence of mastitis and SCC’s. However, recent trial work has not been able to demonstrate this in New Zealand. Selenium is essentially used as an antioxidant in a similar fashion to Vitamin E. But grass is particularly high in Vitamin E, so even though these antioxidants may influence SCC’s and contribute to immune defences, this role is probably adequately catered for by the high Vitamin E intake of our cows compared to cows in other countries.

In summary, attention to trace mineral levels, especially zinc and copper, may help reduce mastitis, but only if all the other predisposing causes have been adequately attended to.