Mastitis: Hidden infections can cost

Heifers are most at risk of mastitis prior to calving.

As the udder develops in size, milk often leaks from open teat canals, allowing in bacteria, such as Streptococcus uberis or coagulase negative staphylococci (CNS), resulting in infection before calving.

A study using the DairyNZ identical twin herd identified that heifers which calved down with a subclinical Strep uberis infection produced 7 per cent less milk than their uninfected twin mates throughout their first lactation. Twins which were detected and treated for clinical mastitis because of S. uberis had similar losses.

This degree of loss has not previously been reported because subclinical cases, which don't create visible changes in milk or the udder, are usually not detected. It is possible that damage to the milk-producing tissues had occurred prior to calving. This research indicates that prevention of all S. uberis infections is important, not just the clinical cases.

A number of approaches have been tested. They focus on four control points:

1.Reducing the risk of udder oedema and milk leakage;

2.Reducing bacteria at the teat end before calving;

3.Placing a barrier at the teat canal to block entry of bacteria;

4.Supporting the animal to deal quickly with new infections.

1. Reducing udder oedema and milk leakage

Oedema is the swelling that occurs under the skin of the udder and sometimes along the belly in a heifer prior to calving. It is a significant risk factor for heifer mastitis, but what causes it is poorly understood. Contributing factors appear to include:

* Excessive feeding immediately prior to calving;

* Excessive dietary sodium or potassium levels;

* Over-fat heifers;

* Hereditary predisposition.

Extra hay or silage in the diet pre-calving has been reported to have no impact to aid oedema or reduce milk leakage.

Twice daily calf pick-up

Milking heifers within the first 12 hours after calving is another way that may reduce udder oedema and milk leakage. It may also reduce the chance of bacteria getting into the teat canal and causing infection. In practice, this involves twice-daily pick-up of new calves, and bringing freshly calved heifers in for both the morning and afternoon milkings.

A New Zealand study identified that halving the interval between calving and first milking, from 20 hours to below 10 hours, led to a 45 per cent reduction in clinical mastitis, less subclinical mastitis and less udder oedema.

2. Reducing bacteria at the teat end: teat spraying before calving

Using normal disinfectant teat spray at regular intervals before calving is a relatively low-cost approach for reducing bacteria numbers on heifer's teats.

A New Zealand study identified that applying an iodine-based teat spray three-times weekly for the last three weeks before calving led to reductions in the number of S. uberis on the teat-ends at 24 to 48 hours before calving. Although there were fewer S. uberis infections at calving and 50 per cent fewer S. uberis clinical cases, the incidence of clinical mastitis caused by all pathogens was not significantly reduced.

3. Placing a barrier at the teat canal

Treatment with an internal teat sealant pre-calving

Using an internal teat sealant has proved to be the most effective strategy for reducing environmental mastitis in heifers. It involves introducing a non-antibiotic material into the udder about four to six weeks before calving to provide a physical barrier to the entry of bacteria.

Following calving, the calf strips out some of the teat sealant when suckling, and the rest is removed by manual stripping, before attaching the teat cups.

However, milking staff need to be aware that flecks of teat sealant may persist in milk for some weeks after calving and may be incorrectly diagnosed as cases of clinical mastitis.

Two New Zealand herd studies have proven the effectiveness of internal teat sealants.

Good hygiene at application is imperative and some vets provide technicians to perform the task. For herds with an above average rate of heifer mastitis (15 per cent or more heifers clinical in the first two weeks after calving), this approach becomes cost effective.

External teat sealant ineffective

By contrast, application of an external teat sealant pre-calving has proved ineffective and cumbersome. The non-irritant latex, acrylic or polymer-based film which produced a thin layer over the teat had to be re-applied weekly and a New Zealand study showed that it didn't significantly reduce cases of clinical mastitis.

4. Supporting the animal to deal quickly with new infections

Studies identified that treatment with long-acting antibiotics before calving showed no benefits. Treating with short-acting antibiotics just prior to calving or on the day itself were effective in reducing clinical mastitis, but it is an expensive option and not recommended because of the risk of inhibitory substances contaminating milk.

Other options

Other helpful strategies are based on commonsense. They include: keeping udders clean by managing pasture allocation following rain, reducing the risk of dystocia or retained foetal membranes, running separate heifer and cow mobs pre- and post-calving to reduce bullying and pre-calving milking as a last resort for heifers with very tight udders. The latter should be used with caution as it may increase the risk of a negative-energy balance in the pre-partum period.

DairyNZ, Technical Series