A mob of travelling stock suffered four deaths in a period of two weeks from mastitis on a TSR near Monteagle NSW in May 2019. The mob was made up of cattle from five different owners and had both adult cows (up to 6-7 years of age) and calves of varying ages. The mob had been on the road for well over 12 months.
The owner drover reported that the animals were noted to be lame on the side of the affected quarter; the quarter was swollen and the animals were dull and anorexic. In three of the four cases the cows deteriorated and died within 3-4 days. The one surviving animal had a calf at foot who continued to suck from all quarters. In the last case, a clear mucous nasal discharge was noted the day before the cow died. Treatment with oxytetracycline antibiotic intramuscularly was unsuccessful in the animals it was tried in. All four of the affected animals were immediately pre-calving or in the first week of lactation.
There were no new additions to the mob in recent months, however a number of the cows were in late gestation or early lactation with numerous calves in the mob at the time of investigation. They had recently been locked up overnight in the communal lockup of the TSR and were on a slow moving travel permit so the cows had to be moving each day. Weather had been variable with a period of low night and day temperatures followed by a week of moderate day temperatures and then another drop to low night and day temperatures in the previous three weeks before cases developed.
A necropsy was performed on the fourth clinical case to confirm mastitis as the cause of the deaths. The milk in the affected quarter was watery and contained clots. The lungs also displayed signs of pneumonia characterised by consolidation and congestion. Culture of the lung and milk reported profuse pure growth of Mannheimia haemolytica sensitive to ampicillin, trimethoprim, tetracycline and cefuroxime.
Mannheimia haemolytica is a common cause of mastitis in sheep but rarely in beef cattle (Radostits et al). Also in this case, it is difficult to determine if the pneumonia was the primary cause of disease and the mastitis secondary. Clinically, cases of mastitis alone due to Mannheimia haemolytica generally progress to gangrenous mastitis in the cow but not a high incidence of deaths. In contrast, in this case the udders remained hot, swollen and hard but deaths occurred within 3-4 days regardless. In Canada in 1955, Maplesden and Carter reported on a similar case of Mannheimia mastitis with concurrent pneumonia cases occurring in the calves at the time. In this travelling stock mob, no obvious signs of pneumonia were present in the other animals in the herd, nor were the signs obvious in the clinical mastitis cases.
Detection of affected animals and treatment in this case is made more difficult by the fact that the mob is travelling on the stock route and so suitable facilities for examination and treatment are limited.
At the time of writing, no further cases of mastitis had occurred in the herd.