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Mastitis: The Research

Milking one beef cow can be a trying chore, let alone milking 106 of them— twice! That’s what researchers at the Western College of Veterinary Medicine (WCVM) in Saskatoon were up against during a study to gauge the prevalence of mastitis in a beef cow herd in Western Canada and determine the effect of a mastitis infection on pre-weaning calf weight.

Though the study failed to establish a definite link between calf weight and sub-clinical mastitis (the presence of mastitis-causing pathogens in the udder without symptoms), it did show that 90-day-old calves suckling cows with one or more dry quarters were 24 pounds lighter on average than calves on cows with four milking quarters. Mastitis is a leading cause of dry quarters.

Based on cultured milk samples taken from each quarter, there was a 38 per cent infection rate for the two most common pathogens associated with mastitis infections — Staphylococcus aureus (S. aureus) and coagulase-negative staphylococcus (CNS) species. This is in line with findings from previous trials indicating that the prevalence of mastitis in beef cow herds in Western Canada ranges from 10 to 37 per cent. However, those studies concluded that sub-clinical mastitis alone could reduce calf weight by seven to 12.5 per cent below the herd average.

Research projects looking at mastitis in beef cows are few and far between — possibly because the cost effectiveness of treating beef cows for mastitis has always been questionable. This particular study, carried out in 1994 by Dr. Craig Kosheluk, seems to be the most recent comprehensive look at the subject.

Some producers who have moved to calving on pasture in recent years have noted an increase in mastitis. While there is no formal evidence that mastitis is on the rise in beef herds, Dr. Steve Hendrick of the WCVM says some of the findings from the 1994 study lend insight as to why this may be occurring on some ranches.


The study involved an initial sampling of milk from each quarter at an average of 40 days post calving. All of the cows were sampled on the same day, therefore, there was a wide range in calf age from nine days to 62 days old. The pairs were split into three groups so the calves were within seven days of 90 days of age at the second sampling. Milk from each quarter of each cow was saved in separate vials.

The raw milk samples were examined to determine the somatic cell count (SCC). SCC is the measurement of white blood cells produced inside the udder in response to the presence of one of numerous infectious agents associated with mastitis. Studies from the dairy industry have shown a decrease in milk yields as the SCC increases. An SCC greater than 200,000 cells per millilitre of milk indicated an infection for the purpose of this study.

At the first sampling, 19 cows had counts above the threshold and were considered infected, while 87 (82 per cent) of the cows were not infected. The second sampling showed that the infection had cleared on its own from 12 of the infected cows. There were six new infections to total 13 (12 per cent). Only seven of the infected cows maintained infections throughout the study.

Cultured samples from each vile collected during the second round showed close to 52 per cent of the cows were infected with one or more of 13 bacterial and fungal organisms potentially associated with mastitis. The infection rate dropped to 38 per cent when only the staphylococcus species were taken into account. S. aureus, which historically has been the major udder pathogen in beef cows, took precedence in classifying the infections, followed by CNS, then “other.” For example, a cow with a S. aureus infection went into the S. aureus group, even if she harboured other agents. Nearly 17 per cent of the cows were infected with S. aureus, however, the non-aureus subspecies was most prevalent in samples from 21 per cent of the cows. Corynebacterium bovis was the most common of the other infectious agents found in 14 per cent of the cows.

There were 11 dry quarters at the time of the second sampling compared with 17 at the first sampling. This suggests they may have been incorrectly classified in the first round if the quarter was producing very little milk, though all cows with dry quarters in the second round had dry quarters in the first round.

The calves and cows were weighed at each milking. The statistical analyses of the first round of sampling revealed that the presence of subclinical mastitis (as indicated by the SCC) did impact calf weight, with the birth weight and actual calf age being important factors as well.

The SCC was not an important factor in the second round. Dry quarters along with calf birth weight and sex were the most important variables in both the 90-day weights and prediction of weaning weights. The reasoning was that by 90 days of age, the calf is utilizing the yield of the entire udder and dry quarters would have a much greater effect than the SCC on the overall milk yield.

There was no significant difference in the average 90-day weights of the calves in the four groups classified according to results of the cultured samples. The average weight of the calves from cows infected with S. aureus was somewhat lower than that of the other groups, however, the weight of the calves from the cows infected with the CNS species and other pathogens was almost the same as that of the calves in the uninfected group.


Mastitis is a disease of the udder, though mastitis caused by bacteria that produce toxins can result in the cow becoming ill quite quickly. The general recommendation is to treat with a systemic antimicrobial and/or an intramammary antibiotic tube. For S. aureus infections, waiting until after weaning to try to clear the mastitis with antibacterial teat infusions or dry up the quarter is often more successful in clearing the infection.

There are a few reasons for the latter recommendation, Hendrick explains. Mastitis is difficult to cure completely and chances of saving the infected quarter(s) aren’t great. Secondly, the study shows that infections commonly clear on their own and that an enlarged, gorged quarter isn’t always a sign of infection. It may be because the calf isn’t sucking all quarters at first, though a calf’s continued refusal to take a teat could lead to mastitis.

Sometimes, you might not even notice a change in the appearance of the udder or the milk, he says. An infected quarter is usually reddish in colour and warmer to the touch than the other quarters. There may be blood or little white flakes in the milk from the infected quarter.E. coliand other coliform bacterial infections cause the milk to become thin and watery, while C. bovis infections result in very thick, clumpy milk. There may be cysts beneath the skin of the affected quarter that eventually break out the side of the udder and may reoccur in the same or different locations.

Suckling requires opening of the teat end, potentially allowing the entry of bacteria and setting the stage for a mastitis infection, he explains. Mastitis could be triggered by a previous subclinical or full-blown infection that was never completely cured, injury to the udder, or environmental stress, such as muddy conditions or insect pressure.

A strategic way to keep mastitis in check is to cull older cows and cows with udders that are showing signs of breaking down. The WCVM study indicates older cows tend to be more susceptible than younger cows. The average age of the cows found to be infected with one or more mastitis pathogens was about 6.5 years, while the average age of uninfected cows was about 4.5 years. The average age of cows infected with S. aureus was almost eight years.

The pathogens are common in the environment and grow on cows’ teats, Hendrick adds. Manured bedding is a source of pathogens in corrals, while wading into dirty sloughs to drink could definitely be a contributing cause of mastitis in cows on pasture. Providing clean bedding and an off-site watering source may help to reduce the incidence of mastitis.

The bacteria grow readily on human skin as well, so it’s important to wash your hands in soapy water before and after touching the udder.

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