The impact of pain due to mastitis
For decades, the treatment of clinical mastitis was focused on resolving the clinical signs, so the cow can continue to be milked. With a growing understanding of the biology and epidemiology of mastitis – as well as tightening market requirements for milk quality – bacteriological cure and a low cell count have become the main objectives of mastitis treatment.
More recently, consumer concerns about animal welfare and the use of antimicrobials in food producing animals have become an issue. The impact of changing societal values and political opinion regarding dairy farming needs to be taken into account to maintain the sustainability of the entire industry. “Return to normal production” is no longer accepted as the sole measurement of treatment success. How the cure was achieved and how much the animal suffered during its course become important aspects of high quality, sustainable dairy production1.
This means that professionals need to be able to recognise suffering in cattle in order to prevent and alleviate pain. Not only for obvious reasons of animal welfare, but also because the producer needs to guarantee the sustainability of marketing his product.
Recognising pain in cows
The reaction to pain is part of an overall set of sickness behaviour, which is aimed at reducing energy-demanding processes in the body. By ‘switching off’ energy from activities that are not immediately necessary for survival, the animal tries to increase the effectiveness of the immune system to overcome the infection. Also in mastitis, such sickness behaviour is evident. In the 24 hours after infection of the udder, cows spend more time “standing idle” and less time feeding, ruminating and self-grooming2. Cows try to minimise their pain by adopting a different stance3 and avoiding subtle movements such as shifting weight from one leg to the other4.
Typically, disease is associated with increased lying times and overall reduced activity. In case of mastitis however, lying times were found to be consistently decreased, independent of the housing system. This is striking, since healthy cows will lie down for approximately 12 hours per day. The observed reduction in lying time may be explained by unwillingness to lie down due to a painful udder. These cows will want to lie down, even more so as they are feeling unwell, yet the pain in their udder prevents them from doing so. Such thwarting behaviour causes frustration and exacerbates suffering3. Cows become increasingly frustrated and restless with time, which explains the increased activity (number of steps taken, increased frequency of lying bouts).
If the udder is sore, it is highly likely that milking causes pain. Indeed, cows with mastitis trip and kick more often while milking (Figure 1)3. The udder is probably highly sensitive: there is evidence in ewes that even subclinical mastitis can be sensed4. While kicking can be annoying for the milkers, it also may cause clusters to fall off, potentially sending air jets (“impacts”) with infected milk up into the udder, causing new cases of mastitis in the herd. Pain also interferes with oxytocin release, resulting in failure of milk let-down and incomplete milk-out of the udder.
Like in other species, pain is a strong inhibitor of appetite in cows. Cows with mastitis visit the feeder less often than their healthy herd mates. When at the feeder, they also eat slower, resulting in a decreased feed intake. In one study, cows with moderate mastitis already showed a decreased feed intake 5 days before the actual mastitis was diagnosed1. The daily feed intake dropped from 16 to 10 kg of dry matter.
Another study showed that such decreased appetite can last for 10 days, even when the milk has already visibly returned back to normal2 (Figure 2). Such a drop in feed intake can worsen the negative energy balance and degree of weight loss, leading to an increased susceptibility to other diseases and compromised fertility.
Chased from the feed barrier
Pain clearly affects the social behaviour of the cow and the place a cow takes in the hierarchy. A painful or depressed cow is more likely to be ousted from the feed barrier by other cows (Figure 3). This explains why cows with moderate mastitis eat less during peak feeding times, when competition for a feeding spot is the highest1.
NSAIDS can help the cow – and the farmer
In other words, there is strong evidence that cows with mastitis are in considerable pain, even if the mastitis is only mild. This supports the interest in the use of an NSAID for mastitis, also in non-severe cases. It is already widely known that nsaids decrease fever, restore rumen motility and reduce udder oedema. A painful udder is more difficult to assess. By using a special device called an “algometer”, significant differences in pain sensitivity between healthy and affected quarters can be measured (Figure 4)8. The device applies pressure to the skin, measuring the power needed to provoke a reactive behavior of the animal. With this technique, the sensitivity of experimentally infected quarters was assessed. Cows that had received an injection of meloxicam showed no increased sensitivity in the infected quarters, in contrast to the placebo group. This illustrates the strong analgesic effect of this drug.
It is the veterinarian’s responsibility to prevent and alleviate pain and distress due to disease whenever possible. By recognising changes in behaviour, farmers and vets may become more aware of the impact of pain in cows suffering from mastitis. Cows in pain have a decreased appetite and feed intake, during critical times where their metabolism is already balancing on the edge of a knife. Besides reducing inflammation and restoring rumen motility, nsaids also provide crucial pain relief, improving the welfare of cows and allowing a fast return to optimal production.