Longevity, sickness and mortality from disease

The health of a nation is often assessed from its life expectancy and infant mortality rate. Similar figures are helpful when assessing the standard of health care and management in farm animals. When mortality rates exceed the levels shown in Table 1.14, there would often be cause for concern amongst stock owners.

Table 1.14. Mortality rates that might be tolerated in industrialized nations before concerns are raised about the welfare of the animals or profitability of the enterprise.

Stock owners will usually take action when mortality rates reach these levels. Their primary aim might be to reduce losses and improve profitability, but there will inevitably be other considerations, depending on circumstances and the individual’s motives. The ethical question is where the interface is between an acceptable and an unacceptable level of mortality, and the answer is ‘It depends on . . .’. In applied ethics a judgement is reached for a given situation, and the decision has to be based on a range of considerations connected with individual circumstances. For example, acceptable mortality from disease on one farm may be unacceptable on a second farm, simply because of differences in ease of control of the underlying cause. Ethics brings together all the prevailing interests in reaching the ‘right’ decision. In the present context the ethical decision would include feasibility of disease control, financial resources of the stock owner to introduce treatment, likely effectiveness of the control measure, impact on profit margin, effect on morale from achieving better control, expectations amongst the rest of the community and legal obligations, as well as concern about suffering experienced by affected animals. Ethics encompasses everything, not just the moral issue.

The acceptability of early death in breeding stock has a similar dimension. One of the simplest signs that something is going wrong at a farm is reduced longevity in the breeding animals. In pig herds in the USA, sows last on average for 1.8 parities, producing 17 pigs (Guo et al ., 2001). In Europe survival is higher, at 3.3 parities and 37 pigs per sow. The primary causes of early culling are breeding failure or poor reproductive performance and leg disorders. It has been suggested that modern genetic selection is to blame, but this may be an oversimplification. The genetic basis for these problems is complex because of the range of conditions that contribute to early culling, and the heritability ( h 2 ) for longevity in dairy cows, sows, beef cows and dairy buffaloes is generally low ( h 2 = 0.02 to 0.27). This implies that it may not be possible to reduce early culling genetically whilst maintaining selection pressure for productivity. Instead, the main hope is with managing the individual causes of the early losses. In general, there is no clear genetic strategy for improving longevity in breeding stock. Reduced longevity may or may not be a welfare compromise, depending on the condition that causes early rejection. If it is lameness, then it clearly has a welfare dimension, but, if it is breeding failure, there may be no suffering, simply a shorter lifespan.

Good health care is more than just calling in a vet when a problem develops. It is also a state of mind that incorporates disease prevention into the daily routine. It has been reported that veal farmers who have a positive attitude towards animal care have lower disease levels in their stock and greater productivity, and this was presumably linked to better prevention of disease (Lensink et al ., 2001b). The signs of ill health in animals can be subtle and need experience and time in recognizing them. For example, cattle and pigs with nematode infestations show very few obvious signs except they are less active. They often spend less time feeding and more time resting, neither of which seems abnormal in itself (Forbes et al ., 2004). When reduced appetite can be recognized, it is a useful indicator in a wide range of disorders (Bareille et al ., 2003). This calls for skill and experience in those who look after stock, and in the longer term a willingness to pass on that knowledge in training the next generation of stock people.