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Phytogenics: Improving calves’ resilience to diseases
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by Delphine Lacombe, Customer Technical Service Manager Ruminant, Delacon, Austria
alves have to undertake a difficult path from birth onwards: during their growth, they have to overcome challenges in terms of feeding transitions, housing and, of course, pathogenic pressure. Next to a good calf management programme, phytogenic feed additives can additionally support animals during
challenging times. Aside from their obvious and direct cost, like treatments and extra work, diseases have a great impact on calf growth and future performance. Indeed, because of the energy spent in fighting disease and recovery, the growth performance of an animal can be reduced. A direct correlation between the average daily gain (ADG) before weaning and the later milk production of the primiparous cow has been demonstrated by Soberon and Van Amburgh (2013): for every extra 1kg of preweaning ADG, first lactation milk yield is increased by 1,550kg. Reducing the incidence of sickness would, then, have a positive effect on the future cows’ performance. It has also been demonstrated that calves having suffered from diseases are more susceptible than “healthy” ones to other outbreaks. Calves affected by diseases are not necessarily bound to die, but they can become a reservoir for the pathogens to spread to other animals. This is why it is important not only to consider the mortality rate of a given disease, but also its morbidity rate, which can influence the rearing cost of the animals. In this article, we will focus on the main diseases and related pathogens that can affect calves in the early life stages and provide some tips in order to reduce their incidence in the heard.
Why are calves so susceptible to diseases?
Calves are quite prone to diseases as they are young animals with a non-mature immune system, undergoing different challenges such as separation from the dam, changes in housing 52 | November 2020 - Milling and Grain
and grouping, weaning and feed transitions, physiological evolution etc... All these challenges are sources of stress, which, in addition to pathogens from the environment and possible management mistakes, can lead to sickness. Out of the different conditions that can afflict calves, two are quite recurrent in farms and can affect a wide range of animals: gut related diseases (diarrhoea) and bovine respiratory disease (BRD). They have various possible causes, as pathogenic agents can take hold at different stages in the calf’s life. Usually, diarrhoea occurs earlier and is the main cause of death, whereas BRD is observed later on and constitute the second biggest threat to a calves’ life (See Table 1). Diarrhoea’s morbidity rate, which reflects the number of sick calves amongst the total group, is quite high in farms: more than one-out-of-two calves having at least one bout of sickness before weaning is affected by diarrhoea. It is the first cause of mortality, accounting for half of the observed dead heifers before weaning, and three-out-of-four deadly cases happen within the first month of age. Even if all the cases don’t lead to the death of the animals, it has a negative impact on the later health and performance of the animal and on the economic performance of the farm, since it increases rearing costs by EU €95 on average, compared to healthy animals. Figure 1 shows that the most critical period for diarrhoea cases, wherever they originate from, happens within the first weeks of life. Calf pneumonia, or BRD, is a complex, multi-factorial disease which results in inflammation and damage to the tissues of the lungs and respiratory tract. It is the most common reason for poor performance and death in growing calves (See Figure 2). The effects of BRD in heifer calves include decreased rate of gain, a higher culling risk, delayed age at first service, delayed age at first calving and, in some cases, lower future milk production. The cost of raising a heifer with one or more recorded cases of BRD during the first 120 days exceeded those for healthy heifers by US $212-to-$237, depending on whether anticipated milk-production differences are considered. Careful calves’ management and strict hygiene rules are an