References
Abstract
Behavioural changes in cattle and sheep are used in clinical diagnosis to detect abnormalities and to help determine the aetiology. In many parasitic diseases, infections can be subclinical, but their impact on performance can still be of importance in a farming setting. A common feature of helminth infections is a reduction in feed intake, which can account for lower growth rates and milk yields, yet inappetence is difficult to detect in free-ranging, grazing livestock. Remote-sensing technology can facilitate data collection and is useful not only in research, but is a feasible option now on commercial farms. If inappetence in grazing sheep and cattle as a result of parasitic gastroenteritis can be easily monitored and assessed, then early interventions may be possible and these can ensure that animal performance is kept on target. Application of such approaches is consistent with the principles of responsible use of anthelmintics and targeted selective treatments, which can be further integrated into complementary elements of parasite control, including grazing management.
Everyone who has regular contact with sheep or cattle is an ethologist and the ability to differentiate normal and abnormal behaviour is fundamental to stockman-ship and clinical veterinary practice (Weary et al, 2009; Gougoulis et al, 2010). Some changes in behaviour can be very obvious, such as sheep hobbling on three legs or grazing on their knees when affected with conditions such as foot rot, but others are more subtle and may require closer observation and monitoring to detect abnormalities. Such ranges in responses are typical of parasitism; the intense pruritus characteristic of diseases like sheep scab is evident even to the casual observer, while a reduction in feed intake, which is a common feature of many helminth infections in cattle and sheep, can be difficult to detect in the field in free-ranging stock.
Behavioural reactions to pathogens generally have an adaptive role in facilitating compensatory responses in the host in order to counter any negative impacts of infection on form and function (Hart, 1990; Hoste, 2001); concurrently, parasites may be manipulating host behaviour for their own benefit (Simpson, 2000; Thomas et al, 2005). A classic example of this is the ability of cercariae of the lancet fluke, Dicrocoelium dendriticum, to change the behaviour of ants, which are intermediate hosts, so that they ascend the vegetation, increasing the opportunities for ingestion by grazing sheep or cattle, the final hosts (Manga-Gonzalez et al, 2001; Martin-Vega et al, 2018).
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