1 Apr 2019
Jennifer Allan runs through preventive strategies for a prevalent disease with a high morbidity rate, including environmental control and boosting calf immunity.
Jenny Allan
Job Title
Figure 1. Infectious calf scour is a multifactorial disease with multiple prevention strategies.
Infectious calf scour is one of the most prevalent pre-weaning diseases in calves, with up to 48.2% morbidity recorded on one study (Johnson et al, 2017).
It is caused by several infectious pathogens (Rotavirus, Coronavirus, Escherichia coli, Salmonella and Cryptosporidium parvum). The role of preventive management in the pre-weaning period of a calf’s life is vital to avoid infection. Treatment of diarrhoea consists of fluid therapy (oral or IV, depending on the degree of dehydration), maintaining adequate nutrition, NSAIDs and antibiotics on a case-by-case basis (Gomez et al, 2017). Rotavirus, Coronavirus, Cryptosporidium and E coli are all self-limiting, provided supportive treatment is quick and adequate.
Salmonella can cause septicaemia quickly and mortality is often higher. Once an outbreak is identified, it is vital the individuals affected are treated, but also the disease is contained and calf-to-calf transmission is prevented.
The major pathway of transmission for all infectious agents involved is faecal-oral, so housing hygiene is paramount.
Isolation is crucial for any clinical cases seen. In the face of an outbreak, infected animals will have shed, and will still be shedding, large amounts of bacteria, virus or oocysts into the surrounding environment.
Sick calves should be dealt with by another person when carrying out day-to-day routines. Boots and hands should be cleaned between dealing with sick and healthy animals. Ideally, the pen where the calf has come from should also be thoroughly cleaned and disinfected.
Calves are housed in a variety of systems in the UK, including individual, paired and large groups. The legal minimum space allowances for group-housed calves are 1.5m2 if they are below 150kg, but it is recommended this is increased up to 3m2 in the first two months (DairyCo, 2012; Red Tractor Assurance, 2017; RSPCA, 2018).
Avoiding overstocking and providing adequate ventilation is crucial to preventing increased moisture in the environment, which would create optimal conditions for pathogens to survive. As well as correct stocking density, general hygiene includes dry bedding in sufficient quantities, adequate drainage and at least partial protection from wet weather to allow for clean, dry lying areas.
Adequate air speed above pens helps to remove moisture, but draughts need to be avoided at calf level. Deep littered pens should be bedded up frequently – every two to three days at a minimum (Medrano-Galarza et al, 2018). The use of automatic milk feeders (AMF) is increasing due to the benefits of increased volumes of milk being fed daily, impacting long-term growth rates.
The use of one teat for multiple calves has been raised as a possible risk factor for disease transmission (Curtis et al, 2016), but adequate hygiene, for example regular swapping/cleaning of teats and cleaning of the machine, helps control of this (Medrano-Galarza et al, 2018).
Cleanliness around the AMF can be an additional challenge. Despite many mixed opinions on AMF and group housing, other factors, such as hygiene and adequate passive transfer of colostrum antibodies, are equally, if not more so, important when looking at prevention of spread (Costa et al, 2016).
Identification of the pathogen is vital, not only to help decisions on treatment protocols, but to allow adequate cleaning protocols to be implemented. The two primary viral causes of neonatal diarrhoea, Rotavirus and Coronavirus, are shed for five to seven days (Coronavirus can be longer) from infected animals, and both are usually endemic on farms and shed periodically from adult cows. Prevention in calf sheds relies on adequate passive immunity and isolation of any sick animals.
The larger problem is with Cryptosporidium and its ability of the oocysts to survive in the environment. Cryptosporidium is difficult to eradicate; the oocysts have robust exterior capsules that make them resistant to many disinfectants. They can survive in the environment for many months in warm, moist conditions (Cho and Yoon, 2014). Treatment for Cryptosporidium is primarily supportive care.
Halofuginone is commonly used to minimise spread, as despite it not preventing infection of calves it will help reduce oocyst shedding (Lallemond et al, 2006). The most effective way to get rid of oocysts is to expose them to heat and moisture (steam clean), with temperatures above 60°C, and leave to dry (Shahiduzzaman and Daugschies, 2012). Only certain disinfectants are effective against them, including hydrogen peroxide, formaldehyde, cresol-based products and, more recently, amine-based Kenocox has been demonstrated to work in-vitro (Naciri et al, 2011).
Plastic and metal are the easiest materials to clean, and do not allow pathogens to “hide”. Well-managed hutches are ideal for hygiene and provide the opportunity to easily steam clean between batches of calves.
Old buildings of brick or wood are often used for calves, and will harbour pathogens. It is impossible to completely clean every crevice (Robinson, 2018).
Some block calving units will house calves in makeshift straw bale pens, which can provide a favourable microclimate. Once calving is finished, pens are disposed of or used for adult animals, starting afresh each year.
Finally, it cannot be stressed enough that calf immunity plays the key role in prevention. It is now well known adequate passive transfer from colostrum provides protection against pre-weaning diseases, but still up to 26% of calves on UK farms fail to receive adequate immunoglobulin transfer (Macfarlane et al, 2015).
The importance of colostrum quantity, 10% bodyweight at the first feed, within the first six hours and adequate quality 50g/L of IgG (which equates to more than 22% on a Brix refractometer; Bielmann et al, 2010) is now proven. Numerous studies into colostrum quality show it is reliant on the quick timing of harvest of the first feed and colostrum cleanliness (Donlon et al, 2018).
Failure of passive transfer is a known risk factor for acquiring diarrhoea and also for having a poorer prognosis once acquired (Boccardo et al, 2017).
Maintaining adequate nutrition levels throughout the pre-weaning period and gradual weaning protocols are also important for adequate growth rates and disease prevention.
Numerous vaccinations are available for Coronavirus, Rotavirus and E coli (K99); these work by inducing lactogenic immunity in the dam and are given between 12 to 3 weeks prior to calving. Before recommending use of these, it is paramount colostrum protocols are adequate and passive transfer is established in at least 85% of calves.
Once these factors are addressed, coupled with clean housing, adequate control is often reached without the need for a vaccine.
Alongside the direct costs of treatment and mortality, the major indirect cost involved in calf diarrhoea is reduced pre-weaning growth rates in recovered animals (Johnson et al, 2018).
Pre-weaning growth rate is directly linked to the age of first calving and first lactation success (Brickell et al, 2009a; 2009b; Sherwin et al, 2017).
Preventive measures to limit calves succumbing to diarrhoea in the first few weeks of life are vitally important to their future productivity.
