First grazing dairy heifers, watch out for post turn out scours

If turn out transition to grass works well and parasite challenge is well managed then scour and growth rate checks should not occur, but when they do, make sure that you investigate. Grazing is also a learned behaviour and it can take a batch of young heifers a number of weeks to learn how to fully graze properly without some older cattle to copy.

When turning out dairy heifers for the first time post turn out scour issues can occur and there are two common differentials to consider first:

Coccidiosis

There are three main pathogenic species of coccidia in cattle, Eimeria bovis, zuernii and alabamensis, the latter commonly associated with diarrhoea in young stock one to two weeks after turn out for the first time in dairy systems. The pre-patent period for E. alabamensis is only six to eight days – much shorter than the other coccidial species of cattle.

The scour that occurs may be interpreted as being due to a diet change and therefore it is important to investigate the potential role of Eimeria alabamensis at this stage. If the same turn out paddocks are used for young stock each year it is common to see the problem repeated each subsequent year.

Some points to consider about coccidiosis diagnosis in general are as follows:

• Acute diarrhoea (dysentery and tenesmus) accounts for less than 50% of the cases we diagnose in both beef and dairy calves. Coccidial oocyst counts can be very high in these cases
• Chronic disease with re-infection, a partial immune response and lower numbers of oocysts excreted is seen commonly. The gut pathology in these cases is usually chronic with evidence of ongoing active damage and partial repair. This syndrome is seen more commonly in dairy calves
• Clinical signs can arise in the pre-patent period with the onset of diarrhoea four days before to one day after oocyst shedding begins
• The patent period can be very short and in acute infections oocyst output can drop sharply after the peak but diarrhoea can continue
• Severe diarrhoea can lead to dilution of oocysts
• It can be useful to sample more than one animal to increase the chance of detecting a high oocyst count
• Request species identification in cases where high oocyst counts have been found post treatment. The short pre-patent period can suggest treatment failure if not confirmed as E. alabamensis

Summer Scour Syndrome

Over the last few years we have recognised a syndrome of unresponsive diarrhoea and wasting in weaned dairy calves at grass.

We think that diet is a large part of the story, as cases often occur soon after turnout in calves which have moved from a straw and concentrate based diet to a grass based diet. Ground that has received N fertilizer or recent slurry applications may be higher risk and the fact that calves are learning to graze may mean that they eat more leaf than stem, reducing their fibre intake if on lush pasture.

Oral and oesophageal ulceration and necrosis have been a feature of some of these cases and Bovine popular stomatitis virus or pseudocowpox virus have been isolated from some of the oral and oesophageal lesions. Our theory is that this is a secondary or opportunist viral infection, but none the less this secondary pathology is significant.

• The cases have typically tested negative for parasitic gastroenteritis, coccidiosis, salmonellosis, yersiniosis, BVD, MCF and IBR
• Morbidity has been variable, but often high, with morbidity and morality rates of up to 40% in some groups
• Typically younger calves are affected (three to six months of age), but the syndrome has been reported in calves up to twelve months of age
• Some animals recover slowly upon housing and return to their previous diet, but others continue to waste

We feel that diet transition is particularly important. It is helpful if calves receive some grass based forage prior to turn out (silage, hay or haylage). When calves are first turned out we suggest they receive their full ration outside that they received when housed to start with as they learn to graze. This diet can then be scaled back as they eat more grass over time.

Please give us a call if you have cases or outbreaks and we can discuss the best way to investigate further.

If you wish to hear further discussions on this you can listen to our podcast on the subject.

Posted by SRUC Veterinary Services on 01/05/2024