Rotavirus Scours

Now is the time to start considering the protection of this season's calves against Rotavirus scours. As we know, Rotavirus is the most common cause of infectious diarrhoea in young neonatal calves - and is easily spread from calf to calf by contaminated faeces in the calf pen. Successful calf rearing can be a real challenge, especially in the large herd situation. Overcrowding in sheds, especially in wet/cold weather, damp sheds, poor colostral transfer and overstretched staff can allow an environment for the proliferation of bugs that cause infectious diarrhoea i.e. Rotavirus, Salmonella, Coccidia.

Prevention of Rotavirus is a sound investment to protect your calves and their welfare. The vaccine Rotavec Corona is administered to the pregnant cow as a single shot between 3 and 12 weeks prior to calving. Therefore a herd should be vaccinated 3 weeks before the PSC to cover a 9 week calving spread.

A second option for cows which have already been vaccinated in previous years with Rotavec, is to boost these cows with Kolibin Neo, a new vaccine from AgriHealth. Kolibin Neo provides protection against the prevalent and NZ relevant rotavirus serotypes. Kolibin Neo has sound trial work, can be administered 2-12 weeks prior to calving, and offers a cost saving when used as a booster vaccine. If Kolibin Neo is used in previously unvaccinated cows, the cow will need two vaccinations in her first year. Therefore the net cost in year one, is slightly more than a single vaccination of Rotavec.

Long Acting Dry Cow Therapies - What's in a name?

Put simply all antibiotic intramammaries which are registered as Dry Cow therapies are long acting when compared to lactational intramammories.

The registered claims for these Dry Cow preparations stretch from 4 weeks to 10 weeks.  Cepravin for example is registered for up to 10 weeks based on clinical trials measuring udder residues (which were conducted in the Northern Hemisphere (NH)).  As dry periods in the NH do not tend to last longer than 10 weeks this trial finished measurements at 10 weeks.  Udder residues at this point in the study still exceeded levels required to control Strep bacteria.

Five years ago our practice in conjunction with MSD looked at Cepravin residues in springer cows with 14 week dry periods and found the majority still had protective levels in the pre-colostrum secretions. This is why it is the only DC antibiotic in NZ that can show proof in reducing early season BMSCC. The downside of course is that it is also by far the most commonly detected inhibitory substance in the early season, thus Cepravin treated cows must adhere to withholding the first 8 milkings from supply.

In short, a successful dry off strategy should cover 3 aims:

• Cure existing infections
• Prevent new infections immediately post-dry off
• Stop the establishment of new infections close to calving (springer period).

As the average dry period in Otago/Canterbury is between 85 and 90 days, few products registered in NZ (e.g. Cepravin) will provide significant protection close to calving.  There is little advantage in investing in products that provide protection for more than 4 weeks but less than 10 weeks if the dry period is going to be greater than 10 weeks.  This is because very few new infections are picked up in the mid-part of the dry period (see image below). If protection close to calving is desired in cows with longer dry periods we recommend Teatsealants.

"Fog Fever" - Cow Deaths

From a mob of in-calf heifers grazing regrowth rape, 3 heifers were noticed with an unusual grunting cough.  Twenty four hours later, two of these heifers died.  Post mortem of these affected heifers showed unusual inflammation in the lungs.  This was confirmed by the lab to be "Acute Bovine Pulmonary Emphysema and Odema" or "Fog Fever" for short.  The third heifer was treated symptomatically but died 36 hours later. Fog Fever is a James Herriot era name and the disease probably has nothing to do with fog and more to do with the fact the disease is more commonly seen in the autumn.  A rapid change in feed (also a risk factor for Vitamin B1 Deficiency) causes a particular gut bacteria to convert L-Tryptophan, a naturally occurring amino acid, to a toxic compound.  The toxin rapidly impairs lung function resulting in death.  No treatment is available but identifying the condition and removing affected animals from the paddock will prevent any new cases.

Early Pregnancy Test Results

The key measures of optimal reproductive performance are the 6-week in-calf rate (ICR) and the final not-in-calf rate.  To achieve the industry target of a 78% 6-week ICR, you need >90% 21 days SR and >60% CR.

The 6 week ICR rates to date have been very variable, with the average 6 week ICR for our area, dropping around 4% to 63% compared to last season (15/16) which was 67% - remembering last season was also down on the 2014/15 season.  Many farms have seen a 5-10% drop this season in 6 week ICR.  With most farms now settling in on a 10-11 week mating period, we can expect empty rates to be once again higher than desired.  Many farms experienced a drop in Submission Rate (SR) this season, and some farms experienced an unexpected drop in Conception Rate (CR) as well - a number of farms' CR dropping 5-8%.

Yersinia

Each summer we investigate several cases of calves souring post weaning.  While there are many causes of diarrhoea in weaned calves i.e. parasitic enteritis, Salmonella, and BVD, we regularly diagnose Yersinia, which is a bacteria that causes diarrhoea.  We often see Yersinia 'roll' through a mob of calves - with a small number of calves being affected at any one time.  Treatment is aimed at correcting dehydration and administration of antibiotics.  Prognosis is usually good except in advanced cases.

There is circumstantial evidence that Yersinia is often associated with concurrent disease i.e. BVD, parasite burden, low trace element status - especially selenium and copper.  Remember - that Yersinia (both Y. pseudotuberculosis and Y. enterocolitica) are zoonotic - and hence are a common cause of food poisoning in people.  Keep the hygiene standards high if you are dealing with scouring animals!  Please contact the clinic if you are concerned about ill thrift or scouring in your weaned calves.