Bovine Adenovirus in R1 Dairy Calves

What is Bovine Adenovirus?

• Bovine Adenovirus (BAdV) is a viral disease that is mainly seen in 6-12 month old calves.

• Outbreaks are typically seen during autumn, winter and spring months.

• It is primarily an acute gastro-intestinal disease, but calves may also have respiratory signs.

BAdV was noted as a disease of increasing occurrence in R1’s during 2014/15. The practice sees 3-4 cases/year.

How do we know?

• Outbreaks tend to be short in duration and although a large number of calves within a mob can be affected mortality rates tend to be low (ie. maybe 1-2 deaths in a group of 160).

• A presumptive diagnosis can often be made based on the history.

• A post mortem is important to confirm specific gastro-intestinal changes from samples sent to the lab.

Case Study - March 2020

• Grazier found two calves from a mob of 160, acutely dead within a day of each other.

• Noted the day before that a couple appeared to be a little bit dull/depressed.

Differential Diagnoses for Enteric Disease & Sudden Death in Calves

Yersinia, Salmonella, mucosal disease, GI parasites, toxicity, clostridial deaths, nitrate poisoning.

History

• Calves had received two doses of a 10-in-1 vaccine.

• Drenching was up to date. No known access to any toxicities.

• PM performed on one of the calves. Very fluidlike intestinal contents.

• Samples sent to the lab - a diagnosis of BAdV was confirmed based on histopathology of the intestine. Viral inclusion bodies seen in the GI tract confirms the diagnosis.

No more deaths were seen in this mob, however about half of the remaining calves appeared a
little bit ‘dull’, ears flat, and slightly snotty nose/slightly gunky eyes. Calves were on liveweight
target however weight gains had fallen in affected calves to 200-300 grams/day. A week or so later
they were looking a lot better and had picked up again. Often the remainder of the mob appear to
remain relatively unscathed and in general good health.

One calf from this mob had been diagnosed with Yersinia infection 3 weeks prior to this outbreak
(lab confirmed diagnosis) and although it had been separated, it was possible that in this case
Yersinia infection may have played a role in disease development. Bovine Adenoviruses are
widespread in the environment and given the relatively low prevalence of disease it is likely
that host and environmental factors play a role in disease development. Cold weather conditions, feed shortages, recent transport, ill thrift, and concurrent parasitism all have the potential to cause stress and predispose to opportunistic infections.

An interesting disease that we have seen more of in the last few years, and certainly on the
differential list when you see ‘sudden death’ in calves.

Body Condition Score

Early April is the time to start drying off lighter cows in order to allow them to gain body condition prior to calving. Gaining this body condition will reduce the risk of calving problems and metabolic issues, saving you precious time and energy during the busy calving period. Cows that are a body condition 3.5 or less should be dried off in the next couple of weeks. Cows that are BCS 4.0 need to have a strategy put in place to reach BCS 4.5 by the start of June. This may include extra feed and/or OAD milking. Light cows may also particularly benefit from a dry off drench to reduce the impact of parasites over the coming months.

Determining cows that are BCS 3.5 or less:

• Stand at the same level of the cow, don’t try and do it from the pit. You need to be able to get your hands on them.

• BCS is determined by looking at 8 key areas of the cow: the backbone, hips, rump, tail head, pins, thigh, short and long ribs (see pictures). If you haven’t body condition scored before, keep it simple and focus on the easiest areas to assess, like the backbone, hips, pins and tail head.

• Backbone - are there notches? BCS <3.5.

• Hips - place a cupped hand over the hip bone, if it doesn’t fill your cupped hand and there are dips between the hip and backbone when viewed from behind then BCS is <3.5.

• Pin bones - are they tap shaped? BCS <3.5.

• Tail head - between the tail and the pins is there any fat? Low fat will form a deep V shape.

DairyNZ has some great resources on their website, including video’s and a quiz to help you get your eye in, if you’re feeling particularly keen. Where physical distancing an be arranged our vets can continue to offer this important service.

A Mating Commentary

The calving/mating period for the 2019/20 would by many be described as ideal. Yes, feed got a little tight in late October/November, but quality reminded good and we did not have the nightmare rains of last November.

There were plenty of reports of high pre-mating activity. Good cow condition, calving patterns tightened a little as well this year and the incidence of dirty cows/per herd was also back. The average 3 weeks submission rate for our clients however remained at 80% (80% in 18/19 and 78% in 17/18 season). This is still 10% lower than the industry target figure of 90%. To attain an industry target of 78% in-calf for 6 weeks - 90% is crucial.

Pregnancy rates in the first 3 weeks averaged 44% in our practice - which sits lower than the target of 53%. for six weeks the average was 66% (up from 65% last year target 78%).

This season we had 28 farms in the practice achieving a 75% or greater for six weeks. This is a top effort and well done to all those in the honour list below. This group has grown from 18 last season.

Some of the newer tools used by our top farmers this season, were the utilisation of early season OAD milking of colostrum cows and better metabolic management through the use of calcium supplements and strategic feeding. This helps minimise condition loss and promote egg quality.

In-shed heat detection systems are increasing and have in the past proved reliable tools for those doing extended AI - providing they are properly maintained. We do find regular issues with tail paint only systems in extended AI/no bull herds where pregnant cows are often repeat mated. This increases the risk of pregnancy loss.

It is a little too early to give final not in-calf rate data.

Staph aureus screening

At the risk of putting the commentators curse on you all, it does seem that many of your pregnancy rates are likely to be better than last year. If this turns out to be correct there will be the opportunity to make some “voluntary culling decisions” this season. If improving mastitis control in your herd is a priority then consider at your last herd test doing a Staph aureus screening test. This test is done on the individual milk samples already collected at herd testing. You can either provide a list of cows you would like screened or even easier provide a list of criteria that decides which cows to screen. For example you could request only 3rd lactation or older cows with a SCC greater than 250 are screened less any cows recorded as empty. Obviously the last SCC won’t be through until after the samples have been processed so if this is something you are likely to consider doing please ring us so we can put a hold on your samples at the lab so they don’t get discarded i.e. let us know so we can warn LIC that based on the last herd test results some of the samples will be required for a Staph screen.

Lameness

The summer period is often a time when lame cow numbers increase, this can be a result of how cows have been managed in the season so far, wet weather, thin soles and stressors that have occurred during the calving period. The numbers can be made worse with people having time off.

• If we get a bout of wet weather it is worth taking the time to improve drainage off the edge of tracks. Take a spade and open up the grass, a spades width wide at regular intervals to allow water to drain off the track. The grey box shows a good spot to cut away the grass.

• If you have an underpass, keep it free of water and slurry. Make sure that sump pumps are working properly, sumps are cleaned out and pumps are turned on when it rains.

• If you have a section of lane that is chronically wet, especially just prior to the yard, consider scrapping the surface. Wet areas slow cow flow which means that more pressure has to be put on cows to get them on the yard and the moisture increases the foot problems. Scrapping lanes can damage the top surface of the lane, but these are often damaged when you get to this stage anyway, however it can allow them to dry out faster and improve cow flow. Look at a more permanent fix over the dry period.

• Have someone who can do lame cows every day or every other day. It becomes much harder to start treating doing them when there are heaps in the mob. They also get a lot worse.