WRML. Summer drenching cattle – Drs Bruce Watt/Mandi Carr, Bathurst NSW

To WormMail mailing list. WRML.20121023. Summer drenching cattle -Drs Bruce Watt (and Mandi Carr)

Recently I posted a newspaper article by Bruce Watt summarising the results of some on-farm trials regarding liver fluke in young cattle in the NSW central tablelands (Tablelands LHPA).

Bruce of course is the Senior District Veterinarian for the Tablelands LHPA and along with Jeff Eppleston and other colleagues (in this case (below), Dr Mandi Carr) does some very interesting trials on-farm in the Central Tablelands of NSW. This is done with the assistance of farmers, and also at various times MLA, pharmaceutical companies, NSW DPI etc.

In a recent (Oct 2012) article for the local (Bathurst) newspaper, Bruce outlined some work done by Mandi Carr. (Reprinted here with permission). I’ll make one or two comments after the article.

“SUMMER DRENCHING CATTLE (AND SHEEP)

It may have snowed last Friday (12 Oct) but this week spring is back. It is warm, snakes and lizards are out, magpies are bombarding bike riders and barley grass is running into head. All this means that our thoughts turn to … summer drenching.

Firstly, what about summer drenching in cattle? As I have mentioned previously, with some exceptions, adult cattle do not need drenching. However, what about young cattle?

We know that cattle for at least the first six months post weaning are susceptible to worms and if untreated can be 60 kg lighter than their counterparts in which worms are controlled.

We also know that as the spring progresses, Ostertagia (small brown stomach worms) that cattle ingest increasingly burrow into the stomach wall for a summer sojourn. They then re-emerge in the autumn, causing diarrhoea and weight loss (known as Type 2 Ostertagiasis).

Therefore it seems like a good idea to treat young cattle in the summer with a mectin type drench (most effective in removing summer sojourning Ostertagia) both to remove the worm burden and to prevent type 2 Ostertagiasis.

Mandi Carr during her time with us sought to answer this question with the help of 18 tablelands cattle producers. She weighed 1,846 spring 2009-drop heifers from these farms in October-November 2010. Half the heifers, chosen at random, were treated with doramectin (Dectomax, Pfizer) at the manufacturer’s recommended dose rate while the other half were not treated. The heifers were re-weighed in February/March 2011.

The heifers on these 18 farms averaged 429 kg at the start of the trial in October November 2010. By the end of the trial, those heifers that were not drenched gained on average 29 kg while those that were drenched gained on average 36 kg.

This 7 kg difference is so small that the statisticians tell us that it could well have been achieved by chance and is therefore not significant.

Of interest, Mandi found that the average worm egg count (WEC) at the start of the trial was 22 epg. At the end of the trial, in the autumn the WEC of the control group was 48 epg, and the treatment group 31 epg. These results show that egg counts in older cattle are usually low and in my opinion, difficult to interpret.

Our conclusion, from this trial is that least over the summer 2010-2011 it was of no benefit to drench 14-16 month old heifers.

As a general recommendation, I therefore advise that tablelands calves should be drenched, vaccinated with 5:1 and pestivirus and treated with selenium at weaning. They should be drenched and treated for fluke about 3 months later followed by a move onto low worm pastures.

If you used a mectin and especially a long acting mectin at weaning, I suggest that this winter drench should preferably be an alternative to a mectin, acting as an exit drench. Finally, calves should be drenched again in spring, again followed by a move onto a low risk pasture. For heifers, as this is before joining, it is also an ideal time to give a pestivirus booster.

Based on Mandi’s trial results a summer drench is unnecessary. However, heifers probably benefit from a drench pre-calving (although I have no evidence either way on this). This is the ideal time for a 5:1 booster.

While it seems that a summer drench is unnecessary for cattle, it is vital for sheep. More on that next week.”

Some comments (incl comments on ostertagiosis, resistance etc)

* As always, when interpreting trial findings, take account of the context. While general principles may hold, the particulars may not apply to other areas.

* Bruce mentions untreated weaner cattle can be 60 kg lighter than their counterparts in which worms are controlled. This is a reference to earlier trials done by Bruce and Jeff. (See a summary slide (below) from a presentation to producers relating to Central Tablelands and Victoria trials with weaner cattle). Untreated weaners were 60 kgs lighter than weaners which were essentially worm free (achieved by suppressive drenching for the sake of the experiment). In between the untreated weaners and the ‘worm’ free weaners were the weaners treated according to common (‘traditional) district practice.

* In my opinion, this trial further confirms that (roundworm) worm egg counts (WECs) on their own are not always a reliable guide to worm burdens in cattle or the impact of these burdens, at least in our backyard (NSW) and extensive grazing systems. (As opposed to Fluke WECs in cattle: in my opinion, any positive fluke WEC is significant).

* You need to consider if your cattle are at risk of Type 2 ostertagiosis. (Experts, presumably classicists, tell me that disease is more properly referred to as ‘ostertagiosis’ but common usage is ‘ostertagiasis’. (I can be likewise pedantic and say most people don’t say ‘angst’ or ‘kilometre’ properly 🙂

This condition (ostertagiosis, not pedantry) occurs as a result of the accumulation of Ostertagia immature (early L4) stages in the wall of the 4th stomach (abomasum). These larvae, which in the case of ‘Type 2’, are in a state of arrested development (hypobiosis, ‘inhibited’), resume development more or less simultaneously, causing much damage to the abomasum, with leakage of protein from the gut, rapid weight loss and profuse diarrhoea.

Prior to the onset, WECs may be low, and the cattle may appear normal. The condition seems to have been somewhat less common since the advent of the ‘mectin’ (macrocyclic lactone) drenches in the 80s. These are the most effective of the broad-spectrum drenches against adult and inhibited Ostertagia in cattle. The next most effective are the BZs (benzimidazoles).

The last case of Type 2 ostertagiosis I saw was when I was a District Veterinarian in the Glen Innes district in the early 1980s (pre-‘mectins’), however colleagues in other areas still see cases of ‘Type 2’.

Of course, if drench resistance in cattle worms becomes more common – and there is no reason why it won’t – we might see more cases of “Type 2”. And, if the findings of Leathwick and Miller (2012) generally hold true (see here https://wormmailinthecloud.wordpress.com/2012/10/09/wrml-efficacy-of-oral-injectable-and-pour-on-formulations-of-moxidectin-against-gastrointestinal-nematodes-in-cattle-in-new-zealand/ ), then it may happen more often if drenches are given frequently by way of pour-on or injection rather than oral (along with the effect of resistance on efficacy) and/or if single active broad-spectrum drenches are used instead of combination broad-spectrum drenches. Unfortunately in Australia we have very few oral ML drenches for cattle. This may change. And of course pour-ons are very convenient – and can assist with ectoparasite control as well – I understand that. We do now have a combination broad-spectrum cattle drench in Australia, the pour-on (topical) drench “Eclipse” (abamectin+levamisole(Merial)). Others may be in the pipeline.

If designing a cattle worm control program, ‘Type 2’ is one thing you need to consider. Disease from ‘Type 2’ Ostertagia infections in beef cattle in NSW typically occurs in summer/autumn in animals around 18 months old, although it can occasionally occur in older (and younger) animals. (‘Type 2’ is as famous among cattle veterinarians as ‘E-Type’ is among Jaguar enthusiasts).

*2010 and 2011 (when Mandi did her trials) were La Niña years with above average rain in most of NSW.

* Rumours that I am Bruce Watt’s publicist are exaggerated.

The above is my interpretive summary of these trials. Note the URLs above so you can read the full reports for yourself.

Regards

SL

#end

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