IT may have snowed last Friday 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 worm controlled counterparts.
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 two 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 doromectin (Dectomax, Pfizer) at the manufacturers 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 an average 29 kg while those that were drenched gained on average 36 kg.
This seven kilogram difference favoured the drenched cattle, as you might expect. However, this difference is so small that the statisticians tell us it could well have been achieved by chance.
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 at least over the summer 2010-2011 it was of no benefit to drench 14-16 month old heifers.
As a general recommendation, I 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 three months later followed by a move to low worm pastures.
Finally, calves should be drenched again in spring, again followed by a move onto a low risk pasture.
Based on Mandi’s trail results a summer drench is unnecessary. However, heifers probably benefit from a drench pre-calving.
While the summer drench for calves is unnecessary, it is vital for sheep. More on that next week.