Getting the right start
Fresh colostrum in the first 12 hours is crucial to get the calf’s immune system up and running. More information on good management practice for calf rearing can be found in the July issue of the Dairy Exporter.
Weston warned against feeding milk sourced from cows treated with antibiotics to calves, saying it was likely the practice would come under increasing scrutiny in the future.
“I know it’s a source of food and it’s free, but there are a number of risks associated with it, one of which is the low-level antimicrobial residues in it.”
The milk-weaning decision needed to be based on individual animal weights rather than mob average, Weston advised.
“If an individual calf isn’t ready to be weaned then it will suffer a severe setback going forward.”
Calves needed to be eating enough meal to mitigate the impact of dropping milk out of the diet.
“That meal helps to keep the nutrition up, but that’s also a stressful time and the time that they are often prone to coccidiosis – pretty much all your calf meals have a coccidiostat in it.”
Coccidiosis is caused by a type of protozoa – a single-celled organism – invading the animal’s intestinal cells, causing the cell to rupture and damage the intestinal lining. It usually affects young stock aged between two and eight months. Diarrhoea is the main observable symptom and it is transferred between animals through contaminated faeces.
The presence of a coccidiostat in calf meal interrupts the growth and reproduction of the protozoa causing the problem.
Weston recommended calves should be eating at least 1kg of calf meal at weaning, and maintaining this after weaning.
Managing drenches
Weston identified internal parasites as one of the biggest problems faced when growing young stock.
The parasite load varies with the season and is generally heavier in the warmer months before declining in late autumn. Higher humidity combined with warm temperatures fast-forwards the parasites’ life cycle and improves larvae survival rates.
Research conducted in the past couple of years by AgResearch showed oral drenches were more effective than pour-on or injectable products, with the prevailing theory being that this is related to how the active ingredient reaches the target after being administered. Injections and pour-ons are absorbed into the bloodstream then re-circulated for release in the gut tissue where the worms live. While the injectable product was absorbed more quickly into the bloodstream, the oral drench was the most effective at killing the gastrointestinal parasites.
Cooperia and Ostertagia were particularly important parasites in the cattle context. Managing drench families to protect against developing resistance was increasingly important. Dealing with Cooperia in particular required careful attention, as Weston warned macrocyclic lactones – the ectins of the various drench types – now seemed to be less effective against that particular parasite.
Focusing on product efficacy rather than convenience was crucial.
“All of those products have their uses, but whatever you are using, check that it is working.
“We still regularly see calves with high worm burdens that have been wormed fairly regularly.”
Faecal egg count reduction tests (FECRT) can show how effective a drench programme is. Weston said best practice FECRT involved taking faecal samples, doing a faecal egg count, drenching the cattle, then taking another faecal egg sample and counting again 5-7 days later.
Factors other than drench resistance should also be considered, such as a poorly calibrated application devices or under-dosing when liveweight is guessed rather than measured.
Weighing young stock and trace elements
Weston said trace element deficiencies were more easily detected in young stock, assuming they are regularly weighed, as they tended to result in sub-par growth rates. Trace elements like copper, selenium, and cobalt (B12) were involved in a lot of different enzyme processes that were important for health and productivity.
“Though there are a variety of different products suitable for treating trace mineral deficiencies, particularly copper and selenium, they can be poisons so you shouldn’t just rip in and do it – there is the potential to cause toxicities if the animals don’t need them.”
Best practice supports developing a blood-testing routine to aid early identification but regular weighing can also act as something of a proxy if animals are not meeting liveweight targets despite having adequate feed levels.
Although copper deficiency is less of an issue in adult cows these days due to the popularity of palm kernel– a product relatively high in copper – young stock are still at risk.
“While New Zealand isn’t low in copper, our problem is that there are a lot of other elements in the soil, in the plants, and sometimes in the water, that interfere with the absorption of copper.”
Bovine viral diarrhoea (BVD)
In adult cows, the main effect of BVD is reproductive wastage and when a cow is infected with BVD in the first four months of pregnancy, she may give birth to a Persistently Infected (PI) calf. It is the PI animals that are the main source of infection in a herd and they do not respond to vaccination. BVD infection in young stock can severely affect growth rates and suppress the immune system leaving animals susceptible to other problems.
“Heifers are going out grazing over their first pregnancy, and unless there is really good BVD control where they are going, there is a risk of bringing a PI back to your farm from a heifer’s calf.
“Because normally a heifer’s calf is not kept, then it’s not so much of a risk. If you are keeping replacements from heifers, you need to make sure they have been tested and vaccinated for BVD so they do not bring home a PI inside them as a Trojan cow.”
Weston warned the PIs are not always easy to identify through observation only and about half survive beyond two years, meaning they made it into the milking herd.
Vaccinations
Leptospirosis is both an animal and human health issue, so vaccinating cattle is crucial. Getting the vaccination and booster into calves pre-Christmas for spring-born animals is important.
“A pilot programme has shown that if calves weren’t vaccinated until they were 8-9 months old, a proportion of those calves were probably becoming infected prior to vaccination – the vaccine doesn’t clear infection, it prevents it.”
Clostridial diseases like blackleg, pulpy kidney, and tetanus could be triggered by common farm practices so best practice involves getting that vaccination done at dis-budding.
