The study, published in Vet Record, found that more than three-quarters of calves on a seasonal-calving dairy unit in Northern Ireland failed to achieve adequate passive transfer of immunity, even though colostrum regularly tested at or above the recommended 22% Brix threshold. All of the calves later developed scour.
The case report, authored by Dr Ryan Davies of Veterinary Technical Consulting and Dr Katie Denholm of the University of Glasgow, raises concerns about relying solely on colostrum quality testing, rather than assessing whether calves have successfully absorbed antibodies.
The findings are particularly relevant for herds investing in dry cow vaccination programmes, including products such as Bovilis, Rotavec, Corona and Bovilis Cryptium. While these vaccines stimulate the production of protective antibodies in colostrum, the authors stress that calves will not benefit if colostrum management protocols fail to ensure effective absorption.
Dr Davies said farmers can be misled into thinking vaccination alone will prevent disease.
“It can often be a case of farmers jabbing the dry cows and thinking the job is done, and when they then see diarrhoea in calves, they assume the vaccine isn’t working.
“As the case study in our paper has shown, that wasn’t the case at all. Calves were still getting scours caused by Bovine rotavirus A (BRV-A) genotype G6P11, despite being vaccinated, as a result of inadequate colostrum management protocols.”
He added that laboratory testing confirmed vaccine-derived antibodies were present in the colostrum.
“We know this because when the colostrum was tested it had sufficient protective antibodies to BRV-A, demonstrating successful vaccine efficacy, but the protocols on-farm were not facilitating optimal transfer of passive immunity in many calves.”
Blood testing of calves on the case study farm showed that 81% had serum total protein levels below 5.2g/dL, indicating poor or only fair passive transfer. Investigations identified delayed feeding, due to limited pasteuriser capacity, and wide variation in colostrum quality between cows, ranging from 20% to 30% Brix, as key contributing factors.
The report supports wider research from the Royal Veterinary College, which previously found failure of passive transfer in more than a quarter of calves across 91 UK herds.
In response to the findings, the Northern Irish farm made several changes, including feeding all calves within 30 minutes of birth, enriching colostrum with whole bovine colostrum powder to standardise quality at 30% Brix, and extending colostrum feeding for the first 10 days of life.
Dr Denholm said minimum standards do not always equate to optimal immunity.
“While 22% Brix is the minimum requirement, calves benefit from 300 g of IgG – and more where multiple feeds are given – to meet passive immunity targets.”
She added that extended feeding of colostrum or transition milk can continue to benefit calves beyond the point at which antibody absorption declines, by supporting gut health.
However, both vets warned that hygiene remains critical when feeding and storing colostrum.
“Bacteria interferes with IgG absorption, so if your hygiene is poor, you won’t see the benefits of colostrum or extended feeding,” Dr Davies said. “Unfortunately, there isn’t a current widely available pen-side test for bacterial loads. It’s essential to scrub and clean all equipment with hot water, brushes and detergents.”
Dr Denholm emphasised that while the revised protocol proved effective on the case study farm, there is no one-size-fits-all solution. She said labour availability, colostrum supply, storage capacity, vaccination programmes and feeding systems must all be considered when designing protocols.
“Passive transfer is a complex process,” she said. “It’s not just about quality – timing, volume, cleanliness, cow health, speed of collection and storage conditions all play a role – it’s the 5Qs of colostrum quality. A weakness in any part of the chain can undermine the whole system.
“Simple adjustments such as reviewing collection practices, checking feeding speed and volumes, logging timings, or re-evaluating storage methods could make the difference between successful passive transfer and costly disease outbreaks. It’s important you work with your vet to look at your own farm protocols and find a protocol that works for you.”
