A high proportion of calves on some farms are failing to achieve adequate passive transfer of immunity – even when colostrum quality appears good – according to a case report published recently.
The report in the Vet Record, based on a seasonal-calving dairy herd in Northern Ireland, found more than three-quarters of calves tested had inadequate passive transfer, despite colostrum testing at the recommended 22 % Brix or above. All calves later developed scours.
Authored by Dr Ryan Davies of Veterinary Technical Consulting and Dr Katie Denholm of Glasgow University, the study highlights the importance of testing calves for passive transfer using blood samples at 24 hours–7 days old, rather than relying on testing colostrum quality alone.
The findings are particularly relevant for herds investing in dry cow vaccination, such as Bovilis Rotavec Corona, which provides antibodies in the colostrum against rotavirus, coronavirus and E. coli F5 (K99) and F41 and Bovilis Cryptium to reduce clinical signs of diarrhoea caused by C. parvum. This is because even when vaccine-derived antibodies are present in colostrum, calves will not benefit if absorption fails.
Dr Davies said: “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.
“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.”
On the case study farm, 81% of calves tested had serum total protein concentrations below 5.2g/dL, indicating poor or fair passive transfer. Delayed feeding due to limited colostrum pasteuriser capacity and variation in colostrum quality (20-30 % Brix) between cows were key factors.
The findings support wider research from the Royal Veterinary College, which found failure of passive transfer in more than a quarter of calves across 91 UK herds.
In response, the Northern Irish farm introduced earlier feeding, so all calves were fed within 30 minutes of birth, colostrum enrichment using whole bovine colostrum powder to standardise quality at 30 % Brix, and extended colostrum feeding using whole bovine colostrum powder for the first 10 days of life.
Dr Denholm said: “While 22 % Brix is the minimum requirement, calves benefit from 300g of IgG – and more where multiple feeds are given – to meet passive immunity targets.”
She added that extended colostrum or transition milk feeding offers local gut health benefits even after antibody absorption declines.
However, both vets caution that when feeding colostrum and transition milk hygiene is a critical factor, particularly when storing colostrum.
Dr Davies said: “Bacteria interferes with IgG absorption, so if your hygiene is poor, you won’t see the benefits of colostrum or extended feeding. 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.”
Tailored colostrum protocols
Dr Denholm emphasised that while this protocol worked for the Northern Irish farm, every unit must tailor its approach:
Factors to consider include:
- Labour availability for harvesting and feeding transition milk;
- Colostrum supply;
- Storage facilities;
- Vaccine protocols; and
- Feeding systems – some automatic feeders can prioritise fresh transition milk for young calves before switching to powder.
Dr Denholm added that passive transfer is a complex process. “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.”
