Herd Health Update

With the final arrival of the grass, housing may still seem a distant prospect for some farmers, but preparing in advance is time well spent. Bovine Respiratory Disease affects 45.9% of calves, either clinically or sub clinically (study on dairy farms) and vaccination pre housing is a key part of effective management. Vaccine protocols depends on what pathogens are present on the farm, but vaccinating in advance of housing stress, maximises immunity and cattle response to vaccine. Shaving backs, appropriate lungworm treatment or prevention, ensuring optimal building ventilation, not mixing age groups and appropriate stocking densities will also help reduce pathogen pressures. APHA post mortem data for winter 2025 showed that 6 out of the top 10 most common causes of death belonged to respiratory diseases, highlighting its huge significance in the cattle sector. Mycoplasma bovis, Pasteurella multocida, and Mannheimia haemolytica can be primary respiratory pathogens but are also frequently secondary respiratory infections, usually following a primary viral respiratory pathogen.

Image – showing lungs affected by viral pneumonia

The rapid grass growth could also predispose to seasonal cases of Hypomagnesemia (grass staggers)  in adult grazing cattle, with little or no clinical signs or warning. There is a relatively low incidence annually (approx 1%) but it is economically significant for those farms affected, as acute cases can result in sudden death and can occur in outbreaks. Cows cant store much magnesium, so rely on a regular daily intake to keep blood levels within a tight range. Many risk factors exist, but older cows, low dry matter and lush wet pastures will increase risk. Hyperexcitability, seizuring and thrashing are the most common encountered clinical signs. There are a variety of preventative measures available and best discussed with your vet, but options can include supplemental concentrate feeding, bolusing, mineral licks and buckets (although these have variable individual uptakes and should be positioned with care to avoid wildlife access and bTB risk) and water supplementation with magnesium flakes (but can become unpalatable and requires a single water source)