Fickle weather raises health risk for herds

Mar 10 2008 by Sam Wood, The Journal

FARMERS have been warned of the danger of grass staggers for spring calving suckler herds.

The English Beef and Lamb Executive said increasingly warm and variable late winter and spring weather made it vital to protect herds in coming weeks.

Eblex beef scientist Dr Liz Genever said: “Grass staggers – hypomagnesaemia – are always a threat with lactating cows on early season ryegrass-based pastures, but they pose far more of a risk when stock grazing young grass are stressed by the sudden changes in spring weather that seem to be becoming more common these days.

“All the more so where the magnesium uptake of the grass is restricted by soils with a high potash status or early spring potassium fertilisation, and in older animals that have been on restricted feeding and losing weight over the winter.”

The incidence of staggers varies widely, both between seasons and locations. It is known to affect up to 2% of cows in a geographical area and up to 30% in some herds, with a high proportion of those animals showing clinical symptoms or dying.

Veterinary treatment costs of £100 or more, together with serious losses of milk production at a critical time for calf performance and links to milk fever add to the attractions of prevention, at less than £5 a cow.

Because cows have no readily available reserves of magnesium to draw upon and absorb the mineral very inefficiently, reliable daily mineral intakes are essential to prevent problems; a typical 600kg animal needing up to 35g magnesium a day, depending on milk production.

Dr Genever said: “Free-access minerals and magnesium in the water supply are the most practical and widely used ways of supplementing suckler cows at pasture.

“However, in both cases, daily intakes have been found to be highly variable. The palatability built into free-access minerals to ensure intake further means that some cows frequently consume more than they need at the expense of others – generally those lower down the social order.

“Pasture dusting with calcined magnesite is even less reliable, while magnesium boluses can be effective but tend to be rather costly to use. None of the available methods provides the level of protection possible in dairy cows by the routine supplementation of concentrate feeds.” Eblex advises herds to provide at-risk cattle with a sheltered paddock to reduce weather stress and avoid unnecessary yarding. It also suggests supplementary feeding with silage or hay in particularly bad weather as well as free-access minerals in licks or blocks placed in general access areas, such as near water troughs, to help avoid bullying.

And it recommends being especially alert for signs of unusual nervousness, tremors and staggering, treating any suspected cases immediately with subcutaneous magnesium sulphate.

English levy payers can obtain free advice at www.eblex.org.uk