Silage has already been cut down in the Tyne Valley and most cows are out. The grass is growing well, and, while the rainfall remains patchy, we may not see so much in the way of "Staggers" as we might expect, but there will still be "Down Cows".
By far the two major causes of metabolic disease at this time are Hypocalcaemia (Milk Fever) and Hypomagnesaemia (Staggers). So I will briefly go through these diseases, setting down some of the important points to be considered.
Hypocalcemia (Milk Fever)
This is probably the most common metabolic disease of cattle, although the myth that it rarely occurs in suckler cattle persists. This may have been the case once, but today it is commonplace. It normally occurs 10 days either side of calving, but has been reported in dry cows and occasionally during mid lactation. The reason it occurs mainly around calving is the sudden large demand for calcium at that time. Calcium has to be pulled physically into the body by the digestive system, involving a complex hormonal system and Vitamin D. This system takes time to adapt to the increased demand for calcium and a shortfall occurs. If this is severe enough, the result is Milk Fever.
The predisposing factors for this disease are as follows:
1) Breed. Channel Island breeds are very susceptible.
2) Age. Rare in first and second calvers, it appears to increase with age.
3) Seasonal factors. The incidence of the disease in cows at grass varies with the seasons. If the weather is dry, the number of cases is low, but if we have long wet spells the opposite occurs. A diet of grass with a low dry matter is thought to be a major cause ( probably because this type of diet causes diarrhoea leading to reduced calcium absorption. Plus we know that the calcium level of lush grass in autumn is usually very high, and the magnesium level low. It appears that this low level of magnesium restricts the cow's ability to absorb calcium and so brings about the high levels of Milk Fever seen in spring and autumn.
4) Nutrition. …