Most springtime diseases - including milk fever, retained membranes, uterine infections, ketosis and LDA (left displaced abomasum) - are linked to how well cows manage the transition period.
This period runs from three weeks before calving to 3–5 weeks after calving, when cows undergo major changes as they grow a calf, calve and begin producing milk, requiring double the energy intake.
Immune system
The cow’s immune system is depressed by the changes during the transition period, making her more susceptible to disease. Having a mineral deficiency (such as selenium, copper or zinc) increases this risk. Multimin contains these minerals, and Virbac has studies that show an injection 3-4 weeks pre-calving can reduce mastitis at calving by 50%.
Fat mobilisation
During the three weeks prior to calving, the cow’s dry matter intake (DMI) naturally reduces, with cows in high body condition (>6.0) at risk of starting to mobilise their fat before they even calve. This increases the risk of ketosis and metabolic disease.
Cows should be offered at least 8-10kgDM, with at least 10MJME/kgDM, in the pre-calving period to prevent more weight loss than necessary. Often, there is a change in diet from being a dry cow to a milking cow, so it is important to adapt the rumen flora to the post-calving diet. Feeding some highly digestible carbohydrates, such as meal, can help increase diet digestibility while also stimulating the rumen papillae to grow and adapt.
Magnesium
The level of magnesium in the diet is important during this time, with supplementation usually required. Due to the lower DMI of dry cows, the magnesium level in the diet needs to be 0.35% for springer cows and 0.4% DM for colostrum cows.
Calcium
At calving, the cow’s daily calcium requirement suddenly doubles. She can increase blood calcium levels in two ways: by absorbing more calcium from the gut and by mobilising calcium stored in her bones.
Parathyroid hormone is required to mobilise the bone calcium, and to increase the level of adsorption of calcium from the gut. However, when pre-calving diets are high in calcium, the cow’s production of parathyroid hormone after calving slows down, particularly in older cows.
Ageing cows also become slower at mobilising calcium from their bones at calving, which is why older cows are at greater risk of milk fever.
Calcium absorption in the gut is reduced by:
High potassium levels in the diet
High rumen nitrogen levels
Low dietary phosphorus
Metabolic alkalosis.
DCAD
Metabolic alkalosis occurs when the diet supplies more strong basic cations — potassium, sodium, calcium and magnesium — than strong acidic anions such as chloride, sulphate and phosphate, to the blood. Manipulating these minerals to help reduce milk fever risk is known as adjusting the dietary cation-anion balance (DCAD).
The aim is to reduce sodium and potassium levels while increasing chloride and sulphate in the diet. High-quality pasture tends to be high in potassium and sodium, particularly where effluent has been applied. This can make DCAD manipulation more challenging in all-grass systems, although it is generally easier to achieve in mixed ration diets.
Diet
One way to reduce the incidence of milk fever is to restrict pasture intake during the last two weeks before calving to less than 2kg DM/cow/day. Hay or straw from areas not fertilised with potash can be fed.
This increases salivation and the excretion of bicarbonate, helping to acidify the blood and improve both calcium mobilisation from the bones and calcium absorption from the gut. The diet can be kept sufficiently digestible by feeding concentrates such as pellets or maize silage, which also helps the rumen adapt to the post-calving diet.
Concentrates are generally low in calcium, so while a low-calcium diet pre-calving can help reduce milk fever risk, extra calcium will need to be supplemented after calving — in addition to standard lime flour supplementation — to make up for the lower calcium levels in the diet.
In summary, between our springer and colostrum mob we want to:
Limit the amount of body fat used for energy around calving
Maximise the appetite of the cow just before, and after calving
Promote a high feed intake after calving
Maintain immune function
Reduce clinical and subclinical milk fever, through magnesium supplementation, manipulation of the salts fed, and manipulating the diet.
Every system is different, and we work with complex systems, so I hope you can find one thing to adjust to make your season start better.
