Calving

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The transition period refers to the time of preparation of the cow for calving and lactation. Calving begins 3-4 weeks before calving! Metabolically, this is a time of great change for the cow.

In the last 3 weeks of pregnancy the cow has a high demand for energy to satisfy the requirements of the calf. During this time her ability to eat large amounts of food decreases (due to the size of the calf). Her voluntary intake of a grass-based diet will fall in the last three weeks, and she will be in an energy deficit. Also, her body is preparing for lactation, when she will suddenly mobilise, and lose large amounts of liquid, energy, protein, and minerals on a daily basis.

Why bother to do anything about this?
A cow who is prepared properly for calving will give more, and better quality, colostrum. She will have a healthier and heavier calf. In addition, she will give more, and better quality, milk during the first month of lactation, and her overall health and fertility will be improved.

On a normal grass based diet, the transition cow is short of energy, short of protein, does not get enough calcium, and gets far too much potassium! The effect is to make the cow prone to calcium deficiency, and unable to eat enough food to satisfy her own body needs, and those of the calf.
The high potassium levels in the grass cause the diet to be unbalanced in terms of electrical charge. This is called the Dietary Cation-Anion Difference, or DCAD.

Potassium is a positive charge ion or cation. Chlorine is a negative charge ion, or anion. Excess potassium makes the diet alkaline, and also interferes with the uptake of calcium, magnesium and sodium. The alkaline diet not only interferes with the uptake of calcium, but also prevents its release from the stores in bone. Therefore, we add ionic salts to the diet to improve the DCAD ratio.

On a grass based diet, the ratio is frequently 400-700. If this is halved, to around 200, there will be a great improvement in magnesium and sodium uptake and in calcium uptake and mobilisation. Inclusion of anionic salts such as magnesium chloride and ammonium chloride in the diet will decrease the DCAD. Unfortunately these salts are unpalatable and unpleasant to handle. The best way to give them is as a pellet, or with maize silage, or other suitable supplement.

In addition to anionic salts for the transition cow, they also need the correct amount of trace elements, some extra energy and protein, and possibly an ionophore to improve dietary utilisation in the rumen. The ideal is to provide all these ingredients in a palatable pellet, which can be given to the cow over the transition period. A pellet can be fed on grass to the springer mob, so does not mean that it has to be fed with forage-based supplement.

Both colostrum and the calf contain large amounts of trace elements and minerals, and the cow has a particular requirement for magnesium, zinc, selenium, copper, cobalt and manganese during the transition period. Calcium dietary levels should be kept low until after calving, this maximises the cow’s ability to absorb calcium from her diet, and to mobilise it from her bone reserves.

Energy can be provided by grain or maize silage. The maize silage provides fibre to stimulate the rumen papillae development. Alternatively, hay or straw can be used in small quantities to provide fibre.
By-pass protein enables the cow to have a protein source that is not dependent on bacterial degradation in the rumen. This means that she has additional protein available to her body. Again, by-pass protein can be provided in a pellet, or in the supplement.

The transition period in the cow is a complex one, with very specific dietary requirements. Attention to detail during this period will give significant production and health gains. However, it is important that this is looked at in relation to nutrition throughout the year. There is no point setting the cow up to eat a maximum amount of food, then finding that there is not enough grass/supplement on the farm to fully feed her!!

Alison Cullum
Intelact Nutrition Dairy Consultant
& Veterinarian (Animal Health Centre – Morrinsville)