Transition Management

It is important to get the balance of calcium, phosphorus and magnesium correct for cows during the dry and transition periods to minimise health problems after calving.

Dry period

Calcium demand is greatly reduced during the dry period, as calcium excretion in milk no longer takes place. Most forage-based diets will be able to meet calcium requirements during this time of about 0.4 per cent of dry matter intake. During the dry period, phosphorus should be 0.25 per cent of dry matter intake and magnesium 0.3 per cent of dry matter intake.

Transition period

During the transition period it is important to make sure that calcium supply is 0.4 to 0.6 per cent of dry matter intake or 40 to 60 g/day for a cow eating 10 kg DM/day. Phosphorus should be increased to 0.25 per cent to 0.45 per cent of dry matter intake (25 to 45 g/day) and magnesium should be increased to 0.4 per cent of dry matter intake (40 g/day). This is to minimise the risk of milk fever and hypomagnesaemia after calving and ensure cows have the best preparation for their upcoming lactation.

Dietary cation-anion difference

Another important mineral-related dietary factor, particularly around calving is the dietary cation-anion difference (DCAD) value of the diet. The DCAD is determined by the potassium and sodium content on one side of the equation versus the chloride and sulphur content on the other side of the equation. Potassium and sodium push the DCAD value up, whereas chloride and sulphur push the DCAD value down. 

Cows in the last four weeks before calving need to have a diet with a DCAD value of around minus 50 (measured in milli-equivalents per kg DM). When this DCAD target is combined with the calcium, phosphorus and magnesium targets described above, it minimises the risk of developing milk fever after calving. To achieve a DCAD value of around minus 50 in the weeks before calving, cows need to be fed a diet low in potassium and sodium, and high in chloride and sulphur. A low potassium/sodium diet generally requires cows to be removed from grazed pasture and fed a low potassium forage instead. Often cows will also need anionic salts supplements which contain chloride or sulphur.

A feed analysis for potassium, sodium, chloride and sulphur is recommended for forages to be used during the transition period. This is due to the variability in potassium and sodium content of grazed and conserved pastures. Once cows have calved, the DCAD value of the diet needs to be 200-250 milli-equivalents (mEq) per kg DM to minimise risk of milk fever and other health related problems.

Mineral levels in diets

Recommendations for mineral levels in diets (% in feed DM) and DCAD levels (mEq/kg DM) for lactating cows, dry cows and transition cows (last four weeks pre-calving).