The transition period is defined as the timeframe from 4 weeks before calving until 4 weeks after calving and is characterised by an increased risk of disease. The changes in metabolic status have a long-term effect on the health, fertility and productivity of dairy cows.  Most metabolic conditions, such as milk fever, ketosis, primarily affect cows during this period as do disorders such as RFMs, metritis, displaced abomasum and lameness.

Feed intake and nutrient density of the diet determine the nutrients available to the cow and developing foetus, so cows need enough energy for them and the foetus.  During the last month of gestation cows (550kg bodyweight) should be provided with at least 8 to 10 kg DM in feed, providing at least 10 MJ/kg DM, to allow for foetal growth without depletion of the cow’s body stores.  Over feeding cows prior to calving can predispose cows to milk fever, udder oedema and mastitis.

It is recommended that cows are dried off in the BCS they are required to calve.  A BCS 5 for cows, 5.5 for heifers are considered optimum to achieve the best results in terms of subsequent production and reproduction. Cows at or above target BCS should be fed 90 percent of their daily energy requirements for two to three weeks before calving.  Cows that are below target BCS should be fed 100 percent of their daily energy requirements.

The management of the transition diet is important to reduce the risk of milk fever.  Pastures high in potassium and sodium should be limited due to their detrimental effect on the DCAD, so avoid access to effluent paddocks.  Adequate magnesium and phosphorus also need to be provided in the late dry period.  

There are a range of ways to supplement with magnesium – magnesium oxide can be mixed in feed or dusted on pastures; magnesium sulphate and magnesium sulphate can be added to the drinking water. Cows need to adjust to treated water - so slowly introduce it, as high levels make the water unpalatable.  Also, magnesium intra-ruminal bullets can be used - they release magnesium over 9-12 weeks.  

Dairy cows have a level of immunosuppression due to the period immediately before, during and after calving.  This means they are more susceptible to disease, and this can be made worse by inadequate trace element nutrition.  Aim for optimal levels of selenium, copper, and zinc.  

The goals of nutritional and environmental management during the transition period are to maximise the appetite of the cow just before and after calving, minimise body fat mobilisation around calving, maintain calcium at and after calving, and to maintain or enhance the animal’s immune function.