Careful management of the transition cow will set the animal up for a successful start to lactation, Ruminant Nutrition Specialist, Aisling Claffey takes a closer look at nutrition during the transition period.
There are a number of key components which play a role in ensuring a successful transition from dry to lactating dairy cow, namely body condition score, magnesium levels in the diet, mineral supplementation and low potassium forage source.
The transition period is considered the last three weeks before the cow calves and the first three weeks of early lactation. The vast majority of clinical disorders occur during this period.
Body condition score should be routinely monitored throughout the dry cow period, particularly for close up cows to ensure that they are receiving adequate nutrition as rapid foetal growth occurs in the last month before calving. Alternatively, over fat cows have a much higher risk of milk fever and excessive mobilisation of condition after calving, increasing the likelihood of negative associated effects of these disorders. This can be a particular challenge for later-calving cows and it is important to not overlook condition in this group throughout the busy weeks ahead.
While it is important that the dry cow receives adequate pre-calver mineral supplementation throughout the final 6-8 weeks of gestation, ensuring optimum trace mineral and vitamin supplementation for foetal growth and dam health is also important.
Magnesium
One of the most critical elements to get correct for the transition cow is the dietary Magnesium (Mg) level. Magnesium is not stored by the cow and therefore she requires a consistent daily supply at a rate of 0.4%/kg DM which is the equivalent of 40 g for a cow consuming 10 kg DM/day of grass silage. Silage will supply approx. 15 g of Magnesium so check the inclusion and feed rate of Magnesium from supplementary sources to ensure you are meeting the herd requirements.
Table 1. Daily Magnesium supply from pre-calver mineral depending on Magnesium inclusion level and feed rate
| What is says on the bag | 20% Mg | 25% Mg |
|---|---|---|
| 100 g feed rate | 20g Mg | 25g Mg |
| 120 g feed rate | 24g Mg | 30g Mg |
Magnesium has an important role to play in supporting a number of the pathways in which Calcium is mobilised – both from skeletal Calcium reserves and reabsorption of dietary Calcium. Ensuring adequate supply and absorption of dietary Magnesium can minimise the risk of sub-clinical and clinical milk fever.
The impacts of milk fever
While farmers are aware of the challenges associated with a down cow from milk fever, sub-clinical milk fever can also result in reduced lactation performance. It can increase the incidences of slow or lazy calvings, retained cleanings and uterine infections due to impaired uterine contractions. Impaired muscle function can also result in poor rumen motility giving rise to supressed dry matter intake and increased severity of negative energy balance. This can impair milk yield and increase the likelihood of metabolic disorders such as ketosis or displaced abomasum. High incidences of mastitis in the first month after calving may also be associated with sub-optimal transition cow management.
High Potassium forages
High Potassium (K) forages impair Magnesium absorption and can also increase the dietary cation-anion balance of the forage which can further reduce the efficacy of Calcium mobilisation. Where high K forages have been identified on your farm, avoid feeding in the final two weeks before calving or if you are observing frequent indicators of sub-clinical milk fever in the first 7-10 days from planned start of calving, utilise an alternative forage source that received little to no slurry or K fertiliser applications and ensure Magnesium supplementation is carefully implemented. Bear in mind this alternative forage source (eg. hay or straw) may not be sufficient to meet the energy or protein demands of the transition cow and supplementation may be required as a result.
Optimal management of BCS, adequate dietary levels and supply of Magnesium, and low Potassium forages during the transition period are essential to support optimal Calcium mobilisation at the point of calving and minimise the risk of transition cow disorders during this period. Sub-clinical and clinical milk fever can be linked or give rise to an increased risk of other metabolic disorders. Careful management of the transition cow will set the animal up for a successful start to lactation.
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