Results from Trouw Nutrition laboratory: high risk forages and milk fever

30 January 2019

A drop in blood calcium around calving can trigger a cascade of events such as mastitis, retained cleansings, dirty calf beds and displaced abomasums.

A drop in blood calcium does not always result in clinical signs of milk fever (downer cows); for every case of milk fever in a herd, four other cows may have below-normal blood calcium levels.

Insufficient blood calcium concentrations around the time of calving are due to the sudden increase in calcium requirements after calving for colostrum and milk production. Post-calving drinks such as Reviva provide a good source of energy and bioavailable calcium for freshly calved cows. In addition, there are a number of other simple nutritional management strategies within the dry cow diet that can be implemented to further help regulate blood calcium levels around calving.

Negative DCAB dry cow diets

Achieving a negative dietary cation and anion difference (DCAD) dry cow diet for 21 days pre-calving has shown to be effective in controlling blood calcium levels around calving. This is done by keeping positively charged minerals such as sodium and potassium low in dry cow diets, whilst providing higher levels of negatively charged minerals such as chlorine and sulphur. By getting the balance of negatively and positively charged minerals correct in the dry cow diet (i.e. the DCAD balance) the enzymes involved in regulating calcium will work more effectively.

The dairy cow can regulate calcium balance best when the DCAD is negative (range -100 to -200 meq/kg of DM).  Even if a negative DCAD is not achieved, any decrease in DCAD will reduce the risk of milk fever.   Getting your dry cow forage analyzed is the first step in identifying high risk forages. Table 1 shows the 2018 average mineral profile of Irish forages tested through Trouw Nutrition laboratory. The results clearly indicate that grass silage and Lucerne contributes a very high potassium percentage and hence DCAB value compared other forages. Lucerne should not be used in dry cow diets due to its extremely high DCAB value. Wholecrop, maize and particularly straw on the other hand are effective forages in dry cow diets for diluting the high DCAB coming from grass silage.

Table 1: Average mineral profile for 2018 Irish forages tested through Trouw Nutrition laboratory

  Potassium % DCAB meq/kgDM
Lucerne 2.31 370
Grass silage 2.24 216
Maize 1.02 132
Wholecrop wheat/barley 1.38 126
Straw 0.76 30

 

In terms of cut number of grass silage, 2018 samples tested through Trouw Nutrition Laboratory would highlight 3rd cut silages to be the highest risk grass silage (highest DCAB), followed by 1st cut silages, with 2nd cut silages being lowest risk (see Table 2). This would be a familiar trend seen in previous years.

Table 2: Average DCAB value of 2018 Irish grass silage cuts tested through Trouw Nutrition laboratory

Grass Silage cut number: Potassium % DCAB meq/kgDM
1st cut 2.29 241
2nd cut 2.28 212 
3rd cut  2.54 304

 

Potassium (potash) from slurry is the main contributor to the high potassium found in grass silage, hence designating a proportion of 2nd cut silage ground specifically for making dry cow silage and applying no slurry on that ground for that cut could help lower the DCAB balance when feeding grass silage to dry cows. Target for dry cow grass silage is <1.8% potassium. Consultant your local nutritionist about getting a forage mineral analysis done. 

It is difficult to achieve a negative DCAB in any grass forage based dry cow system because of the high potassium content. Anionic salts, also known as a CAB corrector pack, can be added to dry cow minerals for 21 days pre-calving to help correct the DCAB value. Always ask your local nutritionist for advice.