Butterfats typically reduce by 0.4% at turnout, with some herds experiencing 1% drops (i.e. 4.4% -> 3.4%). This often results in financial penalties or loss of income through not reaching constituent targets. Butterfat is made up of acetate and butyrate production, with glucose supplying the glycerol requirement. The rumen is made up predominantly of acetate/butyrate bacteria (fibre digesting) and propionic bacteria. The main issue suppressing butterfat is where propionic fermentation exceeds and suppress acetate/butyrate fermentation. This is extremely likely and common at spring grass or where insufficient NDF levels occur in a ration.
(Fig1; Butterfat = Triglyceride, 3 fatty acids)
Spring grass contains low fibre and NDF (Neutral Detergent Fibre), high energy, sugars and RDP (Rumen Degradable Protein), all promoting production and negatively affecting butterfat. Cows will seek out fibre when acidotic conditions occur but often leave fibre in favour of more palatable forage/grass. The common instance at grazing is “back grazing”, where cows prefer fresh shoots (lowest fibre levels of all).
In the above situation butterfat and rumen PH drop because propionic bacteria dominate driving PH lower. So not only do we have insufficient fibre, but we begin to kill off fibre digesting bacteria which cannot operate at lower PH’s, leading to further falls in butterfat and the increased likelihood of acidosis.
The solution is to ensure either grazing down to covers of 1,500-1,600kg/ha or add a back fence when strip grazing. Within a TMR or partial buffer at grass, additional structural fibre (straw, longer chop silage, higher NDF silage) and digestible fibre (sugar beet pulp, soya hulls or nutritionally improved straw (NIS) need to be added, particularly where cows are producing more than 28litres. High yield diets are particularly difficult to manage because we need to supply high levels of glucose to achieve production and aid fertility, however maintaining rumen PH should take priority.
Rumen flows are faster at grass so slowing output ensures better utilisation of grass sugars and RDP. Chopped straw is ideal for this as it also provides structural fibre opening-up TMR/Buffers, stimulating cudding and increased cow bicarb production.
Supplementary rumen buffers may also be required particularly during April/May grazing and if the forage used to buffer has insufficient fibre. 2017 maize silage is particularly low in NDF and so for those who normally buffer with this greater buffering/fibre will be required.
Supplementary C16 fat can be used but these will not work if rumen function is compromised. Therefore, correct rumen function first!
For help managing your milk constituents, please contact Wesley atmailto:email@example.com or your local FCG Office.