Maintaining Healthy Rumen Function
We all enjoy spring pasture growth, as the pressure comes off average pasture cover and our cows can consume optimal pasture intake. The vat is up and we anticipate that everything will take care of itself. But we all know that nature can throw a few unexpected surprises at us. If we understand what drives those challenges, we can successfully head them off via strategic management before they cause grief. So what should we look out for?
It is uncommon to observe lactic acidosis in grazing herds, however there are times when ration balance does challenge rumen health. Spring pastures can be high in sugars and fat (unsaturated fatty acids) – they also tend to be low in physically effective fibre. As the rumen bugs break down this readily digestible feed, organic acids are at times produced more rapidly than they can be transported out of the rumen.
Transporting organic acids (which are a good thing) out of the rumen is an osmotic process that is dependent upon acids coming into contact with the papillae on the rumen wall and rumen fluid tonicity. Three things interfere with this process:
a) Low intake of physically effective fibre that stimulates greater agitation within the digesta
b) High intake of sugars that promote butyric acid, which is known to slow rumen contractions
c) Increased intake of potassium, chlorides and soluble protein that take rumen fluid tonicity closer to the tonicity of blood,
slowing the rate of organic acid transport across the rumen wall
SO WHAT DO WE OBSERVE WHEN THIS OCCURS?
Nothing that screams your cows are unwell. Fecal output often contains a lot more fluid than you would normally observe – it may also contain a higher degree of undigested feed particles. Post grazing residuals may be higher than you would expect and milk solids yield may be a little down on what you would anticipate from the amount of ration on offer.
HOW CAN WE ADDRESS THIS CHALLENGE?
Offering a source of digestible, physically effective fibre is a good start. Feeds such as oaten hay tend to be more effective than straw. You don’t need huge volumes, 1kg DM per cow daily is often adequate.
Swap high sugar content feeds for products that contain slowly degradable starch – essentially cereal grain based products that contain substantial quantities of maize.
Include a mineral buffer in your ration that has a longer rumen retention time than sodium bicarbonate.
Maybe the least understood measure of recent years. Increased levels of soluble crude protein in spring pasture will be converted to ammonia by the rumen bugs. Some of this ammonia will be incorporated into microbial protein while any surplus will diffuse into blood. Ammonia is converted to urea at the liver and is transported by blood for recycling purposes or to be deposited into urine or milk, hence rations high in soluble crude protein contribute to increased MUN results.
Leaf stage at grazing will influence soluble crude protein content of pastures. Grazing before 2.5 leaf stage will spike MUN, as will short rotations when nitrogen fertilisers have been applied. (Remember the 18 days post-nitrogen application grazing rule of thumb.)
Other ration strategies will only reduce MUN if we can increase milk protein yield. Feeds that increase blood glucose and insulin concentrations are required to achieve this and feeds containing slowly degraded starch offer the greatest promise.
Keep analysing pasture samples for nutrient balance during spring and observe what cow health and production is telling you. Make adjustments to your rations as required and you will avoid the potential challenges of spring production.
For more information on maintaining healthy rumen function, especially during spring, talk to your local Dairy Nutrition Specialist.