Milk Urea Canterbury

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Common theme throughout Canterbury this season, ‘the stars are aligning’… Production up 13.7% and 5.3% for North and South Canterbury MilkMap farms respectively. Fonterra announces a $9.50 mid-point for this season, and the hills have finally got snow across them to fill our irrigation schemes.

Clearly, a couple things are going on to drive production this season. Warm dry weather throughout October, well-conditioned animals coming out of winter, weather systems have been limited to one day events, fertiliser programs keeping up nicely and pasture growth well up from previous seasons. Although noticeably, milk urea’s are well up from last season. The below graph highlights the moving average in milk urea (mg/dl) from our Canterbury cohort.

Milk Urea (MU) in its broadest sense regards the excess ammonia and urea in saliva from digestion, with the toxic ammonia being converted to inactive urea which can then be flushed from the cow’s system within milk or as urine/faeces. High levels of MU >30 may indicate excess crude protein in the ration and MU <10 could suggest cows are deficient in protein. However, the simplicities end there as many other factors are at play which can drive this metric up or down.

Further, why should we care. Well with high MU’s we can argue that there is excess nitrogen in the system in the form of non-protein nitrogen (NPN) not being converted by microbes. Excess nitrogen can have unfavourable consequences for the growing embryo. Most farms have recently finished their first 3 weeks of mating, but with such consistently high MU we could be looking towards a series of long returns or phantom cows up on last year. The insemination holds to the first submission but soon after loses it to excess N in the ration. A multitude of other factors can also play into this, but MU is clearly something to consider closely.

Below some key thoughts and recommendations.

Dietary Crude Protein:

For the better part of the season, pasture will be non-limiting from a crude protein (CP) perspective. Of the CP, 16% can be expected to be readily broken down in the rumen, which will drive up ammonia production. Microbes require ammonia, but in the NZ system we will always spill over excess into the liver which is then converted to urea and ends up in the milk.

View excess ammonia as a cost to the cow, she requires energy away from milk production to expel it. In an overseas TMR system this is looked at unfavourably, and MU can get as low as 4-7 mg/dl while still doing exceptional production. However, what we have that overseas systems don’t have is a low-cost feed source from pasture. Therefore, in NZ we look at the bigger picture and say that this small cost is something we can live with.

Energy Intake Relative to Protein:

The microbes within the rumen drive our whole system. Which gives justification for balancing rations accurately if we want to push production efficiently. When your cow consumes a diet extremely high in rumen degradable protein (spring pasture), but her energy intake is not sufficient to meet her demands, then the microbes cannot efficiently utilise the Nitrogen that comes on board. Again, as above, poor utilisation of nitrogen leads to excess ammonia building up within the cow which she then expels in the milk.

Be careful though. If energy, fibre and protein levels on paper are sufficient to meet her production and maintenance demands but you still have low MU, then you likely have a very efficient herd at

converting feed to milk. Walk a line when you compare your figures with the neighbours, MU can be assessed in many different ways.

Environmental Factors:

Moving into the hotter months, we expect MU to continue to rise. Pasture quality drops away, so fermentable energy sources become even more important to help balance an excess of protein. However, heat stress will also disrupt rumen function. Seed head emergence leads to excess fibre in the diet, which slows rumen fermentation, reducing the utilisation of protein available to the cow.

Feed Management:

If you have in shed feeding or a feed pad, take a look and make sure cows are not sorting through the feed. A cow can inadvertently eat an excess of protein or limit energy intake from grain by sorting alone, if this is the case then MU will lift. Make sure feed bins are empty following each milking, regular checks to see if all augers are dispersing feed accurately, check for bridging within silos. On feed pads make sure the ration is blended well, and all cows have reasonable access to the feed face.

Pasture allocations should be offered with consistency whenever possible. When the rumen is full the cow is in the most efficient state to utilise her feed, therefore try to limit how regularly cows have to clean up last night’s break before being moved to their daybreak.

Water Quality and Intake:

Often overlooked, but limited water and/or poor-quality water will reduce the cow’s ability to excrete the urea. Further, a cow will typically drink 50% of her daily allocation 1 hour post milking due to a cascade of oxytocin release at milk let down. She requires water quickly to restore the osmolarity within the blood if to continue milking efficiently during hotter days.

A Milk Urea bound of 20-25 mg/dl is abstract and should not be a target. Try to look at your whole system before reaching conclusions. There is a lot going on within the cow and many different levers will pull this metric one way or the other. Bare it in mind but use with caution.