At this time of year, when cows are usually in and out grazing due to weather conditions, the question often arises as to what percentage of crude protein should be in the dairy nuts you are using?
Crude protein is a very basic measure of the nitrogen component of a feed and the metabolisable protein value, which is measured through protein digestible in the intestine (PDI) and is probably a more accurate description of the quality of a protein source.
At this time of the year, many farmers will have a 16% protein concentrate in their meal bin which is ideal when cows are being housed and going out for on/off grazing.
Typically cows will be eating an 18% crude protein nut, when milking on a complete indoor diet consisting of just silage and concentrates.
Energy is the first limiting factor to production in early lactation and is the focus in terms of feeding the dairy cow well in spring and once this is got right along with fibre (NDF) in the diet, the focus can be to balance protein in the diet.
Crude protein
When ruminants have an adequate supply of energy in the rumen, they can utilise ammonia from protein and nitrogen sources to produce microbial protein to support production.
Every unit of feed energy (UFL) a cow requires, she will need 100-105g of PDI and any excess supply of protein above this requirement is an energy cost to the cow for converting ammonia that is not used back to urea for excretion.
This means that a 17.5 UFL intake should be matched to a diet PDI content of 1,840g per day and this will usually translate to a diet of 15.5% to 17% in crude protein terms.
Silage is typically around 11-12% crude protein which is why a higher protein nut of about 18% crude protein is required to make up the required 15.5% to 17% of crude protein needed in the diet.
However, spring grass has crude protein content of about 20-22% and rising, which means that feeding an 18% protein nut may be wasteful.
This is why altering the crude protein of your nut is crucial as the cow goes from grazing to on/off grazing and silage and to silage full-time.
In a grazing diet it is nearly impossible to limit the amount of excess protein in the diet as weather and grazing can be inconsistent.
When grass can be consistently grazed, and grazed grass makes up the majority of the spring diet, a 14% crude protein nut will be sufficient.
When cows are out at grass, dietary protein value will naturally be higher with the inclusion of grass in the diet, which offers the scope to reduce the crude protein down to 14%.
In the event that cows are rehoused due to poor condition and you only have a 14% nut, there is no real need or benefit to adding extra protein to counter the reduced PDI of grass silage.
Instead, farmers should turn their focus to getting cows back out to grass when they can, implementing on/off grazing where needed.
For poorer ground and heavier soil farms in the spring when cows are in and out altering between silage and grass, then a high energy 16% crude protein nut is advised.
Buying in a higher crude protein nut is usually more expensive and if the excess protein is only being excreted out through urea, then it is wasteful and options to feed a high energy but lower protein nut should be explored.
If grass quality is good and cows are going to optimal cover over a consistent period, then a 12% crude protein nut should be discussed with your advisor to see if it is doable.
No matter what crude protein nut you feed, as you decrease the crude protein in conjunction with the amount of grass in the diet, the UFL value should always be above 0.94 so intake capacity is not limited.
