Nutritionists understand the importance of having sufficient protein in the cow's diet. With that being said, it is possible to provide too much protein which will lead to undesirable effects.
Avoiding too much protein:
Firstly, high protein ingredients are more expensive in general as compared to other ingredients such as grain or forages.
With that being said, the main reason for supplying enough protein is to meet the cow's requirement for milk production.
Protein from feed mainly serves 2 role: 1) part of the protein from each ingredient is degraded in the rumen to serve as fodder for the microbes 2) some protein escapes or bypasses the rumen, which will provide additional protein to the animal in the small intestine.
Crude protein will measure the total nitrogen in the feed ingredient (what goes in the mouth) but it does not necessarily measure the accurate value it provides to the cow.
On the other hand, rumen-undegraded protein (RUP) and rumen-degraded protein (RDP) paints a better picture of what is available for the rumen microbes.
In the past, protein solubility has been used as a method to estimate RDP.
However, recent studies shown that soluble proteins are not always degraded in the rumen.
Some of the soluble protein actually provides RUP to the cow in the small intestine.
Hence, only equating the insoluble portion of the protein that bypasses the rumen to RUP will provide inaccurate RUP value of the feed ingredient.
From Table 1, less than half of the soluble protein in canola meal and linseed meal is broken down in the rumen.
Canola meal was once believed to provide very little RUP.
However, with this new information, less crude protein can be provided in the ration to supply sufficient RUP to the cow.
A better understanding of the role of RUP is key to reducing the overall amount of protein supplied in the ration, thus reducing feed costs.
In Table 2, 4 diets were formulated, consisting of the same basic ingredients.
Protein sources were added to bring the level of protein in the diet up to a uniform 16%.
Proteins compared were urea, soybean meal, cottonseed meal and canola meal.
All 4 rations provided 16% crude protein with urea provided the least while cottonseed meal provided the most.
Milk yield was much lower for the ration with urea as compared to diets with added plant source protein.
Fat yield was highest with diet containing canola meal.
Although cottonseed meal diet provided most protein, cows with canola meal diet produced milk with highest level of protein.
This could be due to a balance of amino acids from canola meal.
A good balance of RUP and amino acids will allow cows to produce milk more efficiently.
A high milk urea nitrogen (MUN) level means that the cows are using energy to synthesize MUN and getting rid of excess crude protein.
This is wasteful as energy can be used to synthesize milk.
Additional cost of overfeeding protein is in the nutrient management.
Excess protein means wasted protein lost in urine or feces as nitrogen.
There are now restrictions regarding amount of nitrogen that can be added to soil causing producers to face restrictions when it comes to spreading manure to the property which means additional cost to the farm.
Direct costs such as cost to add an ingredient or cost to dispose of waste products will eat into the profits of the farm.
Hence, it is crucial to formulate more efficient, lower protein diets to maximise farm's profitability.