Using Daily Test Results to Manage Fertility

April 21, 2021

Access to daily test results yields information about your cow’s health. Milk is a body fluid that is a direct reflection of the cow’s metabolism. Besides SCC, the butterfat, protein and MUN are important indicators of the cow herds’ well being. Mother nature says that the cow’s first priority is maintenance, the second is production and the third is reproduction. We used to say that you have to “feed them to breed them”, but we know now that you have to “feed them RIGHT to breed them.”

Butterfat is an indicator of the cow’s rumen health. High butterfat means we have the right mixture of protein, energy, and fibre. A healthy rumen means we have a healthy cow. As a practitioner, I like to see a BF of 4% or higher. Lower than that we are concerned with acidosis resulting in lameness and poor production.

Milk protein is an indicator of dietary energy. The lower the dietary energy, the lower the milk protein. Low dietary energy results in excessive weight loss in early lactation. A cow that is properly conditioned at calving can maintain a high milk protein value as it reduces body condition. Once the dietary energy level matches production then the cow puts the body condition back on and then her milk protein level rises. I believe that 3.15% is the minimum milk protein value that will allow proper breeding results; if this gets any lower, cows show poor heats and do not have the energy to sustain a pregnancy.

Dietary protein will dictate production. If there is an excess of dietary protein, there will be high milk production but the cow will have a lower milk protein value.

This brings us to the MUN value. MUN is the milk urea indicator. All protein is broken down to urea by the cow’s digestive system. It circulates in the blood and gets excreted in the milk, feces and urine as ammonia, and reflects what is happening physiologically. We can measure urea in the blood as BUN. A cow can tolerate a MUN up to 10. Any amount above this is excreted from the body through the liver and takes PROGESTERONE along with it.  Progesterone is the hormone necessary to maintain a pregnancy! Common dietary protein is your alfalfa, soybean meal, canola meal or feed grade urea. Protein, by definition, is either soluble (digested in first 2 hours), rumen degradable or bypass. The key is to keep an even flow of protein available—so there should be 30-35% of each component. The cow’s rumen works much like a combine where a nice even flow of material for processing is available constantly. Slugs of feed result in wasting of some of it.

To recap, butterfat is rumen health (greater than 4%), milk protein is ration energy levels (greater than 3.15%) and MUN is ration protein (less than 10 MUN).  Natural heats and visible synchronized heats will be the result.

Final thought. The pregnant cows will calve whether they are checked or not. Finding your open cows and the cause of them being open is what keeps you profitable!


If you have any questions on these or other topics, please do not hesitate to contact one of our Veterinarians.

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