A picture puzzle with a cow pushing her nose against another cow has been in our book CowSignals since the first print, over 10 years ago. We continuously update the book, but this one has stayed in as a beautiful example of a UNO. An unexplained, or unclarified, notable observation. You see something, it is most certainly there, but you do not have an explanation for you.
The most likely explanation is that the cow is sleepy or “light in the head” due to a high level of BHBA in the blood. BHBA = beta-hydroxy butyric acid. This is a ketone body. Ketone bodies are energy carriers in the blood of the cow, like fatty acids and glucose. Acetone is another ketone body. Some people can smell acetone very well. I can’t.
When cows have a negative energy balance, more ketone bodies are formed. And when this negative energy balance is too negative, the levels of ketone bodies exceed a certain treshold and the cow gets clinical ketosis.
Other explanations for nose pushing are in the area of physical discomfort, mostly due to discomfort in the abdomen. This is observational. One sees more cows showing this behavior in herds with ruminal acidosis and other signs of nutritional imbalances and problems. But you can argue that in these conditions there are also more cows with high levels of ketone bodies. Which makes sense.
But negative energy balance is not the only reason for high blood levels of BHBA. High amounts of sugar in the feed is another one. This sugar is fermented in the rumen into butyrate, which is absorbed and metabolized by the ruminal wal into BHBA. High amounts of sugar in the ration lead to high amounts of BHBA in the blood.
My own cows where showing this head resting/nose pushing behavior last year, when I was feeding them strictly grass silage with 216 grams sugar per kg of dry matter. That is a lot of sugar! This silage was sweeter than a glass of cola. When I reduced the amount of this grass silage the behavior disappeared, when I fed nothing but this silage it reappeared. See the video.
I personally love UNOs, as these challenge the brain, give rise to great conversations and discussions, and trigger us to always keep an open eye for things that we are not specifically looking for.