MUN from individual cows may vary greatly from the mean and should not be used to interpret ration adequacy. Continuous monitoring of MUN from month to month can signal when forages may have changed and when the amount and type of protein fed should be altered. Protein amounts over what the cows and her rumen bugs can use results in a buildup od nitrogem wastes, like ammonia, in the rumen. Ammonia is absorbed through the rumen wall and is converted to urea by the liver. In an individual cow, high MUN could ne due to kidney problems or a ruptured bladder.
Reproductive inefficiency is one possible outcome.
Days to first service may be extended, average days open longer, and conception rates lower. Another possible consequence of high protein feeding is lameness due to laminitis or the production of thinner soles. MUN level may be used as a marker for high protein feeding when lameness is a consequence. Work with your veterinarian and nutritionist to identify your herd's problems. You might just find that MUN levels may be useful in helping you pinpoint the cause.