The feed evaluation experts at Dairyland Labs, Arcadia, Wis., may be onto something.
In a recent bulletin, they noted that, since starting Near Infrared (NIR) spectroscopy evaluations just one year ago, they have observed that silage samples with high ammonia (or soluble protein) consistently contain lower amino acid levels. They noted some amino acids appear to be affected more than others.
The best guess as to why this may be happening is that amino acids are being deaminated due to poor or extended fermentation during ensiling. As protein is broken down by bacteria and fungi, deamination occurs. Deamination is defined as the process of an amino group being removed from a molecule, which converts the amino acid into ammonia.
Clostridium species are especially known for their proteolytic and deaminating qualities. Clostridia is an anaerobic microbe associated with spoilage of silage harvested at high moisture levels, and can even grow in well-packed silages if the pH is above 5.0.
It appears that – due to their chemical structure – lysine, methionine, and cysteine are more susceptible to breakdown by bacteria and fungi. Isoleucine, leucine, and valine are less prone to deamination.
The Dairyland Labs advisors noted that the alterations these changes may cause to a nutrient profile may not do much damage when they remain within “normal” ranges. But silage quality is rarely distributed evenly, and “the long tail of poorer fermentations can get ugly.”
They showed an example in which a ration’s amino acids and ammonia were moved from a one standard deviation above average to one standard deviation below average. Even this relatively minor change resulted in a change in Cornell Net Carbohydrate and Protein System (CNCPS) predictions of supplies of 44.1 grams less metabolizable protein (MP), 5.3 grams less lysine, 2.9 grams less histidine, 1.3 grams less methionine, and 2.1 pounds lower MP allowable milk.
