Will High Acetate Silages Result in Dry Matter Intake Depression?
By Bill Seglar & Bill Mahanna
Dairymen, nutritionists and veterinarians have theorized that dry matter intake (DMI) depression in cattle may be the result of high acetic acid levels in corn silage. This theory is the result of literature reviews (containing considerable European grass data) that have associated silage fermentation factors with reduced DMI of cattle1. However, other dairymen and consultants have noted that feeding high acetate corn silages (greater than 3% DM basis), yet otherwise relatively high quality silages, seems to have no effect on intake or production.
Forages with elevated levels of acetic (and other) acids could be the result of several factors: 1) prolonged fermentations from being ensiled too wet, 2) contamination with undesirable epiphytes such as acetobacter or yeast or 3) inadequate compaction or poor feed-out management allowing for increased oxygen penetration into the silage mass. Studies prove DMI is not depressed as a result of excessive moisture of the forage at ensiling but rather due to the end products of extended fermentations (acids and protein degradation products). It appears DMI is depressed with increased (free) acetic and butyric acid concentrations because the addition of salts of acetic and lactic acid seems to have no effect on DMI1
Depressed DMI has also been associated with forages high in ammonia, amides, and amine compounds (such as histamine) that are end-products of silage protein degradation that occurs during fermentation. If fermentation is extended, these protein degradation products typically increase in concentration similarly to acid concentrations. Ammonia nitrogen (expressed as % of total nitrogen) of less that 5% indicates high quality silage. However, ammonia, by itself, does not decrease intakes (perhaps because it is bound as ammonia lactate), thus suggesting that the associated proteolytic end products largely contribute to DMI depression. At issue with much of the literature is that several factors are present that can depress DMI including poor quality, improper management, high acids levels and extensive protein degradation. It is difficult to pinpoint the primary cause of DMI depression when so many contributing factors are at play.
A 1998 University of Wisconsin study looked at how much acetate was required to depress DMI in fistulated Holstein cows2. The study indicates that about 1,700 grams of acetate is produced by the rumen per day. DMI decreased from 54.8 to 51.7 lbs./day (P < 005) when the fistulated cows on a high forage diet were infused with and additional 2,160 grams of acetate.
Based on acetate infusion values from the Wisconsin study, one can demonstrate that the amount of acetate contributed from corn silage is minimal compared to the amount produced by the rumen. Using an example where a cow is fed 40-lbs. corn silage with 3% acetic acid, this calculates out to 163 grams of acetate/day being contributed from corn silage. This is only 7% of what was required to depress DMI in the Wisconsin study. If silage contains 7% acetic acid, the daily contribution from corn silage will be 381 grams acetate and is still only 18% of what was required in the study to depress DMI. These calculations suggest it is unlikely high acetic acid in silage is the primary cause of DMI depression. Since nitrogenous end products are known to depress DMI, one needs to determine if ammonia nitrogen, expressed as a % of total nitrogen is elevated. This measure indicates the presence of non-palatable nitrogenous end products such as amines, amides, and other nitrogen containing compounds.
|% Acetic Acid||3%||7%|
|Gm. Acetate Infused - Wisc. Study||2,160||2,160|
|Gm. Acetate from Silage||163||381|
|% Acetate from Corn Silage||7%||18%|
- Erdman, Rich. 1993. Silage Fermentation Characteristics Affecting Feed Intake. Silage Production From Seed to Animal. Proc., From National Silage Production Conference, Syracuse, NY, Feb. 23-25, 1993. P. 210-219.
- Sheperd, A.C., Combs, D.K. 1998. Long-Term Effects of Acetate and Propionate on Voluntary Feed Intake by Midlactation Cows. Jour Dairy Sc., Vol.81, #8, p. 2240-2250
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