We’ve been working with the Nasco Digestion Analyzer (NDA), formerly the Cargill Manure screener, as part of projects to evaluate fiber digestion on-farm. Last October I wrote a Farm Report article discussing an ongoing study looking at fecal analyses relative to fiber digestion and milk production. We will discuss those results in a future issue. Here I would like to review some analyses of the particle fractions obtained with the NDA manure separator.
The NDA separator is comprised of 3 tiers of metal screens: top 4.76 mm, middle 2.38 mm, and bottom 1.59 mm. The sampling method we use is to obtain a ladle full, ~50 ml of feces from at least 10 fresh poops, combined into a single representative sample for the pen. (Number of samples depends on pen size, 10% is recommended). This results in about 500 g of feces to gently wash through the sieves. As the sieved particles are wet, only visual assessment of quantity and quality can be made on farm. Amount of DM or nutrients (starch, NDF, lignin) need drying and lab analysis.
Cargill originally developed a guide with pictures depicting “good” fecal particle distribution in the separator. Their recommendations are that <10% of particles should remain on the top screen, <20% on the middle screen and >50% of particles should remain on the bottom screen. The Cargill interpretations are included; we have not been able to find them on the web.
We thought it would be interesting to compare fecal particle distributions with the NDA between our high cows (Pen 2) mid cows (Pen 1), late cows (Pen 5) and Close-up Dry cows (CUD) relative to the Cargill recommendations and also analyze the particles retained on each sieve for DM, NDF, NDFD24. For this project we added a cloth fabric to retain particles that escape the bottom NDA sieve and then calculated amount of lost particles that passed through all. Starting with 500 g of as is feces, we gently washed the particles through the sieves with a shower nozzle. After about 5 min particles appeared clean and rinse water ran clear. We then observed and collected particles from each sieve into pre-weighed tins to document amount of DM retained. From initial fecal %DM and known starting weight, amount of initial DM of rinsed feces was calculated and used to calculate % of DM retained on each sieve.
Figure 1 displays %DM retained on each sieve and lost. For Pens 1, 2 and CUD there was <10% retained on the top screen, meeting the ideal recommendation. Pen 5, however, had >10% retained. All pens showed <20% retained on the middle sieve and <25% retained on the bottom. About 15% was retained on the fabric for each pen with 38-45% of DM lost across all pens. In spite of the CUD group diet containing about 15% chopped straw, these results show <5% on the top screen resulting from longer rumen retention time, greater rumination of fiber resulting in fewer long particles. Of note, Pens 1 and 2 diets differ from Pen 5 in that they contain BMR corn silage and higher quality haylage, possibly accounting for a greater amount on the top sieve.
As we looked at the NDFD24 of each fraction and as a percent retained it is interesting to note that that the higher production, higher intake/rate of passage cows in pens 1 and 2 had more digestible aNDF retained on the sieves than did the low and dry cows (Figure 2). Not that we want our high cows to be as efficient as dry cows in terms of fiber digestion, but what amount of digestible aNDF in feces is acceptable or related to maximized milk production and rumen health?
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Original Cargill recommendations
and interpretations:
Top Screen with: Ideal <10%
If >10% may indicate these issues
• Inadequate effective fiber
• Sudden ration change
• Low rumen degradable protein
• Inadequate sugar or starch
• Excess unsaturated fat
Long fiber particles, whole/large kernel fragments, cotton seed, soybeans
• Too much effective fiber
• Inadequate grinding of grains
• Excess grain feeding rates
• Rumen acidosis
• Imbalance of NFC:RDP
• Wet TMR (<40% DM)
Middle Screen with: Ideal <20%
If >30% of total sample
• Imbalance of NFC:RDP
• Poor balance of starch and protein degradability
• Inadequate grinding of grains
• Excessive grain feed rate
Bottom Screen: Ideal >50%
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