Lactational, In Vitro, and Chemical Evaluation of Untreated and Formaldehyde-Treated Casein Supplements

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Abstract
Supplemental feeding of casein treated with 0.8% wt/wt formaldehyde was compared with untreated casein or no supplement for 8 Holsteins averaging 29 kg milk/day. Compared to untreated casein, formaldehyde-treated casein supplementation had no significant effect on yield of milk or milk components except for a small increase in secretion of milk urea. When supplemental treated casein was compared with no supplement, yields of milk, total protein, true protein and urea in milk increased. Urea and albumin concentrations in plasma were not affected by dietary treatments, and there was a small correlation between urea in plasma and milk. Ruminal in vitro and chemical tests on the treated casein and small batches of casein treated with 0.2-4.0% wt/wt formaldehyde showed curvilinear decreases in the in vitro release of ammonia and total amino acids with increased formaldehyde. Although the release of ammonia and amino acids from treated casein in the feeding study was near 0, release of ammonia was negative for preparations treated with more than 1.5% formaldehyde. Formaldehyde treatment resulted in smaller losses in available lysine than expected, and most of the reacted formaldehyde was bound to amino acid residues other than lysine.