RESPONSE OF DAIRY COWS TO FORMALDEHYDE-TREATED CANOLA MEAL DURING EARLY LACTATION

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Abstract
Forty Holstein cows were assigned to one of four isocaloric diets 2 wk postpartum in a 2 × 2 factorial arrangement. Factor I was dietary crude protein (CP) level, either 17.4% or 14.6% CP. Factor II was formaldehyde (FA) treatment of canola meal, either treated or untreated. The experimental period lasted 12 wk. Treatment with FA had no effect on milk yield, milk composition, dry matter (DM) intake or on apparent digestibilities of DM, nitrogen (N) or acid detergent fiber (ADF). FA treatment reduced ammonia-N (NH3-N) levels in rumen liquor (P < 0.05), tended to increase (P < 0.1) plasma levels of total essential amino acids and had no effect on plasma urea. High dietary CP increased (P < 0.05) milk and lactose yields, had no effect on rumen liquor NH3-N levels and increased (P < 0.05) plasma levels or urea and total essential amino acids. Treatment with FA appears to have increased absorption of total essential amino acids from the gut but did not increase milk production. Possibly, amino acid supply to the mammary gland did not limit milk synthesis in this experiment. Alternatively, FA treatment may have failed to increase absorption of the amino acids whose availability did limit milk synthesis. FA treatment apparently destroyed 58% of canola meal tyrosine and 29% of the lysine and this may be partially responsible for the lack of a response in milk production. Key words: Holstein, formaldehyde, canola meal, milk production, protein level, amino acids