Partial Substitution of Milk Protein with Spray-Dried Fish Solubles or Soy Protein Concentrates in Calf Milk Replacers

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Abstract
Male Holstein calves received (starting at 4 days of age) milk replacers as the only nutrients for 6 wk. Percent and source of protein were 13% milk; 19% milk; 19% with 13% from milk and 6% from spray-dried fish solubles; 19% with 13% milk and 6% soy protein concentrate; 19% with 13% milk, 3% spray-dried fish solubles, and 3% soy protein concentrate; 23% milk; 23% with 13% milk and 10% spray-dried fish solubles. In a 3-location comparison, growth and health were poorer from fish solubles than from all milk protein with soy protein intermediate. Amino acids in blood plasma sampled at 3 and 6 wk of age showed higher total essential amino acids for 19 and 23% than for 13% milk protein or milk substitute diets. A xylose absorption test at 6 wk showed no impaired capacity of gut absorption from feeding lower quality protein. Organic matter was less digestible for diets containing fish solubles (75.7%) and soy protein concentrate (78.7%) than for milk protein (90.6%). N retention showed similar patterns. Superior performance on milk protein was associated primarily with higher digestibility of organic matter, greater N retention and higher concentrations of essential amino acids in plasma.