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Thermoalkali-processed soy protein concentrates (experimental soy concentrate) were compared with sodium caseinate and a commercial soy protein concentrate (Promocaf) as protein sources in milk replacers, supplying .75 of the protein in 20%-protein replacers. Week-old Holstein calves were fed the replacers in two 4-wk trials. Average gains of calves fed experimental soy concentrate (processed 5 min at 85 C and pH 10.5), caseinate, and Promocaf replacers were 3.0, 6.6, and 6.6 kg. Calves fed experimental soy concentrate replacers heated for shorter or longer times lost .8 to 3 kg weight during the first 2 wk but gained .6 to 1.7 kg during the, last 2 wk. Occasionally calves had loose feces, mainly during the first 2 wk, with no significant differences between groups. Efficiency with which rats used protein of nonfat, spray-dried, milk-replacer ingredients correlated .96 with growth of calves fed corresponding replacers. Growths and protein efficiency ratios were similar when rats were fed lyophilized, thermoalkali-processed soy products heated for various times up to 1 h at either 85 C and pH 10.5 or 75 C and pH 9. Rats fed the experimental soy concentrate performed satisfactorily; calves, less satisfactorily. The protein efficiency ratio of experimental soy products determined with rats correlated .68 with in vitro protein digestibility, −.60 with soluble nitrogen, and −.59 with trypsin inhibitor activity. |
