Protein metabolism and productive performance of rats consuming raw cowpea (Vigna unguiculata) grain meal to substitute commercial soybean cake

Abstract

Thirty six male Sprague-Dawley rats of 100 +/- 5 g live weight were selected, according to a completely randomised design with three replications and six rats per treatment, to study the physiological effect of the consumption of raw grain meals of Vigna unguiculata var INIFAT-93, as substitute of the commercial soybean cake, on protein metabolism and productive performance. Treatments consisted of six experimental diets, a maize and commercial soybean cake control and five rations in which the latter was substituted by raw grain meal of cowpea at 20, 40, 60, 80 and 100 %. Out of the indicators measured, neither the apparent biological value (ABV) nor the nitrogen balance (NB) were altered in any case, ranging between 50-54 % and 2-2.4 g, respectively. However, there was a decrease in the apparent faecal nitrogen digestibility (AFND) and the protein efficiency ratio (PER) of 10 and 20 %, respectively, in all treatments, compared to the control. In the first case; the values were from 81 to 71 % and, in the second, from 2.2 to 1.7. Carcass weight and average daily gain decreased starting up in 80 % substitution of the soybean cake by cowpea from 71.2 to 58.9 g and from 3.9 to 3.0 g/d, respectively. All severe alterations were found at levels higher than 80 % substitution of soybean cake by cowpea. Therefore, it is concluded that the substitution at the inferior level (60 %) in diets for rats, as model for physiological studies of non-ruminant species, is feasible.