Effect of Energy Concentration and Source of Nitrogen on Numbers and Types of Rumen Protozoa

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Abstract
Two rumen-fistulated Holstein heifers were fed 3 protein-free semipurified diets: 70% roughage, 30% concentrate; 50% roughage, 50% concentrate and 30% roughage, 70% concentrate. Wheat straw was the roughage, and the concentrate was a pelleted mixture of corn starch, dextrose, fat, urea, vitamins and minerals. Each animal received the 3 dietary treatments in a randomized complete block design. On days 1, 3 and 5 following a 21-day adaptation, rumen fluid samples were taken before feeding and at 1, 2, 3, 4 and 5 h after feeding. Total protozoa concentrations for low, medium and high concentrate diets were 1.5, 2.5 and 4.1 .times. 105/ml. Dasytricha concentrations were not affected by diet, but Entodinium, Diplodinium, Isotricha, Epidinium and Ophryoscolex increased with increases of the concentrate proportion of the diets. Entodinium, the predominant protozoa with all diets, increased as concentrate proportion of the diet increased. In a 2nd experiment the 2 heifers from experiment 1 were fed semipurified diets that contained either urea or soybean meal as the N source. There were larger populations of Dasytricha and Isotricha when the diet contained soybean meal and larger populations of Charon, Entodinium and total protozoa when the diet contained urea. In both experiments, holotrichs were highest 1-2 h after feeding, and entodiniomorphs were highest before feeding and 4-6 h after feeding. An active protozoan population can exist in the rumen of cattle fed diets virtually devoid of natural protein, and protozoa are influenced by energy and N source.