Effects of potential dietary antiprotozoal supplements on rumen fermentation and digestibility in heifers

Antiprotozoal activity of dietary supplements of tannin, saponin, and linoleic acid were tested with four ruminally and duodenally cannulated heifers in a 4 × 4 Latin square experiment. The four dietary treatments were control (basal diet), quebracho (source of tannin), quillaja (source of saponin), and safflower oil (source of linoleic acid). The basal diet was based on rolled barley grain and barley silage. Three additional experimental diets were prepared by incorporating in the basal diet (g/kg of dry matter) quillaja extract (8); quebracho (6); or high linoleic acid safflower oil (27); replacing equal amounts of barley grain. The diets were fed as total mixed rations in four experimental periods of 47 days. Safflower oil caused a log reduction in numbers of protozoa as compared to the control, whereas the protozoa populations in the rumen of heifers fed quabracho, quillaja were only slightly lower than that of the control. On all diets, the proportion of Entodinia in the total protozoa population was more than 0.85. Cellulolytic, amylolytic and deaminative enzyme activities as well as concentrations of ammonia and volatile fatty acids in ruminal fluid were not affected by treatment. There was no indication that dietary supplements altered digestibility or the flow of non-ammonia nitrogen or bacterial nitrogen to the duodenum. It was concluded that although the supplements tended to lower the number of protozoa in ruminal fluid, this decline was not sufficient to significantly decrease predation of bacteria. Consequently, neither reduction in rumen ammonia nor an increase in duodenal flow of bacterial nitrogen to the duodenum was observed. Administering these additives in concentrations that are high enough to reduce protozoal numbers, without having adverse affects on feed intake or digestibility, may be difficult. © 2006 Elsevier B.V. All rights reserved.