Effects of <i>Isotricha</i>, <i>Eudiplodinium</i>, <i>Epidinium</i> + <i>Entodinium</i> and a mixed population of rumen protozoa on the in vitro degradation of fish meal, soybean meal and casein

Abstract

An in vitro rumen simulation system was used to study effects of different types of rumen protozoa (Isotricha, Eudiplodinium, Epidinium + Entodinium, total mixed fauna) on the degradation of three feed proteins (fish meal, soybean meal, casein). A comparison of the fermentations containing different feed proteins was made with the control fermentations containing no added feed protein. Rumen contents used in the fermentations originated from defaunated sheep, or from sheep containing a single genus of protozoa (Isotricha spp. or Eudiplodinium spp.), a mixture of genera Entodinium spp. and Epidinium spp., or a total mixed fauna. In the presence of the total mixed fauna the degradabilities were 82.0, 51.1 and 26.5% for casein, soybean meal and fish meal, respectively. The absence of protozoa resulted in decreased (P &lt; 0.05) degradation of fish meal and soybean meal but had no effect (P &gt; 0.05) on casein. The single genus Isotricha spp. decreased (P &lt; 0.05) the degradation of all three protein sources compared with the defaunated fermentations or those containing the total mixed fauna. Eudiplodinium did not affect (P &gt; 0.05) fish meal or soybean meal, but it decreased (P &lt; 0.05) the degradation of casein compared with the defaunated fermentations. However, when this organism was compared with the total mixed fauna the degradability of fish meal was not affected (P &gt; 0.05), but that of soybean meal or casein was decreased (P &lt; 0.05). The combination of Epidinium + Entodinium decreased (P &lt; 0.05) the degradation of all three protein sources when compared with the total mixed fauna. When compared with the defaunated fermentations, the protozoal combination had no effect on fish meal (P &gt; 0.05), but the degradation of soybean meal and casein was decreased (P &lt; 0.05). Total volatile fatty acid (VFA) production was systematically reduced (P &lt; 0.05) by the sole presence of Isotricha. The presence of other genera or the total mixed fauna had variable effects on the production of VFA or gases for different sources of protein. It was concluded that the mode of action of a single species or genus of protozoa on nitrogen metabolism in the rumen is different from that of total mixed fauna. The protozoal effect on protein degradation varies according to the type of protozoa present and the nature of the protein. Key words: Protozoa, in vitro degradation, fish meal, soybean meal, casein, rumen