The role of rumen protozoa in the utilization of paspalum (Paspalum dilatatum) hay by cattle

Abstract

1. Six Friesian heifers (250 kg live weight) with permanent cannulas in the rumen and abomasum were allocated at random into two groups of three. One group was treated with Teric GN9 (ICI (Aust.) Ltd) to defaunate the animals during the first two of the four periods of the experiment, after which they were refaunated. The second group was treated with Teric at the end of the first two periods. The dietary treatments were: paspalum (Paspalum dilatatum) hay (4.1 kg/d) given alone and the hay supplemented with urea (20 g/kg dry matter).2. Defaunation was not complete but the approximate volume of protozoa in the rumen of treated animals was less than 6% of that in the untreated animals. 3.The amount of organic matter (OM) digested in the stomach was lower (P < 0.01) in animals with reduced fauna than in those with normal fauna. There were reductions in both the apparent OM digestibility in the total tract (from 0.56 to 0.52, P c 0.01) and the proportion of the digestible OM digested in the rumen (from 0.82 to 0.79, not significant) of animals with reduced fauna. Apparent digestibilities of acid-detergent fibre and neutral-detergent fibre were significantly lower (P < 0.01) in animals with reduced fauna.4. The amount of nitrogen disappearing from the stomach was significantly higher (P < 0.01) with the urea supplement; effects due to concentrations of protozoa were not significant. The flow of non-ammonia-N from the abomasum was higher ( P < 0.05) in animals with reduced fauna than in animals with normal fauna. The flows of bacterial N from the abomasum and the efficiencies of bacterial N synthesis were not significantly affected by the treatments. N retention was higher (P < 0.01) in animals receiving the urea supplement but differences due to protozoa were not significant. 5. Protozoal contribution to the microbial N flowing from the rumen of animals with normal fauna was estimated to be 24 and 27% with and without the urea supplement respectively. 6.Concentrations of rumen-fluid ammonia-N were reduced (P < 0.05) and those of volatile fatty acids were increased (P < 0.01) with reduction in protozoal numbers. Molar proportions of propionic acid increased (P < 0.05) and of butyric acid decreased (P < 0.01) with reduced rumen fauna.7. Rumen water volume was lower (P < 0.05) and the mean retention time of indigestible acid-detergent lignin tended to be higher in animals with reduced fauna. Rumen dry-matter pool and mean retention time of CrEDTA were not significantly different between treatments.

Effects of partial ruminal defaunation on urea-nitrogen recycling, nitrogen metabolism, and microbial nitrogen supply in growing lambs fed low or high dietary crude protein concentrations1

“…In addition, the decrease in urinary N excretion in PDFAUN lambs could also result from a greater proportion of urea-N output being recycled to the GIT and its increased sequestration for microbial protein synthesis in the rumen or hindgut or both. In agreement with our results, others (Ikwuegbu and Sutton, 1982;Punia et al, 1987) have also observed decreases in urinary N excretion as a result of defaunation. Total N losses were 5.2 to 9.0 g/d less (P = 0.004) in PDFAUN compared with FAUN lambs; as a proportion of N intake, PDFAUN lambs excreted 5.4 to 6.8 percentage units less (P = 0.06) N compared with FAUN lambs.…”

“…Although complete defaunation was not achieved in the present study, substantial reductions in ruminal protozoal populations were achieved, coupled with positive responses in N utilization. Also, partial defaunation can be beneficial as it has been associated with a greater flow of NAN to the duodenum (Punia et al, 1987), improved feed:gain ratio in sheep (Ivan et al, 2004) and increases in milk yield in dairy cows (Moate, 1989).…”

Effects of defaunation on digestion and growth, in sheep receiving a mixed diet (fresh Digitaria decumbens grass and concentrate) at four protein to energy ratios

“…Few trials give an indication on nitrogen urinary excretion [21,25,28,36]. Our data shows a lower nitrogen urinary excretion in ciliate-free animals as already observed [17].…”

“…Moreover, the better feed conversion ratio after defaunation may be mainly attributed to the higher yield of metabolic utilisation of absorbed nutrients, for maintenance and growth [5]. Indeed, the duodenal nitrogen flow increased in ciliate free rams, and both the dietary and the microbial nitrogen flows contributed to this increase [23,28,30]. On the one hand, in ciliate-free animals, due to a lower proteolytic activity in the rumen, the ruminal degradation of dietary protein decreased and consequently the flow of intestinal by pass dietary protein increased [25].…”

Total Protozoa Counts and Ammonia in the Rumen of Mature Dry Friesian Cows on Hay-based Rations

“…Furthermore, as pointed out in the introduction, faunated ruminants are known to have higher ruminai NH 3 concentration (with the one exception of DEMEYER et al (1982); for review, see WILLIAMS and COLEMAN (1988) or VAN NEVEL and DEMEYER (1988)) than ciliate-free animals, and high ruminai NH 3 concentrations have even tend ed to be associated with large protozoal numbers (VEIRA et al, 1983; mainly in the dor sal sac of the rumen: YANG and VARGA, 1989). Thus, increased levels of rumen NH 3 -N in the presence of protozoa may possibly result from protozoal action on dietary and bacterial proteins (PUNIA et al, 1987).…”