Determination of the optimum level of a soybean oil drench with respect to rumen ecosystem, feed intake and digestibility in cattle

Nguyen Thi Hong Nhan, Nguyen Trong Ngu, Nguyen Thiet, T R Preston^* and R A Leng^**

College of Agriculture, Cantho University, Cantho, Vietnam
nthnhan@ctu.edu.vn   ;   ntngu@ctu.edu.vn   ;   nthiet@ctu.edu.vn
^*UTA Colombia, AA48 Socorro, Santander, Colombia
^**PO Box 814, Coolum Beach 4573, Australia

Abstract

Four rumen-fistulated Sindhi-Yellow cattle were fed a basal diet of rice straw and grass (1:1 DM basis) and given a single drench of 2, 4, 6 or 8 ml/kg LW of soybean oil in successive 30 day periods according to a 4*4 Latin square arrangement. Days 1 to 10 in each period were for adaptation (or re-faunation for 2nd, 3rd and 4th periods). The single oil drench was given and measurements of rumen ecology, feed intake and digestibility were done in successive sub-periods of 5 days (days 1-5; 6-10, 11-15, 16-20 after defaunation).

Oil treatment removed most of the protozoa, lowered the concentration of ammonia and increased the numbers of bacteria. There were linear increases in DM intake and DM digestibility according to the level of oil drench in the periods of 10 to 15 days and 16 to 20 days after giving oil. The use of 6 ml of oil/kg is suggested as the most appropriate dose level.

Keywords: bacteria, digestibility, feed intake, oil drench, protozoa

Introduction

Eliminating protozoa from the rumen with chemicals such as Dioctyl sodium sulfosuccinate (Demeyer and Van Nevel 1979) or Ethoxylated nonyl phenol (Bird et al 1979) is a difficult procedure, which may result in the death of animals. Thus, despite the potential benefits in animal productivity (Bird and Leng 1984), there was little impact of this technology at farmer level (Leng R A, personal communication).

Soybean oil containing elevated proportions of long-chain poly-unsaturated fatty acids has been used  for defaunation in sheep (Broudiscou et al 1990). However, a practical way of applying this technique has been developed only in Vietnam (Nhan et al 2001) and confirmed in Cambodia (Seng Mom et al 2001). In those studies, it was shown that an oil dose of 5 ml/kg LW had positive effects on cattle performance in terms of faster growth rate and better feed conversion ratio. So far, an appropriate oil level for drenching and how it affects the rumen ecosystem has received little attention. Therefore, the following trial was set up to examine responses of cattle to different levels of oil drench.

Materials and methods

Animals and diets

Four Sindhi x Yellow cattle of 180 - 200 kg fitted with permanent rumen cannulae were allocated to treatments according to a 4*4 Latin square design. Each period consisted of 30 days in which, the first 10 days were for adaptation followed by oil administration and data collection of rumen ecology, feed intake and digestibility in successive 5-day sub-periods 1-5; 6-10; 11-15 and 16-20 days after oil administration. The animals were fed on a basal diet of rice straw and natural grass (1:1 DM basis) and given a single drench of soybean oil at 2, 4, 6 or 8 ml/kg LW. The chemical composition of the experimental diets is presented in Table 1.

Experimental procedure

Feces, feed offered and refused were recorded daily from day 1 to day 20 for digestibility evaluation. Samples of rumen fluid (100 ml) were taken by a plastic tube and syringe every day in the morning before feeding, and 2h and 6h post-feeding. Protozoa biomass and numbers of bacteria were counted under a microscope using 0.1 and 0.2 mm counting chambers. pH value was determined by a digital pH meter. Ammonia concentration was measured by steam distillation of a 20 ml sample rumen fluid, with collection of the ammonia in boric acid solution and titration with 0.1 N H₂SO₄.

Data analysis

Values of pH, protozoa and bacteria number, ammonia were averaged over sampling periods of 5 collection days and analyzed by the General Linear Model of the ANOVA program in the Minitab Software (version 13.2).
 

Results

Rumen ecosystem

The oil drench eliminated most of the protozoa population in the rumen (Table 2 and Figure 1) and, as a consequence, the numbers of rumen bacteria were remarkably increased (Table 3 and Figure 2). In fact, the higher the oil administration the lower the numbers of protozoa observed in all sub-periods. At levels of 6 and 8 ml of oil/kg LW, the protozoa population was less than 1*10⁵, while these values were 4 times higher in treatments of 2 and 4 ml of oil/kg LW. In an opposite trend, higher bacteria populations were counted in treatments of 6 and 8 ml of oil/kg LW with significant difference (P<0.01) in all sub-periods except for the first one.

Intake and apparent digestibility

In general, feed intake was affected in all treatments in the first sub-period as cattle were stressed and did not show any wish to drink or eat during the first day after being drenched. However, this activity improved daily and by day 5 the cattle were totally recovered. DM intake was therefore lowest in the first sub-period (Table 4) and did not show any significant differences among 4 levels of oil administration (P>0.05). In the 3^rd and 4^th sub-period, DM intake increased with the increase in the oil drench (P<0.01). For example, at 2 ml of oil/kg LW, cattle consumed 2.99 kg DM/d, but this value increased up to 3.13, 3.40 and 3.64 kg DM/d in treatments of 4, 6 and 8 ml of oil/kg LW, respectively. In addition, levels of oil supplement had a close relationship with DM intake as reflected by the determination coefficient value (R²=0.98) (Figure 3).

In spite of similar feed intake in some sub-periods, DM digestibility was found statistically different at all oil levels in the whole period of 20 days after the oil drench. Significantly higher DM digestibility was measured in treatments of 6 and 8 of oil/kg LW particularly in the last sub-period; the difference was about 15% units in digestibility between the lowest and highest oil supplement (P<0.01) (Table 4). A high correlation between DM digestibility and different oil levels was also recorded as shown in Figure 4.

Discussion

The protozoa population was reduced by more than 70% due to the toxic effect of the unsaturated fat in the soybean oil on surface and absorption activities of protozoa cell walls (Dawson and Kemp 1969). This is supported by several studies done in sheep (Ikwuegbu and Sutton 1982) and in cattle (Seng Mom et al 2001). Moreover, irrespective of time, a higher level of  oil drench resulted in lower numbers of protozoa counted in the rumen. In this study, an oil level of 6 or 8 ml/kg LW had a similar influence on eliminating a large proportion of protozoa, thus for economical reasons, the lower dose is suggested for cattle defaunation.

There is conclusive evidence on the interaction between bacteria and protozoa. The remarkable increase in bacteria numbers in this experiment reflected this interaction and is supported by various findings, one of which was a study done by Rowe et al (1985), who reported a considerably higher number of bacteria in defaunated animals. The higher bacterial growth efficiency in the absence of the protozoa in the rumen is probably related to the fact that protozoa engulf and digest bacteria (Coleman 1975). This is supported by Leng (1990), who discovered that removal of protozoa or a decrease in protozoal density in the rumen can be expected to increase ruminant production under most feeding conditions pertaining to roughage-fed ruminants.

The increase of feed intake over a longer period in cattle received a high level of oil administration is in agreement with the results of Bird et al (1994) and Seng Mom et al (2001), who reported a higher intake in defaunated sheep and cattle. Similar results were also demonstrated by Trach and Thom (2004), in which defaunated cattle receiving 5 ml of oil/kg LW consumed more rice straw than normal animals. In terms of DM intake, an oil level of 6 or 8 ml/kg LW seems to be appropriate in defaunating cattle according to the present study. However, defaunation does not always lead to increased feed intake as, according to Ankrah et al (1990) and Chaudhary et al (1995),  intakes of DM in sheep and buffalo calves, respectively,  were not affected by defaunation.

There are conflicting reports as to the extent that defaunation affects digestibility.  Veira et al (1983) reported a positive influence on apparent digestibility of both OM and starch. Bird and Leng (1985) also found an improvement up to 18% units of DM digestibility in defaunated sheep, which is comparable to the value of approximately 15% units of digestibility increase in the current research. Similar results were found in buffaloes by Chaudhary and Srivastava (1995) and in cattle by Nhan et al (2001).  In contrast, Rowe et al (1985) reported a significant reduction of OM digestibility in the whole digestive tract while Chaudhary et al (1995) found no difference in DM and OM digestibility in goats fed a straw-based diet with and without elimination of protozoa. The linear correlation between DM digestibility and levels of oil drench suggests the effectiveness of elimination of protozoa on feed digestion in this study. On the contrary, other researchers seem to agree on the important role of protozoa in the degradation of plant materials and therefore they may have positive effects on the nutrition of the host (Kayouli et al 1983; Ushida and Jouany 1990). The explanation for the improvement in feed digestibility can be that (i) feed digestion by bacteria and fungi has compensated for those digested by protozoa and (ii) the elimination of predatory activity of protozoa has increased the number of bacteria (Bird et al 1994).
 

Conclusions

• Oil treatment removed most of the protozoa and increased the numbers of bacteria.
  
  
• There were linear increases in DM intake and DM digestibility according to the increasing levels of oil drench in the sub-periods 10-15 and 16-20 days after oil administration.
  
  
• The use of 6 ml of oil/kg LW is suggested as the most appropriate dose in cattle defaunation.

References

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Received 14 July 2007; Accepted 27 July 2007; Published 6 August 2007

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