Effect of different levels of phosphorus on rumen microbial fermentation and synthesis determined using a continuous culture technique

Abstract

I , A continuous culture technique was used to study the phosphorus requirements of rumen micro-organisms. Solutions of artificial saliva containing 120, 80, 40 and 0 mg inorganic phosphorus (PJ/I were infused into the reaction vessels previously inoculated with rumen contents, resulting in Pi concentrations in the vessel contents of 48, 28, 4 and < 1 mg/l respectively. Various fermentative and synthetic characteristics were examined.2. In the vessel contents, concentrations of protozoa (about 0.9 x 105/ml) were not significantly affected by pi concentration. Total volatile fatty acids (VFA) produced averaged about 6.83 mmol/h with Pi levels of 48 and 28 mg/l. Reduction in Pi concentrations to 4 and < 1 mg/l resulted in significant reductions in total VFA to approximately 6.25 and 3.75 mmol/h respectively, accompanied by a rise in pH from 6.5 to 7.3. Ammonia-nitrogen values, which averaged about 131 mg/l at the higher I: concentrations, also increased with the lowest level of P, 5.It was estimated that the minimum pi concentrations required in rumen fluid in vivo to maintain maximum degradative and synthetic microbial activities was in the range 75-100 mg/l and that the over-all P requirement of the microbes was of the order of 5.1 g/kg apparently digested organic matter intake. Phosphorus deficiency is a major problem in many areas of the world. Most of the normal forages consumed by ruminants are little more than adequate with respect to their P content. Furthermore, increasing use of poor-quality roughages and by-products such as sugar-beet pulp, generally deficient in P, tends to exacerbate the problem. It has frequently been shown that feeding P-deficient diets could lead to decreased voluntary feed intake (Preston & Pfander, 1964;Coombe et al. 1971 ;Smith, 1984) with consequent effects on growth rate, milk production, etc. (Hemingway, 1967). These effects may be at least in part a result of impaired rumen function (Fishwick et al. 1977, Bass et al. 198 1 ;Durand et al. 1982; Breves & Holler, 1983). In general, ruminant feeds sustain the symbiotic rumen micro-organisms and only indirectly the host animal (Hungate, 1966) and it has been suggested that the P requirements of these organisms may be greater than that of the host animal (Preston & Pfander, 1964). There is, however, a strong interaction between the host animal and the rumen micro-organisms with respect to P supply and utilization, and in order to ascertain precise requirements of the micro-organisms, studies need to be carried out in situations which are not influenced by the host animal.In vitro work with pure cultures of rumen bacteria have shown the essentiality of P for growth (Bryant et al. 1959) and its effects on growth rates and yields (Caldwell et al. 1973;

Effects of phosphorus deficiency on rumen microbial activity associated with the solid and liquid phases of a fermentor (Rusitec)

“…&horbar; P deficiency reduced overall protein synthesis by 45 %, which confirms results obtained in vivo by Breves and H61ler (1985) and Lessmann, Breves and H61ler (1985) and in vitro by Bonilla (1976) and Komisarczuk, Merry and McAllan (1987). In the P-deficient medium, the P supply was solely of dietary origin.…”

“…The drastic reduction in ATP concentrations in the P-deficient vessels confirms previous results obtained in the continuous culture system (Komisarczuk, Merry and McAllan, 1987). This effect cannot be due to protozoa, as their number was not significantly reduced by the lack of P, nor to a shortage of intracellular inorganic phosphorus in the bacteria.…”

“…However, in vivo these authors did not observe significant differences in microbial yield between P-supplemented -and P-depleted sheep when they were fed 8 times a day. Similarly, F deficiency did not alter microbial yield in the continuous culture system (Komisarczuk, Merry and McAllan, 1987).…”

“…The composition of the low-P diet used as a substrate was similar to that used by Komisarczuk, Merry and McAllan (1987). Data concerning the digestive parameters (organic matter and cell wall degradation, volatile fatty acids and gas production) have been published elsewhere (Komisarczuk et al, 1986 Czerkawski and Breckenridge (1977).…”

“…ln vivo studies on the effect of P deficiency on rumen microbial digestion and protein synthesis have not always shown clear-cut results because of large variations in the responses of the hosts in terms of food intake and endogenous P return (Witt and Owens, 1983 ;Milton and Ternouth, 1985). However, some authors using semi-purified diets have pointed out the clear-cut effect of reduced P intake on the degradative capacities of rumen microbes (Farries and Krasnodebska, 1972 ;Durand et al, 1983), urea N utilization (Durand et al, 1983 ;H61ler, Breves and Martens, 1983) and microbial N turnover (Lessmann, Breves and H61ler, 1985 ;Breves, Hbller and Lessman, 19851. Recently, a range of inorganic phosphorus concentrations was experimented (Komisarczuk, Merry and McAllan, 1987) Czerkawski and Breckenridge (1977), allows a longer retention time of the solid material and could reproduce better in vivo digestion characteristics. Also, with this system the solid and liquid phases could be easily separated.…”