1. The effects of three levels of linseed oil (LSO) supplementation of a basal diet on rumen digestion and flow of nutrients to the proximal duodenum of three mature sheep provided with permanent rumen and duodenal re-entrant cannulas were studied.2. A basal diet of 200 g hay and 400 g concentrates daily, providing approximately 7.0 MJ digestible energy and 13 g N/d, was given alone or with supplements of 13, 26 or 40 ml LSO/d in two equal portions at 06.00 and 18.00 hours. The flow of duodenal digesta was measured by spot-sampling using chromic oxide paper as the marker. Bacterial protein synthesis (BPS) was measured by the diaminopimelic acid technique.3. Addition of LSO reduced the digestion of energy and organic matter, particularly acid-detergent fibre, in the stomach. Digestion in the intestines increased but at the higher levels of supplementation this failed to compensate completely for the reduction in rumen digestion. Total volatile fatty acid concentrations were not affected but molar proportions of acetate and butyrate were decreased by approximately 18 and 61% respectively while the molar proportion of propionate was increased twofold by the highest concentration of oil. The higher concentrations of LSO virtually eliminated protozoa from the rumen.4. The second increment of LSO (26 ml/d) produced the highest duodenal flow of total N and bacterial N and the highest efficiency of BPS. The highest concentration of oil (40 ml/d) was without effect. Rumen and duodenal ammonia concentrations and plasma urea concentrations tended to be reduced by the higher concentrations of LSO.5. It is argued that the results support suggestions made elsewhere that free oils reduce the efficiency of BPS but that they also reduce the numbers of protozoa which can cause an increase in the efficiency of BPS. The net effect of free oil supplementation on BPS is thus likely to be variable and difficult to predict.

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The effect of varying the amount of linseed oil supplementation on rumen metabolism in sheep

1. Six wether sheep were each provided with a permanent cannula in the rumen and re-entrant cannulas in the proximal duodenum.2. In a preliminary study, the sheep consumed 200 g hay and 400 g concentrates supplemented with up to 40 g linseed oil, coconut oil or cod-liver oil daily. Feed was refused at higher levels of supplementation.3. Five of the sheep were used in a 5 × 5 Latin-square experiment. They were given 200 g hay and 400 g concentrates alone (B) or supplemented with 40 g linseed oil (L), coconut oil (C), protected linseed oil or protected coconut oil daily. The protected oils were prepared by emulsifying the free oils with formaldehyde-treated sodium caseinate. Formaldehyde-treated sodium caseinate was also included in the other three diets.4. Digestion in the stomach was measured by spot sampling duodenal digesta, using chromic oxide-impregnated paper as the marker. Microbial flow at the duodenum was measured by use of both diaminopimelic acid (DAPA) and RNA as microbial markers.5. Both the free oils had broadly similar effects despite their very different fatty acid compositions. Digestion in the stomach of organic matter (OM) was reduced from 0·48 (diet B) to 0·29 (diets L and C) and that of neutral-detergent fibre from 0·50 (diet B) to 0·19 (diet L) and 0·12 (diet C). The molar proportions of acetic acid and n-butyric acid were decreased and that of propionic acid was increased. Protozoal numbers were reduced by 78% (diet L) and 90% (diet C). The flow of total nitrogen and microbial N was increased by both oils and the efficiency of microbial protein synthesis (g N/kg OM apparently digested in the rumen) was increased from 30 (diet B) to 85 (diet L) and 74 (diet C) when based on DAPA and from 41 (diet B) to 94 (diet L) and 81 (diet C) when based on RNA. The efficiency when based on true digestion of OM (g N/kg OM truly digested in the rumen) was increased from 23 (diet B) to 46 (diet L) and 44 (diet C) when based on DAPA and from 29 (diet B) to 49 (diet L) and 46 (diet C) when based on RNA. The amounts of microbial OM (g/d) at the duodenum were increased from 68 (diet B) to 124 (diet L) and 106 (diet C) when based on DAPA and from 92 (diet B) to 136 (diet L) and 115 (diet C, non-significant) when based on RNA.6. When the oils were given in the protected form, the effects on digestion in the stomach were reduced but not eliminated. No significant increases in the amount of total N or microbial N at the duodenum were established, though there was a tendency for an increase in the efficiency of microbial protein synthesis with protected linseed oil. The results suggested that the method of protection used reduced the effects of the oils on rumen digestion and synthesis but was only partially successful in preventing hydrogenation of the fatty acids.7. It is concluded that free oils can markedly increase the efficiency of microbial protein synthesis, possibly by their defaunating effect, and that this may enhance the potential for using non-protein-N on oil-supplemented diets.

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Digestion and synthesis in the rumen of sheep given diets supplemented with free and protected oils

A biochemical model coupled with an iterative nonlinear least-squares program was used to estimate stoichiometric parameters for fermentat ion of soluble carbohydrate, starch, hemicellulose, cellulose and protein in the rumen. Fermentat ion parameters were deduced for two sets of l i terature data, on (1) a roughage group of 60 diets fed to 137 animals and (2) a concentrate group of 48 diets fed to 374 animals. Soluble carbohydrate and starch fermentat ion parameters were much different for the roughage and concentrate groups. Differences were also noted in fermentat ion parameters for hemicellulose and cellulose. Model sensitivity to imposed changes of iteratively deduced parameters supported the conclusion that the estimated values are unique for all substrates except protein. In vitro estimates of isolated substrate fermentat ion from the literature agreed favorably with those indicated for hemicellulose. Cellulose fermentation was estimated to yield an acetate to propionate ratio of 7.8 to 13.1:1. This was higher than estimates in the li terature of 1.3 to 3.6:1. Predicted fermentat ion patterns were within the range of normal biological variation noted for actual patterns. Systematic error components were identified as lignin plus ash as a percentage of feed dry matter and percentage roughage in the diet for the roughage and concentrate groups, respectively. Significant bias remained only in the roughage group for acetate and butyrate. Predicted vs observed acetate, propionate and butyra te production, for diets where comparison data were available, had slopes (correlation coefficients) of .84

Estimation of Stoichiometric Parameters for Rumen Fermentation of Roughage and Concentrate Diets

Wheat straw was subjected to aerobic and anaerobic decomposition in suspensions of soil. The products of the aerobic process stimulated the root extension of barley seedlings, whereas the anaerobic fermentation yielded products which inhibited growth. Acetic acid was the phytotoxin present in the greatest amount.

Phytotoxicity of acetic acid produced in the anaerobic decomposition of wheat straw.

(1974). Anaerobic digestion of organic matter. C R C Critical Reviews in Environmental Control: Vol. 4, No. 1-4, pp. 131-191.

Anaerobic digestion of organic matter

Three dry cows, each fitted with a permanent rumen fistula, were fed hay and flaked maize or hay and rolled barley in widely different proportions. All rations were offered at 7 kg dry matter daily for 3 weeks following hay alone. The cows refused all cereal 3 or 4 days after introduction of rations including 80 and 100% flaked maize; recovery of intake occurred in most instances within a further 3–10 days. On the 100% flaked maize ration, the refusals were associated with very low pH and high concentrations of lactic acid in the rumen.Refusalsof rolled barley were small and showed no clear pattern. Rumen fermentation was reasonably stable during the last week of each period except with the 100% barley rations. On the rations containing flaked maize, molar proportions of volatile fatty acids (VFA) varied widely but on only one occasion did the proportion of acetic acid fall below 55% and in two cows that consumed flaked maize alone, the proportion of acetic acid in the rumen exceeded 60%. On the rations containing rolled barley, increasing proportions of barley were associated with large decreases in the proportion of acetic acid and increases in the proportion of propionic acid. The maximum proportion of n-butyric acid was found on the rations containing 50% cereal. It is suggested that, when large proportions of cereals are fed, the proportions of VFA bear no clear relationship to the crude fibre content of the ration but that an association with rumen pH may exist.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0021859600020086

J. D. Sutton

Papers

Fermentation in the rumen of cows given rations containing hay and flaked maize or rolled barley in widely different proportions.