Effect of soya oil hydrolysate on rumen digestion in defaunated and refaunated sheep

Responses of anaerobic rumen fungal diversity (phylum Neocallimastigomycota) to changes in bovine diet

AIMS

Anaerobic rumen fungi (Neocallimastigales) play important roles in the breakdown of complex, cellulose-rich material. Subsequent decomposition products are utilized by other microbes, including methanogens. The aim of this study was to determine the effects of dietary changes on anaerobic rumen fungi diversity.

METHODS AND RESULTS

Altered diets through increasing concentrate/forage (50 : 50 vs 90 : 10) ratios and/or the addition of 6% soya oil were offered to steers and the Neocallimastigales community was assessed by PCR-based fingerprinting with specific primers within the barcode region. Both a decrease in fibre content and the addition of 6% soya oil affected Neocallimastigales diversity within solid and liquid rumen phases. The addition of 6% soya oil decreased species richness. Assemblages were strongly affected by the addition of 6% soya oil, whereas unexpectedly, the fibre decrease had less effect. Differences in volatile fatty acid contents (acetate, propionate and butyrate) were significantly associated with changes in Neocallimastigales assemblages between the treatments.

CONCLUSIONS

Diet clearly influences Neocallimastigales assemblages. The data are interpreted in terms of interactions with other microbial groups involved in fermentation processes within the rumen.

SIGNIFICANCE AND IMPACT OF THE STUDY

Knowledge on the influence of diet on anaerobic fungi is necessary to understand changes in microbial processes occurring within the rumen as this may impact on other rumen processes such as methane production.

Effects on animal performance and fat composition of two fat concentrates in diets for growing-fattening bulls

Two experiments were carried out with growing-fattening bulls, offered a fattening diet based on concentrate and supplemented with soya oil or steam-flaked linseed. Soya oil (200 g/kg) was mixed with middlings (800 g/kg). Linseed (500 g/kg) and whole barley (500 g/kg) were steam flaked. The fat incorporation resulted in an increase of the ether extract content from 26·5 g/kg dry matter to about 45 g/kg. The incorporation of soya oil increased the average daily gain (P> 0·05). The saturated: unsaturated fatty acid ratio was reduced in perirenal fat due to an increase of oleic acid and a reduction of stearic acid. The inclusion of steam-treated linseed resulted in a lower slaughter weight (P< 0·05) and a shorter fattening period (P> 0·05). The fatty acid composition of perirenal fat was affected significantly: the concentrations of oleic, linoleic and linolenic acid were increased and the concentrations of myristic, palmitic and stearic acids were reduced. This resulted in a reduced saturated: unsaturated fatty acid ratio.

In a third experiment, samples of the two fat concentrates were incubated in nylon bags in the rumen. The ether extract disappearance was high with both concentrates. Furthermore, the fatty acid composition was altered to a large extent for soya oil while large proportions of unsaturated fatty acids were still present with steam-flaked linseed.

Effect of refined soy oil or whole soybeans on intake, methane output, and performance of young bulls

An experiment was conducted to establish the effects of feeding refined soy oil (RSO) or whole soybeans (WSB) containing soy oil on DMI, animal performance, and enteric methane (CH4) emissions in young bulls. Thirty-six Charolais and Limousin cross-bred, young beef bulls (338 +/- 27 kg of BW, 218 +/- 17 d of age at the beginning of the experiment) were blocked by BW, age, and breed before being assigned in a randomized complete block design to 1 of 3 experimental treatments (n = 12). The experimental period lasted for 103 d, with enteric CH4 output recorded for 2 periods of 5 consecutive days on d 37 to 41 and d 79 to 83. The 3 dietary treatments consisted of a barley/soybean meal-based concentrate with 0 g/d of RSO; oil from WSB as 6% of DMI (WSB treatment); and oil from RSO as 6% of DMI (RSO treatment). Each diet had a 10:90 forage:concentrate ratio, using barley straw as the forage source. Diet affected DMI (P < or = 0.001) and GE intake (P < 0.05 during the CH4 measurement periods), with the WSB treatment producing the lowest values. The addition of WSB decreased ADG (P < 0.05) compared with the RSO treatment. The WSB treatment also decreased (P < 0.05) average daily carcass gain (ADCG). Both the RSO and WSB concentrates decreased (P < 0.05 to P < 0.001) daily enteric CH4 output when expressed in terms of liters per day, liters per kilogram of DMI, percentage of GE intake, liters per kilogram of ADG, and liters per kilogram of ADCG. Diet had no effect (P = 0.557) on ruminal protozoal numbers. The reductions in enteric CH4 were achieved at relatively high oil inclusion levels. Such oil levels have previously been reported to decrease DMI of high-forage diets, although no effect on DMI was noted with the low-forage diets fed in this experiment. This impact on DMI of high-forage diets may limit the range of diets for which this CH4 reduction strategy may be applicable. The inclusion level of WSB in the current experiment (27%) was beyond the palatability threshold of the bulls used and resulted in a marked decline in intake and performance. Therefore, WSB may have a role to play in ruminant diets, but only at a reduced inclusion rate.

Rumen dry matter and crude protein degradability of extracted or untreated oilseeds and Leucaena leucocephala leaves

A study was undertaken to determine the rumen DM and CP degradability characteristics of soyabean, canola seed, peanut, palm kernel and Leucaena leucocephala leaves. The oilseeds were either treated with n-hexane to extract the fat or left untreated. Nylon bags were incubated in each of four rumen cannulated sheep for 0, 2, 4, 6, 12, 24 and 48 h. Animals were fed on a diet consisting of meadow hay (ad libitum) and 150 g of concentrate twice daily. Fat extraction caused a decrease (P < or = 0.05) in DM disappearance of soyabean at 0, 2, 4, 6 and 12 h and of peanuts at all incubation times. CP disappearance from peanuts was reduced (P < or = 0.05) as a result of fat extraction at 0, 2, 4, 6 and 12 h. Fat extraction of canola seed increased CP disappearance at 0, 2, 4, 6 and 24 h (P < or = 0.05). However, in the case of defatted canola seed, an increase in DM disappearance (P < or = 0.05) was observed in the first 4 incubation times and a decrease (P < or = 0.05) in the later times. Fat extraction increased (P < or = 0.05) DM disappearance of palm kernel at 0 and 48 h, but reduced it at 4, 6 and 24 h. CP disappearance of palm kernel was improved by treatment (P < or = 0.05) at 0, 4, 24 and 48 h and decreased at 12 h. In the case of palm kernel the largest differences in DM and CP disappearance occurred between the 24 and 48 h incubation times. Degradability characteristics for DM and CP of full-fat soyabean, canola seed and peanut were comparable to those of the full fat samples. Effective DM degradability of soyabean, canola seed and peanuts was 72.2 and 71.9; 74.1 and 66.8; and 85.9 and 70.8 for full fat and extracted feeds, respectively. Effective CP degradability was similar in all oilseeds with the exception of the extracted canola seed. Therefore, the incorporation of full-fat soyabean, canola seed and peanut into ruminant rations can be considered as a means of increasing the energy balance. Both palm kernel DM and CP degradabilities were characterized by slow rates of degradation by negative values "b". This suggests the predominance of microbial colonization over disappearance during incubation. DM and CP disappearance of Leucaena leucocephala leaves originating from Cuba were lower than those from Nigeria. Degradability characteristics for CP and DM of Cuban leucaena leaves showed that the linear model resulted in a better fit than the exponential one.

Control of rumen methanogenesis

During the last decades, considerable research on methane production in the rumen and its inhibition has been carried out. Initially, as methane production represents a significant loss of gross energy in the feed (2-15%), the ultimate goal of such intervention in rumen fermentation was an increase in feed efficiency. A second reason favouring research on methane inhibition is its role in the global warming phenomenon and in the destruction of the ozone layer. In this review, the authors describe briefly several interventions for reducing methane emission by ruminants. The objective can be reached by intervention at the dietary level by ration manipulation (composition, feeding level) or by the use of additives or supplements. Examples of additives are polyhalogenated compounds, ionophores and other antibiotics. Supplementation of the ration with lipids also lowered methanogenesis. More biotechnological interventions, e.g., defaunation, probiotics and introduction of reductive acetogenesis in the rumen, are also mentioned. It can be concluded that drastic inhibition of methane production is not unequivocally successful as a result of several factors, such as: instantaneous inhibition often followed by restoration of methanogenesis due to adaptation of the microbes or degradation of the additive, toxicity for the host animal, negative effects on overall digestion and productive performance. Therefore, methanogenesis and its inhibition cannot be considered as a separate part of rumen fermentation and its consequences on the animal should be taken into account.

Transformations and effects of lipids in the rumen: three decades of research at Gent University

A survey is given of research results on ruminant lipid digestion obtained at the authors' laboratory. Results are presented in terms of lipid changes occurring in the rumen and in terms of effects on nature, extent and site of digestion. The rumen can be adapted to an extremely high capacity for triglyceride lipolysis, preferentially releasing polyunsaturated fatty acids that are then further hydrogenated with accumulation of oleic acid isomers in vitro only. Evidence was obtained for both microbial incorporation and synthesis of polyunsaturated acids. In vitro lipolysis is inhibited by pH values below 6.3 and by ionophores. Free fatty acids inhibit methanogenesis with associated increases in propionate production and decreases in acetate and butyrate productions; the latter being related to their defaunating effect. Both in the faunated and defaunated rumen, free fatty acids decrease fibre digestion, which is shifted to the hindgut, at least in sheep. Defaunation increases rumen microbial growth efficiency and may result in a higher duodenal flow of both feed and microbial protein, provided these increases are not overcome by a decreased apparent rumen OM digestibility. Considerable between animal variability exists for these effects, associated with variable effects on rumen particle and liquid volumes and outflow rates.

Manipulation of microbial activity in the rumen

Different methods of optimizing feed conversion into nutrients in the rumen are now available to scientists. But the rumen must be considered as an integrated system and this makes it difficult to rationalize manipulation. The observed result of any treatment is a combination of several interactive reactions. Any change to one component of the system has several uncontrolled effects on other components. The positive effects aimed for are sometimes associated with undesirable effects. Numerous chemical additives have been studied during the last two decades among which ionophore antibiotics represent the most important group. The interest of non-ionophore antibiotics, methane inhibitors, and compounds inhibiting proteases or deaminases, has also been considered during the last years. The observed effects of these chemical additives on animals, and their possible mode of action on rumen microbes and on animal metabolism, are discussed. However, the risks of the presence of residues in meat and milk are questioned by consumers. Microbial activity in the rumen can be altered by feeding animals with large amounts of certain food constituents (fats, starch) or minerals (buffer substances). The responses in the rumen to these dietary conditions are analyzed in terms of the digestive effects on plant cell wall degradation and microbial protein synthesis. Modification of the rumen microbial population is now considered as a possible approach to rumen manipulation by scientists. The effects on digestion of the elimination of ciliate protozoa (defaunation) are presented. The feasibility of these objectives, from a practical standpoint, is discussed. Finally, there is an overview of the effects of the addition of live yeasts (Saccharomyces cerevisciae), or fungi (Aspergillus orizae), used as probiotics. A possible mode of action of probiotics on the rumen ecosystem is suggested.

Comparison of three methods for incorporation of liquid fat into diets for lactating dairy cows

Two experiments were conducted to determine whether method of incorporation of tallow (iodine value = 57.7) into a TMR for lactating dairy cows affected DMI, milk production or composition, ruminal characteristics, or nutrient digestibilities. In Experiment 1, 8 Holstein and 8 Jersey cows were fed diets containing 1) control, no fat; 2) fat (5% of DM) added first to the concentrate; 3) fat added first to the haylage; and 4) fat added as the last ingredient in the TMR. The DMI was lower when fat was added last to the TMR; DMI was decreased for Jerseys, but not Holsteins, when fat was added first to the concentrate. Milk production was increased, and milk fat percentage decreased, by fat supplementation, but neither differed among application methods. Milk protein percentage was decreased by fat supplementation but was decreased less when fat was added last to the TMR. Production of milk CP, true protein, and casein protein was greater when fat was first mixed with haylage or added last to the TMR. In Experiment 2, four Holstein cows with ruminal cannulas were fed the same diets. Ruminal fermentation characteristics and apparent total tract digestibilities of DM, OM, CP, NDF, ADF, and ash were not different among diets. Digestibility of total fatty acids was decreased when fat was added first to haylage or last to the TMR. Incorporation method had relatively minor effects on variables.