X.Z. Sun

Lambs Fed Fresh Winter Forage Rape (Brassica napus L.) Emit Less Methane than Those Fed Perennial Ryegrass (Lolium perenne L.), and Possible Mechanisms behind the Difference

The objectives of this study were to examine long-term effects of feeding forage rape (Brassica napus L.) on methane yields (g methane per kg of feed dry matter intake), and to propose mechanisms that may be responsible for lower emissions from lambs fed forage rape compared to perennial ryegrass (Lolium perenne L.). The lambs were fed fresh winter forage rape or ryegrass as their sole diet for 15 weeks. Methane yields were measured using open circuit respiration chambers, and were 22-30% smaller from forage rape than from ryegrass (averages of 13.6 g versus 19.5 g after 7 weeks, and 17.8 g versus 22.9 g after 15 weeks). The difference therefore persisted consistently for at least 3 months. The smaller methane yields from forage rape were not related to nitrate or sulfate in the feed, which might act as alternative electron acceptors, or to the levels of the potential inhibitors glucosinolates and S-methyl L-cysteine sulfoxide. Ruminal microbial communities in forage rape-fed lambs were different from those in ryegrass-fed lambs, with greater proportions of potentially propionate-forming bacteria, and were consistent with less hydrogen and hence less methane being produced during fermentation. The molar proportions of ruminal acetate were smaller and those of propionate were greater in forage rape-fed lambs, consistent with the larger propionate-forming populations and less hydrogen production. Forage rape contained more readily fermentable carbohydrates and less structural carbohydrates than ryegrass, and was more rapidly degraded in the rumen, which might favour this fermentation profile. The ruminal pH was lower in forage rape-fed lambs, which might inhibit methanogenic activity, shifting the rumen fermentation to more propionate and less hydrogen and methane. The significance of these two mechanisms remains to be investigated. The results suggest that forage rape is a potential methane mitigation tool in pastoral-based sheep production systems.

Deriving fractional rate of degradation of logistic-exponential (LE) model to evaluate early in vitro fermentation.

Water-soluble components of feedstuffs are mainly utilized during the early phase of microbial fermentation, which could be deemed an important determinant of gas production behavior in vitro. Many studies proposed that the fractional rate of degradation (FRD) estimated by fitting gas production curves to mathematical models might be used to characterize the early incubation for in vitro systems. In this study, the mathematical concept of FRD was developed on the basis of the Logistic-Exponential (LE) model, with initial gas volume being zero (LE0). The FRD of the LE0 model exhibits a continuous increase from initial (FRD 0) toward final asymptotic value (FRD F) with longer incubation time. The relationships between the FRD and gas production at incubation times 2, 4, 6, 8, 12 and 24 h were compared for four models, in addition to LE0, Generalization of the Mitscherlich (GM), c th order Michaelis-Menten (MM) and Exponential with a discrete LAG (EXPLAG). A total of 94 in vitro gas curves from four subsets with a wide range of feedstuffs from different laboratories and incubation periods were used for model testing. Results indicated that compared with the GM, MM and EXPLAG models, the FRD of LE0 model consistently had stronger correlations with gas production across the four subsets, especially at incubation times 2, 4, 6, 8 and 12 h. Thus, the LE0 model was deemed to provide a better representation of the early fermentation rates. Furthermore, the FRD 0 also exhibited strong correlations (P < 0.05) with gas production at early incubation times 2, 4, 6 and 8 h across all four subsets. In summary, the FRD of LE0 model provides an alternative to quantify the rate of early stage incubation, and its initial value could be an important starting parameter of rate.

Sampling procedure for the measurement of dissolved hydrogen and volatile fatty acids in the rumen of dairy cows1

Dissolved hydrogen (dH) influences the pathways of VFA production and is a precursor of methane formation in the rumen. Measurements of dH in rumen fluid taken at the same time as measuring other rumen fermentation end products would improve our quantitative understanding of the role of dH as a controller of rumen fermentation. Sample collections though a rumen cannula and using oral stomach tubing were compared for measurements of dissolved gases and fermentation end products in the rumen fluid of 4 ruminally cannulated dairy cows fed a total mixed ration of corn silage and concentrate. Rumen fluid was collected at 0, 2.5, and 6 h after morning feeding through the cannula from cranial dorsal rumen, cranial ventral rumen, central rumen, caudal dorsal rumen, and caudal ventral rumen and in parallel by oral stomach tubing at 2 insertion depths of 180 cm (sampling the central rumen) and 200 cm (sampling the caudal dorsal rumen). The cranial dorsal rumen had the greatest pH and smallest VFA concentration among 5 sites sampled. Samples collected by oral stomach tubing had greater ( < 0.001) rumen pH and less ( < 0.001) dissolved methane (dCH) and lower VFA concentration than that collected through rumen cannula. The dH concentrations were positively correlated ( > 0.8) in rumen samples collected by the 2 sampling techniques, with a concordance correlation coefficient larger than 0.8 and scale shift being about 0.1 away from unity. The variations in the measurement of dH, dCH, pH, and VFA in samples collected by oral stomach tubing are most likely the result of saliva contamination. The time of sampling relative to feeding had significant influence ( < 0.01) on dissolved gases and fermentation end products, with the greatest concentrations of dH, dCH, and VFA measured 2.5 h after morning feeding. The dH was correlated positively ( > 0.58) with dCH and negatively ( < -0.65) with the estimated net H production relative to the amount of VFA produced. This indicated that greater dH enhanced rumen CH production and also led to fermentation pathways that produce less H, such as enhanced propionate and butyrate production. In summary, oral stomach tubing could be a feasible method to measure ruminal dH in intact animals, but caution should be taken to minimize saliva contamination. Measurements made using both techniques yield similar conclusions for the effects of dH on fermentation pathways and CH generation.

Forage brassica: a feed to mitigate enteric methane emissions?

A series of experiments was conducted in New Zealand to evaluate the potential of forage brassicas for mitigation of enteric methane emissions. Experiments involved sheep and cattle fed winter and summer varieties of brassica forage crops. In the sheep-feeding trials, it was demonstrated that several species of forage brassicas can result, to a varying degree, in a lower methane yield (g methane per kg of DM intake) than does ryegrass pasture. Pure forage rape fed as a winter crop resulted in 37% lower methane yields than did pasture. Increasing the proportion of forage rape in the diet of sheep fed pasture linearly decreased methane yield. Feeding forage rape to cattle also resulted in 44% lower methane yield than did feeding pasture. In conclusion, reductions in methane emission are achievable by feeding forage brassicas, especially winter forage rape, to sheep and cattle. Investigating other aspects of these crops is warranted to establish their value as a viable mitigation tool in pastoral farming.

Genotypic variation in in sacco dry matter degradation kinetics in perennial ryegrass (Lolium perenne L.)

Fast degrading perennial ryegrass (Lolium perenne L.) is a desirable characteristic to select for because it can result in increased feed intake by grazing ruminants. Sufficient range in genotypic variation of dry matter (DM) degradation kinetics is a prerequisite for selection. To investigate the genotypic variation, 77 perennial ryegrass accessions sourced internationally, grown in autumn in the same conditions and harvested in the vegetative state, were examined using an in sacco technique. From the time course of DM disappearance, soluble fraction ‘A’, potentially degradable fraction ‘B’, indigestible fraction ‘C’ and the degradation rate k of fraction ‘B’ were estimated. The results indicated that a large range in genotypic variation was present in all degradation parameters. Fraction ‘A’ ranged from 0.48 to 0.60, with the highest five accessions being 21% higher than the lowest five. Degradation rate k of fraction ‘B’ ranged from 0.069 to 0.199/h, with the fastest five being 125% higher than the slowest five. There were no strong correlations between degradation parameters and chemical composition. In conclusion, there was considerable genotypic variation in DM degradation kinetics among perennial ryegrass accessions and this presents plant breeders with ample opportunity to select for fast degrading perennial ryegrasses.

Sheep numbers required for dry matter digestibility evaluations when fed fresh perennial ryegrass or forage rape

Research trials with fresh forages often require accurate and precise measurement of digestibility and variation in digestion between individuals, and the duration of measurement periods needs to be established to ensure reliable data are obtained. The variation is likely to be greater when freshly harvested feeds are given, such as perennial ryegrass (Lolium perenne L.) and forage rape (Brassica napus L.), because the nutrient composition changes over time and in response to weather conditions. Daily feed intake and faeces output data from a digestibility trial with these forages were used to calculate the effects of differing lengths of the measurement period and differing numbers of sheep, on the precision of digestibility, with a view towards development of a protocol. Sixteen lambs aged 8 months and weighing 33 kg at the commencement of the trial were fed either perennial ryegrass or forage rape (8/treatment group) over 2 periods with 35 d between measurements. They had been acclimatised to the diets, having grazed them for 42 d prior to 11 days of indoor measurements. The sheep numbers required for a digestibility trial with different combinations of acclimatisation and measurement period lengths were subsequently calculated for 3 levels of imposed precision upon the estimate of mean dry matter (DM) digestibility. It is recommended that if the standard error of the mean for digestibility is equal to or higher than 5 g/kg DM, and if sheep are already used to a fresh perennial ryegrass or forage rape diet, then a minimum of 6 animals are needed and 4 acclimatisation days being fed individually in metabolic crates followed by 7 days of measurement.