Rumen function and digestion parameters associated with differences between sheep in methane emissions when fed chaffed lucerne hay

An indoor experiment involving 10 rumen-cannulated Romney sheep was conducted in May and June 1998 at AgResearch Grasslands, Palmerston North, New Zealand, under restricted feeding conditions. in order to test the hypothesis that animal factors, in particular rumen fractional outflow rate (FOR) and rumen volume, have an influence on the between-sheep variation in methane (CH4) emission. Sheep were fed 2-hourly on chaffed lucerne hay. Following an acclimatization period of 21 days, the experiment lasted 16 days. Energy and nitrogen (N) balances were measured on days 1-6. Cr-EDTA marker was continuously infused into the rumen from day 9 to 16, and rumen contents emptied and sampled on days 13 and 16. Particulate and fluid FOR were estimated using feed lignin and Cr-EDTA, respectively. Daily CH, production was measured by the sulphur hexafluoride tracer technique on days 2, 5, 6, 12 and 15 of the experiment. CH4 production (g/day) was positively correlated with the pool size of organic matter (OM) in the rumen (OM pool, g) (r = 0.84, P = 0.002), OM intake (OMI, g/day) (r = 0.67, P = 0.04), and the rumen fill (g. wet digesta) (r = 0.76, P = 0.01). Multiple regression analysis showed that CH4 production was best predicted (R-2 = 0.88) as a function of OM pool and the molar % of butyrate; however, OM pool alone accounted for a large proportion (R-2 = 0.71) of the variation in CH4 production. CH4 yield (% gross energy intake, % GEI) was negatively correlated with the particulate FOR (%/h) ( r= -0.75, P = 0.01) and buffering capacity of rumen fluid (mmol HCl) (r = -0.72, P = 0.02) but positively correlated with the digestibility of cellulose (r = 0.66, P = 0.04). Multiple regression analysis showed that CH, yield was best predicted as a function of particulate FOR, OMI (g/kg liveweight(0.75)) and the molar % of butyrate (R-2 = 0.88). Particulate FOR alone explained a large proportion (R-2 = 0.57) of the variation in CH4 Yield. Particulate FOR was negatively correlated with rumen fill (r = -0.69, P = 0.03) and digestibility of cellulose (r = -0.65, P = 0.04). These results suggest that sheep with lower rumen particulate FOR (i.e. longer rumen retention times) had larger rumen fills and higher fibre digestibilities and CH4 yields. If rumen particulate FOR is to be used as a tool for CH4 mitigation, the repeatability of its relationship to CH4 emission must be assessed, preferably under grazing conditions

Persistence of differences between sheep in methane emission under generous grazing conditions

Four low and four high methane (CH4) emitters were selected from a flock of 20 Romney sheep on the basis of CH4 production rates per unit of intake, measured at grazing using the sulphur hexafluoride (SF,) tracer technique. Methane emissions from these sheep were monitored at grazing for four periods (P): October, November, January and February 1999/2000. All measurements were carried out on perennial ryegrass/white clover pasture under generous herbage allowance, and the sheep were maintained on similar pastures during non-measurement periods. The tracer technique was used for all the CH4 measurements and feed DM intake was calculated from total faecal collection and estimated DM digestibility. Data for liveweight (LW), gross energy intake (GEI) and CH4 emission were analysed using split-plot analysis of variance. In addition, a between-period rank order correlation analysis was carried out for CH4 emission data. Low CH4 emitters were heavier (P < 0.05) than the high emitters in all the periods, but they did not differ (P < 0.05) in their gross energy intakes (GEL MJ/kg LW0.75). Low and high CH4 emitters consistently maintained their initial rankings in CH4 yield (% GEI) throughout the subsequent periods and the correlation analysis of rank order for CH4 yield showed strong between-period correlation coefficients, although this was weaker in the last period. It is suggested that feeding conditions that maximize feed intake (e.g. generous allowance of good quality pasture under grazing) favour the expression and persistence of between-sheep differences in CH4 yield

Methane emission by alpaca and sheep fed on lucerne hay or grazed on pastures of perennial ryegrass/white clover or birdsfoot trefoil

Based on the knowledge that alpaca (Lama pacos) have a lower fractional outflow rate of feed particles (particulate FOR) from their forestomach than sheep (San Martin 1987), the current study measured methane (CH4) production and other digestion parameters in these species in three successive experiments (1, 2 and 3): Experiment 1, lucerne hay fed indoors; Experiment 2, grazed on perennial ryegrass/white clover pasture (PRG/WC); and Experiment 3, grazed on birdsfoot trefoil (Lotus corniculatits) pasture (Lotus). Six male alpaca and six castrated Romney sheep were simultaneously and successively fed on the forages either ad libitium or at generous herbage allowances (grazing). CH4 production (g/day) (using the sulphur hexafluoride tracer technique), voluntary feed intake (VFI), diet quality, and protozoa counts and volatile fatty acid concentrations in samples of forestomach contents were determined. In addition, feed digestibility, energy and nitrogen (N) balances and microbial N supply from the forestomach (using purine derivatives excretion) were measured in Experiment 1. Diets selected by alpaca were of lower quality than those selected by sheep, and the voluntary gross energy intakes (GEI, MJ) per kg of liveweight(0.75) were consistently lower (P0.05) in their CH4 yields (% GEI) when fed on lucerne hay (5.1 v. 4.7), but alpaca had a higher CH4 yield when fed on PRG/WC (9.4 v. 7.5, P0.05) in diet N partition or microbial N yield, but alpaca had higher (P<0.05) neutral detergent fibre digestibility (0.478 v. 0.461) and lower (P<0.01) urinary energy losses (5.2 v. 5.8 % GEI) than sheep. It is suggested that differences between these species in forestomach particulate FOR might have been the underlying physiological mechanism responsible for the differences in CH4 yield, although the between-species differences in VFI and diet quality also had a major effect on it

Measuring enteric methane emissions from individual ruminant animals in their natural environment

Ruminant livestock are an important source of meat, milk, fiber, and labor for humans. The process by which ruminants digest plant material through rumen fermentation into useful product results in the loss of energy in the form of methane gas from consumed organic matter. The animal removes the methane building up in its rumen by repeated eructations of gas through its mouth and nostrils. Ruminant livestock are a notable source of atmospheric methane, with an estimated 17% of global enteric methane emissions from livestock. Historically, enteric methane was seen as an inefficiency in production and wasted dietary energy. This is still the case, but now methane is seen more as a pollutant and potent greenhouse gas. The gold standard method for measuring methane production from individual animals is a respiration chamber, which is used for metabolic studies. This approach to quantifying individual animal emissions has been used in research for over 100 years; however, it is not suitable for monitoring large numbers of animals in their natural environment on commercial farms. In recent years, several more mobile monitoring systems discussed here have been developed for direct measurement of enteric methane emissions from individual animals. Several factors (diet composition, rumen microbial community, and their relationship with morphology and physiology of the host animal) drive enteric methane production in ruminant populations. A reliable method for monitoring individual animal emissions in large populations would allow (1) genetic selection for low emitters, (2) benchmarking of farms, and (3) more accurate national inventory accounting

Methane production in ruminant animals

Agriculture is a significant source of GHGs globally and ruminant livestock animals are one of the largest contributors to these emissions, responsible for an estimated 14% of GHGs (CH4 and N2O combined) worldwide. A large portion of GHG fluxes from agricultural activities is related to CH4 emissions from ruminants. Both direct and indirect methods are available. Direct methods include enclosure techniques, artificial (e.g. SF6) or natural (e.g. CO2) tracer techniques, and micrometeorological methods using open-path lasers. Under the indirect methods, emission mechanisms are understood, where the CH4 emission potential is estimated based on the substrate characteristics and the digestibility (i.e. from volatile fatty acids). These approximate methods are useful if no direct measurement is possible. The different systems used to quantify these emission potentials are presented in this chapter. Also, CH4 from animal waste (slurry, urine, dung) is an important source: methods pertaining to measuring GHG potential from these sources are included

Bovine Host Genetic Variation Influences Rumen Microbial Methane Production with Best Selection Criterion for Low Methane Emitting and Efficiently Feed Converting Hosts based on Metagenomic Gene Abundance

Methane produced by methanogenic archaea in ruminants contributes significantly to anthropogenic greenhouse gas emissions. The host genetic link controlling microbial methane production is unknown and appropriate genetic selection strategies are not developed. We used sire progeny group differences to estimate the host genetic influence on rumen microbial methane production in a factorial experiment consisting of crossbred breed types and diets. Rumen metagenomic profiling was undertaken to investigate links between microbial genes and methane emissions or feed conversion efficiency. Sire progeny groups differed significantly in their methane emissions measured in respiration chambers. Ranking of the sire progeny groups based on methane emissions or relative archaeal abundance was consistent overall and within diet, suggesting that archaeal abundance in ruminal digesta is under host genetic control and can be used to genetically select animals without measuring methane directly. In the metagenomic analysis of rumen contents, we identified 3970 microbial genes of which 20 and 49 genes were significantly associated with methane emissions and feed conversion efficiency respectively. These explained 81% and 86% of the respective variation and were clustered in distinct functional gene networks. Methanogenesis genes (e.g. mcrA and fmdB) were associated with methane emissions, whilst host-microbiome cross talk genes (e.g. TSTA3 and FucI) were associated with feed conversion efficiency. These results strengthen the idea that the host animal controls its own microbiota to a significant extent and open up the implementation of effective breeding strategies using rumen microbial gene abundance as a predictor for difficult-to-measure traits on a large number of hosts. Generally, the results provide a proof of principle to use the relative abundance of microbial genes in the gastrointestinal tract of different species to predict their influence on traits e.g. human metabolism, health and behaviour, as well as to understand the genetic link between host and microbiome

Effects of feeding silage and extending lactation on the pastoral dairy farm : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Animal Science at Massey University, Palmerston North, New Zealand

It is a common practice in the New Zealand seasonal dairying system to dry-off the herd at an earlier date in order to prevent excessive loss of body condition and average pasture cover. Thus, short lactation length is one of the main reasons for the low milk yield per cow in New Zealand. An experiment was carried out in April and May 1995 (54 days) at the Dairy Cattle Research Unit (DCRU), Massey University in order to measure the effects of extending the lactation, and feeding silage on the dairy farm system. On the 4th April, 54 of the lower yielding cows of the herd (118 cows) were dried-off and divided into two equal herds (D or control system). The remaining 64 cows were also divided into two equal herds, and milked for another 54 days (M system). Each of the four herds was grazed on a self-contained farmlet, at 2.9 cows/ha stocking rate. D herds received only grazed pasture (16 kg dry matter (DM)/cow/day allowance), while M herds received pasture (30 kg DM/cow/day allowance) plus silage (5.5 kg DM/cow/day). All of the replicated farmlets were feed budgeted to common targets of 2,000 Kg DM/ha pasture cover and condition score 5.0 at 29th May. At the end of the experiment the M system had produced 57.7 kg milksolids (MS, fat+protein) per cow, but had lower (P<0.01) average pasture cover (by 584 kg DM/ha) and body condition scores (by 0.33 units/cow) than the D system. The target conditions were achieved by the D system, but not by the M system (deficits of 400 kg DM/ha pasture cover and 0.38 units CS/cow). When the feed required to overcome the deficits (when compared with the D system) in pasture cover and condition score of the M system was added to the silage fed, and these were all expressed in terms of their "pasture equivalences", a total marginal response to the silage feeding and extra days in milk of 116 g MS/kg equivalent pasture DM was calculated. Findings of this and previous farm system studies show that milk production response to late lactation (autumn) supplementary feeding is higher than was commonly believed, provided that it is associated with extra days in milk. Nevertheless, feed planning and management must be specially vigilant to ensure that the extended lactation does not cause reduced body condition score and pasture cover at the start of the next season

Methane emission from forage-fed sheep, a study of variation between animals : a thesis presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Animal Science in the Institute of Veterinary, Animal and Biomedical Sciences, College of Sciences, Massey University, Palmerston North, New Zealand

Rumen methanogenesis represents a loss of between 2 to 15% of the energy intake by the animal, and methane (CH4) has a role in the global warming phenomenon. Thus, any reduction of ruminant CH4 emission would have both environmental and nutritional benefits. The development of cost-effective strategies to mitigate ruminant CH4 without causing a negative impact on animal production, especially for systems based on forages, is a major challenge. Large between-sheep (within a breed) variations in CH4 emission, under controlled and grazing conditions, have been described in the literature (Chapter 1). This thesis studied the nature and causes of the between-sheep variation in CH4 emission, with the objective of using it as a tool to reduce CH4 emission. The sulphur hexafluoride (SF6) tracer technique was used to measure CH4 emission throughout this study, therefore three trials were conducted with penned sheep in order to evaluate this technique against the standard respiration chamber (Chapter 2). Poor ventilation in the building and prolonged in rumen deployment of the SF6 permeation tubes were identified as reasons for poor agreement between the techniques in the initial trials. However, when these problems had been overcome, good agreement (r=0.79, p=0.02) between the techniques was found, with the tracer CH4 values being 10% lower than the chamber values. The tracer technique was then used to screen grazing sheep for their rates of CH4 emission, and three groups of sheep (8, 10 and 8 animals), each comprising sheep with low or high CH4 emissions, were selected, and their CH4 emissions were monitored during 12, 12 and 5 months, respectively (Chapter 3). This study showed that sheep did not maintain their rankings with respect to CH4 emission when they were brought from pasture to restricted indoor feeding conditions. However, they did maintain their rankings under generous grazing conditions, although the persistence of rankings weakened with time. A detailed study of rumen digestion (Chapter 4) was carried out with sheep fed indoors on lucerne hay at a restricted level (1.2 maintenance). This study revealed that particulate fractional outflow rate from the rumen (particulate FOR, % h-1) explained a large proportion (R2=0.57) of the between-animal variation in CH4 emission (%GEI). In addition to the negative relationship to CH4 emission (%GEI), particulate FOR was negatively correlated with rumen fill (g) (r=-0.69, p=0.03) and with digestibility of cellulose (r=-0.65, p=0.04). Based on the latter results, a simple field index for screening grazing sheep for rumen particulate FOR or rumen volume, based on changes in liveweight, was tested (Experiment 1, Chapter 5). LW change during short-term grazing, following overnight fasting, was strongly correlated with maximum rumen fill (determined at the end of evening grazing). This index was used to screen sheep and to select 10 sheep with 'small' rumen volumes and 10 sheep with 'large' rumen volumes. However, this index was not repeatable in subsequent measurements (Experiment 2, Chapter 5). In a later study (Chapter 6), sheep (6 animals) and alpaca (6 animals), two animal species with known differences in forestomach particulate FOR (lower in alpaca), were successively fed ad libitum on three different forages: (1) indoors on chaffed lucerne hay, (2) grazed on ryegrass/white clover pasture (RG/WC), and (3) grazed on Lotus corniculatus pasture (Lotus). In general, the quality of diets selected by the sheep, their voluntary feed intakes (per kg metabolic liveweight) and their CH4 emissions (g d-1) were higher than those of alpaca, but their CH4 emissions per unit of intake (%GEI) were lower than those of alpaca. On lucerne hay, the digestibility of cell walls was higher and the urinary energy loss lower in alpaca than in sheep. The sheep produced much less CH4 (%GEI) while grazing on Lotus than on the other feeds, whereas alpaca grazing Lotus showed low values for apparent digestion of cell walls. In conclusion, this thesis showed that particulate FOR, an animal-related factor, was a major contributor to the between-sheep variation in CH4 emission (%GEI) and particulate FOR was also suggested to be the underlying mechanism by which alpaca and sheep differed in their rates of CH4 emission (%GEI). Sheep ranked initially low or high for CH4 emission rates (%GEI) persisted in their rankings only under generous grazing conditions and this persistence weakened with time. Changes in diet selection or particulate FOR in response to the seasonal changes in pasture quality and composition may have been the reasons for the weakened persistence in CH4 emission. Future developments in techniques which can measure between-sheep differences in particulate FOR or rumen volume with large numbers of animals under grazing will be useful in the assessment of the benefits of these animal factors for CH4 mitigation. The depressing effect of Lotus corniculatus on CH4 emissions by sheep shown in this study represents another benefit of condensed tannin-containing temperate legumes for sustainable pastoral production systems