S. J. Meale

Methane Production of Different Forages in In vitro Ruminal Fermentation.

An in vitro rumen batch culture study was completed to compare effects of common grasses, leguminous shrubs and non-leguminous shrubs used for livestock grazing in Australia and Ghana on CH4 production and fermentation characteristics. Grass species included Andropodon gayanus, Brachiaria ruziziensis and Pennisetum purpureum. Leguminous shrub species included Cajanus cajan, Cratylia argentea, Gliricidia sepium, Leucaena leucocephala and Stylosanthes guianensis and non-leguminous shrub species included Annona senegalensis, Moringa oleifera, Securinega virosa and Vitellaria paradoxa. Leaves were harvested, dried at 55°C and ground through a 1 mm screen. Serum bottles containing 500 mg of forage, modified McDougall’s buffer and rumen fluid were incubated under anaerobic conditions at 39°C for 24 h. Samples of each forage type were removed after 0, 2, 6, 12 and 24 h of incubation for determination of cumulative gas production. Methane production, ammonia concentration and proportions of VFA were measured at 24 h. Concentration of aNDF (g/kg DM) ranged from 671 to 713 (grasses), 377 to 590 (leguminous shrubs) and 288 to 517 (non-leguminous shrubs). After 24 h of in vitro incubation, cumulative gas, CH4 production, ammonia concentration, proportion of propionate in VFA and IVDMD differed (p<0.05) within each forage type. B. ruziziensis and G. sepium produced the highest cumulative gas, IVDMD, total VFA, proportion of propionate in VFA and the lowest A:P ratios within their forage types. Consequently, these two species produced moderate CH4 emissions without compromising digestion. Grazing of these two species may be a strategy to reduce CH4 emissions however further assessment in in vivo trials and at different stages of maturity is recommended.

Board-invited review: Opportunities and challenges in using exogenous enzymes to improve ruminant production.

The ability of ruminants to convert plant biomass unsuitable for human consumption into meat and milk is of great societal and agricultural importance. However, the efficiency of this process is largely dependent on the digestibility of plant cell walls. Supplementing ruminant diets with exogenous enzymes has the potential to improve plant cell wall digestibility and thus the efficiency of feed utilization. Understanding the complexity of the rumen microbial ecosystem and the nature of its interactions with plant cell walls is the key to using exogenous enzymes to improve feed utilization in ruminants. The variability currently observed in production responses can be attributed to the array of enzyme formulations available, their variable activities, the level of supplementation, mode of delivery, and the diet to which they are applied as well as the productivity level of the host. Although progress on enzyme technologies for ruminants has been made, considerable research is still required if successful formulations are to be developed. Advances in DNA and RNA sequencing and bioinformatic analysis have provided novel insight into the structure and function of rumen microbial populations. Knowledge of the rumen microbial ecosystem and its associated carbohydrases could enhance the likelihood of achieving positive responses to enzyme supplementation. The ability to sequence microbial genomes represents a valuable source of information in terms of the physiology and function of both culturable and unculturable rumen microbial species. The advent of metagenomic, metatranscriptomic, and proteomic techniques will further enhance our understanding of the enzymatic machinery involved in cell wall degradation and provide a holistic view of the microbial community and the complexities of plant cell wall digestion. These technologies should provide new insight into the identification of exogenous enzymes that act synergistically with the rumen microbial populations that ultimately dictate the efficiency of feed digestion.

Development of ruminal and fecal microbiomes are affected by weaning but not weaning strategy in dairy calves

The nature of weaning, considered the most stressful and significant transition experienced by dairy calves, influences the ability of a calf to adapt to the dramatic dietary shift, and thus, can influence the severity of production losses through the weaning transition. However, the effects of various feeding strategies on the development of rumen or fecal microbiota across weaning are yet to be examined. Here we characterized the pre- and post-weaning ruminal and fecal microbiomes of Holstein dairy calves exposed to two different weaning strategies, gradual (step-down) or abrupt. We describe the shifts toward a mature ruminant state, a transition which is hastened by the introduction of the solid feeds initiating ruminal fermentation. Additionally, we discuss the predicted functional roles of these communities, which also appear to represent that of the mature gastrointestinal system prior to weaning, suggesting functional maturity. This assumed state of readiness also appeared to negate the effects of weaning strategy on ruminal and fecal microbiomes and therefore, we conclude that the shift in gastrointestinal microbiota may not account for the declines in gain and intakes observed in calves during an abrupt weaning.

Dose-response of supplementing marine algae (Schizochytrium spp.) on production performance, fatty acid profiles, and wool parameters of growing lambs.

Microalgae are the original source of docosahexaenoic acid (DHA; 22:6n-3) in the marine food chain, and its inclusion in animal feeds has been considered as a means of increasing the DHA level in foods of animal origin. As such, this study aimed to investigate the effects of supplementing an algal meal, high in DHA derived from Schizochytrium spp. (DHA-G), in the diet of Canadian Arcott lambs, on growth, carcass characteristics, wool production, and fatty acid (FA) profiles of subcutaneous adipose tissues (SAT), perirenal adipose tissues (PAT), and skirt muscle (SM). Forty-four lambs were randomly assigned to dietary treatments. Diets consisted of a pelleted, barley-based finishing diet with DHA-G supplemented at 0, 1, 2, or 3% DM as a replacement for flax oil and barley grain. Feed deliveries and orts were recorded daily. Lambs were weighed weekly and slaughtered once they reached ≥ 45 kg live weight. Carcass characteristics, ruminal pH, and liver weights were determined at slaughter. Wool yield was determined on mid-side patches of 100 cm(2) shorn at d 0 and on the day before slaughter (d 105 or 140). Dye bands were used to determine wool growth, fiber diameter, and staple length. Adipose tissues and SM samples were taken at slaughter and analyzed for FA profiles. Data were analyzed using mixed procedure in SAS with orthogonal contrasts testing for linear, quadratic, or cubic responses to increasing levels of DHA-G. Daily DMI, ADG, and G:F were similar as were wool quality and yield (P > 0.05). Carcass characteristics were generally unaffected (P > 0.05), except for body wall thickness (mm), which showed a quadratic response (P = 0.01) with increasing DHA-G. The concentration of eicosapentaenoic acid (EPA; 20:5n-6; mg/100 g fresh tissue) linearly increased (P < 0.001) with DHA-G in both adipose tissues and responded quadratically in SM (P = 0.05). Similarly, DHA (mg/100 g fresh tissue) increased linearly (P < 0.01) with DHA-G in all tissue types (P < 0.001). Supplementing DHA-G decreased (P < 0.001) the n-6:n-3 ratio in all tissues. No effects (P ≥ 0.05) on PUFA or SFA were observed across the 3 tissues, with no response (P ≥ 0.10) in the SFA:PUFA ratio in either SM or SAT; however, the SFA:PUFA ratio linearly decreased in PAT (P = 0.01) as DHA-G increased. These results indicate that DHA-G can be successfully included in the diets of growing lambs, up to 3% DM, with the potential to improve carcass characteristics and the FA profile of adipose tissue and muscle.

Strategies to reduce greenhouse gases from ruminant livestock

Abstract Globally, methane emissions account for 40–45% of greenhouse gas emissions from ruminant livestock, with over 90% of these emissions arising from enteric fermentation. Consequently, enteric CH4 emissions are by far the single most important emission source that can be targeted for mitigation within the ruminant production cycle. This review aims to update nutritional and management abatement strategies for enteric methane emissions. Each ruminant production system is unique, and therefore a holistic, life cycle assessment should be considered when determining the potential value of any abatement strategy. It is important to bear in mind that any abatement strategy will only be adopted if it passes regulatory requirements and if there is an economic incentive for its implementation.

Effects of crude glycerin supplementation on wool production, feeding behavior, and body condition of Merino ewes.

The increasing availability of crude glycerin from the biodiesel industry has led to an interest in its use as an energy source in ruminant diets. However, its effects on ruminal fermentation patterns and methane (CH4) production are unclear, and there are no reports on the effect of its inclusion in the diet on wool production or growth of Merino sheep. Thus, the objectives of this study were to determine the effects of increasing levels of crude glycerin on in vitro ruminal fermentation and CH4 production and DMI, BW, feeding behavior, and wool growth and quality in Merino ewes. Crude glycerin (99.2% pure, colorless, odorless, viscous liquid) replaced whole wheat grain in completely pelleted diets at levels of 0%, 6%, and 12% DM in both in vitro and in vivo studies. For in vitro studies, diets were dried and ground through a 1-mm screen and incubated on 2 different days for 24 h. Modified McDougals buffer and rumen liquor were mixed 3:1, and gas production and CH4 concentration was measured after 6, 12, and 24 h of incubation with pH and IVDMD measured at 24 h. Cumulative gas (mL/g DM) and methane (mL) production was similar (P ≥ 0.35) among dietary treatments. In vitro dry matter disappearance (%) increased (P < 0.01) with increasing concentrations of crude glycerin. For the in vivo study, 39 Merino ewes were randomly assigned to 3 treatments (n = 13 ewes/treatment). Pelleted diets were available continuously for a 10-wk period through the use of automatic feeders. Ewes were weighed every 7 d. Wool yield was determined on mid-side patches of 100 cm(2) shorn at d 0 and d 70. Dye bands were used to determine wool growth and fiber length. Intake and ADG were similar among treatments (P = 0.59). Neither wool yield, length, spinning fineness, nor fiber diameter (μm) were affected after supplementation with crude glycerin (P ≥ 0.13). This study indicates the potential for crude glycerin to be included in the diets of Merino sheep at up to 12% DM without negatively affecting wool yield and quality.

Effect of diet on microRNA expression in ovine subcutaneous and visceral adipose tissues.

Knowledge of the molecular mechanisms that regulate ovine adipogenesis is very limited. MicroRNAs (miRNA) have been reported as one of the regulatory mechanisms of adipogenesis. This study aimed to compare the expression of miRNA related to ovine adipogenesis in different adipose depots and to investigate whether their expression is affected by dietary fatty acid composition. We also investigated the role of miRNA in adipogenic gene regulation. Subcutaneous and visceral adipose tissue samples were collected at slaughter from 12 Canadian Arcott lambs fed a barley-based finishing diet where an algae meal (DHA-Gold; Schizochytrium spp.) replaced flax oil and barley grain at 0 or 3% DM (n = 6). Total RNA from each tissue was subjected to quantitative real time (qRT-) PCR analysis to determine the expression of 15 selected miRNA including 11 identified from bovine adipose tissues and 4 conserved between bovine and ovine species. MicroRNAs were differentially expressed according to diet in each tissue depot (miR-142-5p and miR-376d) in visceral and miR-142-5p, miR-92a, and miR-378 in subcutaneous adipose tissue; P ≤ 0.05) and in each tissue depot depending on diet (miR-101, miR-106, miR-136, miR-16b, miR-196a-1, miR-2368*, miR-2454, miR-296, miR-376d, miR-378, and miR-92a in both control and DHA-G diets and miR-478 in control; P ≤ 0.05). Six miRNA were subjected to functional analysis and 3 genes of interest (ACSL1, PPARα, and C/EBPα) were validated by qRT-PCR. Both diet and tissue depot affected expression levels of all 3 genes (P < 0.05). miR-101, miR-106, and miR-136 were negatively correlated with their respective predicted gene targets C/EBPα, PPARα, and ACSL1 in subcutaneous adipose tissue of lambs fed DHA-G. Yet miR-142-5p and miR-101 showed no correlation with ACSL1 or C/EBPα. The variability in expression patterns of miRNA across adipose depots reflects the tissue specific nature of adipogenic regulation. Although the examined miRNA appear to be conserved across ruminant species, our results indicate the presence of ovine specific regulatory mechanisms that can be influenced by diet.

RUMINANT NUTRITION SYMPOSIUM: Use of genomics and transcriptomics to identify strategies to lower ruminal methanogenesis

Globally, methane (CH4) emissions account for 40% to 45% of greenhouse gas emissions from ruminant livestock, with over 90% of these emissions arising from enteric fermentation. Reduction of carbon dioxide to CH4 is critical for efficient ruminal fermentation because it prevents the accumulation of reducing equivalents in the rumen. Methanogens exist in a symbiotic relationship with rumen protozoa and fungi and within biofilms associated with feed and the rumen wall. Genomics and transcriptomics are playing an increasingly important role in defining the ecology of ruminal methanogenesis and identifying avenues for its mitigation. Metagenomic approaches have provided information on changes in abundances as well as the species composition of the methanogen community among ruminants that vary naturally in their CH4 emissions, their feed efficiency, and their response to CH4 mitigators. Sequencing the genomes of rumen methanogens has provided insight into surface proteins that may prove useful in the development of vaccines and has allowed assembly of biochemical pathways for use in chemogenomic approaches to lowering ruminal CH4 emissions. Metagenomics and metatranscriptomic analysis of entire rumen microbial communities are providing new perspectives on how methanogens interact with other members of this ecosystem and how these relationships may be altered to reduce methanogenesis. Identification of community members that produce antimethanogen agents that either inhibit or kill methanogens could lead to the identification of new mitigation approaches. Discovery of a lytic archaeophage that specifically lyses methanogens is 1 such example. Efforts in using genomic data to alter methanogenesis have been hampered by a lack of sequence information that is specific to the microbial community of the rumen. Programs such as Hungate1000 and the Global Rumen Census are increasing the breadth and depth of our understanding of global ruminal microbial communities, steps that are key to using these tools to further define the science of ruminal methanogenesis.

Weaning age influences the severity of gastrointestinal microbiome shifts in dairy calves

Ruminants microbial consortium is responsible for ruminal fermentation, a process which converts fibrous feeds unsuitable for human consumption into desirable dairy and meat products, begins to establish soon after birth. However, it undergoes a significant transition when digestion shifts from the lower intestine to ruminal fermentation. We hypothesised that delaying the transition from a high milk diet to an exclusively solid food diet (weaning) would lessen the severity of changes in the gastrointestinal microbiome during this transition. β-diversity of ruminal and faecal microbiota shifted rapidly in early-weaned calves (6 weeks), whereas, a more gradual shift was observed in late-weaned calves (8 weeks) up to weaning. Bacteroidetes and Firmicutes were the most abundant ruminal phyla in pre- and post-weaned calves, respectively. Yet, the relative abundance of these phyla remained stable in faeces (P ≥ 0.391). Inferred gene families assigned to KEGG pathways revealed an increase in ruminal carbohydrate metabolism (P ≤ 0.009) at 9, compared to 5 weeks. Conversely, carbohydrate metabolism in faeces declined (P ≤ 0.002) following a change in weaning status (i.e., the shift from pre- to post-weaning). Our results indicate weaning later facilitates a more gradual shift in microbiota and could potentially explain the negative effects of early-weaning associated with feeding a high-plane of pre-weaning nutrition.

The Structural and Functional Capacity of Ruminal and Cecal Microbiota in Growing Cattle Was Unaffected by Dietary Supplementation of Linseed Oil and Nitrate

Microorganisms in the digestive tract of ruminants differ in their functionality and ability to use feed constituents. While cecal microbiota play an important role in post-rumen fermentation of residual substrates undigested in the rumen, limited knowledge exists regarding its structure and function. In this trial we investigated the effect of dietary supplementation with linseed oil and nitrate on methane emissions and on the structure of ruminal and cecal microbiota of growing bulls. Animals were allocated to either a CTL (control) or LINNIT (CTL supplemented with 1.9% linseed and 1.0% nitrates) diet. Methane emissions were measured using the GreenFeed system. Microbial diversity was assessed using amplicon sequencing of microbial genomic DNA. Additionally, total RNA was extracted from ruminal contents and functional mcrA and mtt genes were targeted in amplicon sequencing approach to explore the diversity of functional gene expression in methanogens. LINNIT had no effect on methane yield (g/kg DMI) even though it decreased methane production by 9% (g/day; P < 0.05). Methanobrevibacter- and Methanomassiliicoccaceae-related OTUs were more abundant in cecum (72 and 24%) compared to rumen (60 and 11%) irrespective of the diet (P < 0.05). Feeding LINNIT reduced the relative abundance of Methanomassiliicoccaceae mcrA cDNA reads in the rumen. Principal component analysis revealed significant differences in taxonomic composition and abundance of bacterial communities between rumen and cecum. Treatment decreased the relative abundance of a few Ruminococcaceae genera, without affecting global bacterial community structure. Our research confirms a high level of heterogeneity in species composition of microbial consortia in the main gastrointestinal compartments where feed is fermented in ruminants. There was a parallel between the lack of effect of LINNIT on ruminal and cecal microbial community structure and functions on one side and methane emission changes on the other. These results suggest that the sequencing strategy used here to study microbial diversity and function accurately reflected the absence of effect on methane phenotypes in bulls treated with linseed plus nitrate.