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 towards 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.

The ruminant gastrointestinal tract (GIT) faces the challenge of protecting the host from luminal contents and pathogens, while supporting the absorption and metabolism of nutrients for growth and maintenance. The GIT of the calf in early life undergoes some of the most rapid microbial and structural changes documented in nature, and these adaptations in GIT function make the young calf susceptible to GIT diseases and disorders. Despite these challenges, the calf's GIT has a certain degree of plasticity and can sense nutrient supply and respond to bioactive ingredients. Calf GIT research has historically focused on the transition during weaning and characterizing ruminal papillae development using microscopy and digesta metabolite responses. Through the use of new molecular-based approaches, we have recently shown that delaying the age of weaning and providing a step-down weaning protocol is associated with a more gradual shift in ruminal microbiota to a postweaned state. In addition to ruminal adaptations during weaning, nutrient flow to the lower gut changes dramatically during weaning, coinciding with a wide array of structural and microbiological changes. Structural and gene expression changes suggest that the lower gut of the dairy calf undergoes alterations that may reduce barrier function when solid feeds are consumed. More recently, in vivo data revealed that the weaning transition increases total gut permeability of the calf. Interestingly, the lower gut may be able to communicate with the forestomach, meaning that a nutrient can be sensed in the lower gut and cause subsequent adaptations in the forestomach. An improved understanding of how diet, microbiota, and functional ingredients interact to affect growth and barrier function of the intestinal tract would greatly benefit the dairy calf industry. A mechanistic understanding of such adaptations would also aid in the formulation of specific management regimens and provision of functional ingredients required to characterize and enhance gut function in young calves.

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.

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.

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.

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 cm² 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.