Despite considerable effort to develop and optimise additives to reduce methane emissions from cattle, little information on additive effectiveness exists for cattle under grazing scenarios. As the majority of Australian cattle production occurs on grazing land it is pertinent to report on the use of additives under simulated conditions. The current study evaluated the addition of nine additives to Rhodes grass hay under in vitro conditions, to estimate their impact on methane (CH4), gas production, and rumen fermentation parameters (volatile fatty acids, rumen pH and in vitro dry matter digestibility [IVDMD]). Citral extract at 0.1% of rumen media decreased all CH4 production parameters, but reduced gas production and digestibility, compared to a 100% hay control. Similarly, Sandalwood essential oil decreased CH4 production at 48 h, IVDMD and gas production, compared to the control. Biochar + nitrates at 5 and 8% DM, and Biochar + Asparagopsis at 5% DM decreased cumulative CH4 production (15.6%, 25.9%, 23.8%, respectively; P < 0.01), compared to the control. No changes in IVDMD and gas production were observed. As such, the biochar additives were considered the most promising additives from those evaluated with a substrate designed to replicate Australian grazing systems.

Background: A foal undergoes considerable growth and development from birth to weaning, progressing from a milk-based diet to complete herbivory. The symbiotic relationships between bacteria, archaea and fungi substantiate this energy demand by colonising the hindgut and remaining flexible throughout the diet transitions. Methods: A total of 70 faecal samples were collected from 14 mares and their foals across five studs in NSW as they aged from 0 to 5 months old. DNA was extracted from faecal samples and underwent amplification and sequencing of the 16S rRNA gene V4 hypervariable region of archaea and bacteria, and the fungal internal transcribed spacer-1 (ITS1) region. The fungal and bacterial community structure was assessed using Bray-Curtis dissimilarities, and the effect of age at sampling and location was determined using PERMANOVA. Results: Age at sampling had a substantial effect on the foal's archaeal and bacterial faecal microbiota (PERMANOVA: R 2 = 0.16; p < 0.01), while the effect of geographical location was smaller but still significant (PERMANOVA: R 2 = 0.07; p < 0.01). The overall abundance, diversity and richness of bacterial and archaeal populations increased (p < 0.01) as foals aged, most noticeably rising between foals 1 to 2 and 2 to 3 months of age. The 15 most relatively abundant fungal species were all environmental saprophytes, most strongly affected by geographical location (p < 0.01) rather than age at sampling. There was an effect of location on Preussia Africana (p = 0.02) and a location × age interaction for fungal species Preussia persica (p < 0.01), Acremonium furcatum (p = 0.04), and Podospora pseudocomata (p = 0.01). There was no effect of age, location, or location × age interaction on the relative abundance of the remaining fungal species. Conclusions: The faecal microbiome appeared to stabilise for most bacterial and archaeal genera by 2 to 3 months of age, resembling an adult mare. Bacterial genera isolated from faecal samples belonged mainly to the Firmicutes phylum. Age at sampling more strongly affected the archaeal and bacterial faecal microbiota than the effect of the geographical location where the horse was sampled. The lack of effect of location on microbe populations suggests that although environmental factors may influence population structure, there are distinct differences at each stage of foal maturation.

Context Beef cattle feed efficiency is challenged in northern Australian production systems due to the limited dietary protein, leading to changes in rumen bacterial populations and fermentation outcomes. Aims Two types of diets with different dietary protein contents were used to evaluate changes in rumen bacterial composition and diversity, aiming to correlate rumen bacterial populations with feed and rumen efficiency parameters. Methods In total, 90 Brahman steers (341 ± 45 kg BW) were selected for this trial, but rumen fluid was collected from 85 Brahman steers, at 0 and 4 h after feeding, during a feed-efficiency trial. The steers were fed with a low-protein diet, including 70% rumen-degradable protein and 8.8% crude protein (CP) for 60 days, followed by a high-protein diet for the same period (13.5% CP). Liveweight and dry-matter intake measurements, as well as urine, faeces and rumen fluid samples, were collected to determine feed and rumen efficiency, and ruminal bacteria composition. Steers were clustered into groups using principal component analysis and Ward’s hierarchical method, and differences in feed-efficiency parameters among clusters were compared. Key results Rumen bacterial composition differed between diets (P < 0.01) and diversity changes were more related to bacterial richness (P < 0.01). In a low-protein diet, there were four distinct clusters of steers, on the basis of rumen bacteria, in which the most efficient steers, with a better residual feed intake (P = 0.06) and lower rumen ammonia concentration (P < 0.01) before feeding, had the highest relative abundance of Prevotella (P < 0.01). While in a high-protein diet, no differences were observed on feed or rumen fermentation parameters among steer clusters. Conclusion In a low-protein diet, rumen bacterial shifting might contribute to upregulate nitrogen recycling, favouring feed efficiency. Implications Identifying ruminal bacterial populations involved in nitrogen recycling upregulation might be useful to select the most efficient cattle fed low-protein diets.