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.

The objective was to evaluate the effects of a specific strain of live yeast (LY) on growth performance, fermentation parameters, feed efficiency and bacterial communities in the rumen of growing cattle fed low-quality hay. In experiment (Exp) 1, twelve Droughtmaster bull calves (270 kg ± 7.6 kg initial BW) were blocked by BW into two groups, allocated individually in pens, and fed ad libitum Rhodes grass hay (8.4% of crude protein [CP]), and 300 g/bull of supplement (52% CP) without (Control) or with LY (8 x 10 9 CFU/day Saccharomyces cerevisiae CNCM I-1077, Lallemand Inc., Montreal, Canada) for 28 d, followed by seven days in metabolism crates. Blood and rumen fluid were collected before feeding and 4 h after feeding. In Exp 2, for assessment of growth performance, 48 Charbray steers (329 kg ± 20.2 kg initial BW) were separated into two blocks by initial BW and randomly allocated into 12 pens. The steers were fed Rhodes grass hay (7.3% CP) and 220 g/steer of supplement (60% CP) without or with LY (8 x 10 9 CFU/day) for 42 d, after a two-week adaptation period. In Exp 1, fiber digestibility was calculated from total fecal collection and in Exp 2, indigestible NDF was used as marker. Inclusion of LY increased (P = 0.03) NDF intake by 8.3% in Exp 1, without affecting total tract digestibility. No changes were observed in microbial yield or in the efficiency of microbial production. There was a Treatment × Time interaction (P &lt; 0.01) for the molar proportion of short chain fatty acids, with LY increasing propionate before feeding. Inclusion of LY decreased rumen ammonia 4 h after feeding (P = 0.03). Addition of LY reduced rumen bacterial diversity and the intraday variation in bacterial populations. Relative populations of Firmicutes and Verrucomicrobia varied over time (P &lt; 0.05) only within the Control group. At the genus level, the relative abundance of an unclassified bacterial genus within the order Clostridiales, a group of cellulolytic bacteria, was reduced from 0 to 4 h after feeding in the Control group (P = 0.02) but not in the LY group (P = 1.00). During Exp 2, LY tended to increase ADG (P = 0.08) and feed efficiency (P = 0.10), with no effect on NDF intake or digestibility. In conclusion, S. cerevisiae CNCM I-1077 reduced the intraday variation of rumen bacteria and increased the amount of NDF digested per day. These observations could be associated with the tendency of increased ADG and feed efficiency in growing cattle fed a low-quality forage.

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.

Animal temperament evaluation can be included in the cattle selection program also because of an existing correlation with performance. However, there are different assessment methods such as flight speed (time and speed that an animal takes to leave the crush) and exit score (indicating in which pace it does). Flight zone (FZ) refers to the distance that an animal allows human proximity without signs of fear (e.g., moving away and/or aggression) and it was used in this study as an alternative approach to measure temperament without putting cattle through the crush. Apparently, there is no study correlating FZ with performance. Therefore, a pilot trial was conducted to evaluate the correlation between average daily gain (ADG), dry matter intake (DMI) and feed conversion ratio (FCR) of ten Brahman steers. Steers were classified into temperament groups (Docile <2 m; Moderate between 2 to 2.9 m; and Lively ≥3 m). Even though no significant differences were found for ADG (P = 0.65), DMI (P = 0.36), and FCR (P = 0.46), the docile group gained 133 grams/day more than lively counterparts, most likely because of the extra 50 grams consumed. Furthermore, lively steers required an extra 1 kg of feed per kg of gain in comparison to docile animals, 8.24 vs. 7.28 kg FCR, respectively. These results are promising and indicate that FZ could be an efficient way to measure temperament in cattle. Thus, in order to confirm these findings, a new experiment with a more representative number of steers (n = 30) will be conducted.

The objective of this study was to determine the influence of a total-mixed ration including unsalable carrots at 45% DM on the rumen microbiome; and the plasma, rumen and liver metabolomes. Carrots discarded at processing were investigated as an energy-dense substitute for barley grain in a conventional feedlot diet, and improved feed conversion efficiency by 25%. Here, rumen fluid was collected from 34 Merino lambs at slaughter (n = 16 control; n = 18 carrot) after a feeding period of 11-weeks. The V4 region of the 16S rRNA gene was sequenced to profile archaeal and bacterial microbe communities. Further, a comprehensive, targeted profile of known metabolites was constructed for blood plasma, rumen fluid and biopsied liver metabolites using a gas chromatography mass spectrometry (GC–MS) metabolomics approach. An in vitro batch culture was used to characterise ruminal fermentation including gas and methane (CH4) production. In vivo rumen microbial community structure of carrot fed lambs was dissimilar (P < 0.01; PERMANOVA), and all measures of alpha diversity were greater (P < 0.01), compared to those fed the control diet. Unclassified genera in Bacteroidales (15.9 ± 6.74% relative abundance; RA) were more abundant (P < 0.01) in the rumen fluid of carrot-fed lambs, while unclassified taxa in the Succinivibrionaceae family (11.1 ± 3.85% RA) were greater (P < 0.01) in the control. The carrot diet improved in vitro ruminal fermentation evidenced as an 8% increase (P < 0.01) in DM digestibility and a 13.8% reduction (P = 0.01) in CH4 on a mg/ g DM basis, while the control diet increased (P = 0.04) percentage of propionate within total VFA by 20%. Fourteen rumen fluid metabolites and 27 liver metabolites were influenced (P ≤ 0.05) by diet, while no effect (P ≥ 0.05) was observed in plasma metabolites. The carrot diet enriched (impact value = 0.13; P = 0.01) the tyrosine metabolism pathway (acetoacetic acid, dopamine and pyruvate), while the control diet enriched (impact value = 0.42; P ≤ 0.02) starch and sucrose metabolism (trehalose and glucose) in rumen fluid. This study demonstrated that feeding 45% DM unsalable carrots diversified bacterial communities in the rumen. These dietary changes influenced pathways of tyrosine degradation, such that previous improvements in feed conversion efficiency in lambs could be explained.

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 &lt; 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.

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