Forage Diet Research Articles

Impact of Feed Composition on Rumen Microbial Dynamics and Phenotypic Traits in Beef Cattle

The rumen microbiome is central to feed digestion and host performance, making it an important target for improving ruminant productivity and sustainability. This study investigated how feed composition influences rumen microbial abundance and phenotypic traits in beef cattle. Fifty-nine Angus bulls were assigned to forage- and grain-based diets in a randomized block design, evaluating microbial dynamics, methane emissions, and feed efficiency. Quantitative PCR (qPCR) quantified bacterial, archaeal, fungal, and protozoal populations. Grain-based diets reduced bacterial and fungal counts compared to forage diets (1.1 × 1011 vs. 2.8 × 1011 copies of 16S rRNA genes and 1.5 × 103 vs. 3.5 × 104 copies of 18S rRNA genes/mL, respectively), while protozoan and methanogen populations remained stable. Microbial abundance correlated with feed intake metrics, including dry matter and neutral detergent fiber intakes. Methane emissions were lower in grain-fed bulls (14.8 vs. 18.0 L CH4/kg DMI), though feed efficiency metrics showed no direct association with microbial abundance. Comparative analysis revealed adaptive microbial shifts in response to dietary changes, with functional redundancy maintaining rumen stability and supporting host performance. These findings provide insights into how feed composition shapes rumen microbial dynamics and host phenotypes, highlighting the functional adaptability of the rumen microbiome during dietary transitions.

The effect of a sugarcane polyphenol extract on intake, apparent total tract digestibility, rumen fermentation, pH, methane emissions, and rumen microbiome of beef heifers fed a high forage diet

The effect of a sugarcane polyphenol extract on intake, apparent total tract digestibility, rumen fermentation, pH, methane emissions, and rumen microbiome of beef heifers fed a high forage diet

Influence of Dietary Forage Neutral Detergent Fiber on Ruminal Fermentation, Chewing Activity, Nutrient Digestion, and Ruminal Microbiota of Hu Sheep

Influence of Dietary Forage Neutral Detergent Fiber on Ruminal Fermentation, Chewing Activity, Nutrient Digestion, and Ruminal Microbiota of Hu Sheep

Forage sources in total mixed rations on rumen fermentation, gut fill, and development of the gastrointestinal tract of dairy calves

The inclusion of forage sources in calf diets is often discussed, and the main point debated is whether the inclusion level, particle size, source, and how forage is offered may impact gut fill and reduce body weight gain, as well as impact gastrointestinal tract development. This study aimed to determine the effects of feeding forage sources with different qualities on rumen fermentation, gut fill, and development of the gastrointestinal tract of dairy calves. Forty-eight Holstein dairy calves were blocked according to sex and body weight (BW) at 28 days of life and randomly assigned to 1 of 4 dietary treatments. Treatments consisted of a no-forage coarsely ground starter (CON) or total mixed rations containing 7.5% on DM basis of Tifton hay of either medium quality (MH) or low quality (LH) or 10% on DM basis of corn silage (CS). The nutritional content, including crude protein, NDF, lignin, and in vitro digestibility, was used as forage quality criteria. During the first 28 days of life, all calves received 3 L of whole milk twice daily, a commercial pelleted starter ad libitum, and no forage. After that, the solid diet was changed to the respective dietary treatments. Rumen samples were taken to determine rumen pH and volatile fatty acid (VFA) proportions. Calves were gradually weaned from 52 to 56 d of age, and 20 calves, 5 per treatment, were harvested two weeks after weaning. The anatomical parts of the gastrointestinal tract were weighed with and without contents, and histological analysis of rumen epithelium was conducted. The CON diet increased total VFA concentration compared to forage diets. The forage diets increased rumen pH, fecal pH, and gut fill. However, regardless of the source, the forage provision did not affect empty body weight. In addition, the forage provision increased the number of papillae in the rumen, but diets did not influence the length and width of papillae. The results suggest that 7.5% of Tifton hay, regardless of the quality, and 10% of corn silage in high-starch mixed diets benefit rumen health and promote greater gut fill without negative effects on final body weight.

Medicinal forage and herbal diets: a new approach to sustainable farming

Medicinal and aromatic plants have long been used in traditional medicine, for preparing food or feeding livestock as well as during religious ceremonies and to manufacture cosmetics. The concept of “medicinal forage” refers to plants that provide both nutrition and medicinal benefits to animals, forage crops containing active compounds or secondary metabolites, as well as the method of intercropping medicinal plants with forage crops. Aromatic plants, herbs and their derivatives such as essential oils have been studied in the literature for their potential application to replace antibiotics in ruminant diets. In the research world, scientists are examining natural plant compounds like tannins, saponins and essential oils which could become part of alternative applications for antibiotics. Herbal diets can reduce, and sometimes negate the disease incidence in animals; increase reproductive health of livestock and sustainable weight gain. The economic benefits are typically decreased veterinary expenses, higher profits because of a lower cost to production ratio and the premium consumers will pay for organic products. The inclusion of medicinal forage and herbs in the diet can be used as a tool to increase animal welfare and productivity but also brings agriculture towards sustainability through animals raised organically by associating different species.

Optimising compensatory growth in pastoral beef production systems: insights into feed efficiency, body composition, carcass characteristics and meat quality attributes.

Exploitation of compensatory growth (CG) is a widely practised management strategy in beef production, especially under pastoral conditions due to its potential to reduce feed costs. The aim of this experiment was to evaluate the effect of nutritional restriction during backgrounding in Angus steers slaughtered at either similar age and/or similar BW on feed efficiency, body composition, carcass characteristics and meat quality attributes under either a forage or feedlot-based finishing diet. Eighty steers (BW: 444±39kg, age: 18±1months) were blocked and randomly assigned within block to either an optimal (0.6-0.7kg/day) or suboptimal (0.3-0.4kg/day) growth rate, during 97days of backgrounding. Following, half of the steers in each group were finished on a forage diet while the other half were finished on feedlot-based diet. Half of the steers in each treatment were then slaughtered at similar age (24months), whilst all remaining steers were slaughtered at similar BW (∼620kg). Two extra slaughters were done with other representative steers on day 0 and day 97, to provide baseline parameters for carcass and non-carcass measurements. During the backgrounding period, optimal steers gained more than suboptimal (P<0.01), resulting in higher BW and hot carcass weight (HCW; P<0.01). During the finishing period, the suboptimal group increased BW gain (P<0.01) and displayed an improved feed conversion ratio (FCR; P<0.01). Differences (P<0.01) in BW and HCW remained between the treatments when slaughtered at a similar age. When the steers were slaughtered at similar BW, after additional days of finishing for the suboptimal groups, no differences (P>0.05) in backgrounding treatment on HCW, carcass grading, body composition or FCR for the entire period (backgrounding and finishing) were apparent. Indeed, no differences (P>0.05) by backgrounding growth strategy were observed for any meat quality variables assessed using instrumental or sensory evaluations. During the finishing period, feedlot steers had increased (P<0.01) BW and HCW gains, improved (P<0.05) FCR and carcass grading, and had higher (P<0.05) HCW compared to forage finished steers. However, no differences (P>0.05) were observed for any meat quality variables assessed by finishing system. Overall, exploiting CG within pasture-based beef cattle production systems improves growth rate and FCR in both forage and feedlot finishing. Suboptimal backgrounded steers required additional days on feed to achieve similar BW to their contemporaries. Nevertheless, at similar BW, there were no residual differences in body composition, FCR during the entire period, meat tenderness or overall meat liking because of the backgrounding conditions.

Impact of dietary forage proportion and crossbreeding on feed efficiency and methane emissions in lactating dairy cows

Impact of dietary forage proportion and crossbreeding on feed efficiency and methane emissions in lactating dairy cows

Site Matters: Differences in Gene Expression Profiles Along the Bovine Rumen Papilla During Subacute Rumen Acidosis.

Subacute rumen acidosis (SARA) is a significant concern in dairy cattle fed grain-rich diets. To elucidate the underlying pathophysiological mechanisms, ruminal papilla biopsies are often used. This study aimed to assess how the sampling site along the ruminal papilla influences gene expression profiles in rumen epithelium during SARA. Rumen biopsies from five ruminal-cannulated non-lactating Holstein cows were collected during feeding of a forage diet (FD) and seven (wk1) and 21 days (wk3) after transition to high-grain (HG) feeding. Gene expression in apical (AP), basal (BP), and total length (TP) papillae were compared using RT-qPCR. Significant diet-induced effects were observed in AP for DSG1 (wk3, p = 0.0317), ZO1 (wk1 and wk3, p = 0.0159), GLUT3 (wk3, p = 0.0159), TLR4 (wk3, p = 0.0635), and NFKB (wk1, p = 0.0159), but hardly in BP or TP. Within wk1, TP showed higher transcript levels of ZO1 and TLR4 (p = 0.0079) and SGLT1 (p = 0.0317) compared to AP and BP independently from diet effects. These findings suggest that the apical parts of rumen papillae biopsies are most suitable for gene expression analyses to investigate diet-induced effects on rumen physiology and underscore the importance of considering the sampling site for accurate gene expression studies in rumen epithelium during SARA, providing valuable insights for future research and diagnostic approaches in managing rumen health in dairy cattle.

Effect of contrasting water-soluble carbohydrate to crude protein ratio’s in perennial ryegrass on nitrogen metabolism in lambs

ABSTRACT The effect of high and low water-soluble carbohydrate (WSC) to crude protein (CP) ratios on nitrogen balance in lambs was evaluated. Ryegrasses containing either 35.4% WSC and 12% CP (High WSC) or 14.8% WSC and 23.8% CP (High N) were harvested, frozen and fed to lambs in metabolism crates. These contrasts in WSC and CP delivered diets with markedly different WSC:CP ratios (3.17:1 and 0.70:1). These ratios were higher than those reported in ryegrass previously. There was no difference in urinary nitrogen concentration (0.46 vs 0.48 g/l) but as the total urinary volume was higher on the High N diet (4.2 vs 1.5 l/d, P < 0.001), the end result was that more N was excreted in the urine on the high N diet (18.8 vs 7.3 g/d, P < 0.001). However, the proportion of nitrogen intake that was excreted in urine and faeces was higher on the High WSC diet so there was no evidence that a high WSC forage diet improved nitrogen utilisation.

Synergistic Effects of Mannan Oligosaccharides and Onion Peels on In Vitro Batch Culture Fermentation of High Concentrate and Forage Diets.

The current study evaluated the effect of combining mannan oligosaccharide (MOS) and onion peel (OP) on ruminal in vitro total gas (GP), greenhouse gas emissions, dry matter and fiber fraction digestibility, partitioning factor (PF24; mg degradable DM per mL gas), microbial mass, and volatile fatty acids using two dietary substrates: high forage (HF) and high concentrate (HC) diets. The study was arranged as a 2 × 2 × 6 factorial design with two dietary substrates, two time points (6 and 24 h), and six treatments. The treatments included a control group with no MOS or OP administration and groups administered with 2% of a mixture containing MOS and OP in the following ratios: 1:0 (MOS), 0:1 (OP), 1:1 (MOS:OP), 1:2 (MOS:2OP), and 1:3 (MOS:3OP). No significant diet × treatment interactions were observed for any of the measured parameters. However, treatments decreased (p < 0.05) the undegraded portion of HC, and treatment × substrate interactions were significant (p < 0.05) for PF24 and microbial mass. The treatments in the HC diet produced higher GP (p < 0.001) at 6 h compared to the treatments in the HF diet. Administration of MOS:2OP to the HC diet increased GP at 24 h of incubation, while the lowest GP was observed with the OP in the HF diet. The administration of MOS, OP, and MOS:2OP to the HC diet decreased methane production at 24 h of incubation. Additionally, MOS:2OP and MOS:3OP increased (p < 0.001) degradable acid detergent fiber (dADF) in the HC diet at 6 h of incubation. Both OP and MOS:3OP decreased the degradability of acid detergent lignin in the HC diet (p < 0.001). The OP also resulted in the lowest DM disappearance (p < 0.001) at 24 h of incubation in the HF diet, while the MOS:3OP had the highest dADF. At the end of incubation, the highest productions of total volatile fatty acids and acetate were observed (p = 0.002) with the MOS:OP administration in the HC diet, whereas the lowest values were observed with MOS and OP administration to the HF diet. The inclusion of mannan oligosaccharide and onion peel combinations as additives improved substrate (HC and HF) fermentation, leading to higher GP and volatile fatty production, and modulated fiber degradability by improving the breakdown of acid detergent fiber and acid detergent lignin.

Impacts of winter crop choice and ewe body condition score change on whole farm profitability and production

Variations in body condition score (BCS) in ewes influences lamb survival, ewe survival and ewe lactation performance. Feeding a low protein diet such as fodder beet to ewes in mid-to-late pregnancy increases lamb losses and reduces lamb weaning weight even further. However, using high yielding forages such as fodder beet can reduce the area of winter crop required, introducing potential whole-farm benefits which may alter profitability. We analysed the effects of winter crop choice (brassica or fodder beet) and BCS (maintaining or reducing) on whole-farm production and profitability, using a targeted supplement to offset the impacts of fodder beet feeding. Eight farms were selected to represent low or high rainfall (590 and 1090 mm/annum respectively) regions of the South Island. Impacts of changing BCS on ewe and lamb survival at lambing, and lamb liveweight gain to weaning were calculated when fed either adequate (brassica) or low protein (fodder beet) diets in mid-to-late pregnancy. Production statistics and profitability were calculated using Farmax. Whole farm profitability was analysed using BCS change and winter forage crop as main treatments, blocked by low or high rainfall. Applying the effects of BCS and low protein diets on reproductive performance from prior published studies resulted in variation of 102 to 141 lambs weaned per 100 ewes mated, with the lowest value when the low protein, fodder beet only diet was used. Greatest number of lambs weaned was achieved when BCS was maintained through winter through provision of a balanced supplement, regardless of winter forage diet (P&lt;0.05). Lamb sale dates were later when fodder beet was used, due to lower lamb weaning weights, resulting in marginally higher prices due to changes in pricing schedule. Farm profitability was increased by 25% when BCS was maintained though winter (P&lt;0.05) irrespective of the diet used. Use of fodder beet must be accompanied by targeted supplementation to avoid ewe BCS loss increased lamb losses and the negative effects on wastage and animal welfare. Extra profitability could only be generated by opportunities to sell surplus feed during the summer. These responses were similar in both high and low rainfall environments. This study is unique in testing measured responses of BCS and targeted nutritional supplementation under specific physiological conditions on whole-farm profitability. Farmer decisions on feed utilisation and sale also have a significant influence on the potential to mitigate the effects of variations in winter forage choice.

Stability of Gastric Fluid and Fecal Microbial Populations in Healthy Horses under Pasture and Stable Conditions.

Equine gastrointestinal microbial communities vary across the gastrointestinal tract and in response to diet or disease. Understanding the composition and stability of gastric fluid microbiota in healthy horses is a prerequisite to understanding changes associated with the development of disease. The objective of this study was to describe microbial communities in the gastric fluid and feces of healthy horses longitudinally. Horses were maintained on pasture (6 weeks), stabled (5 weeks), then returned to pasture. A consistent forage diet was provided throughout. Native gastric fluid and feces were collected weekly for full-length 16S ribosomal DNA sequencing and microbial profiling analysis. Fewer taxa were identified in the gastric fluid (770) than in the feces (5284). Species richness and diversity were significantly different between sample types (p < 0.001), but not between housing locations (p = 0.3). There was a significant effect of housing and horse on the Bray-Curtis compositional diversity of gastric (p = 0.005; p = 0.009) and fecal (p = 0.001; p = 0.001) microbiota. When horses moved from pasture to stable, the relative proportions of gastric fluid Lactobacillaceae increased and Streptococcaceae decreased, while fecal Firmicutes increased and Bacteriodota decreased. Within each housing condition, there was no significant week-to-week variation in gastric (p = 0.9) or fecal (p = 0.09) microbiota. Overall, these findings support the maintenance of stable gastric and fecal microbial populations under each management condition, providing a basis for further investigation of gastric fluid microbiota in diseases of the foregut.

Residual feed intake measured as replacement heifers is indicative of residual feed intake measured as mature cows

This study aimed to quantify the relationship between residual feed intake (RFI) measured in 500 heifers and subsequently as mid-gestation cows at the Roy Berg Kinsella Research Station (KIN; n=227) and Lacombe Research and Development Centre (LRDC; n=273). Heifers were initially tested for RFI adjusted for end of test rib fat (RFIfat) at 8-12 mo of age and then again as 3-yr old first-calf heifers at KIN and as 4-13 yr old cows at LRDC. Heifer RFIfat measured in drylot on a forage diet was associated (R2 &gt;0.53; P &lt; 0.001) with RFIfat measured again as older cows. Each 1 kg DM d-1 change in heifer RFIfat equaled 0.48±0.10 and 0.75±0.19 kg DM d-1 change in cow RFIfat for KIN and LRDC, respectively. Linear effects were also reported for RFIfat component traits, where DMI (P&lt;0.001), ADG (P&lt;0.060), mid-test metabolic weight (P&lt;0.001) and end of test rib fat (P&lt;0.001) measured as heifers were related when measured again as older cows. In addition, the linear effects of heifer RFIfat on cow RFIfat were constant across cow age groups from 4-10 yr of age. These results show that selection for RFI in heifers will result in cows that are also more feed efficient.

Supplementation of isoacids to lactating dairy cows fed low or high forage diets: Effects on performance, digestibility, and milk fatty acid profile

Our objective was to determine the effects of isoacids (ISO) on the lactation performance, digestibility, and milk fatty acid (FA) profile of Holstein cows fed 2 forage NDF levels (FL). The study was 10-wk long (including 2-wk for covariate) utilizing a randomized complete block design. Sixty-four mid-lactating Holstein cows [662 ± 71 kg BW, 119 ± 51 DIM, 2 ± 0.9 parity] were blocked by parity, DIM, and prior milk yield (MY) for multiparous cows or genetic merit for primiparous cows, and randomly assigned to 1 of the 4 diets (n = 16). Diets were arranged as a 2 × 2 factorial, with 2 FL containing 21 (HF) and 17% forage NDF (LF) without (WIA) or with ISO supplementation (IA, 7.85 mmol/kg DM and 3.44 mmol/kg DM for isobutyrate and 2-methylbutyrate, respectively). Diets were balanced for similar NEL (1.58 Mcal/kg DM), CP (16.0%) and total NDF (27.2%). Feed intake and MY were recorded daily. Nutrient digestibility for each cow was determined using indigestible NDF as a marker, and fecal samples were collected at 8-time points (4 h intervals between samples). Individual cow milk samples composited over a 10-wk period were analyzed using gas chromatography for FA profile. The statistical model included FL, ISO, and FL × ISO as fixed effects and block as a random effect (lme4 in R). The ISO did not affect DMI (P = 0.13), while LF had greater DMI than HF diets (27.8 vs. 26.0 kg/d; P < 0.01). However, ISO increased MY (34.7 vs. 37.2 kg/d; P < 0.01) and ECM (41.9 vs. 39.0 kg/d; P < 0.01) by 7% in HF but not in the LF diet, suggesting FL × ISO interaction (P = 0.04). Interestingly, ISO increased ADG (0.4 kg/d) but decreased MUN by 9% only in LF diet as indicated by FL × ISO interaction (P < 0.01). Additionally, ISO increased DM, OM, NDF, and CP digestibility by 10-24% in HF (P < 0.01), but not in LF (FL × ISO; P > 0.05). As expected, ISO increased milk odd chain FA profiles in the IA groups irrespective of FL, e.g., the IA had greater C15:0 (1.87 vs. 1.54 g/100g FA; P = 0.03) and a tendency to be greater C17:0 levels (0.86 vs. 0.76 g/100g FA; P = 0.05) compared with WIA groups. Overall, ISO improved MY and nutrient digestibility in the HF whereas it increased ADG and decreased MUN in LF diet. Additionally, ISO increased milk odd chain FA (C15:0 and C17:0) regardless of FL.

Isoacid supplementation influences feed sorting, chewing behaviors, and enteric methane emissions differentially in mid-lactation dairy cows depending on dietary forage level

Past studies have shown that isoacids (ISO) improve dairy cow performance, with effects varying based on dietary forage levels, leading us to speculate that ISO supplementation may also differentially affect enteric methane (CH4) emissions depending on dietary forage levels. Therefore, our primary objective was to examine the effects of ISO supplementation on enteric CH4 emissions in lactating dairy cows fed 2 forage NDF levels (FL), along with monitoring feed particle sorting and chewing behaviors to assess any potential interactions. Sixty-four (64) mid-lactation Holstein cows were utilized in a 10-wk long randomized complete block design trial. Parity, DIM, and prior milk yield (MY) for multiparous cows or genetic merit for primiparous cows were used as blocking factors. Cows were randomly assigned to 1 of 4 diets (n = 16 per diet) with a 2 × 2 factorial arrangement of treatment combinations, including 2 FL, 17 (LF) and 21% forage NDF (HF), without or with ISO supplementation (7.85 mmol/kg DM for isobutyrate and 3.44 mmol/kg DM for 2-methylbutyrate, respectively). Enteric CH4 and chewing activity (rumination and eating time) were measured using the GreenFeed system and sensor-based ear tag system, respectively. The particle size of each diet and ort from individual cows was measured using the Penn State Particle Separator, and a sorting index was calculated. A sorting index of 100 indicates no sorting, while values above or below 100 indicate sorting for or against, respectively. Data were analyzed using a mixed model including FL, ISO, and FL × ISO as fixed effects and block as a random effect (lme4 in R). Our result shows that ISO increased sorting index for long particle in LF (96.1 vs. 109; P < 0.01) but decreased it in HF (100.8 vs. 92.5; P = 0.04). In contrast, ISO did not affect the physically effective particle sorting index (P = 0.51) or intake (P = 0.27) regardless of FL. In alignment with the long particle sorting index, ISO decreased eating and chewing time in the HF but increased them in the LF diet (P < 0.01). In contrast, rumination time was comparable between FL (P = 0.70) and ISO levels (P = 0.19). In the LF diet, ISO supplementation reduced daily CH4 production (g/d) by 9% and intensity (g/kg of MY) by 18% (P < 0.01). In the HF diet, ISO supplementation led to a 10% increase in daily CH4 (P < 0.01) but did not change CH4 intensity (P = 0.17; g/kg of MY) due to improved milk production. Overall, ISO altered feed sorting, feeding behaviors and enteric CH4 emissions depending on FL.

PSX-15 Effect of starch supplementation on rumen bacterial abundance in Bos taurus indicus steers consuming low-quality forage

Abstract Deficient ruminally available nitrogen caused by a basal diet of low-quality forage can limit microbial growth in the rumen and decrease forage utilization. Protein supplementation is well-documented to improve forage digestibility and performance. Additionally, starch has been evaluated to increase energy supply to grazing cattle when the forage cannot support adequate levels of production. However, most research in this area has been conducted in Bos taurus taurus, especially the response of the rumen microbiome to supplementation. Accordingly, the objective of this study was to evaluate the effects of increasing starch supplementation on rumen bacterial populations in Bos taurus indicus steers supplemented protein and consuming low-quality forage. Ruminal samples were collected from five ruminally-cannulated Brahman steers (BW 420 ± 55 kg) used in a 4×4 Latin square fed a basal diet of King Ranch Bluestem Hay (3.5% CP and 73% NDF) provided ad libitum, and one of four isonitrogenous (130 mg N/kg BW) supplements with increasing levels of starch (2% starch= 100% soybean meal; 20% starch= 73% soybean meal, 26.2% corn, 0.8% urea; 38% starch = 47% soybean meal, 51.6% corn, 1.4% urea; 56% starch= 19% soybean meal, 78.6% corn, 2.4% urea). Rumen content samples were collected via rumen cannula at 4h post-feeding. Microbial DNA was extracted; full length 16S rRNA amplicon libraries were prepared using Kinnex kits and then sequenced on the PacBio Revio platform. Reads were analyzed using DADA2 and QIIME2. Statistical analysis was performed with the GLIMMIX procedure of SAS 9.4 (SAS Inst. Inc., Cary, NC). Firmicutes, Bacteroidata, Actinobacteriota, Verrucomicrobiota, and Euryarchaeota were the most abundant phyla in all treatments (83, 10, 3, 0.4, and 1%, respectively), and were not affected by treatment (P ≥ 0.10). Christensenellaceae R-7 group, Rikenellaceae RC9 gut group, Lachnospiraceae-XPB1014-group, Butyrvibrio, Lachnospiraceae-NK3A20-group, and Prevotella represented the most abundant genera for all treatments (7, 5, 11, 9, 7, and 3%, respectively). Lachnospiraceae-XPB1014-group and Lachnospiraceae-NK3A20-group responded quadratically (P ≤ 0.02) to increasing starch with decreased abundance for the 20% and 38% starch supplement. Comparatively, relative abundance of Butyrvibrio responded quadratically (P &amp;lt; 0.01) with increased abundance in the 20% and 38% starch supplement. Pseudobutyrvibrio increased with supplementation of 20% starch and then decreased as starch supplementation increased (quadratic, P = 0.04). In conclusion, supplementation of starch elicited changes in microbial relative abundance at the genus level with the response in Butyrivibrio suggesting greater fibrolytic activity. Forage and total digestible NDF intake in these steers decreased with increased starch supplementation; however, TDOMI was not affected by starch provision.

PSXI-18 Effects of different fiber levels on rumination and inflammatory markers in feedlot cattle

Abstract Adding fiber to feedlot diets is essential to maximize performance, optimize feed conversion and maintain animal health. Monitoring blood inflammatory markers and rumination behavior can help to identify fiber levels that maximize performance and animal well-being. We aimed to evaluate the effect of fiber levels on inflammatory markers, lactate dehydrogenase and haptoglobin and rumination of Nellore cattle in confinement fed with diets containing 12% and 7% forage NDF, over a period of 50 d. Diets included corn silage as the source of forage fiber with 23.3% and 13.6% corn silage in the dry matter 64% and 73.5% ground corn, and 0.2 and 0.5% potassium chloride, respectively for the 12% and 7% fNDF. Soybean meal (1.5%); cottonseed (7%), urea (1.2%), and mineral mixture (2.7%) containing 25 ppm of monensin were present in both treatments. Average initial body weight (BW) was 460 ± 38 kg and average age was 20 mo. Bulls (n = 20) were randomly distributed for each treatment with animal being the experimental unit. The feeding behavior was monitored on d 21 and 42, with observations at each 10-min interval, over 24 h and data obtained were averaged for analysis and blood samples were collected immediately after behavior analysis. Blood samples were obtained by puncturing the jugular vein, centrifuged to separate the serum, stored at -20°C and subsequently analyzed. Lactate dehydrogenase was analyzed in an automatic biochemistry system using cattle specific cattle kits (LABTEST Diagnóstica SA). Haptoglobin analyses were carried out by ELISA (Vidavet-Veterinary Lab). Data were evaluated by PROC GLIMMIX from SAS. A significant interaction was observed between minutes of rumination and fNDF levels in relation to the concentration of lactate dehydrogenase (P &amp;lt; 0.0001), expressed by the solution: Lactate = 1,272.12 + 908.86 * (tract = 7) + 1,1427 -3.3170 * (treat = 7) * rumination. For animals receiving the 7% fNDF diet, the concentration of lactate dehydrogenase decreased as the minutes of rumination increased, with a significant linear effect (P &amp;lt; 0.001). On the other hand, for animals treated with 12% fNDF, no significant correlation was observed (P = 0.34) with increasing rumination time. There was also an interaction between minutes of rumination and fNDF levels for haptoglobin concentration (P &amp;lt; 0.01), expressed by the solution: Haptoglobin = 0.1901 + 0.4865 * (treat = 7) + 0.000828 - 0.00163 * (treat = 7) * rumination. In animals treated with 7% fNDF, haptoglobin concentration decreased with increasing minutes of rumination, with a significant linear effect (P = 0.02). Our data demonstrates that, for the low forage diet, as bulls increased rumination time there was an improvement (a decrease) in inflammatory markers concentrations.

PSIX-18 Multiomic analysis to identify host and microbiome contributions to digestibility in beef cattle

Abstract This study evaluated beef heifers selected for high (efficient) or low (inefficient) digestible fiber intake (DFI). Initial analysis showed that high DFI animals had reduced methane production versus low-DFI under a high forage diet. Using the same cohort of animals maintained on a further 4 diets of varying forage:concentrate ratios, we employed multi-kingdom amplicon sequencing and metagenome shotgun sequencing of rumen digesta and feces alongside RNA sequencing of rumen epimural samples to evaluate the compositional and functional interplay between different microbial groups, and their relationship with host gene expression in cattle divergent for DFI. Samples were collected from 16 cattle during 2 metabolism trials, comprising 5 diets. Amplicon sequencing analysis was conducted using QIIME2; 16S rRNA and 18S rRNA reads were analyzed using the SILVA database, while LSU (fungal) sequences were analyzed using a custom D1/D2 database. Additional analysis of archaeal 16S rRNA sequences was conducted using the Rumen and Intestinal Methanogens (RIM) database. Metagenome shotgun reads underwent a two-pass classification with Kraken2 using a database of prokaryotic genomes derived from the GTDB taxonomy, with the unclassified output undergoing classification using a custom database containing all NCBI protozoa, fungi, and phage genomes, enriched with selected rumen-specific ciliate and fungal genomes. Downstream analysis of taxonomic data from all microbiome work was conducted in R, and differentially abundant taxa were identified using ANCOM-BC and Aldex2. Functional analysis of metagenome contigs using the CAZY database implemented in dbCAN3 is ongoing. RNA-seq data were analyzed using the ARS-UCD reference genome, with identification of DE genes conducted using DeSeq2. Preliminary results indicate no major effect of DFI ranking on host gene expression, bacterial 16S rRNA, or metagenome compositional profiles. Several bacterial genera were differentially abundant between digestibility groups (P &amp;lt; 0.05), but these were all minor (&amp;lt; 0.01%) members of the microbiome. Fungal and methanogen communities different significantly (P &amp;lt; 0.05) according to DFI group, with efficient (high DFI) containing and more diverse communities under high-grain diet (P &amp;lt; 0.05). The same difference showed a tendency toward significance for the 18S rRNA protozoa data (P &amp;lt; 0.1). These preliminary data indicate that the microbial factors underpinning divergence in efficiency measured by DFI vary according to diet and may be more prominent in the non-bacterial fraction of the microbiome. Ongoing functional analysis of metagenome data as well as integration of multiomic data will provide deeper insight into these relationships and how they contribute to feed digestibility and efficiency in cattle.

401 Effect of protein and starch supplementation level on intake and digestibility by steers consuming low-quality forage: I. Bos taurus

Abstract A deficiency of ruminally available N (RAN) caused by a basal diet of low-quality forage depresses forage utilization. Supplemental protein improves forage utilization by increasing RAN, resulting in increased intake and potentially improving digestion. Addition of starch to a supplement can increase total digestible organic matter (OM) intake (TDOMI); however, too much starch decreases RAN and pH potentially decreasing forage utilization. Our objective was to determine the effect of starch supplementation on intake and digestion in Bos taurus indicus steers. Accordingly, five ruminally cannulated Brahman steers [body weight (BW) = 420 ± 55 kg) were used in a 4 × 4 Latin square to evaluate the effect of decreasing supplemental starch when consuming King Ranch Bluestem hay (3.5% CP, 73% NDF). Steers received four isonitrogenous (130 mg N/ kg BW) supplements providing increasing levels of starch (2% starch = 100% soybean meal; 20% starch = 26.3% corn, 73% soybean meal, 0.7% urea; 38% starch = 51.6% corn, 47% soybean meal, 1.4% urea; 56% starch = 78.6% corn, 19% soybean meal, 2.4% urea). Five 14-d periods were conducted, consisting of 9 d adaptation and 4 d to measure intake and digestion, and 1 d for ruminal fermentation. As designed, supplement OM intake (SOMI) increased linearly (P &amp;lt; 0.01) as starch level increased. Other measures of intake, including forage OM intake (FOMI), total OM intake (TOMI), and total neutral detergent fiber intake (TNDFI) decreased in a cubic manner in response to increasing starch (P ≤ 0.04). Forage OMI also responded with a cubic decrease (72.2, 68.9, and 69.5 g/kg BW0.75) when the protein supplement contained 2, 20, and 38% starch, respectively, but decreased to 61.2 g/kg BW0.75 when the 56% starch supplement was provided. Similarly, TOMI decreased 5.3% when starch inclusion increased from 38 to 56%. Total tract OM digestion and NDF digestion were not significantly affected (P ≥ 0.86) by starch level in the supplement; therefore, despite TOMI and TNDFI decreasing, there was no effect on total digestible OM intake and (TDOMI) and total digestible NDF intake (TDNDFI). In conclusion, providing supplemental starch over 38% decreased forage utilization. Decreases in FOMI with starch inclusion may be attributed to competition for RAN between fiber fermenting and starch fermenting bacteria.

PSII-8 The effects of diet and finishing phase on the behavioral time budgets of feedlot cattle

Abstract Feedlot cattle undergo many transitions in diet, social group structure, and environment during the finishing period. Little is known about how their behavior may be altered by these transitions. The objective of our pilot project was to compare the behavior of younger feedlot cattle fed a low-concentrate diet to that of finishing cattle, and to create 24-h time budgets for activity and oral behaviors in these groups. Cattle [n = 20; body weight (BW) = 305 ± 21 kg, mean ± SD] were fed a low-concentrate feedlot diet (60:40, concentrate:forage; ST) and cattle (n = 20; BW = 522 ± 45 kg) received a finishing diet (90:10, concentrate:forage; FI) twice daily. Animals were separated by diet and housed in groups of 10. Trained observers recorded behaviors of each group by live instantaneous recording every 5 min for a continuous 48 h, resulting in 192 h of data collected. We predicted that ST cattle would spend more time eating and ruminating due to the higher forage diet. We also expected that FI animals would rest more and spend less time standing and walking as a result of being more familiar with the environment and their social group structure. We also quantified a wide range of oral behaviors including rumination, grooming and manipulation of non-feed items in the pen. Behaviors were summarized by 24-h period, animal, group, and diet, then averaged by animal, and then averaged again by group (n = 2/diet). Missing values accounted for 3% of the activity data and 11% of the oral behaviors. T-tests revealed that ST cattle ruminated more than FI (352 ± 3 vs. 304 ± 1 min/d, mean ± SE, P = 0.02), but differences between treatments were not detected for time spent eating (196 ± 15 vs. 131 ± 3 min/d), standing (584 ± 13 vs. 588 ± 29 min/d), walking (46 ± 10 vs. 35 ± 5 min/d), or lying (768 ± 16 vs. 772 ± 7 min/d; P ≥ 0.13). When fed the ST diet, cattle spent 5 ± 2 min/d grooming group mates, while FI cattle groomed others for 11 ± 1 min/d, although this was not analyzed statistically because it was rare. Similarly, there were numerical differences in the amount of time spent orally manipulating non-food items (8 ± 3 and 18 ± 1 min/d for ST and FI animals, respectively) that have not been previously described. These results suggest that behavioral differences might be more apparent with larger sample sizes, but with the present experimental design, the predictions were not supported. Nonetheless, these are the first behavioral observations of feedlot cattle and provide a comprehensive time budget of their activity, including a range of oral behaviors over a 48-h period.