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Background: Commercial horse feeds use cereal grains and by‐products; however, their effects on the caecal environment remain poorly characterised. Objective: Characterise the effect of commonly used feed ingredients on caecal pH and volatile fatty acid (VFA) concentration. Study design: 6 × 6 Latin square. Methods: Two days prior to the start of the study, 6 caecally cannulated Quarter horses were moved into individual stalls where Smooth bromegrass hay (brome) was offered at 2.0% BW/d split between 2 feedings (0600 and 1800). On day 0, caecal digesta was collected every 2 h for 12 h relative to the 0600 feeding to establish control values for horses consuming only brome (HAY). On day 1, horses began consuming their respective treatments which consisted of beet pulp (BP), maize (M), dehydrated alfalfa (A), oats (OAT), soybean hulls (SBH), or wheat middlings (WM) at 0.25% BW/d split into 2 feedings. On day 7 of each treatment period, caecal digesta was collected every 2 h for 12 h and analysed for pH and VFA. Data were analysed using mixed ANOVA with repeated measures, fixed effects of treatment and time and random effects of horse and period. Results: There was a main effect of hour (P ≤.05) indicative of post‐prandial shifts in caecal metabolites. There were no main effects of treatment on pH or VFA concentration (P ≥.3). Effects of hour × treatment (P ≤.04) were observed for all response variables. Regardless of treatment or hour, caecal pH remained well within normal limits. Three horses exhibited signs of lower oesophageal choke immediately after consumption of BP pellets. Limitations: Interactions between ingredients when mixed for formulation of a concentrate warrant further research. Furthermore, a short adaptation period was chosen to mimic common management practices. Conclusion: Minimal differences in caecal fermentation parameters were detected when ingredients were fed at a common inclusion level. [ABSTRACT FROM AUTHOR]

The effect of hay type on the microbiome of the equine gastrointestinal tract is relatively unexplored. Our objective was to characterize the cecal and fecal microbiome of mature horses consuming alfalfa or Smooth Bromegrass (brome) hay. Six cecally cannulated horses were used in a split-plot design run as a crossover in two periods. The whole plot treatment was ad libitum access to brome or alfalfa hay fed over two 21-d acclimation periods with subplots of sampling location (cecum and rectum) and sampling hour. Each acclimation period was followed by a 24-h collection period where cecal and fecal samples were collected every 3 h for analysis of pH and volatile fatty acids (VFA). Fecal and cecal samples were pooled and sent to a commercial lab (MR DNA, Shallowater, TX) for the amplification of the V4 region of the 16S rRNA gene and sequenced using Illumina HiSeq. The main effects of hay on VFA, pH, and taxonomic abundances were analyzed using the MIXED procedure of SAS 9.4 with fixed effects of hay, hour, location, period, and all possible interactions and random effect of horse. Alpha and beta diversities were analyzed using the R Dame package. Horses fed alfalfa had greater fecal than cecal pH (P ≤ 0.05), whereas horses fed brome had greater cecal than fecal pH (P ≤ 0.05). Regardless of hay type, total VFA concentrations were greater (P ≤ 0.05) in the cecum than in feces, and alfalfa resulted in greater (P ≤ 0.05) VFA concentrations than brome in both sampling locations. Alpha diversity was greater (P ≤ 0.05) in fecal compared with cecal samples. Microbial community structure within each sampling location and hay type differed from one another (P ≤ 0.05). Bacteroidetes were greater (P ≤ 0.05) in the cecum compared with the rectum, regardless of hay type. Firmicutes and Firmicutes: Bacteroidetes were greater (P ≤ 0.05) in the feces compared with cecal samples of alfalfa-fed horses. In all, fermentation parameters and bacterial abundances were impacted by hay type and sampling location in the hindgut. [ABSTRACT FROM AUTHOR]

Eight cecally cannulated Quarter Horses were used in a replicated 4 × 4 Latin square experiment conducted in four 14-d periods to determine effects of sodium caseinate (casein) on hindgut fermentation and fiber digestion. During each period, horses were assigned to one of four treatments consisting of control (water; CON), 0.125 g casein/kg BW (LOW), 0.25 g casein/kg BW (MED), or 0.5 g casein/kg BW (HI). Casein was solubilized in 800 mL water and dosed directly into the cecum at 0700 and 1900 hours using a metal dosing syringe. Smooth Bromegrass hay (CP 8.50%), water, and salt were provided ad libitum. New hay was fed at 0700 and 1900 hours, and orts were recorded at 1900 daily. During the final 3 d of each period, cecal digesta were collected every 6 h, pH was measured, and samples were frozen for subsequent analyses of VFA and NH3 concentrations. Feed intake during the final 4 d of each period was recorded. Feces were collected during the 3-d sampling period, pooled, subsampled, and frozen. Fecal samples were analyzed for pH and used to determine digestibilities of DM, OM, NDF, and ADF. Statistical analyses were performed via the GLIMMIX procedure of SAS 9.4. Linear and quadratic effects of sodium caseinate on pH, VFA concentrations, and apparent digestibility were assessed by SAS. Digestibilities of DM, OM, ADF, and NDF were unaffected by treatment (P > 0.40). Horses dosed with CON and MED treatments had greater cecal pH than those fed LOW or HI treatments (P < 0.01). Cecal NH3 concentrations increased linearly in response to the amount of casein administered (P < 0.01). Cecal NH3 decreased 6 h after dosing and addition of new hay, regardless of treatment (P < 0.01). Total cecal VFA were unaffected by treatment (P > 0.10), but VFA changed over time with the greatest concentrations observed 6 h after treatments were administered and introduction of new hay (P < 0.01). Treatment did not affect DMI (P ≥ 0.17). In this experiment, cecal infusions of sodium caseinate had minimal to no effect on fermentation parameters or fiber degradation in the horse. A type II error may have occurred due to small population size or the medium quality hay fed to these horses provided sufficient N for microbial fermentation. [ABSTRACT FROM AUTHOR]

The objective of this study was to evaluate the impact of liquid blueberry juice (BJ65) or blueberry puree (BP30) used as a binding agent on pellet durability and palatability of a typical equine concentrate when included at 4% of the pellet. Molasses was used as a control. Production data, pellet durability and moisture content were evaluated in 1 replicate for each treatment. Because moisture content of condition mashes were 17.59% and 18.11% for BJ65 and BP30 treatments, respectively, greater inclusion of blueberry product would likely cause roller slippage and complicate the pelleting process due to increased liquid (Fahrenholz, 2012). Pellet durability met industry standards for all treatments. Pellets were fed in a 3 x 3 Latin square design to 9 two-year-old horses to determine the effect of blueberry products on acceptability. All animals were allowed 10 minutes to consume 1.36 kg at 0700 h and 1700 h each day for 3 d. Consumption time and amount consumed were recorded to calculate intake, intake rate, and intake ratio (IR). No horse consumed all pellets within the allotted time, and thus, there were no differences between intake rate and intake. Period tended to impact intake (P = 0.0909), with horses consuming less during period 1 than period 3 (P = 0.0317), but period had no effect (P = 0.2881) on IR. Treatment influenced intake (P < 0.0001), with decreased intake of BP30 compared to control and BJ65 (P = 0.0001). Intake ratio was greater (P = 0.0075) for BJ65 than BP30 with IR of 0.5069 and 0.4227, respectively. Consumption of BJ65 was no different than control. Fahrenholz, A. 2012. Evaluating factors affecting pellet durability and energy consumption in a pilot feed mill and comparing methods for evaluating pellet durability. Doctoral thesis. Kansas State University, Manhattan, KS. [ABSTRACT FROM AUTHOR]

An experiment was conducted with 6 cecally cannulated horses (524 ± 65.5 kg BW) to evaluate effects of increasing dietary starch on equine cecal microbiota. Starch was supplied via corn pellets and was increased by 0.5 g starch/kg BW/meal every 7 d until horses received 3.5 g starch/kg BW/meal. Throughout the experiment, Smooth Bromegrass hay and water were offered ad libitum. Meals were fed every 6 h, starting at 0600 h. On d 7 of each period, cecal digesta was collected every 2 h for 12 h. Within period, cecal samples for each horse were pooled and DNA was extracted for PCR amplification of the 16 S rRNA gene (V3 and V4 regions) and sequencing via Illumina MiSeq. Alpha and beta diversity were measured. Data were analyzed as a randomized complete block with fixed effect of starch level and random effect of horse (SAS version 9.4). If a horse presented with colic, it was removed from the experiment. Parameters when feeding 1.5 g starch/kg BW/meal were compared between horses which completed the trial and those removed using covariate of 0 g starch/kg BW/meal. Feeding 1.5 g starch/kg BW/meal elicited the greatest changes in microbiota, indicated by reduced (P = 0.02) operational taxonomical units and Faith phylogenetic diversity and different (P = 0.017) beta diversity compared to all other treatments. Across treatments, Firmicutes was the most abundant phyla, followed by Bacteroidetes. Feeding 1.5 g starch/kg BW/meal led to lowest (P = 0.0342) relative abundance (RA) of Prevotella, Treponema, Phascolarctobacterium, and [Prevotella]. Horses that persisted throughout the experiment had reduced (P = 0.0163) RA of Ruminococcus and greater RA of Phascolarctobacterium (P = 0.0057) when consuming 1.5 g starch/kg BW/meal compared to those removed. This is the first report describing effects of gradually increasing dietary starch on equine cecal microbiota in vivo. [ABSTRACT FROM AUTHOR]