Defining risk for low reticuloruminal pH during the diet transition period in a commercial feedlot in western Canada.

The objective of the current study was to measure reticuloruminal pH in cattle in a commercial feedlot setting to determine the incidence and extent of low reticuloruminal pH for steers and heifers as they transition to a high-concentrate finishing diet. Reticuloruminal pH was measured in 16 "mixed breed" steers (4 steers/pen with 4 pens) and 16 "mixed breed" heifers (4 heifers/pen with 4 pens) housed in commercial feedlot pens, with 227 ± 13 and 249 ± 6 cattle/pen cohort steers and heifers, respectively, for the diet transition period. Cattle were transitioned from a diet of 53.5% forage and 46.5% concentrate to a diet of 9.5% forage and 90.5% concentrate on a DM basis using a 40-d transition with 5 dietary steps with the diets containing 41.4, 44.8, 49.8, 52.5, 55.1, and 64.0% nonfibrous carbohydrate. In addition, wheat replaced barley as the grain source during the dietary transition. Reticuloruminal pH was measured using orally administered pH measurement devices that were retrieved at slaughter. Data were analyzed using a mixed model including the fixed effects of sex, diet, and the 2-way interaction to evaluate the effect of diet and sex and with the fixed effects of sex, diet, and day relative to each dietary change along with the 2- and 3-way interactions to evaluate temporal responses as a result of diet change. A repeated measures statement was included for the effect of day. Both the mean and minimum reticuloruminal pH values decreased as the proportion of concentrate in the diet increased ( < 0.001). The area and duration that pH was <5.6 increased with greater inclusion of concentrate in the diet ( < 0.001). The number of cattle experiencing low reticuloruminal pH, defined as pH < 5.6 for >180 min, increased with increasing concentrate, and by the end of the 40-d dietary transition, 83% of the cattle had experienced at least 1 bout of low reticuloruminal pH, with most experiencing between 1 and 3 bouts/diet. These data are interpreted to suggest that cattle are at high risk for experiencing low reticuloruminal pH during the dietary transition but that the extent of low reticuloruminal pH is mild. Moreover, the data suggest that the risk for low reticuloruminal pH increases with increasing proportion of concentrate in the diet. The results also suggest that susceptibility to low reticuloruminal pH may differ between steers and heifers.

Incidence, prevalence, severity, and risk factors for ruminal acidosis in feedlot steers during backgrounding, diet transition, and finishing.

The objective of this study was to determine the incidence, prevalence, severity, and risk factors for ruminal acidosis in feedlot steers during backgrounding, diet transition, and finishing. Steers were purchased from a local auction market (n = 250; mean ± SD; 330 ± 20.0 kg initial BW) and were grouped together with 28 steers fitted with a ruminal cannula (248 ± 25.5 kg initial BW). Steers were randomly allocated to 1 of 8 pens (3 to 4 cannulated steers per pen with a total of 35 steers/pen). The feeding period (143 d) was divided into 4 phases: backgrounding (BKGD; d 1 to 20), diet transition (TRAN; d 21 to 40), and the first (FIN1; d 41 to 91) and second half (FIN2; d 92 to 143) of finishing. The BKGD diet contained (% DM) barley silage (45.7%), barley grain (41.6%), canola meal (4.2%), and a pelleted mineral and vitamin supplement (8.5%). Steers were transitioned to a finishing diet containing (% DM) barley silage (5%), barley grain (80.9%), canola meal (4.9%), and a pelleted mineral and vitamin supplement (9.2%) using 4 transition diets. Feed was offered to achieve 5% refusals (as-is basis). Ruminal pH was recorded in cannulated steers every 10 min throughout the study, and feed refusals and BW were recorded at 2 wk intervals. Mean ruminal pH (P < 0.01) was 6.4, 6.3, 6.2, and 6.0 ± 0.01 during the BKGD, TRAN, FIN1, and FIN2, respectively. The duration (P < 0.01) pH < 5.5 was 4.1, 12.1, 78.7, and 194 ± 9.4 min/d during BKGD, TRAN, FIN1, and FIN2, respectively. Using a threshold of ruminal pH < 5.5 for at least 180 min to diagnose ruminal acidosis, incidence was defined as the number of times steers experienced ruminal acidosis during each period and prevalence was defined as the percentage of steers that experienced acidosis during each period. On average, the incidence rate (P < 0.01) of ruminal acidosis was 0.1, 0.3, 6.7, and 14.8 ± 0.97 episodes during BKGD, TRAN, FIN1, and FIN2, respectively. In the same order, the prevalence (P < 0.01) was 0.7, 1.7, 15.4, and 37.8 ± 2.0%. Based on multiple regression, factors associated with prevalence of ruminal acidosis and the duration pH < 5.5 were feeding phase (P < 0.01) and DMI (P < 0.01). Overall, the greatest incidence, prevalence, and severity of ruminal acidosis were observed towards the end of the finishing phase and were associated with days on feed and DMI.

Short communication: Interrelationship between butyrate and glucose supply on butyrate and glucose oxidation by ruminal epithelial preparations.

The aim of this study was to determine whether dietary Na-butyrate supplementation affects butyrate and glucose oxidation by ruminal epithelial preparations and whether this effect can be acutely modulated by substrate (glucose and butyrate) supply. Eighteen Suffolk wether lambs (6 lambs/treatment) were blocked by body weight and, within block, randomly assigned to the control treatment (CON) or to diets containing differing Na-butyrate inclusion rates (1.58 or 3.16%) equating to 1.25 (B1.25), and 2.50% (B2.50) butyrate on a dry matter basis, respectively. All lambs received their diet for a period of 14 d. After dietary adaptation, lambs were killed and the ruminal epithelium was harvested from the ventral sac, minced finely, and used for in vitro incubations. Incubation medium contained either a constant concentration of glucose (4 mM) with increasing butyrate concentrations (0, 5, 15, 25, or 40 mM) or a constant butyrate concentration (15 mM) with increasing glucose concentrations (0, 1, 2, 4, or 8 mM) to allow for the evaluation of whether acute changes in the concentration of metabolic substrates affect the oxidation of glucose and butyrate. We observed no interactions between the in vivo and in vitro treatments. Increasing dietary butyrate supplementation linearly decreased glucose oxidation by ruminal epithelial preparations, but had no effect on butyrate oxidation. Increasing butyrate concentration in vitro decreased (cubic effect) glucose oxidation when butyrate concentration ranged between 5 and 15 mM; however, glucose oxidation was increased with a butyrate concentration of 40 mM. Butyrate oxidation decreased (cubic effect) as glucose concentration increased from 1 to 4 mM; however, butyrate oxidation increased when glucose was included at 8mM. The results of this study demonstrate that dietary butyrate supplementation can decrease glucose oxidation by the ruminal epithelium, but the relative supply of glucose and butyrate has a pronounced effect on substrate oxidation.