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The objective of this study was to determine the early responses to a moderate concentrate increase in cattle diets with regards to various behavioral and physiological responses in cattle. Eight ruminally cannulated Angus crossbred beef heifers were adapted to a 70% concentrate diet (T70) and then switched to a 90% concentrate diet (H90). Measurements of feeding behavior, ruminal pH and temperature, rumen motility, liquid passage rate, and blood acid–base status were conducted on T70 as well as first day (d1) and second day (d2) of high-grain H90feeding to monitor the beginning of the transition period. Ruminal pH was below 5.6 for longer on both days of H90 compared with T70, suggesting animals experienced subacute ruminal acidosis while switching from T70 to H90. Transitioning did not affect dry matter intake (DMI). Eating rate during meals was reduced on d1 and d2 H90 compared with T70. Ruminal contraction amplitude was reduced on both days of H90 feeding. Contraction duration was reduced on d1 H90, and returned to T70 values by d2 H90. Results indicated that a moderate transition to a finishing diet influenced feeding behavior and reduced rumen motility at the beginning time after transition, but did not influence voluntary DMI.

Previous research has demonstrated that exposure to ergot alkaloids reduces vasoactivity of serotonin (5HT) receptors. Chemical suppression of tall fescue seedhead production is a tool to reduce the level of exposure to ergot alkaloids by a grazing animal. Therefore, the objective was to evaluate contractility of lateral saphenous veins biopsied from mixed breed steers following a 87- to 101-d grazing period on 3-ha pastures of bermudagrass (Cynodon dactylon; n = 5 steers; BW = 340 ± 9 kg), or toxic endophyte-infected tall fescue (Lolium arundinaceum) that was not treated (n = 5 steers; BW = 300 ± 6; 0.56 ppm ergovaline) or was treated (n = 5 steers; BW = 294 ± 9 kg; 0.24 ppm ergovaline) with herbicide containing aminopyralid and metsulfuron-methyl. To evaluate contractility, biopsied veins were mounted in a multimyograph and exposed to increasing concentrations of a tall fescue seed extract (EXT; ergovaline source) and 5HT1B (CP 93129), 5HT1D (L-694,247), and 5HT2A (TCB2) agonists. All contractility data were normalized to a maximal response of 1 × 10-4 M norepinephrine and were analyzed as a split plot treatment design using SAS for effects of pasture treatment, agonist concentration, and the interaction. There was no contractile response to any concentration of 5HT1B agonist in any of the pasture treatments. There were pasture × concentration interactions for contractile responses to 5HT2A agonist (P < 0.01) and EXT (P < 0.01). For both EXT and TCB2, veins from bermudagrass steers were more vasoactive to the higher concentrations of these compounds (P < 0.05), and there were no differences between veins collected from the unsuppressed or seedhead-suppressed treatments (P = 0.66). There was also a pasture × concentration interaction for the contractile responses to 5HT1D agonist (P < 0.01). However, these responses were not sigmoidal and reached a zenith at 5 × 10-7 and 1 × 10-6 M. At these concentrations, the response was greatest for veins from the unsuppressed treatment (P < 0.05) and did not differ between veins from suppressed and bermudagrass treatments (P = 0.41). Although reduced levels of ergovaline in seedhead-suppressed pastures did not alter vasoactivity of 5HT2A or 5HT1B receptors in the lateral saphenous vein, elevated vasoactivity of 5HT1D in veins from unsuppressed tall fescue pasture treatment suggests that lower ergovaline levels in seedhead-suppressed pastures can influence the vascular effects of ergot alkaloids.

The objective was to study the transition of beef cattle from a 70% to a 90% concentrate diet to increase understanding of mechanisms contributing to behavioral and physiological adaptations to a high-concentrate diet. Eight ruminally-cannulated Angus-cross heifers (BW=497 ± 24 kg) were adapted to a 70% concentrate diet (T70) fed ad libitum once daily. Baseline measurements were taken for 2 days and averaged. Then, heifers were switched to a 90% concentrate diet (H90), and responses were measured and averaged by animal and day or hour. Data were analyzed using PROC MIXED of SAS with repeated measures. Ruminal pH was below 5.6 for longer on both days of the H90 diet than during T70 feeding (P

Previous research has demonstrated that exposure to ergot alkaloids reduces vasoactivity of serotonin (5HT) receptors. Chemical suppression of tall fescue seedhead production is a tool to reduce the level of exposure to ergot alkaloids by a grazing animal. Therefore, the objective was to evaluate contractility of lateral saphenous veins biopsied from mixed breed steers following a 87- to 101-d grazing period on 3-ha pastures of bermudagrass (Cynodon dactylon; n = 5 steers; BW = 340 ± 9 kg), or toxic endophyte-infected tall fescue (Lolium arundinaceum) that was not treated (n = 5 steers; BW = 300 ± 6; 0.56 ppm ergovaline) or was treated (n = 5 steers; BW = 294 ± 9 kg; 0.24 ppm ergovaline) with herbicide containing aminopyralid and metsulfuron-methyl. To evaluate contractility, biopsied veins were mounted in a multimyograph and exposed to increasing concentrations of a tall fescue seed extract (EXT; ergovaline source) and 5HT(1B) (CP 93129), 5HT(1D) (L-694,247), and 5HT(2A) (TCB2) agonists. All contractility data were normalized to a maximal response of 1 × 10(−4) M norepinephrine and were analyzed as a split plot treatment design using SAS for effects of pasture treatment, agonist concentration, and the interaction. There was no contractile response to any concentration of 5HT(1B) agonist in any of the pasture treatments. There were pasture × concentration interactions for contractile responses to 5HT(2A) agonist (P < 0.01) and EXT (P < 0.01). For both EXT and TCB2, veins from bermudagrass steers were more vasoactive to the higher concentrations of these compounds (P < 0.05), and there were no differences between veins collected from the unsuppressed or seedhead-suppressed treatments (P = 0.66). There was also a pasture × concentration interaction for the contractile responses to 5HT(1D) agonist (P < 0.01). However, these responses were not sigmoidal and reached a zenith at 5 × 10(−7) and 1 × 10(−6) M. At these concentrations, the response was greatest for veins from the unsuppressed treatment (P < 0.05) and did not differ between veins from suppressed and bermudagrass treatments (P = 0.41). Although reduced levels of ergovaline in seedhead-suppressed pastures did not alter vasoactivity of 5HT(2A) or 5HT(1B) receptors in the lateral saphenous vein, elevated vasoactivity of 5HT(1D) in veins from unsuppressed tall fescue pasture treatment suggests that lower ergovaline levels in seedhead-suppressed pastures can influence the vascular effects of ergot alkaloids.

The objectives of this study were to develop instrumentation for measuring feed intake and forestomach motility for individually housed cattle and create data analysis algorithms to characterize feeding behavior and reticuloruminal contractions. Feed bunks were mounted onto S-beam load cells and suspended outside the animal stalls. Load cells were connected to a data logger which recorded bunk weight at 1-min intervals. Thus, periods of feed disappearance from the bunk could be equated to meals. A meal detection script was developed in MATLAB to import the weight data, filter the weight to reduce noise, detect meals by evaluating the difference between consecutive measurements, and export the meal start time, duration, and size of each meal. Evaluation of the meal detection script by visual review resulted in a combined error rate of 1.8%. A water-filled (2 L) balloon attached to a catheter was placed into the ventral sac of the rumen through the rumen cannula and connected to a disposable pressure transducer. The transducers were connected to a PowerLab data acquisition system via bridge amplifiers, and the ruminal pressure signal was visualized in real-time using LabChart computer software. A script was prepared in MATLAB for filtering pressure data, detecting contractions using the findpeaks function within the Signal Processing Toolbox of MATLAB, and evaluating contraction amplitude, duration, and frequency. Evaluation of the ruminal contraction script by visual review resulted in a combined error rate of 4%. After successful evaluation of the algorithms, an experimental application of these systems characterized meals and ruminal contractions for 8 animals in response to an increase in grain in the diet. This trial produced average daily results for feeding behavior and ruminal motility that were within the range of other published studies. With the low error rate and biologically acceptable values, the instrumentation and data analysis algorithms are appropriate means of characterizing feeding behavior and ruminal motility. These systems and algorithms could have important applications for ruminant physiology and behavior research.