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At least 19 recordsLinked to original sources
PubMed1994

[A comparative study between cortically induced fictive mastication and actual mastication in acute and chronic rabbits].

To explore the mechanism of coordinated jaw, tongue and hyoid movements during mastication, electromyograms of jaw, tongue and hyoid muscles were recorded simultaneously in rhythmic jaw movements during both cortically induced fictive mastication (CIFM) and actual mastication. 1. The jaw movement patterns of different stage of actual mastication were similar with the corresponding basic patterns of CIFM. 2. Masseter, Styloglossus and Sternohyoideus, which were activated mainly in the jaw-closing phase, were facilitated in proportion to the hardness of the chewing materials during both types of mastications. However, digastric, genioglossus and geniohyoideus, which were activated mainly in the jaw-opening phase, were not facilitated in either type of mastication. 3. The modulations of burst durations by hardness of chewing materials were some different between two types of mastications. These results suggested that physiological properties of CIFM are similar to those of actual mastication, and thus CIFM may be used as a model of actual mastication.

Animals↗
PubMedDate not supplied

Cortical control of mastication in the cat: properties of mastication-related neurons in motor and masticatory cortices.

The aim of this study is to examine mastication-specific activity of orofacial neurons in the motor and masticatory cortices of the awake cat. We examine properties of mastication-related neurons (MRNs) in masticatory (MA, the rostral region of the orbital gyrus) and motor (area P, the lateral wall of the presylvian sulcus) cortical areas that are related to mastication of cats. MRNs in MA and area P had in common mechanoreceptive fields (RFs) in perioral, mandibular and lingual regions, and many MRNs had bilateral RFs in the tongue and mandibular regions. Facial RF size was the largest in area P. Eleven percent of MRN recording sites in MA, and 43% in area P evoked various motor effects with the use of intracortical microstimulation (ICMS). MRNs of the pre-movement type showing activities prior to mastication, or masticatory or lingual EMG, were 14% in MA and 45% in area P. Based on wheat germ agglutinin-horseradish peroxidase (WGA-HRP) injection into area P and MA, cortico-cortical connections were examined. After the unilateral area P injection, were reciprocal connections between the contralateral area P and bilateral MA were demonstrated. After the unilateral MA injection, there were reciprocal connections between the contralateral MA, bilateral area P and bilateral orofacial SI (the orofacial region of the first somatosensory area). These findings suggest that accurate masticatory movements may be executed by the cortical processing in MA and area P.

Animals↗
PubMed2005

In vitro and in vivo antimicrobial effects of mastic chewing gum against Streptococcus mutans and mutans streptococci.

BACKGROUND AND OBJECTIVE: Dental caries is associated with oral pathogens and Streptococcus mutans (S. mutans) is one of the primary cariogenic organisms. Mastic gum, from Pistacia lentiscus, has been shown to have antibacterial properties. The objective of this study was to determine antibacterial activity of mastic chewing gum against S. mutans and mutans streptococci in vitro and in vivo conditions. SETTING: Cukurova University, Dental School, in 2002. MATERIALS AND METHODS: Antimicrobial activity of mastic gum was evaluated using standard S. mutans strain by disc diffusion method in vitro. Cytotoxicity effect of mastic gum on HEp-2 cells was evaluated by conventional haemocytometer using the trypan blue exclusion method. Clinical studies were then performed on 25 periodontally healthy volunteers. The inhibitory effect of chewing mastic gum against mutans streptococci in saliva was compared to a placebo gum. Saliva samples were taken from the subjects immediately before and after chewing the mastic gum and the placebo gum for 15 min. Additional saliva samples were collected every 30 min. The samples were inoculated onto mitis salivarius-bacitracin agar and incubated for 48 h anaerobically at 37 degrees C. The total number of viable bacteria was then counted. RESULTS: Among tested solvents (chloroform, acetone, petrolium ether and ethanol), it was found that the acetone was found to be more convenient than the others to dissolve the mastic gum. In the cytotoxicity assay, concentrations up to 75 mg/ml of the mastic gum were not toxic for the replication of HEp-2 cells. Thus, lower concentrations of mastic gum (20 and 50 mg/ml) were used for the experiments. In vitro experiments, the diameters of growth inhibition zones of mastic gum were in the range 9.0-27.0 mm. In the clinical trials, the mean number of bacteria in samples taken after chewing the mastic gum and placebo gum were following; at minute 15 was 112 x 10(4)+/-268 x 10(3) and 175 x 10(4)+/-417 x 10(3)cfu/ml, for minute 45 was 85 x 10(4)+/-219 x 10(3) and 165 x 10(4)+/-329 x 10(3)cfu/ml, at minute 75 was 65 x 10(4)+/-100 x 10(3) and 160 x 10(4)+/-216 x 10(3)cfu/ml, at minute 105 was 60 x 10(4)+/-127 x 10(3) and 150 x 10(4)+/-138 x 10(3)cfu/ml, and at minute 135 was 55 x 10(4)+/-65 x 10(3) and 145 x 10(4)+/-354 x 10(3)cfu/ml, respectively. Significantly fewer bacteria was found in saliva samples collected after chewing mastic gum compared to those after chewing paraffin (p<0.001). CONCLUSIONS: This preliminary study showed that mastic gum had significant antibacterial activity against S. mutans and mutans streptococci and it may be a useful adjunct in the prevention of caries.

Adult↗
PubMed1989

Dynamic responses in adult and infant monkey craniums during occlusion and mastication.

Using occlusion without food as a basis, this study elucidated the dynamic responses and associated buffer mechanisms in the monkey cranium and its component bones during mastication. In addition, investigations were carried out on the relationship of these factors to the growth and development of the cranium. Using strain gauges, the masticatory buffer capacity and dynamic responses in the bone were investigated from the standpoint of the magnitude and direction of strain in the individual bones of the cranium. Compared with the occlusion without food, there were greater stresses during mastication in the bones of both the masticating and non-masticating sides of the cranium. These stresses were greater when masticating hard than soft foods, and greater in the cranium of the adult than infant monkey. On the masticating side of the cranium, the buffer effect to masticatory forces in the adult cranium was carried out by the inherent form of each bone in response to the firmness of the food, while in the infant cranium it was carried out by the entire cranium independent of the firmness of the food. On the non-masticating side of the cranium in both the adult and infant craniums, the zygomatic arch, temporal bone, and the bones of the temporomandibular joint region balanced the masticatory forces of the masticating side of the cranium, and played an important role in buffering these forces. The direction of the principal strain arising in the bones of the infant cranium corresponded to the direction of growth and development of the respective bone. However, in spite of the fact that large strains were observed in each bone on the non-masticating side during mastication of hard foods, the strains were very small on this side during mastication of soft foods. Consequently, it is necessary to masticate hard foods in order to promote the growth and development of the cranial bones. Viscoelasticity in the cranial bones could be explained by a three-element model.

Animals↗
PubMed2005

Effects of thorough mastication on postprandial plasma glucose concentrations in nonobese Japanese subjects.

Thorough mastication has the potential to affect postprandial plasma glucose concentrations by improving digestibility and absorption of nutrients. To evaluate the effects of mastication on postprandial plasma glucose concentration, we compared usual and thorough mastication in subjects with normal glucose tolerance (NGT group, n = 16) and subjects predisposed to type 2 diabetes (first-degree relatives of type 2 diabetic patients, subjects with impaired glucose tolerance, and type 2 diabetic patients) (predisposed group, n = 10) in a crossover trial of 52 test meals. Plasma glucose and serum insulin concentrations were measured for 3 hours postprandially, and the insulinogenic index (the ratio of incremental serum insulin to plasma glucose concentration during the first 30 minutes after meal) was calculated. In the NGT group, thorough mastication reduced the postprandial plasma glucose concentration at 90 minutes (5.8 +/- 0.3 vs 6.5 +/- 0.4 mmol/L, P < .05) and 120 minutes (5.4 +/- 0.2 vs 6.3 +/- 0.4 mmol/L, P < .05) and the area under the curve (AUC) from -15 to 180 minutes (19.1 +/- 0.6 vs 20.6 +/- 0.8 [mmol . L]/h, P < .05) without an increase in the AUC for insulin. In the predisposed group, thorough mastication significantly augmented plasma glucose and serum insulin concentrations and the AUCs compared with usual mastication. Thorough mastication elicited a significantly higher insulinogenic index than usual mastication in the NGT group (205.0 +/- 27.6 vs 145.6 +/- 17.7 pmol/mmol, P < .05), whereas the predisposed group showed significantly less early-phase insulin secretion than the NGT group. In the NGT group the postprandial plasma glucose concentration upon thorough mastication of meal was significantly lower, most probably because of the potentiation of early-phase insulin secretion. In the subjects predisposed to type 2 diabetes, thorough mastication did not potentiate early-phase insulin secretion and elicited a higher postprandial plasma glucose concentration.

Adult↗
PubMed2006

Mastication-induced modulation of orofacial sensory inputs as seen in the jaw reflex and single neuronal activities in the face primary somatosensory cortex of the rabbit.

The aim of the present study was to compare the effect of mastication on non-nociceptive orofacial sensory transmission of the somatosensory pathways and that on the jaw reflex arc. To achieve this, single-unit activities of the face primary somatosensory cortex (face-SI) neurons responding to low-intensity electrical stimulation of the inferior alveolar nerve (IAN) and the jaw-opening reflex (JOR) were recorded during mastication in awake rabbits. The entire masticatory sequence was divided into the preparatory period (PP), the rhythmic-chewing period (RC) and the preswallow period (PS). A total of 112 face-SI neurons were tested for the effects of mastication. The responsiveness of most neurons and the JOR were modulated during different periods of mastication. The IAN-evoked activity was attenuated in a majority of the neurons during at least one of the masticatory periods. The JOR was suppressed during the RC and PS, while the modulatory effect was variable during the PP. Regression analysis showed that the modulatory effect of mastication on the IAN-evoked neuronal activity and that on the JOR was not well correlated. It was notable that a considerable number of face-SI neurons showed mastication-related activity although their responsiveness to IAN stimulation was strongly suppressed (i.e. almost "gated out") during mastication. The findings indicate that (1) sensory transmissions of the somatosensory and reflex pathways may be modulated in a different manner during mastication, and that (2) activity of face-SI neurons during mastication may not necessarily be a simple reflection of movement-induced stimulation of orofacial mechanoreceptors.

Animals↗
PubMed2003

A pilot study on antiplaque effects of mastic chewing gum in the oral cavity.

BACKGROUND: Chemical plaque control is a useful aid in mechanical oral hygiene, and various chemical agents have been evaluated as antiplaque agents. It has been shown that mastic chewing gum has antibacterial effects on Helicobacter pylori. In this study, the antiplaque effect of mastic chewing gum was investigated. METHODS: Twenty dental students who were both systemically and periodontally healthy participated in this study. The effects of mastic gum were assessed from 2 double-blinded, randomized studies. In the first trial, after mechanical toothbrushing, the inhibitory effect of mastic gum on bacteria in saliva following its use was compared to a placebo gum. Saliva samples were collected at the end of 1, 2, 3, and 4 hours; diluted; inoculated onto 10% horse blood chocolate agar plates; and cultured anaerobically at 37 degrees C for 48 hours. The total number of bacterial colonies on each plate was calculated (n = 20). In the second trial, the effects of mastic gum on de novo plaque formation on tooth surfaces and gingival inflammation were evaluated over a 7-day period without mechanical oral hygiene following random use of either mastic or placebo chewing gum. The degree of plaque accumulation and gingival inflammation were compared between the 2 groups (n = 10). RESULTS: The total number of bacterial colonies was significantly reduced during the 4 hours of chewing mastic gum compared to the placebo gum (P < 0.05, Student t test). The mastic group showed a significantly reduced plaque index (2.69 +/- 0.29 versus 3.15 +/- 0.24; P = 0.001, Student t test) and gingival index (0.44 +/- 0.15 versus 0.66 +/- 0.23, P = 0.021, Student t test) compared to the placebo group. CONCLUSION: These results suggest that mastic chewing gum is a useful antiplaque agent in reducing the bacterial growth in saliva and plaque formation on teeth.

Adult↗
PubMed2002

Evaluation of mastication-induced change in sympatho-vagal balance through spectral analysis of heart rate variability.

Mastication modulates the autonomic nervous activity of the digestive glands and the heart. The autonomic nervous balance is evaluated with spectral analysis of heart rate variability. In the present study, we investigated the effects of mastication of chewing gum base on heart rate variability to clarify the role of mastication in the sympatho-vagal balance for the regulation of the heart rate. Mastication of a chewing gum base stimulated the salivary secretion and shortened the R-R intervals in the electrocardiogram of healthy young subjects without swallowing of saliva at a fixed rate of respiration. Based on the analysis of heart rate variability, mastication increased the low-frequency band spectral power (LF), and decreased the high-frequency band spectral power (HF). The LF/HF was markedly increased by the mastication. Mastication enhances the sympathetic nervous activity and/or suppresses the parasympathetic nervous activity for the heart. Feeding behaviour with mastication might play a role in the modulation of the autonomic nervous activity.

Adult↗
PubMed1995

Modification of mastication and respiration during swallowing in the adult human.

1. The normal interactions between respiration, mastication, and swallowing were studied in seated adult humans. Respiratory movements and movements of the larynx were recorded with mercury-elastic strain gauges placed around the rib cage and neck. A rigid body containing infrared-emitting diodes (IREDs) was attached to the forehead, and a single IRED was applied to the chin. Jaw and head movements were transduced using the OPTOTRAK spatial motion analysis system. Recordings were made before, during, and after the mastication of pieces of carrot. 2. Movements of the larynx were used as a marker for swallowing. Measurements were made of the duration of masticatory and respiratory cycles, and the phase relationship between the two rhythms was determined. Deviations in masticatory and respiratory movements during swallowing were detected; the phases of the masticatory and respiratory cycles in which the deviations occurred were determined, and the interval between each deviation and the swallowing marker was calculated. 3. Three characteristic swallowing patterns were observed: interposed, terminal, and spontaneous. Interposed swallows occurred within a masticatory sequence, terminal swallows ended the sequence, and spontaneous swallows occurred sporadically between masticatory sequences. 4. Results revealed that mastication could have a profound effect on the respiratory rhythm in some subjects. One subject, whose data were excluded from further analyses, became apneic for a long period, followed by short and shallow breaths near the end of the masticatory sequence. In most subjects, respiratory rate increased during mastication and then dropped below baseline as soon as mastication ended. The end-inspiration diameter of the rib cage tended to decrease in the preswallow period and increase postmastication relative to baseline. 5. There was a weak but significant tendency for inspiration to begin during the jaw opening phase of mastication, but phase coupling did not become stronger as swallowing was approached. 6. Deviations in respiration during swallowing occurred during the late expiratory phase of the breathing cycle. Swallows within a masticatory sequence occurred most frequently during the early opening phase of the masticatory cycle, and terminal swallows occurred after the end of the sequence with the mandible in the resting, postural position. Swallowing temporarily reset both the masticatory and respiratory rhythms. Most swallows prolonged the duration of one or two respiratory cycles, however; swallows were often repetitive, and in some subjects two or three swallows fell within a single respiratory cycle, prolonging it for several seconds. 7. A tight temporal relationship was observed between deviations in respiration and the swallowing marker: all deviations occurred before or coincident with the marker. The time of deviations in mastication relative to the swallowing marker depended on swallow type. There was no link between the start of pauses in the two rhythms, suggesting that the commands from the swallowing central pattern generator to the other two pattern generators are independent. 8. We suggest that disordered coordination of mastication and swallowing with respiration may cause prolonged apnea in susceptible individuals.

Adult↗
PubMed2005

[Neuronal activities related to right-sided mastication detected with functional magnetic resonance imaging].

OBJECTIVE: To observe neuronal activities related to right-sided mastication in cortex and to explore the effect of mastication on brain function. METHODS: Neuronal activities related to right-sided mastication were detected with functional magnetic resonance imaging in 10 healthy volunteers. Image data was analyzed by SPM99 software with the use of t test. RESULTS: Localization of activation in brain was different among subjects. Brain activation during mastication included left basal ganglion, Broca's area, angular gyrus and right supramarginal gyrus. CONCLUSIONS: The functional areas related to right-sided mastication and speech were closely connected, which indicated close relationship between mastication and speech. The central control of mastication might share part of common neural mechanism with that of speech. The roles of activated brain regions in mastication still remained to be elucidated.

Adult↗
PubMed2001

Modulation of H reflex of pretibial and soleus muscles during mastication in humans.

A previous study in our laboratory demonstrated that the soleus H reflex was facilitated during mastication in humans. In the present study, we investigated whether there was any modulation of the magnitude of the pretibial H reflex during mastication in five healthy adult volunteers. The pretibial H reflex was significantly facilitated during mastication, and there was no significant difference in the facilitation between jaw-closing and jaw-opening phases; that is, the gain of the H reflex was modulated tonically but not in a phase-dependent manner during mastication. Furthermore, in the same subjects, we confirmed that the soleus H reflex was facilitated during mastication. Based on our findings, we conclude that the H reflexes in both the pretibial and soleus muscles undergo a nonreciprocal facilitation during mastication. It is suggested that mastication contributes to stabilization of postural stance in humans.

Adult↗
PubMed2005

Cortical control for mastication in cats: changes in masticatory movements following lesions in the masticatory cortex.

In a previous paper (Hiraba and Sato 2004) we reported that an accurate mastication might be executed by the cortical processing in bilateral masticatory area (MA)and motor cortices. The aim of this study was to determine if cats with lesion of either unilateral or bilateral MA showed changes in mastication. After exploring mechanoreceptive fields and motor effects of mastication-related neurons (MRNs) in MA using the single unit recording and intracortical microstimulation methods, we made various lesions in MAs with injections of kainic acid (0.1%, 2.0 microl). Since the MA was divided into facial (F) and intraoral (I) projection areas as reported in the previous paper, cats with the unilateral lesion in F or I, and with the bilateral lesion in F and F, I and I or F and I (F on one side and I on other side) were prepared. Cats with unilateral lesion in F or I and with bilateral lesion in F and I showed no changes in mastication except for prolongation of the food intake and masticatory periods. Cats with bilateral lesion into F and F, or I and I showed wider jaw-opening during mastication. Particularly, the latter group showed enormous jaw-opening, delay in the start of mastication and difficulty in manipulating food on the tongue. In all cats with lesions of each type, masticatory and swallowing rhythms remained normal. These findings suggest that accurate mastication is executed by the close integration between F and F and I and I of the bilateral MA.

Animals↗
PubMed1992

Changes in respiratory activity induced by mastication in humans.

We studied the influence of mastication on respiratory activity in nine healthy volunteers who were requested to masticate a 5-g chewing gum bolus at a spontaneous rate (SR) for 5 min and "at the maximum possible rate" (MPR) for 1 min. Significant increases in respiratory frequency were induced by SR mastication due to a decrease in both the inspiratory and expiratory time. Tidal volume displayed slight nonsignificant decreases, but minute ventilation and mean inspiratory flow significantly increased. The duty cycle (TI/TT) did not change significantly. Total airway resistance significantly increased. Both peak and rate of rise of the integrated electromyographic activity of inspiratory muscles presented marked increases, accompanied by the appearance of a low level of tonic muscular activity. Similar but more intense effects on respiratory activity were induced by MPR mastication; in addition, a significant decrease in tidal volume and a significant increase in TI/TT were observed. Rhythmic handgrip exercise performed at metabolic rates comparable to those attained during SR or MPR mastication induced similar changes in the drive and time components of the breathing pattern, although accompanied respectively by nonsignificant or significant increases in tidal volume. Furthermore, the frequency of SR mastication significantly entrained the respiratory rhythm. The results suggest that mastication-induced hyperpnea does not merely represent a ventilatory response to exercise but also reflects complex interactions between respiratory and nonrespiratory functions of the upper airway and chest wall muscles.

Adolescent↗
PubMed2002

Systemic release of endotoxins induced by gentle mastication: association with periodontitis severity.

BACKGROUND: Periodontitis has recently been identified as a potential risk factor for systemic pathologies such as cardiovascular disease, the hypothesis being that periodontal pockets could release pro-inflammatory bacterial components, for instance endotoxins, into the bloodstream. It is known that the oral cavity can be a source of circulating bacteria, but this has never been shown for bacterial endotoxins, and no evidence exists so far that the risk of systemic injury is related to the severity of periodontitis. The aim of the present study was to test the influence of gentle mastication on the occurrence of endotoxemia in patients with or without periodontal disease. METHODS: A total of 67 subjects were periodontally examined and grouped according to their periodontal status. This classification was based on an original index of severity of periodontal disease (periodontal index for risk of infectiousness, PIRI) aimed at reflecting the individual risk of systemic injury from the periodontal niches. Thus, the patients were classified into 3 risk groups: low, PIRI = 0; n = 25; moderate, 1 < or = PIRI < or = 5, n = 27; and high 6 < or = PIRI < or = 10, n = 15. Blood samples were collected before and 5 to 10 minutes after a standardized session of gentle mastication for detection of circulating endotoxins. Blood samples were tested with a chromogenic limulus amoebocyte lysate assay. RESULTS: Overall, blood levels of endotoxin after mastication were found to be significantly higher than before mastication (0.89 +/- 3.3 pg/ml versus 3.0 +/- 5.8 pg/ml; P= 0.0002). Likewise, the incidence of positive endotoxemia rose from 6% before mastication to 24% after mastication (P = 0.001). When accounting for the PIRI index, endotoxin levels and positive endotoxemia proved to be significantly higher in patients with severe periodontal disease than in the subjects with low or moderate periodontitis. CONCLUSIONS: Gentle mastication is able to induce the release of bacterial endotoxins from oral origin into the bloodstream, especially when patients have severe periodontal disease. This finding suggests that a diseased periodontium can be a major and underestimated source of chronic, or even permanent, release of bacterial pro-inflammatory components into the bloodstream.

Adult↗
PubMed2007

Short-term effect of mastic gum on salivary concentrations of cariogenic bacteria in orthodontic patients.

OBJECTIVE: To determine antibacterial activity of chewing mastic gum against the salivary levels of Streptococcus mutans, the total number of viable bacteria, and lactobacilli in patients undergoing therapy with fixed orthodontic appliances. MATERIALS AND METHODS: In this study, the levels of S mutans, lactobacilli, and total cultivated bacteria were measured before and after chewing mastic gum. The antibacterial effects of chewing mastic gum against these microorganisms in saliva were compared with a placebo gum. The counts for orthodontically treated patients were evaluated before chewing gum; just after chewing gum; and after 45, 75, 105, and 135 minutes. Saliva samples taken from the patients were inoculated onto trypticase-yeast-cystine-bacitracin agar for mutans streptococci and onto Rogosa agar for lactobacilli. The agar plates were incubated for 48 hours anaerobically at 37 degrees C. The total number of viable bacteria was then counted. RESULTS: Just after chewing the mastic gum for 15 minutes, a significant decrease of total bacteria and S mutans was observed (P < .001). The reduction in lactobacilli was not significant at later first stage (P > .05). However, at the end of 135 minutes, there were significantly fewer S mutans (P < .001), total viable bacteria (P < .001), and lactobacilli (P < .001) in the oral cavity after chewing mastic gum than after chewing paraffin (P < .001). The results show that chewing mastic gum decreased the total viable bacteria, S mutans, and lactobacilli in saliva in orthodontically treated patients with fixed appliances. CONCLUSION: Chewing mastic gum might be useful in preventing caries lesions.

Adolescent↗
PubMed1994

Effects of mastication on digestion of whole cereal grains by cattle.

A study was conducted to evaluate the effects of mastication on the physical breakdown and ruminal digestion of whole cereal grains by cattle. Three Hereford cows (initial BW 557 kg; SD, 17) surgically fitted with ruminal and esophageal fistulas were fed 5.5 kg/d (as-fed basis) of whole barley, corn, or wheat in an experiment designed as a 3 x 3 Latin square. Eating time and chews per kilogram of DM were greater (P < .10) for corn than for barley or wheat. Whole corn was substantially damaged after ingestive mastication, and the majority of kernels were broken into small pieces. Many barley and wheat kernels showed signs of dentition, but most kernels remained intact. Less saliva (P < .10) was added to whole wheat than to barley or corn during ingestive mastication. Cattle fed whole barley spent twice (P < .10) as long ruminating per kilogram of DM as those fed corn, with intermediate times for wheat. Less than 30% of the DM disappeared from unmasticated whole grains during 96 h of ruminal incubation. Ingestive mastication increased DM digestion to 53, 69, and 66% for barley, corn, and wheat, respectively. Mastication alters the kinetics of ruminal digestion of unprocessed cereal grains. Combined with the inherent protein and starch digestibilities of the grain, mastication affects the type and extent of processing required to optimize the utilization of cereal grains by cattle. Unlike barley and wheat, corn kernels are extensively damaged during ingestive mastication, reducing the need for physical processing.

Ammonia↗
PubMed2005

Effects of size of ingestively masticated fragments of plant tissues on kinetics of digestion of NDF.

Ingestively masticated fragments were collected and sized via sieving. Different sizes of esophageal masticate and ruminal digesta fragments, and ground fragments of larger masticated pieces were incubated in vitro, and undigested NDF remaining at intervals of up to 168 h of incubation was determined. The ruminal age-dependent time delay (tau) for onset of digestion of NDF was positively correlated (P < 0.004) with the mean sieve aperture estimated to retain 50% of the fragments between successive sieve apertures (MRA). Degradation rate of potentially degradable NDF (PDF) and level of indigestible NDF were not related (P > 0.10) to MRA of masticated and ground fragments. Estimates of tau were positively related to MRA, with slopes of bermudagrass < corn silage < ruminal fragments of corn silage. It was concluded that fragment size-, and consequently, ruminal age-dependent onset of PDF degradation of a mixture of different fragment sizes results in an age-dependent rate of degradation of the more rapidly degrading of two subentities of PDF. Models are proposed that assume a tau before onset of simultaneous degradation of PDF from two pools characterized as having gamma-modeled age-dependency and age-constant rates. The ruminal age-dependent pool seems to be associated with the faster-degrading pool, and its rate parameter increases with range in MRA in the population of fragments. Conceptually, the ruminal age-dependent rate parameter for PDF degradation seems to represent a composite of several effects: 1) effects of the size-dependent tau; 2) range in MRA of the population of ingestively masticated fragments; and 3) subentities of PDF that degrade via more rapid age-dependent rates compared with subentities of PDF that degrade via age-constant rates. The estimated fractional rates of ruminative comminution of ingestively masticated fragments (0.060 to 0.075/h) were of a magnitude similar to the mean fractional rates of PDF digestion (0.030 to 0.085/h), which implies that ruminative comminution may be first-limiting to fractional rate of PDF digestion. The in vivo roles of ingestive and ruminative mastication of fragments on PDF degradation must be considered in any kinetic system for estimating PDF digestion in the rumen. These results and others in the literature suggest that the rate of surface area exposure rather than intrinsic chemical attributes of PDF may be first-limiting to degradation rate of PDF in vivo.

Animal Nutritional Physiological Phenomena↗