Saliva secretion and its relation to feeding in cattle

Comparison of metabolites in rumen fluid, urine, and feces of dairy cow from subacute ruminal acidosis model measured by proton nuclear magnetic resonance spectroscopy

OBJECTIVE

In this study, metabolites that changed in the rumen fluid, urine and feces of dairy cows fed different feed ratios were investigated.

METHODS

Eight Holstein cows were used in this study. Rumen fluid, urine, and feces were collected from the normal concentrate diet (NCD) (Italian ryegrass 80%: concentrate 20% in the total feed) and high concentrate diet (HCD) groups (20%: 80%) of dairy cows. Metabolite analysis was performed using proton nuclear magnetic resonance (NMR) identification, and statistical analysis was performed using Chenomx NMR software 8.4 and Metaboanalyst 4.0.

RESULTS

The two groups of rumen fluid and urine samples were separated, and samples from the same group were aggregated together. On the other hand, the feces samples were not separated and showed similar tendencies between the two groups. In total, 160, 177, and 188 metabolites were identified in the rumen fluid, urine, and feces, respectively. The differential metabolites with low and high concentrations were 15 and 49, 14 and 16, and 2 and 2 in the rumen fluid, urine, and feces samples, in the NCD group.

CONCLUSION

As HCD is related to rumen microbial changes, research on different metabolites such as glucuronate, acetylsalicylate, histidine, and O-Acetylcarnitine, which are related to bacterial degradation and metabolism, will need to be carried out in future studies along with microbial analysis. In urine, the identified metabolites, such as gallate, syringate, and vanillate can provide insight into microbial, metabolic, and feed parameters that cause changes depending on the feed rate. Additionally, it is thought that they can be used as potential biomarkers for further research on subacute ruminal acidosis.

Comparing the responses of grain fed feedlot cattle under moderate heat load and during subsequent recovery with those of feed restricted thermoneutral counterparts: plasma biochemistry

Responses to heat stress in ruminants reflect the integration of local climatic conditions, environment/production system and the animal's homeostatic and homeorhetic capacities. Thus, the goal of ameliorating heat stress requires experimental settings that, within limits, closely resemble the target production system and cohort. We investigated the blood biochemical changes of two sequential cohorts of twelve 518 ± 23 kg grain fed Black Angus steers. Each cohort consisted of two treatments of 6 head/group: a thermally challenged (TC) treatment and a feed restricted thermoneutral (FRTN) treatment. Both groups were housed in climate controlled rooms for 19 days, with the TC group experiencing three distinct periods: PreChallenge, Challenge and Recovery. PreChallenge and Recovery delivered thermoneutral conditions, while Challenge consisted of 7 days of moderate diurnal heat load. The FRTN group was maintained in thermoneutral conditions at all times. Both groups were then relocated to outdoor pens for a further 40 days to detect any enduring change to metabolism as a consequence of the treatments. We compared blood biochemical responses of the treatments and inferred likely metabolic changes. Relative to the FRTN group, the TC animals experienced limited supply of triglycerides, cholesterol and glutamine during moderate heat load, suggesting constraints to energy metabolism. Lower blood urea during Recovery and in outdoor pens implied a requirement to capture N rather than allow its excretion. Altered liver enzyme profiles indicated a higher level of hepatic stress in the TC group. By the completion of feedlot finishing, the groups were not separable on most measures.

Effect of Duration of High-Grain Feeding on Chewing, Feeding Behavior, and Salivary Composition in Cows with or without a Phytogenic Feed Supplement

Switching diets from forage to a high-grain (HG) diet increases the risk of rumen fermentation disorders in cattle. However, the effects of the duration of the HG feeding, after the diet switch, on animal behavior and health have received considerably less attention. This experiment primarily aimed to assess the effects of the duration of an HG diet on the chewing, eating, and lying behavior and salivation dynamics in a control group (CON) and a group of cows receiving a phytogenic feed supplement (TRT) at 0.04% (DM basis), which included L-menthol, thymol, eugenol, mint oil, and cloves powder. The experiment was a crossover design with nine non-lactating cows, and two experimental periods with an intermediate washout of four weeks. In each period, the cows were first fed a forage diet for a week to collect baseline measurements representing week 0; then, the diet was switched over a week to HG (65% concentrate), which was fed for four continuous weeks (week 1, week 2, week 3, and week 4 on an HG diet, respectively). The cows were divided in two groups of four and five animals and were randomly allocated to CON or TRT. The data analysis revealed that at the start of the HG feeding, the dry matter intake and the cows’ number of lying bouts increased, but the eating time, rumination time, and meal frequency decreased, resulting in a greater eating rate. We also found that an advanced duration on an HG diet further decreased the rumination time, total chewing time, chewing index, and sorting in favor of short feed particles, with the lowest values in week 4. The feed bolus size increased but feed the ensalivation decreased in week 4 compared to week 0. The dietary switch increased salivary lysozyme activity, and the advanced duration on the HG diet increased salivary pH, but salivary phosphate decreased in weeks 1 and 2 on the HG diet. Supplementation with TRT increased sorting in favor of physically effective NDF (peNDF) in week 2 and increased salivary pH in week 4 on an HG diet. Overall, the negative effects of the HG diet in cattle are more pronounced during the initial stage of the HG feeding. However, several detrimental effects were exacerbated with the cows’ advanced duration on feed, with host adaptive changes still observed after 3 and 4 weeks following the diet switch. The TRT mitigated some of the negative effects through the temporal improvement of the salivary properties and the intake of peNDF, which are known to modulate rumen fermentation.

Heat stress response in slick vs normal-haired Criollo Limonero heifers in a tropical environment

To assess the effect of hair type on the heat stress response, 20 Criollo Limonero heifers with slick (n = 11) or normal hair (n = 9) were studied. Under a high temperature-humidity index (THI) environment, heat stress response was assessed through physiological variables that included respiration rate (RR), heart rate (HR), ruminal frequency (RMF), rectal temperature (RT), saliva pH (SPH), and lymphocyte count (LC) in the morning (5:00 AM, 27.4 °C, 64% relative humidity, THI = 77) and afternoon (1:00 PM, 34.5 °C, 70% relative humidity, THI = 88). A case-control study using a split plot design was used. Data were analyzed using ANOVA (PROC MIXED SAS 2010) and a statistical model comprising the fixed effects of hair length, sampling hour, interaction of hair length by sampling hour, and the random effect of animal nested within hair type on physiological variables associated with heat stress response. Sampling hour influenced (P < 0.0001) RR, RT, and (P < 0.003) SPH. Hair length influenced RR (P < 0.01) and RT (P < 0.04) and tended to influence LC (P < 0.07). The interaction of sampling hour by hair influenced RR (P < 0.04), RT (P < 0.0002), and both SPH and LC (P < 0.05). During afternoon hours, slick-haired heifers had lower values for RR (81 ± 4.2 vs 102 ± 4.7 bpm; P < 0.01), RT (39.5 ± 0.1 vs 40.3 ± 0.1 C°; P < 0.002), and LC (60 ± 3.2 vs 72.3 ± 3.6; P < 0.09) than normal-haired heifers. In normal-haired heifers, SPH increased during afternoon compared to morning-hours (8.66 ± 0.1 vs 9.11 ± 0.1; P < 0.04). It was concluded that slick-coated heifers exhibited an enhanced capability to cope with heat stress compared to normal-haired heifers likely due to an enhanced capacity for heat dissipation.

Supplementation With Phytogenic Compounds Modulates Salivation and Salivary Physico-Chemical Composition in Cattle Fed a High-Concentrate Diet

Saliva facilitates feed ingestion, nutrient circulation, and represents an important pH buffer for ruminants, especially for cattle fed high-concentrate diets that promote rumen acidification. This experiment evaluated the short-term effects of nine phytogenic compounds on salivation, saliva physico-chemical composition as well as ingested feed boli characteristics in cattle. A total of nine ruminally cannulated Holstein cows were used. Each compound was tested in four of these cows as part of a high-concentrate meal (2.5 kg of total mixed ration in dry matter basis for 4 h) in low or high dose, and was compared to a control meal without compound. Saliva was sampled orally (unstimulated saliva) for physico-chemical composition analysis. Composition of the ingested saliva (stimulated saliva), salivation and feed boli characteristics were assessed from ingesta collected at the cardia during the first 30 min of the meal. Analysis of unstimulated saliva showed that supplementation with capsaicin and thyme oil increased buffer capacity, while supplementation with thymol, L-menthol and gentian root decreased saliva pH. In addition, supplementing angelica root decreased saliva osmolality. Regression analysis on unstimulated saliva showed negative associations between mucins and bicarbonate as well as with phosphate when garlic oil, thyme oil or angelica root was supplemented. Analysis of stimulated saliva demonstrated that supplementation with garlic oil increased phosphate concentration, thyme oil tended to increase osmolality, capsaicin and thymol increased buffer capacity, and ginger increased phosphate content. Furthermore, salivation rate increased with ginger and thymol, and tended to increase with garlic oil, capsaicin, L-menthol and mint oil. Feed ensalivation increased with capsaicin. A positive association was found between feed bolus size and salivation rate when any of the phytogenic compounds was supplemented. Overall, our results demonstrate positive short-term effects of several phytogenic compounds on unstimulated and stimulated saliva physico-chemical properties, salivation or feed boli characteristics. Thus, the phytogenic compounds enhancing salivary physico-chemical composition have the potential to contribute to maintain or improve ruminal health in cattle fed concentrate-rich rations.

Dynamic changes in salivation, salivary composition, and rumen fermentation associated with duration of high-grain feeding in cows

Salivary secretions are essential for the regulation of digestive processes, as well as rumen and cow health. This research evaluated the effects of the duration of high-grain feeding, and of the time relative to a meal, on salivation, saliva properties, feed bolus characteristics, chewing activity, ruminal and reticular volatile fatty acids, as well as salivary and ruminal pH. Nine nonlactating cannulated Holstein cows were sampled at 1 and 23 d after transition to a 65% grain diet (short term and long term, respectively). Both before and after a controlled meal (2.5 kg of dry matter, offered over 4 h), unstimulated saliva was taken orally for composition analysis. Stimulated salivation and feed boli characteristics were evaluated by collection of ingesta from cardia during 30 min. Chewing and ruminal pH were measured during the controlled meal and for a total of 6 h thereafter. Results from unstimulated saliva showed no effect of the duration of high-grain feeding on bicarbonate, phosphate, total proteins, mucins, lysozyme, and buffer capacity, but increased osmolality at the long term. Lysozyme activity did not differ with high-grain feeding duration, but tended to be lower after the meal. In contrast to short-term-fed cows, the long-term-fed cows increased both meal consumption and feed bolus size, but decreased chewing and feed ensalivation (5.2 vs. 4.6 ± 0.50 g of saliva/g of dry matter), and had lower pH of the stimulated saliva (7.00 vs. 6.67 ± 0.076). These cows also had decreased chewing index (66.5 vs. 45.4 min/kg of neutral detergent fiber), and despite the increase in stimulated saliva buffer capacity (0.027 vs. 0.039 ± 0.006), mean ruminal pH decreased (6.31 vs. 6.11 ± 0.065) during ad libitum feeding. Both in the rumen and reticulum, the concentration of total volatile fatty acids was lower and propionate proportion was higher at the long term. Linear regression analyses revealed a positive influence of the flow rates of salivary bicarbonate and phosphate on ruminal pH during the short term. For every 1-mol increment in the flow of bicarbonate or phosphate, ruminal pH increased by 0.062 or 0.439 units, respectively. Overall, salivary buffers are key determinants of ruminal pH regulation, especially during short-term grain feeding. However, in the long term, ruminal pH drop during ad libitum feeding was stronger, and this effect seems to be exacerbated by increased feed bolus size, accompanied by reductions in feed ensalivation, stimulated saliva pH, and chewing index.

Effects of forage source and particle size on chewing activity, ruminal pH, and saliva secretion in lactating Holstein cows

The present study investigated the effects of dietary forage source (quality) and particle size on chewing activity, saliva secretion, and ruminal pH. Twelve multiparous lactating Holstein cows, four of which were ruminally cannulated, were used in a replicated 4 × 4 Latin square experimental design with a 2 × 2 factorial arrangement of treatments. Cows fed wild-rye hay diets had longer daily eating times than cows fed oaten hay diets. Treatments had no effect on ruminating time; therefore, resting time varied inversely to eating time. Neither the rate nor the amount of saliva secretion while eating, ruminating, or resting was affected by diet, resulting in similar total daily saliva secretions across treatments (231 L/day). Total volatile fatty acids (VFAs) in the ruminal fluid from animals fed oaten hay diets were higher than those from animals fed wild-rye hay diets; further, VFAs increased with decreasing forage particle size (FPS). Consistent with elevated VFA concentrations, reducing FPS and including oaten hay in the diet decreased mean ruminal pH and increased the daily time of ruminal pH under 5.8. Results of this study suggest that forage source and particle size affect ruminal pH might be via variations in VFA production rather than increased salivary recycling of buffering substrates.

Responses of late-lactation cows to forage substitutes in low-forage diets supplemented with by-products

In response to drought-induced forage shortages along with increased corn and soy prices, this study was conducted to evaluate lactation responses of dairy cows to lower-forage diets supplemented with forage substitutes. By-product feeds were used to completely replace corn grain and soybean feeds. Forty-eight late-lactation cows were assigned to 1 of 4 diets using a randomized complete block design with a 2-wk covariate period followed by a 4-wk experimental period. The covariate diet contained corn grain, soybean meal, and 61% forage. Experimental diets contained chopped wheat straw (WS)/sugar beet pulp at 0/12, 3/9, 6/6, or 9/3 percentages of diet dry matter (DM). Corn silage (20%), alfalfa silage (20%), pelleted corn gluten feed (25.5%), distillers grains (8%), whole cottonseed (5%), cane molasses/whey blend (7%), and vitamin and mineral mix with monensin (2.5%) comprised the rest of diet DM. The WS/sugar beet pulp diets averaged 16.5% crude protein, 35% neutral detergent fiber, and 11% starch (DM basis). Cows consuming the experimental diets maintained a 3.5% fat- and protein-corrected milk production (35.2 kg; standard deviation=5.6 kg) that was numerically similar to that measured in the covariate period (35.3 kg; standard deviation=5.0 kg). Intakes of DM and crude protein declined linearly as WS increased, whereas neutral detergent fiber intake increased linearly. Linear increases in time spent ruminating (from 409 to 502 min/d) and eating (from 156 to 223 min/d) were noted as WS inclusion increased. Yields of milk fat and 3.5% fat-and protein-corrected milk did not change as WS increased, but those of protein and lactose declined linearly. Phosphorous intakes were in excess of recommended levels and decreased linearly with increasing WS inclusion. Nutritional model predictions for multiparous cows were closest to actual performance for the National Research Council 2001 model when a metabolizable protein basis was used; primiparous cow performance was better predicted by energy-based predictions made with the National Research Council or Cornell Net Carbohydrate and Protein System models. Model predictions of performance showed a quadratic diet effect with increasing WS. Lactating dairy cows maintained production on low-forage diets that included forage substitutes, and in which by-product feeds fully replaced corn grain and soybean. However, longer-term studies are needed to evaluate animal performance and to improve model predictions of performance on these nontraditional diets.

Polymeric immunoglobulin receptor expression and local immunoglobulin A production in bovine sublingual, submandibular and parotid salivary glands

The submandibular and parotid glands are the main sources of immunoglobulins A (IgAs) in human and rat saliva. These glands express the polymeric immunoglobulin receptor (pIgR), which transports IgAs into saliva. The main source of IgAs in saliva and pIgR expression in salivary glands has not been well documented in cattle. Expressions of pIgR were determined in the major bovine salivary glands (sublingual, submandibular, and parotid) by RT-PCR for mRNA and by Western blot analysis and immunohistochemistry (IHC) using an anti-human pIgR antibody for protein. The protein detected with the antibody was identified by nano-liquid chromatography-quadrupole time of flight mass spectrometry. Additionally, the distribution of Ig-producing plasma cells was analyzed by IHC. RT-PCR showed that pIgR was expressed in the sublingual and submandibular glands, but not in the parotid gland. Higher protein levels were observed in sublingual glands than in submandibular glands by Western blot. By IHC, pIgR was mainly located on the apical side of the cytoplasmic membrane in the sublingual gland, whereas it was observed only on the basal side in the submandibular gland. The highest density of plasma cells expressing IgAs was observed in the sublingual gland. These results suggest that the sublingual gland plays an important role in first-line defence of the oral cavity in cattle in contrast to humans and rats.

Increasing sodium bicarbonate level in high-concentrate diets for heifers. II. Effects on chewing and feeding behaviors

Four Holstein heifers (264 ± 12 kg initial BW) were used in a 4 × 4 Latin square design with 21-day experimental periods to determine the effect of increasing levels of sodium bicarbonate (BICARB) (0%, 1.25%, 2.5% and 5%, of concentrate dry matter (DM) basis) on chewing and feed intake behavior when fed high-concentrate diets. Concentrate (13.41% CP, 13.35% NDF) and barley straw were fed once a day at 0830 h ad libitum. Feed bunks placed on scales and video recording were used to measure 24-h feed intake and chewing behavior, respectively. The patterns of feeding behavior (feed intake, meal size and length) and chewing behavior (eating, ruminating and total chewing) were studied by dividing the day into 12 intervals of 2-h each, beginning at feeding (interval 1 through 12). Number of meals per day and eating rate decreased linearly with increasing buffer level, but meal length increased linearly. No treatment effects were observed in sum of daily meal lengths or average meal size. The treatment × interval interaction was significant on meal size, length and feed intake. The size and length of those meals occurring during the 4 h post-feeding increased linearly. However, meal size tended to decrease in the evening between 8 and 12 h, whereas feed intake decreased linearly from 6 to 10 h and from 12 to 14 h post-feeding. Buffer concentration did not affect the percentage of time spent ruminating, eating or drinking per day but the buffer level × interval interaction was significant. Time spent eating expressed as min per kg of DM or organic matter (OM) intake increased linearly with buffer levels. Proportion of time spent eating increased linearly during the intervals between 0 and 4 h post-feeding. Time spent ruminating decreased linearly during the 2 h post-feeding, and also in the evening from 12 to 14 h, and at night from 18 to 22 h post-feeding, but the effect was quadratic between 8 and 10 h when intermediate buffer levels showed the greatest ruminating time. Time spent drinking decreased linearly from 6 to 8 h but increased during the 2 h following feeding and from 10 to 12 h post-feeding. Daily eating rate and meal frequency decreased linearly as the buffer level increased, but average meal size and daily chewing times were not affected. However, significant time of the day × buffer level interactions were observed for feed intake, meal size and length and chewing behavior.

Evidence for NHE3-mediated Na transport in sheep and bovine forestomach

Na absorption across the cornified, multilayered, and squamous rumen epithelium is mediated by electrogenic amiloride-insensitive transport and by electroneutral Na transport. High concentrations of amiloride (>100 μM) inhibit Na transport, indicating Na+/H+ exchange (NHE) activity. The underlying NHE isoform for transepithelial Na absorption was characterized by mucosal application of the specific inhibitor HOE642 for NHE1 and S3226 for NHE3 in Ussing chamber studies with isolated epithelia from bovine and sheep forestomach. S3226 (1 μM; NHE3 inhibitor) abolished electroneutral Na transport under control conditions and also the short-chain fatty acid-induced increase of Na transport via NHE. However, HOE642 (30 μM; NHE1 inhibitor) did not change Na transport rates. NHE3 was immunohistochemically localized in membranes of the upper layers toward the lumen. Expression of NHE1 and NHE3 has been previously demonstrated by RT-PCR, and earlier experiments with isolated rumen epithelial cells have shown the activity of both NHE1 and NHE3. Obviously, both isoforms are involved in the regulation of intracellular pH, pHi. However, transepithelial Na transport is only mediated by apical uptake via NHE3 in connection with extrusion of Na by the basolaterally located Na-K-ATPase. The missing involvement of NHE1 in transepithelial Na transport suggests that the proposed “job sharing” in epithelia between these two isoforms probably also applies to forestomach epithelia: NHE3 for transepithelial transport and NHE1 for, among others, pHi and volume regulation.

A note on the relationship between the rate of secretion of saliva and the rate of swallowing in cows at rest

The variations that occur in saliva flow in cattle at rest may affect digestive processes in the reticulo-rumen (Bailey and Balch, 1961). To learn more about the effects of variations in saliva flow on digestion, it would be of value to have a reliable method of measuring saliva flow in intact animals. Stevens and Sellers (1959) showed that emptying the rumens of cows altered the rate at which saliva was swallowed and suggested that this was a result of changes in the rate of secretion. The rate of swallowing was measured during the course of experiments on saliva secretion described earlier (Bailey and Balch, 1961). Those earlier values are here analysed to study the relationship between rate of secretion of saliva and rate of swallowing.

Differences between the in vitro digestibility of extrusa collected from oesophageal fistulated steers and the forage consumed

In a study that included C4 tropical grasses, C3 temperate grasses and C3 pasture legumes, in vitro dry matter digestibility of extrusa, measured as in vitro dry matter loss (IVDML) during incubation, compared with that of the forage consumed, was greater for grass extrusa but not for legume extrusa. The increase in digestibility was not caused by mastication or by the freezing of extrusa samples during storage but by the action of saliva. Comparable increases in IVDML were achieved merely by mixing bovine saliva with ground forage samples. Differences were greater than could be explained by increases due to completely digestible salivary DM. There was no significant difference between animals in relation to the saliva effect on IVDML and, except for some minor differences, similar saliva effects on IVDML were measured using either the pepsin–cellulase or rumen fluid–pepsin in vitro techniques. For both C4 and C3 grasses the magnitude of the differences were inversely related to IVDML of the feed and there was little or no difference between extrusa and feed at high digestibilities (>70%) whereas differences of more than 10 percentage units were measured on low quality grass forages. The data did not suggest that the extrusa or saliva effect on digestibility was different for C3 grasses than for C4 grasses but data on C3 grasses were limited to few species and to high digestibility samples. For legume forages there was no saliva effect when the pepsin–cellulase method was used but there was a small but significant positive effect using the rumen fluid–pepsin method. It was concluded that when samples of extrusa are analysed using in vitro techniques, predicted in vivo digestibility of the feed consumed will often be overestimated, especially for low quality grass diets. The implications of overestimating in vivo digestibility and suggestions for overcoming such errors are discussed.

Development of a Mechanistic Model to Represent the Dynamics of Liquid Flow Out of the Rumen and to Predict the Rate of Passage of Liquid in Dairy Cattle

A mechanistic and dynamic model was developed to represent the physiological aspects of liquid dynamics in the rumen and to quantitatively predict liquid flow out of the reticulorumen (RR). The model is composed of 2 inflows (water consumption and salivary secretion), one outflow (liquid flow through the reticulo-omasal orifice (ROO), and one in-and-out flow (liquid flux through the rumen wall). We assumed that liquid flow through the ROO was coordinated with the primary reticular contraction, which is characterized by its frequency, duration, and amplitude during eating, ruminating, and resting. A database was developed to predict each component of the model. A random coefficients model was used with studies as a random variable to identify significant variables. Parameters were estimated using the same procedure only if a random study effect was significant. The input variables for the model were dry matter intake, body weight, dietary dry matter, concentrate content in the diet, time spent eating, and time spent ruminating. Total water consumption (kg/d) was estimated as 4.893 x dry matter intake (kg/d), and 20% of the water consumed by drinking was assumed to bypass the RR. The salivary secretion rate was estimated to be 210 g/min during chewing. During ruminating, however, the salivation rate was assumed to be adjusted for the proportion of liquid in the rumen. Resting salivation was exponentially related to dry matter intake. Liquid efflux through the rumen wall was assumed to be the mean value in the database (4.6 kg/h). The liquid outflow rate (kg/h) was assumed to be a product of the frequency of the ROO opening, its duration per opening, and the amount of liquid passed per opening. Simulations of our model suggest that the ROO may open longer for each contraction cycle than had been previously reported (about 3 s) and that it is affected by dry matter intake, body weight, and total digesta in the rumen. When compared with 28 observations in 7 experiments, the model accounted for 40, 70, and 90% of the variation, with root mean square prediction errors of 9.25 kg, 1.84 kg/h, and 0.013 h(-1) for liquid content in the rumen, liquid outflow rate, and fractional rate of liquid passage, respectively. A sensitivity analysis showed that dry matter intake, followed by body weight and time spent eating, were the most important input variables for predicting the dynamics of liquid flow from the rumen. We conclude that this model can be used to understand the factors that affect the dynamics of liquid flow out of the rumen and to predict the fractional rate of liquid passage from the RR in dairy cattle.

Determination of parotid sulfate secretion in sheep by means of ultrasonic flow probes

The bilateral output of sulfate in parotid saliva, the relationship with its plasma level and with parotid flow, and its variation according to feeding behavior were determined in ad libitum, normal-sulfate (0.28% DM)-fed sheep (n = 6) using a transit time ultrasonic flow meter system to measure salivary flow. Ultrasonic flow meter probes were bilaterally implanted, under general anesthesia, around parotid ducts previously fitted through their oral ends with nonobstructive sampling catheters. Salivary flows were continuously recorded during 24 h, and saliva and blood samples for sulfate determinations were obtained hourly. Jaw movements were monitored with the submandibular balloon technique. The sulfate concentration in parotid saliva (mean of the group = 4.9 +/- 3.7 microg/mL) showed high variability between sheep (individual means from 0.4 +/- 0.3 to 9.3 +/- 5.9 microg/mL) and averaged 12.3% of the more stable plasma level (41.2 +/- 8.1 microg/mL). Pronounced intraindividual variations were also evident (0.1 to 26.3 microg of sulphate/mL of parotid saliva), in strong association with the fluctuations of salivary output. In 4 sheep, a decreasing exponential relationship was observed between parotid sulfate concentration and salivary secretion rate (r2 = 0.36, P < 0.01). This fact and the absence of a relationship between sulfate levels in plasma and in saliva suggest a sulfate secretory process during the passage of primary saliva through the ductal tree of the gland. The greatest rates of bilateral salivary sulfate output were observed during feeding (14.1 +/- 14.0 microg/min) and rumination (12.7 +/- 11.0 microg/min). Nevertheless, 49% of the sulfate output in parotid saliva was present during rest, as a result of the length of the resting times. The contribution of parotid sulfate to the ruminal S pool was highly variable and averaged 13.2 mg/d, representing less than 1% of the S intake. In conclusion, the accurate, reliable, nonobstructive, and bilateral salivary flow monitoring, using a previously characterized ultrasonic flow meter technique, allowed a detailed determination of the secretory dynamics of sulfate in parotid saliva, without disturbing the animal's routine or altering the physiological regulation of salivary output. The results indicated that, in the absence of S deficiency, the recycling of sulfate via saliva seems not to be a major factor in sheep nutrition.

Effects of grain or hay supplementation on the chewing behaviour and stability of rumen fermentation of dairy cows grazing perennial ryegrass-based pasture in spring

Cows grazing highly digestible pasture in early spring can have very low rumen fluid pH that can negatively impact on the efficiency of microbial digestion. In this experiment, cows in early lactation grazed perennial ryegrass (Lolium perenne L.)-based pasture alone at low or high allowances, or at a low allowance supplemented with either a cereal grain pellet, a chopped hay cube or a cube containing cereal grain and chopped hay to determine the effects of the addition of neutral detergent fibre as hay on chewing behaviour and stability of rumen fermentation. The hypotheses tested were that: (i) supplementing high digestibility ryegrass pasture with pelleted cereal grain would increase the proportion of the day that the pH of rumen fluid was below 6.0 and would decrease the rate of degradation of neutral detergent fibre in pasture and hay; and (ii) the inclusion of chopped hay with the cereal grain supplement in cubes would reduce the proportion of the day that the rumen fluid pH was below 6.0 and restore the rate of degradation of neutral detergent fibre in pasture and hay to that in unsupplemented cows. Rumen fluid pH was highest (P<0.05) in cows fed a chopped hay cube and lowest (P<0.05) in cows fed a cube containing cereal grain and chopped hay, with no significant (P>0.05) difference between those fed pasture only or cereal grain pellets. The introduction of grain, with or without hay, did not substantially alter the pattern or magnitude of changes in rumen fluid pH, but did reduce (P<0.05) the rate of degradation of neutral detergent fibre in pasture (5.3 v. 7.6%/h) and hay (2.7 v. 5.0%/h) in the rumen. Rumen degradation rates of pasture dry matter and neutral detergent fibre were not improved by adding chopped hay. Total volatile fatty acid concentrations in rumen fluid were highest (P<0.05) on the high pasture allowance treatment and lowest (P<0.05) on the low pasture allowance and the chopped hay cube treatments. Supplementation with grain reduced (P<0.05) the proportion of acetate and increased (P<0.05) the proportion of propionate in total volatile fatty acids. There were no significant (P>0.05) effects of dietary treatment on time spent grazing or on rate of biting while grazing. Cows in treatments receiving grain supplements (532 min) and those in the high pasture allowance treatment (566 min) spent more (P<0.05) time ruminating than those in the low pasture allowance (415 min) and chopped hay cube (465 min) treatments. The relative contributions of low pH and of starch to the reduction in rates of dry matter and neutral detergent fibre degradation in the rumen cannot be determined from this experiment, however, it is likely that both factors contribute to a relative increase in the metabolic activity of non-cellulolytic microorganisms.

Effects of forage particle size, forage source, and grain fermentability on performance and ruminal pH in midlactation cows

Our study investigated the effects of, and interactions between, forage particle size, level of dietary ruminally fermentable carbohydrate (RFC), and level of dietary starch on performance, chewing activity, and ruminal pH for dairy cows fed one level of dietary NDF. Twelve cows (48 DIM) were assigned to six treatments in a replicated 6 x 6 Latin square. Treatments were arranged in an incomplete 2 x 2 x 2 factorial design. Factors were: dry cracked shelled corn (DC, low RFC) or ground high-moisture corn (HMC; high RFC), finely chopped or coarse silage, and alfalfa silage as the only forage or a 50:50 ratio (DM basis) of alfalfa and corn silage. Diets combining HMC with only alfalfa silage were not included in the experiment. Diets were fed for ad libitum intake as a TMR with a concentrate:forage ratio of 61:39. Diets based on only alfalfa silage and diets based on a mix of alfalfa and corn silage averaged 18.6 and 15.8% CP, 25.8 and 24.7% NDF, 17.7 and 14.8% ADF, and 29.1 and 37.3% starch, respectively. Mean particle sizes were 5.3, 2.7, 5.6, and 2.8 mm for coarse alfalfa, fine alfalfa, coarse corn silage, and fine corn silage, respectively. Decreasing forage particle size decreased DMI (23.3 vs. 21.6 kg) and organic matter intake (22.0 vs. 20.2 kg). Increasing RFC decreased DMI (22.8 vs. 21.0 kg) and organic matter intake (21.5 vs. 20.0 kg). Decreasing forage particle size increased energy-corrected milk for alfalfa based diets (34.9 vs. 37.4 kg). Percentage of milk fat decreased with decreasing forage particle size (3.07 vs. 2.90%) and increased level of RFC (3.04 vs. 2.57%). Percentage of protein increased when corn silage partially replaced alfalfa silage (2.84 vs. 2.90%) but decreased when HMC replaced DC (2.90 vs. 2.84%). Apparent total tract digestibility of DM (66.7 vs. 68.5%), OM (65.9 vs. 70.7%), and starch (88.9 vs. 93.4%) increased when level of RFC was increased. Increasing level of RFC decreased mean ruminal pH from 5.82 to 5.67 and decreased minimum pH. Hours per day at which pH was <5.8, and area <5.8, increased when corn silage partially replaced alfalfa silage (2.6 vs. 4.4 h and 8.9 h x pH vs. 11.4 h x pH) and decreased further when level of RFC was increased (4.4 vs. 6.4 h and 11.4 h x pH vs. 14.3 h x pH). Decreasing forage particle size in HMC diets increased hours and area <5.8, but for DC diets, the effect of forage particle size depended on forage source. Interactions were found between level of physically effective fiber, forage source, and level of RFC on production and pH, complicating the inclusion of these effects in dairy ration formulation and evaluation.

Fibrolytic enzymes and parity effects on feeding behavior, salivation, and ruminal pH of lactating dairy cows

Four multiparous and four primiparous lactating dairy cows fitted with ruminal cannulas were used in a duplicated 4 x 4 Latin square design to study the effects of parity and inclusion of a fibrolytic enzyme product (Agribrands International, St. Louis, MO) on feeding and chewing behavior, salivation, and ruminal pH. Diets consisting of rolled barley, barley silage, and alfalfa haylage (55% forage, DM basis) differed in enzyme application: 1) control, 2) enzyme applied to concentrate (45% of TMR), 3) enzyme applied to supplement (4% of TMR), and enzyme applied to a premix (0.2% of TMR). Enzyme supplementation did not alter daily time spent eating or ruminating, but when enzymes were added to the ration daily, saliva production increased, with no difference among enzyme application treatments. Multiparous cows consumed a greater amount of feed, but spent a similar amount of time eating, compared to primiparous cows. Primiparous cows had shorter ruminating episodes, resulting in lower daily ruminating time compared with multiparous cows. Primiparous cows had lower daily saliva output compared with multiparous cows. These results indicate that application of this fibrolytic enzyme product did not alter the physical structure of the feed, as measured by feeding and chewing variables. The increase in total saliva production observed in cows fed enzyme-supplemented diets may be attributed to a physiological response to compensate for the increase in fermentation products during digestion. The increased intake for multiparous cows is attributed to increased eating rate and not to increased time spent eating. The higher DMI of multiparous cows resulted in increased rumination time needed to process the additional feed and increased salivation to buffer the greater production of VFA.

Effects of forage particle size and grain fermentability in midlactation cows. II. Ruminal pH and chewing activity

Our study investigated the effects of, and interactions between, level of dietary ruminally fermentable carbohydrate (RFC) and forage particle size on rumen pH and chewing activity for dairy cows fed one level of dietary NDF. Also, correlations between intake, production, chewing, and ruminal pH parameters were investigated. Eight cows (61 days in milk) were assigned to four treatments in a double 4 x 4 Latin square. Treatments were arranged in a 2 x 2 factorial design; finely chopped alfalfa silage (FS) and coarse alfalfa silage (CS) were combined with concentrates based on either dry, cracked-shelled corn (DC; low RFC) or ground, high-moisture corn (HMC; high RFC). Diets were fed ad libitum as a total mixed rations with a concentrate:forage ratio of 60:40. Diets averaged 18.7% crude protein, 24.0% neutral detergent fiber, 18.3% , acid detergent fiber and 27.4% starch on a DM basis. Mean particle size of the four diets were 6.3, 2.8, 6.0, and 3.0 mm for DCCS, DCFS, HMCCS, and HMCFS, respectively. Decreasing forage particle size decreased ruminal pH from 6.02 to 5.81, and increasing level of RFC decreased pH from 5.99 to 5.85. Minimum daily ruminal pH decreased from 5.66 to 5.47 when level of RFC was increased, and decreased from 5.65 to 5.48 when forage particle size decreased. Time below pH 5.8 per day increased from 7.4 h to 10.8 h when level of RFC increased, and increased from 6.4 h to 11.8 h when forage particle size was decreased. Area below 5.8 showed the same relationship with RFC and forage particle size. Also, forage particle size affected the postprandial pH pattern. Cows spent more time eating when fed CS compared with FS (274 vs. 237 min/d), and time spent eating decreased when level of RFC was increased (271 vs. 241 min/d). Decreasing forage particle size decreased time spent ruminating (485 vs. 320 min/d), rumination periods (15.3 vs. 11.7), and duration of rumination periods (29 vs. 26 min). Increasing level of RFC increased time spent ruminating per kg NDF intake (68.5 vs. 79.5 min/kg). Milk fat percentage was correlated to mean ruminal pH (r = 0.41), time spent below pH 5.8 (r = -0.55), and area below 5.8 (r = -0.57), but not to intake or chewing variables. DMI of particles retained on a screen equivalent in size to the top screen of the Penn State particle separator was the intake parameter explaining most of the variation in mean ruminal pH (r = 0.27) and was correlated to time spent ruminating (r = 0.61) and chewing (r = 0.61).

Effect of concentrate level and feeding management on chewing activities, saliva production, and ruminal pH of lactating dairy cows

Eight ruminally cannulated lactating Holstein cows were used in a double 4 x 4 Latin square to determine the effects of 1) proportion of barley silage [40, 50, and 60% of dry matter (DM)] in the diet, and 2) feeding a total mixed ration (TMR) compared with separate ingredients (SI) on chewing activities, saliva production, and ruminal pH. Although cows fed SI were offered a diet containing 50% silage, they actually consumed a diet containing 43% silage (DM basis). Dry matter intake and milk yield were similar for all diets (18.2 kg of DM/d and 27.2 kg/d, respectively). Cows fed the 40% silage TMR spent more time eating than cows fed SI (243 vs. 198 min/d), but rumination time was similar (546 min/d). Eating time was similar among the TMR diets, but rumination time increased from 498 to 516 and 584 min/d as silage in the TMR increased from 40 to 50, and then to 60%, respectively. The secretion of saliva per gram of feed was 4.43, 3.18, and 1.19 ml/g of DM with consumption of silage, TMR, and concentrate, respectively. Resting salivation rate was similar for all diets (101 ml/min). Regardless of the diet, cows secreted 239 +/- 17 L/d of saliva, and ruminal pH was below 5.8 for 10 h/d. Results indicated increased chewing time did not increase total daily saliva secretion because increased eating and ruminating saliva was associated with decreased resting saliva. Feeding SI increased the risk of acidosis, because cows ate a higher proportion of concentrate than intended.

Chewing activity, saliva production, and ruminal pH of primiparous and multiparous lactating dairy cows

Four multiparous (MP) and four primiparous (PP) ruminally cannulated lactating Holstein cows were used in a double 4 x 4 Latin square design to study the chewing behavior, saliva production, and ruminal pH of cows in the first or subsequent lactation. Cows were fed one of four diets; three total mixed rations containing 40, 50, or 60% silage (DM basis), and a separate ingredient diet containing 50% concentrate. Dry matter intake was higher for MP cows than for PP cows (19.2 vs. 17.1 kg/d) but not as a percentage of body weight (2.97 +/- 0.06%). Multiparous cows spent more time eating than PP cows (260 vs. 213 min/d, respectively), even after adjustment for dry matter intake (13.8 vs. 12.4 min/kg DM). Multiparous cows also spent more time ruminating per day than PP cows (560 vs. 508 min/d, respectively). Eating salivation rate was not affected by parity, but resting salivation rate was higher for MP cows than for PP. Although MP cows spent more time chewing than PP cows, total daily saliva production was only numerically higher for MP cows because the increase in saliva produced during chewing was accompanied by a decrease in saliva produced during resting. Furthermore, pH profiles tended to be lower for MP cows than for PP cows. Multiparous cows may have a greater risk of incurring acidosis than PP cows because increased salivary secretion associated with increased chewing may not sufficiently compensate the increment of fermentation acids produced in the rumen due to high feed intake.

Effects of cholinergic stimulation and aldosterone administration on salivary parotid secretion in the brushtail possum, Trichosurus vulpecula

Parotid salivation was stimulated by infusion of bethanechol chloride into anaesthetized brushtail possums to ascertain maximal flow rates, salivary composition and dietary adaptations of salivary function. Secretion rates for one gland ranged from 5.3 +/- 0.16 to 84.3 +/- 3.20 microliters/min (2.4 +/- 0.07 to 37.8 +/- 1.43 microliters/min per kg body weight). Salivary osmolality (160.8 +/- 15.39 to 248.2 +/- 8.70 mosmol/kg) and the concentrations of Na (63.1 +/- 10.93 to 124.1 +/- 5.52 mmol/l) and HCO3 (19.5 +/- 3.41 to 89.0 +/- 3.19 mmol/l) were positively correlated with flow rate. The concentrations of urea (7.8 +/- 0.64 to 4.6 +/- 0.33 mmol/l), PO4 (2.6 +/- 0.25 to 0.96 +/- 0.10 mmol/l), H+ (46.2 +/- 16.30 to 9.0 +/- 1.51 nequiv/l), K (21.4 +/- 3.73 to 13.7 +/- 2.33 mmol/l), Ca (3.7 +/- 0.53 to 2.2 +/- 0.27 mmol/l) and Mg (0.3 +/- 0.07 to 0.04 +/- 0.007 mmol/l) fell with increasing flow rate. The relations between flow rate and amylase activity (22.6 +/- 10.47 to 10.5 +/- 3.68 mu kat/l), protein concentration (2.7 +/- 0.61 to 1.3 +/- 0.28 g/l), and Cl concentration (62.1 +/- 6.88 to 50.6 +/- 6.37 mmol/l) were inconsistent between experiments. Salivary Na/K ratios were not decreased by infusion of aldosterone (2.2-22.2 nmol/h for 5 h), showing that the gland of Na-replete possums is unresponsive to short-term increases in mineralocorticoids. The low salivary amylase activity, less than that of kangaroos, presumably reflects the interaction of evolutionary history of the possum with its natural low-starch diet.(ABSTRACT TRUNCATED AT 250 WORDS)

The absorption of phosphate from the digestive tract of ruminant animals

Under normal dietary conditions in which the phosphorus (P) intake of ruminant animals is adequate, the absorption of phosphate (Pi) ions takes place from both the fore-stomachs and the small intestine. The rate of Pi absorption from the latter appears to be at least three times greater than that from the former. When absorption of Pi ions from the reticulorumen is severely reduced, as in dietary P deficiency, the absorption of both calcium and magnesium ions from the reticulorumen becomes impaired. Thus, dietary P deficiency may play a role in the aetiology of acute grass tetany.

Ingestion and mastication of feed by dairy cattle

For fiber in dairy cattle diets to be effective it must be masticated initially during feeding and again during rumination. Time spent chewing is directly related to saliva secretion, which helps buffer the rumen environment and optimizes fiber digestion. Reduction in feed particle size occurs during chewing, which is a prerequisite for passage of feeds from the forestomach, but the extent of particle breakdown during chewing depends upon the feed. Manipulating the dietary concentration of plant cell walls or the physical form of forage can alter chewing behavior and rumen function of the dairy cow, thereby optimizing productivity.

Total protozoa counts and ammonia in the rumen of mature dry Friesian cows on hay-based rations

The present work was an attempt to determine whether the variations in ruminal ammonia concentrations could be directly correlated to corresponding changes in total protozoa numbers of cattle. Four dry Friesian cows fed with hay-based rations were used through several experiments in which the twice daily feeding (6.15-15.30 h) as well as a 30 h-fasting period were studied. Simultaneously to a continuous or a regular collection of rumen liquor (for NH3), samples of rumen contents (for total protozoa numbers) were regularly withdrawn from the ventral sac. Any definite nycthemeral cycle of the protozoa numbers could not be related to feeding time. Moreover, no significant relationship could be found between the ruminal ammonia and the corresponding total protozoa numbers measured in the nocturnal interprandial period or during starvation. The data suggest that the nycthemeral ammonia profiles recorded in cattle are not directly related to protozoal activity.

Efficacy of simulated, slow release sodium bicarbonate in stabilizing ruminal milieu and acid-base status in lactating dairy cattle

Four primiparous, ruminally fistulated, lactating Holstein cows were assigned to a 4 X 4 Latin square to study the effects of NaHCO3 infusion time on ruminal milieu and systemic acid-base balance. Sodium bicarbonate, approximating .8% of diet DM, was mixed with water and infused into the rumen for 1, 2, 4, or 6 h postfeeding to simulate different timed-release rates of NaHCO3. All cows received a corn silage and concentrate diet mixed at a 40:60 ratio on a DM basis and fed in amounts that were consumed within 1 h. Ruminal fluid, blood, and urine samples were collected at 0, 1, 2, 3, 4, 5, 6, 8, and 10 h postfeeding. Length of infusion time did not alter ruminal, blood, or urine pH, but all three variables were affected by sampling time, with the 5, 1, and 3-h sampling intervals yielding the lowest values for the three measurements, respectively. Ruminal VFA molar percentages of acetate, propionate, butyrate, isovalerate, and valerate were not influenced by infusion interval but were all different due to time of sampling. Blood pCO2 and HCO3 were affected by sampling time but not by infusion interval. With the exception of blood HCO3, all treatment X sampling time interactions were nonsignificant. It appears that timed release of NaHCO3 does not alter ruminal function or acid-base balance.