Review: Rumen sensors: data and interpretation for key rumen metabolic processes.

Rumen sensors provide specific information to help understand rumen functioning in relation to health disorders and to assist in decision-making for farm management. This review focuses on the use of rumen sensors to measure ruminal pH and discusses variation in pH in both time and location, pH-associated disorders and data analysis methods to summarize and interpret rumen pH data. Discussion on the use of rumen sensors to measure redox potential as an indication of the fermentation processes is also included. Acids may accumulate and reduce ruminal pH if acid removal from the rumen and rumen buffering cannot keep pace with their production. The complexity of the factors involved, combined with the interactions between the rumen and the host that ultimately determine ruminal pH, results in large variation among animals in their pH response to dietary or other changes. Although ruminal pH and pH dynamics only partially explain the typical symptoms of acidosis, it remains a main indicator and may assist to optimize rumen function. Rumen pH sensors allow continuous monitoring of pH and of diurnal variation in pH in individual animals. Substantial drift of non-retrievable rumen pH sensors, and the difficulty to calibrate these sensors, limits their application. Significant within-day variation in ruminal pH is frequently observed, and large distinct differences in pH between locations in the rumen occur. The magnitude of pH differences between locations appears to be diet dependent. Universal application of fixed conversion factors to correct for absolute pH differences between locations should be avoided. Rumen sensors provide high-resolution kinetics of pH and a vast amount of data. Commonly reported pH characteristics include mean and minimum pH, but these do not properly reflect severity of pH depression. The area under the pH × time curve integrates both duration and extent of pH depression. The use of this characteristic, as well as summarizing parameters obtained from fitting equations to cumulative pH data, is recommended to identify pH variation in relation to acidosis. Some rumen sensors can also measure the redox potential. This measurement helps to understand rumen functioning, as the redox potential of rumen fluid directly reflects the microbial intracellular redox balance status and impacts fermentative activity of rumen microorganisms. Taken together, proper assessment and interpretation of data generated by rumen sensors requires consideration of their limitations under various conditions.

Effect of supplemental concentrate during the dry period or early lactation on rumen epithelium gene and protein expression in dairy cattle during the transition period.

We previously reported 2 experiments with rumen-cannulated Holstein-Friesian dairy cows showing that during the transition period, rumen papillae surface area, and fractional absorption rate of volatile fatty acids (VFA) increase after calving. However, supplemental concentrate during the dry period and rate of increase of concentrate allowance during lactation affected papillae surface area, but not VFA absorption. Here we report the changes in gene and protein expression in rumen papillae related to tissue growth and VFA utilization. The lactation experiment treatment consisted of a rapid [RAP; 1.0 kg of dry matter (DM)/d; n = 6] or gradual (GRAD; 0.25 kg of DM/d; n = 6) increase of concentrate allowance (up to 10.9 kg of DM/d), starting at 4 d postpartum (pp). The dry period experiment treatment consisted of 3.0 kg of DM/d of concentrate (n = 4) or no concentrate (n = 5) during the last 28 d of the dry period. Real-time quantitative PCR analysis of rumen papillae showed that the expression of apoptosis-related genes was neither affected by day nor its interaction with treatment for both experiments. Expression of epithelial transporter genes was not affected by day or treatment in the lactation experiment, except for NBC1. In the dry period experiment, expression of MCT1, NBC1, DRA, NHE2, NHE3, and UT-B generally decreased after calving. A day and treatment interaction was observed for ATP1A1 in the dry period experiment, with greater expression at 18 and 8 d antepartum for concentrate than no concentrate. Generally, expression of VFA metabolism-related genes was not affected by day or its interaction with treatment. In the lactation experiment, immunoblotting of 5 selected genes showed that protein expression of DRA and PCCA was greater at 16 d pp compared with 3 and 44 d pp. Expression of NHE2 was greater, and that of ATP1A1 lower, at 16 and 44 d pp compared with 3 d pp, suggesting alterations in intracellular pH regulation and sodium homeostasis. Both MCT1 and PCCA protein were upregulated by RAP from 3 to 16 d pp, indicating modulations in VFA metabolism. Our data suggests that VFA absorption and metabolic capacity changed little per unit of surface area during the transition period, and suggests that a change in mitosis rate rather than apoptosis rate is associated with the increased ruminal VFA production, resulting in tissue growth. A significant but weak correlation between the examined gene and protein expression levels was observed only for PCCA, indicating that care must be taken when interpreting results obtained at either level.

Changes in rumen microbiota composition and in situ degradation kinetics during the dry period and early lactation as affected by rate of increase of concentrate allowance.

Changes in rumen microbiota and in situ degradation kinetics were studied in 12 rumen-cannulated Holstein Friesian dairy cows during the dry period and early lactation. The effect of a rapid (RAP) or gradual (GRAD) postpartum (pp) rate of increase of concentrate allowance was also investigated. Cows were fed for ad libitum intake and had free access to a mixed ration consisting of chopped wheat straw (dry period only), grass silage, corn silage, and soybean meal. Treatment consisted of either a rapid (1.0 kg of dry matter/d; n = 6) or gradual (0.25 kg of dry matter/d; n = 6) increase of concentrate allowance (up to 10.9 kg of dry matter/d), starting at 4 d pp. In whole rumen contents, bacterial community composition was assessed using samples from 50, 30, and 10 d antepartum (ap), and 3, 9, 16, 30, 44, 60, and 80 d pp, and protozoal and archaeal community composition using samples from 10 d ap, and 16 and 44 d pp. Intake of fermentable organic matter, starch, and sugar was temporarily greater in RAP than GRAD at 16 d pp. Bacterial community richness was higher during the dry period than during the lactation. A rapid increase in concentrate allowance decreased bacterial community richness at 9 and 16 d pp compared with a gradual increase in concentrate allowance, whereas from 30 d pp onward richness of RAP and GRAD was similar. In general, the relative abundances of Bacteroidales and Aeromonadales were greater, and those of Clostridiales, Fibrobacterales, and Spirochaetales were smaller, during the lactation compared with the dry period. An interaction between treatment and sampling day was observed for some bacterial community members, and most of the protozoal and archaeal community members. Transition to lactation increased the relative abundance of Epidinium and Entodinium, but reduced the relative abundance of Ostracodinium. Archaea from genus Methanobrevibacter dominated during both the dry period and lactation. However, during lactation the abundance of the methylotrophic Methanomassiliicoccaceae and Methanosphaera increased. The in situ degradation of organic matter, neutral detergent fiber, starch, and crude protein was neither affected by treatment nor by transition from the dry period to lactation. Results show that the composition of the rumen microbiota can change quickly from the dry period to the lactation period, in particular with a rapid increase in fermentable substrate supply postpartum, but this was not associated with changes in rumen degradation kinetics.

Enteric methane production in lactating dairy cows with continuous feeding of essential oils or rotational feeding of essential oils and lauric acid.

Rumen microbes can adapt to feed additives, which may make the decrease in enteric CH4 production upon feeding an additive a transient response only. This study investigated alternate feeding of 2 CH4 mitigating feed additives with a different mode of action on persistency of lowering CH4 production compared with feeding a single additive over a period of 10 wk. Four pairs of cows were selected, and within pairs, cows were randomly assigned to either the control (AR-AR) or the alternating (AR-LA) concentrate treatment. The AR concentrate contained a blend of essential oils (Agolin Ruminant, Agolin SA, Bière, Switzerland; 0.17 g/kg of dry matter) and the LA concentrate contained lauric acid (C12:0; 65 g/kg of dry matter). A basal concentrate without Agolin Ruminant and lauric acid was fed during the pretreatment period (2 wk). Thereafter, the cows assigned to the AR-AR treatment received the AR concentrate during all 10 treatment weeks (5 periods of 2 wk each), whereas cows assigned to the AR-LA treatment received AR and LA concentrates rotated on a weekly basis. Methane emission was measured in climate respiration chambers during periods 1, 3, and 5. From period 3 onward, dry matter intake and milk protein concentration were reduced with the AR-LA treatment. Milk fat concentration was not affected, but the proportion of C12:0 in milk fat increased upon feeding C12:0. Molar proportions of acetate and propionate in rumen fluid were lower and higher, respectively, with the AR-LA than with the AR-AR treatment. Methane yield (g/kg of dry matter intake) and intensity (g/kg of fat- and protein-corrected milk yield) were not affected by treatment. Methane yield and intensity were significantly lower (12 and 11%, respectively) in period 1 compared with the pretreatment period, but no significant difference relative to pretreatment period was observed in period 3 (numerically 9 and 7% lower, respectively) and in period 5 (numerically 8 and 4% lower, respectively). Results indicate a transient decrease in CH4 yield and intensity in time, but no improvement in extent or persistency of the decline in CH4 due to rotational feeding of essential oils and C12:0 in lactating dairy cows.

The effect of supplemental concentrate fed during the dry period on morphological and functional aspects of rumen adaptation in dairy cattle during the dry period and early lactation.

Ten rumen-cannulated Holstein-Friesian cows were used to examine the effect of feeding supplemental concentrate during the dry period on rumen papillae morphology and fractional absorption rate (ka) of volatile fatty acids (VFA) during the dry period and subsequent lactation. Treatment consisted of supplemental concentrate [3.0kg of dry matter (DM)/d] from 28d antepartum (ap) until the day of calving, whereas control did not receive supplemental concentrate. Cows were fed for ad libitum intake and had free access to the dry period ration (27% grass silage, 28% corn silage, 35% wheat straw, and 11% soybean meal on a DM basis) and, from calving onward, to a basal lactation ration (42% grass silage, 42% corn silage, and 16% soybean meal on a DM basis). From 1 to 3d postpartum (pp), all cows were fed 0.9kg DM/d of concentrate, which increased linearly thereafter to 8.9kg of DM/d on d 11 pp. At 28, 18, and 8d ap, and 3, 17, 31, and 45d pp, rumen papillae were collected and kaVFA was measured in all cows. On average, 13.8 (standard deviation: 3.8) papillae were collected each from the ventral, caudodorsal, and caudoventral rumen sacs per cow per day. The kaVFA was measured by incubating a standardized buffer fluid (45 L), containing 120mM VFA (60% acetic, 25% propionic, and 15% butyric acid) and Co-EDTA as fluid passage marker, in the evacuated and washed rumen. Treatment did not affect ap or pp DM and energy intakes or milk yield and composition. Treatment increased papillae surface area, which was 19 and 29% larger at 18 and 8d ap compared with 28d ap, respectively. Surface area increased, mainly due to an increase in papillae width. However, treatment did not increase kaVFA at 18 and 8d ap compared with 28d ap. In the control group, no changes in papillae surface area or kaVFA were observed during the dry period. In the treatment group, papillae surface area decreased between 8d ap and 3d pp, whereas no decrease was observed for control. From 3 to 45d pp, papillae surface area and kaVFA increased for all cows by approximately 50%, but the ap concentrate treatment did not affect kaVFA pp. In conclusion, the efficacy of supplemental concentrate during the dry period to increase papillae surface area and kaVFA in preparation for subsequent lactation is not supported by the present study. Current observations underline the importance of functional measurements in lieu of morphological measurements to assess changes in the adapting rumen wall.

Short communication: Using diurnal patterns of (13)C enrichment of CO2 to evaluate the effects of nitrate and docosahexaenoic acid on fiber degradation in the rumen of lactating dairy cows.

Nitrate decreases enteric CH4 production in ruminants, but may also negatively affect fiber degradation. In this experiment, 28 lactating Holstein dairy cows were grouped into 7 blocks. Within blocks, cows were randomly assigned to 1 of 4 isonitrogenous treatments in a 2×2 factorial arrangement: control (CON); NO3 [21g of nitrate/kg of dry matter (DM)]; DHA [3g of docosahexaenoic acid (DHA)/kg of DM]; or NO3+DHA (21g of nitrate/kg of DM and 3g of DHA/kg of DM). Cows were fed a total mixed ration consisting of 21% grass silage, 49% corn silage, and 30% concentrates on a DM basis. Based on the difference in natural (13)C enrichment and neutral detergent fiber and starch content between grass silage and corn silage, we investigated whether a negative effect on rumen fiber degradation could be detected by evaluating diurnal patterns of (13)C enrichment of exhaled carbon dioxide. A significant nitrate × DHA interaction was found for neutral detergent fiber digestibility, which was reduced on the NO3 treatment to an average of 55%, as compared with 61, 64, and 65% on treatments CON, DHA, and NO3+DHA, respectively. Feeding nitrate, but not DHA, resulted in a pronounced increase in (13)C enrichment of CO2 in the first 3 to 4 h after feeding only. Results support the hypothesis that effects of a feed additive on the rate of fiber degradation in the rumen can be detected by evaluating diurnal patterns of (13)C enrichment of CO2. To be able to detect this, the main ration components have to differ considerably in fiber and nonfiber carbohydrate content as well as in natural (13)C enrichment.

Changes in ruminal volatile fatty acid production and absorption rate during the dry period and early lactation as affected by rate of increase of concentrate allowance.

The aim of the present experiment was to study changes in volatile fatty acid (VFA) production using an isotope dilution technique, and changes in VFA fractional absorption rate (kaVFA) using a buffer incubation technique (BIT) during the dry period and early lactation, as affected by the postpartum (pp) rate of increase of concentrate allowance. The current results are complementary to previously reported changes on rumen papillae morphology from the same experiment. From 50 d antepartum to 80 d pp, VFA production rate was measured 5 times and kaVFA was measured 10 times in 12 rumen-cannulated Holstein Friesian cows. Cows had free access to a mixed ration, consisting of grass and corn silage, soybean meal, and (dry period only) chopped straw. Treatment consisted of either a rapid (RAP; 1.0 kg of DM/d; n=6) or gradual (GRAD; 0.25 kg of DM/d; n=6) increase of concentrate allowance (up to 10.9 kg of DM/d), starting at 4 d pp, aimed at creating a contrast in rumen-fermentable organic matter intake. For the BIT, rumen contents were evacuated, the rumen washed, and a standardized buffer fluid introduced [120 mM VFA, 60% acetic (Ac), 25% propionic (Pr), and 15% butyric (Bu) acid; pH 5.9 and Co-EDTA as fluid passage marker]. For the isotope dilution technique, a pulse-dose of (13)C-labeled Ac, Pr, and Bu and Co-EDTA as fluid passage marker was infused. The rate of total VFA production was similar between treatments and was 2 times higher during the lactation (114 mol/d) than the dry period (53 mol/d). Although papillae surface area at 16, 30, and 44 d pp was greater in RAP than GRAD, Bu and Ac production at these days did not differ between RAP and GRAD, whereas at 16 d pp RAP produced more Pr than GRAD. These results provide little support for the particular proliferative effects of Bu on papillae surface area. Similar to developments in papillae surface area in the dry period and early lactation, the kaVFA (per hour), measured using the BIT, decreased from 0.45 (Ac), 0.53 (Pr) and 0.56 (Bu) at 50 d antepartum to 0.28 (Ac), 0.34 (Pr) and 0.38 (Bu) at 3 d pp. Thereafter, kaVFA (/h) rapidly increased up to 0.67 (Ac), 0.79 (Pr), and 0.79 (Bu) at 80 d pp. Although papillae surface area was greater at 16, 30, and 44 d pp in RAP than GRAD, no differences in kaVFA between RAP and GRAD were observed during these days showing papillae surface area is not the limiting factor for kaVFA during early pp adaptation.

The effects of a ration change from a total mixed ration to pasture on rumen fermentation, volatile fatty acid absorption characteristics, and morphology of dairy cows.

To investigate the effect of the change from a concentrate and silage-based ration (total mixed ration, TMR) to a pasture-based ration, a 10-wk trial (wk 1-10) was performed, including 10 rumen- and duodenum-fistulated German Holstein dairy cows (182±24 d in milk, 23.5±3.5kg of milk/d; mean ± standard deviation). The cows were divided in either a pasture group (PG, n=5) or a confinement group (CG, n=5). The CG stayed on a TMR-based ration (35% corn silage, 35% grass silage, 30% concentrate; dry matter basis), whereas the PG was gradually transitioned from a TMR to a pasture-based ration (wk 1: TMR only; wk 2: 3 h/d on pasture wk 3 and 4: 12 h/d on pasture wk 5-10: pasture only). Ruminal pH, volatile fatty acids (VFA), NH3-N, and lipopolysaccharide (LPS) concentrations were measured in rumen fluid samples collected medially and ventrally on a weekly basis. Ruminal pH was continuously recorded during 1 to 4 consecutive days each week using ruminal pH measuring devices. In wk 1, 5, and 10, rumen contents were evacuated and weighed, papillae were collected from 3 locations in the rumen, and subsequently a VFA absorption test was performed. In the PG, mean rumen pH and molar acetate proportions decreased, and molar butyrate proportions increased continuously over the course of the trial, which can most likely be ascribed to an increased intake of rapidly fermentable carbohydrates. During the first weeks on a full grazing ration (wk 5-7), variation of rumen pH decreased, and in wk 5 a lower rumen content, papillae surface area, and potential for VFA absorption were observed. In wk 8 to 10, variation of rumen pH and total VFA concentrations increased again, and acetate/propionate ratio decreased. In wk-10 rumen content, papillae area and VFA absorption characteristics similar to initial levels were observed. Although continuous rumen pH assessments and LPS concentrations did not reveal an increased risk for subacute rumen acidosis (SARA) during the adaption period, histopathology of rumen papillae and potential for VFA absorption indicated a possible risk for rumen health. An increased risk for SARA was observed in wk 9 and 10 in the PG, but rumen LPS concentrations and histopathology were not adversely affected. Results of the present study suggest that after behavioral and metabolic adaptation to the transition from a TMR to a pasture-based ration, no adverse effects on rumen morphology and absorption capacity occurred, although rumen pH after adaptation to pasture indicated increased risk of SARA.

Morphological adaptation of rumen papillae during the dry period and early lactation as affected by rate of increase of concentrate allowance.

Knowledge of the morphological adaptation of rumen papilla, which plays an important role in volatile fatty acid absorption, in dry and early lactation dairy cattle is limited. Therefore, macro- and microscopic changes in papilla morphology during the dry period and lactation and the effect of rate of increase of concentrate allowance were studied. Samples were collected from 12 rumen-cannulated Holstein Friesian dairy cows during a pretreatment period, 50, 30, and 10 d antepartum (the dry period) and 3 d postpartum (pp), and a treatment period, 9, 16, 30, 44, 60, and 80 d pp. Cows had free access to either a dry period ration [27% grass silage, 27% corn silage, 35% wheat straw, and 11% soybean meal on a dry matter (DM) basis] or a basal lactation ration (42% grass silage, 41% corn silage, and 17% soybean meal on a DM basis, and 0.9 kg of DM/d concentrate). Treatment consisted of either a rapid (1.0 kg of DM/d; RAP; n=6) or gradual (0.25 kg of DM/d; GRAD; n=6) increase of concentrate allowance (up to 10.9 kg of DM/d), starting at d 4 pp, aimed at creating a contrast in rumen-fermentable organic matter (FOM) intake. Papillae were collected from the ventral, ventral blind, and dorsal blind rumen sacs and measured digitally. Intake of DM (11.9 kg/d) and FOM (5.7 kg/d) did not change during the pretreatment period, but increased during the treatment period to 24.5 and 15.0 kg/d at 80 d pp, respectively. Concentrate treatment and sampling day interacted for FOM intake, which was 22% greater in RAP at 16 d pp compared with GRAD. Papilla surface area decreased during the pretreatment period by 19% to 28.0mm(2) at 3 d pp, thereafter increasing to 63.0mm(2) at 80 d pp. Concentrate treatment and sampling day interacted for surface area, which was greater in RAP compared with GRAD at 16 (46.0 vs. 33.2mm(2)), 30 (55.4 vs. 41.2mm(2)), and 44 (60.5 vs. 49.7 mm(2)) days pp, showing that papillae can respond to a rapid rate of increase of FOM intake by increasing growth rate. Microscopic morphology was affected by sampling day, but neither by concentrate treatment nor by their interaction, with a decrease in papilla and epithelium thickness during the lactation. In conclusion, the rumen papillae respond to changes in FOM intake and the magnitude of this response depends on the rate of increase of FOM intake. This response in surface area of the rumen papillae potentially facilitates the absorption of the volatile fatty acids.

Efficacy of allicin from garlic against Ascaridia galli infection in chickens.

The use of garlic as a treatment against helminth infections is increasing in organic layer farms in several European countries. Its efficacy against these parasites, however, has not been demonstrated thus far. Therefore, a study was conducted to determine the efficacy of a commercially available garlic product consisting of a high concentration of allicin (i.e., the main active component of garlic) against experimentally induced Ascaridia galli infection in chickens. In total, 450 Lohmann LSL-Classic cockerels were used. Group 1, the uninfected, untreated group, consisted of 50 chickens. Groups 2 to 5, each consisting of approximately 100 chickens, were inoculated with 300 embryonated A. galli eggs/chicken at 6 wk of age. Group 2 was not treated, whereas groups 3 through 5 were given daily individual oral treatments from 13 wk of age onward. Group 3 received the recommended dose of allicin for 2 wk, whereas group 4 received a 10-fold dose of allicin. Group 5 was given 10 mg of flubendazole/kg of BW for 1 wk. Necropsy of 20 birds of all groups was performed weekly between 13 and 16 wk of age to determine adult worm loads. Group 1 remained free of A. galli. The experimental infection in the other groups resulted in a mean adult worm load of approximately 16 worms/bird. No significant differences were observed in worm counts of the allicin-treated groups (groups 3 and 4) compared with the infected, untreated group (group 2) at any week (P > 0.05). In contrast, no worms were found in chickens after flubendazole treatment (group 5). It was concluded that allicin does not represent an alternative to flubendazole for the treatment of A. galli infections in chickens.