The effect of size and density on the mean retention time of particles in reindeer (Rangifer tarandus)

Particle passage from the reticulorumen (RR) depends on particle density and size. A classic way of assessing these effects is the use of plastic markers of varying density and size that are recovered in the faeces. Here, we report results of an experiment where four fistulated reindeer (Rangifer tarandus, 96 ± 12 kg) were fed two different diets (browse, voluntary dry matter intake [DMI] 70 ± 10 g/kg0.75/d; or a pelleted diet, DMI 124 ± 52 g/kg0.75/d) and dosed via fistula with 8 different particle types combining densities of 1.03, 1.22 and 1.44 g/ml and sizes of 1, 10 and 20 mm. Generally, particles that passed the digestive tract intact (not ruminated) did so relatively early after marker dosing, and therefore had shorter mean retention times (MRT) than ruminated particles. On the higher intake, the overall mean retention time (MRT) of particles was shorter, but this was not an effect of shorter MRT for either intact or ruminated particles, but due to a higher proportion of intact particles at the higher intake. This supports the concept that ruminants do not adjust chewing behaviour depending on intake, but that a lower proportion of digesta is submitted to rumination due to pressure-driven escape from the forestomach at higher gut fills. Compared to cattle (Bos primigenius taurus), muskoxen (Ovibos moschatus) and moose (Alces alces) that had received the same markers, reindeer had a lower proportion of 1 mm particles that passed intact. Our results support the concept that the critical size threshold for particles leaving the ruminant forestomach is dependent on body size. While the results likely do not represent findings peculiar for reindeer, they indicate fundamental mechanisms operating in the forestomach of ruminants.

Comparative study of feeding and rumination behaviour of goats and sheep fed mixed grass hay of different chop length

Rumination is reported to be more pronounced in sheep compared to goats. This study compared the feeding and rumination behaviour of small ruminants and consisted of two experiments (E1 and E2). In E1, four sheep and four goats were offered low-quality hay (NDFom: 692 g/kg dry matter [DM]), processed to two chop lengths (long hay [LH]: 35 mm; short hay [SH]: 7 mm) in a 2 × 2 factorial (2 species × 2 chop lengths), cross-over design. In E2, the same animals were offered moderate-quality hay (NDFom: 636 g/kg DM) processed as LH and SH. Hay was offered for ad libitum consumption. Feeding and rumination behaviour was evaluated using video recordings. Aspects of rumination like chewing frequency were evaluated for 30 min per day. Faecal samples were analysed for faecal-N and particle size. There was no species effect on feed intake and organic matter digestibility (faecal N as proxy); however, goats consumed more LH than SH in E1 and E2. There was an effect of species on rumination:eating duration (R:E) ratio (higher in sheep) in E1 but not in E2, where there was a tendency for a species effect on rumination duration. In E1 and E2, sheep had a higher R:E ratio for SH than for LH. For rumination behaviour, there was a species effect for number of daily boli, chewing frequency and chews per day (more in sheep) in E1 and E2. No effect of species was found for faecal particle size. Despite much concordance, feed comminution behaviour differed in some aspects between sheep and goats. In an evolutionary context, a shift of significance of rumination could be triggered by a higher amount of abrasives in natural diets of sheep, rendering a shift of chewing towards ruminally prewashed material a rewarding strategy.

Prediction of key milk biomarkers in dairy cows through milk mid-infrared spectra and international collaborations

At the individual cow level, suboptimum fertility, mastitis, negative energy balance, and ketosis are major issues in dairy farming. These problems are widespread on dairy farms and have an important economic impact. The objectives of this study were (1) to assess the potential of milk mid-infrared (MIR) spectra to predict key biomarkers of energy deficit (citrate, isocitrate, glucose-6 phosphate [glucose-6P], free glucose), ketosis (β-hydroxybutyrate [BHB] and acetone), mastitis (N-acetyl-β-d-glucosaminidase activity [NAGase] and lactate dehydrogenase), and fertility (progesterone); (2) to test alternative methodologies to partial least squares (PLS) regression to better account for the specific asymmetric distribution of the biomarkers; and (3) to create robust models by merging large datasets from 5 international or national projects. Benefiting from this international collaboration, the dataset comprised a total of 9,143 milk samples from 3,758 cows located in 589 herds across 10 countries and represented 7 breeds. The samples were analyzed by reference chemistry for biomarker contents, whereas the MIR analyses were performed on 30 instruments from different models and brands, with spectra harmonized into a common format. Four quantitative methodologies were evaluated to address the strongly skewed distribution of some biomarkers. Partial least squares regression was used as the reference basis, and compared with a random modification of distribution associated with PLS (random-downsampling-PLS), an optimized modification of distribution associated with PLS (KennardStone-downsampling-PLS), and support vector machine (SVM). When the ability of MIR to predict biomarkers was too low for quantification, different qualitative methodologies were tested to discriminate low versus high values of biomarkers. For each biomarker, 20% of the herds were randomly removed within all countries to be used as the validation dataset. The remaining 80% of herds were used as the calibration dataset. In calibration, the 3 alternative methodologies outperform the PLS performances for the majority of biomarkers. However, in the external herd validation, PLS provided the best results for isocitrate, glucose-6P, free glucose, and lactate dehydrogenase (coefficient of determination in external herd validation [R2v] = 0.48, 0.58, 0.28, and 0.24, respectively). For other molecules, PLS-random-downsampling and PLS-KennardStone-downsampling outperformed PLS in the majority of cases, but the best results were provided by SVM for citrate, BHB, acetone, NAGase, and progesterone (R2v = 0.94, 0.58, 0.76, 0.68, and 0.15, respectively). Hence, PLS and SVM based on the entire dataset provided the best results for normal and skewed distributions, respectively. Complementary to the quantitative methods, the qualitative discriminant models enabled the discrimination of high and low values for BHB, acetone, and NAGase with a global accuracy around 90%, and glucose-6P with an accuracy of 83%. In conclusion, MIR spectra of milk can enable quantitative screening of citrate as a biomarker of energy deficit and discrimination of low and high values of BHB, acetone, and NAGase, as biomarkers of ketosis and mastitis. Finally, progesterone could not be predicted with sufficient accuracy from milk MIR spectra to be further considered. Consequently, MIR spectrometry can bring valuable information regarding the occurrence of energy deficit, ketosis, and mastitis in dairy cows, which in turn have major influences on their fertility and survival.

Teeth and the gastrointestinal tract in mammals: when 1 + 1 = 3

Both teeth and the digestive tract show adaptations that are commonly interpreted in the context of trophic guilds-faunivory, herbivory and omnivory. Teeth prepare food for the digestive tract, and dental evolution focuses on increasing durability and functionality; in particular, size reduction of plant particles is an important preparation for microbial fermentative digestion. In narratives of digestive adaptations, microbes are typically considered as service providers, facilitating digestion. That the majority of 'herbivorous' (and possibly 'omnivorous') mammals display adaptations to maximize microbes' use as prey-by harvesting the microbes multiplying in their guts-is less emphasized and not reflected in trophic labels. Harvesting of microbes occurs either via coprophagy after separation from indigestible material by a separation mechanism in the hindgut, or from a forestomach by a 'washing mechanism' that selectively removes fines, including microbes, to the lower digestive tract. The evolution of this washing mechanism as part of the microbe farming niche opened the opportunity for the evolution of another mechanism that links teeth and guts in an innovative way-the sorting and cleaning of not-yet-sufficiently-size-reduced food that is then re-submitted to repeated mastication (rumination), leading to unprecedented chewing and digestive efficiency. This article is part of the theme issue 'Food processing and nutritional assimilation in animals'.

A pilot investigation on the effect of induced saliva flow on digestive parameters in sheep, and a comparison with cattle

Sheep with a relatively low methane yield were observed to have shorter fluid and particle mean retention times (MRT). Because the application of pilocarpine, a saliva stimulant, was successful in reducing retention times in ruminants in previous studies, we applied this substance to sheep, expecting a reduction in MRT and methane yield. Three non-pregnant sheep (74 ± 10 kg) were fed a hay-only diet in a 3 × 3 Latin square design with oral doses of 0, 2.5 and 5 mg pilocarpine/kg body weight and day. Measurements included feed and water intake, MRT of liquid and particulate phases in the reticulorumen (RR) and total gastrointestinal tract (GIT), ruminal microbial yield (via urinary purine bases and metabolic faecal nitrogen), total tract methane emission, apparent nutrient digestibility and rumen fluid parameters. Data were investigated for linear and quadratic effects using orthogonal polynomial contrasts. The MRT of liquid and small particles in the RR and total GIT, and the short-chain fatty acid concentration in rumen fluid, linearly declined with increasing pilocarpine dosage, while no quadratic relationship was detected. Intake of feed DM and water, apparent nutrient digestibility, methane yield and microbial yield were not affected by pilocarpine. When combining the sheep data with that of a similar experiment in cattle, we found that the MRT of the liquid phase was positively associated with estimated NDF digestibility and with methane production per digested NDF, but was not associated with microbial yield or the ratio of acetate to propionate. The ratio between MRT of the particulate and the liquid phase was smaller for sheep than that for cattle, and was not affected by treatment. Differences in this ratio might explain why species reacted differently to the saliva-inducing agent, which might help to explain the discrepancy between species in the effect of induced saliva flow on digestive parameters.

Does age matter?-Efficiency of mechanical food break down in Tupaia belangeri at different ages

The relationship of food comminution and individual age in Tupaia belangeri is investigated. It is hypothesized that with increasing age the performance of the molar dentition decreases due to progressive tooth wear. While this relationship is well-documented for herbivores, age-related test series are largely lacking for insectivorous mammals. 15 individuals of Tupaia belangeri were fed exclusively with mealworms, and their faeces were analyzed for the number and size of chitin particles. The exoskeleton of a mealworm is resistant to digestive fluids in the gastrointestinal tract, and the size of individual chitin particles indicates the effectiveness of mechanical comminution that occurs in the oral cavity during mastication. It is hypothesized that a more precise occlusion of the dentition results in smaller particle size. Although individuals of all ages (juvenile, adult, and senile) were able to effectively process mealworms with their dentition prior to digestion, a larger area of very large chitin particles (98% quantile of all particles in senile animals as compared to in the same quantile in adults) in the feces of senile animals was detected. Even though the particle size of indigestible material is irrelevant for the digestive process, these findings either document somatic senescence in the functionality of the teeth, or alternatively a change in chewing behaviour with age.

Equid nutritional physiology and behavior: an evolutionary perspective

Like other members of the even-toed ungulates (the perissodactyls), equids once had a higher species diversity in the fossil record than they have today. This is generally explained in comparison to the enormous diversity of bovid ruminants. Theories on putative competitive disadvantages of equids include the use of a single toe as opposed to two toes per leg, the lack of a specific brain cooling (and hence water-saving) mechanism, longer gestation periods that delay reproductive output, and in particular digestive physiology. To date, there is no empirical support for the theory that equids fare better on low-quality forage than ruminants. In contrast to the traditional juxtaposition of hindgut and foregut fermenters, we suggest that it is more insightful to sketch the evolution of equid and ruminant digestive physiology as a case of convergence: both evolved a particularly high chewing efficacy in their respective groups, which facilitates comparatively high feed and hence energy intakes. But because the ruminant system, less based on tooth anatomy but more on a forestomach sorting mechanism, is more effective, equids depend more on high feed intakes than ruminants and may well be more susceptible to feed shortages. Arguably, the most under-emphasized characteristic of equids may be that in contrast to many other herbivores including ruminants and coprophageous hindgut fermenters, equids do not use the microbial biomass growing in their gastrointestinal tract. Equids display behavioral and morphophysiological adaptations to high feed intakes, and their cranial anatomy that facilitates the cropping of forage while performing grinding chewing at the same time might be unique. Rather than looking for explanations how equids are better adapted to their present niches than other organisms, considering them remnants of a different morphophysiological solution may be more appropriate.

Individual differences in digesta retention and their relation to chewing in cattle-A pilot investigation

While information on individual differences in digesta mean retention time (MRT) might be interesting when selecting phenotypes for digestive efficiency, MRT measurements are prohibitively labour-intensive for large-scale application. Therefore, more easily measured proxies of MRT might be helpful. We used the opportunity of an experiment applying saliva stimulant in cattle to investigate the effect of different individual chewing behaviour on fluid and particle MRT with a consistent diet. Four non-lactating cattle (670-850 kg body mass [BM]) were used in a 4 × 4 Latin square design, treated with the saliva stimulant pilocarpine in dosages of 0, 1, 2.5 and 5 mg/kg BM per day. The cattle were fed hay with dry matter intake (DMI) assigned according to their metabolic body weight. MRT in the whole gastrointestinal tract (GIT), the reticulorumen (RR) and the distal tract were measured using Co-EDTA, Cr-mordanted fibre and La-mordanted fibre as markers representing fluid, small particles (2 mm) and large particles (1 cm), respectively. The chewing behaviour was measured via noseband pressure sensor and expressed as chewing frequency (chews per time) and chewing intensity (chews per DMI), both for total chewing (ingestion plus rumination) and rumination chewing alone. The animals differed considerably in chewing behaviour and MRT measures. BM did not show a significant effect on chewing behaviour and MRT measures, though it tended to negatively correlated to total chewing intensity. Chewing intensity exerted a significant negative influence on MRT of fluid and particles in the RR, which was not the case for chewing frequency. Chewing frequency showed a significant relationship with MRT of large particles in the GIT. We suggest that chewing behaviour could influence MRT in two ways: (i) by affecting saliva production via the masticatory-salivary reflex and subsequently, the fluid inflow to the RR; (ii) by contributing to particle size reduction. Should the link between chewing behaviour and MRT be corroborated in larger studies, chewing measures, with their large interindividual variation, could emerge as an easy-to-measure proxy for MRT characteristics.

Is there a difference in ruminal fermentation control between cattle and sheep? A meta-analytical test of a hypothesis on differential particle and fluid retention

Ruminant species differ in digestive physiology. The species-specific ratio of mean retention time of particles and fluid (MRT_particle/MRT_fluid) in the reticulorumen has been interpreted as controlling ruminal fermentation: a higher ratio indicates of a more distinct 'washing' of particulate digesta by liquid. This should increase the harvest of microbes from the reticulorumen, and keep the microbiome in a state of more intense growth; at the same time, this should increase the metabolic losses of faecal nitrogen of microbial origin, leading to lower values for the apparent digestibility of crude protein (aD CP). A systematic difference has been hypothesized between cattle (higher ratio) and sheep (lower ratio), with a lower MRT_fluid in cattle due to a higher saliva production. Here, we test these hypotheses in a meta-analysis, using only studies that investigated cattle and sheep simultaneously. The datasets included 12 studies on MRT (of which 11 contained information on feed intake), yielding 102 (or 89) individual data; and 26 studies on protein digestibility (of which 18 contained information on intake), yielding 349 individual data. Cattle had a higher MRT_particle/MRT_fluid (2.1) than sheep (1.7), mainly due to longer MRT_particle; only if body mass was included in the model, MRT_fluid was significantly shorter in cattle in the larger MRT dataset (and tended to be shorter in the slightly smaller dataset). Cattle had a significantly lower aD CP than sheep, while there was no such difference in overall (dry or organic matter) digestibility. The dataset confirms a shift in fermentation strategy towards microbial production in cattle. While this has been suggested for ruminants in general, cattle appear particularly far on an evolutionary trajectory of maximizing microbial yield from the forestomach. The application of more specific digestive physiology data (like endogenous losses) gained from sheep to cattle should be done bearing these differences in mind.

Relationship between reticular pH parameters and potential on-farm indicators in the early lactation of dairy cows

Subacute ruminal acidosis (SARA) is an important nutritional disorder affecting animal welfare and economy of milk production. Definitions rely on ruminal pH but due to limitations of its measurement, indicators reflecting low pH are highly desirable. The aim of this study was to investigate the relationship between reticular pH and 18 on-farm indicators in milk, blood, faeces, urine and chewing behaviour in early lactating dairy cows. Ten farms were visited for 3 weeks and in total samples of 100 cows (10 per farm) were taken. The statistics and graphical visualization were performed using Pearson correlation and linear regression models on an animal individual level as well as with linear mixed models. Eight indicators (milk fat, fat-to-protein ratio, rumination time, feed intake time, rumination frequency, rumination boluses, lying time and faecal pH) were statistically significant associated with the daily animal individual reticular pH average. However, none of the models including the potential explanatory variables explained more than 5% of the pH variations. The study confirms the necessity of pH measurement to detect SARA risk animals in early lactation dairy cows.

Macrowear effects of external quartz abrasives of different size and concentration in rabbits (Oryctolagus cuniculus)

External quartz abrasives are one of the driving forces of macrowear in herbivorous animals. We tested to what extent different sizes and concentrations influence their effect on tooth wear. We fed seven pelleted diets varying only in quartz concentration (0%, 4%, and 8%) and size (fine silt: ∼4 μm, coarse silt: ∼50 μm, fine sand: ∼130 μm) to rabbits (Oryctolagus cuniculus, n = 16) for 2 weeks each in a randomized serial experiment. Measurements to quantify wear and growth of incisors and the mandibular first cheek tooth, as well as heights of all other cheek teeth, were performed using calipers, endoscopic examination, and computed tomography scans before and after each feeding period. Tooth growth showed a compensatory correlation with wear. Absolute tooth height (ATH) and relative tooth height (RTH); relative to the 0% quartz "control" diet) was generally lower on the higher concentration and the larger size of abrasives. The effect was more pronounced on the maxillary teeth, on specific tooth positions and the right jaw side. When offered the choice between different sizes of abrasives, the rabbits favored the silt diets over the control and the fine sand diet; in a second choice experiment with different diets, they selected a pelleted diet with coarse-grained sand, however. This study confirms the dose- and size-dependent wear effects of external abrasives, and that hypselodont teeth show compensatory growth. The avoidance of wear did not seem a priority for animals with hypselodont teeth, since the rabbits did not avoid diets inducing a certain degree of wear.

Reticular contraction frequency and ruminal gas dome development in goats do not differ between grass and browse diets

In investigations of differences between ruminant species feeding on browse or grass, it is often unclear whether observed differences are animal- or forage-specific. Ruminant species have been classified as 'moose-type', with little rumen content stratification, or 'cattle-type' with a distinct rumen contents stratification, including a gas layer. To which extent putative differences in forestomach motility are involved in these patterns is unknown. Using sonography, we investigated the frequency of reticular contractions and the stratification of rumen contents in goats fed exclusively on grass hay (n = 6) or dried browse (n = 5) directly after feeding, and after another 6 and 12 h with no access to feed. The frequency of reticular contractions decreased from immediately after feeding (1.8 ± 0.3 min^-1 ) to 6 h afterwards (1.2 ± 0.2 min^-1 ) and then remained constant, with no difference between diets. A gas dome became more visible over time, but neither its incidence nor its extent differed between diets. The results are in accord with classifying goats as 'cattle-type' in terms of their digestive physiology, and they add to a growing body of evidence that differences in digestive physiology between ruminant species are more due to species characteristics than different kinds of ingested forages.

Effect of induced saliva flow on fluid retention time, ruminal microbial yield and methane emission in cattle

Both in vitro and animal studies indicated that a higher dilution rate is related to a more efficient microbial synthesis and a lower methane (CH₄ ) yield. The latter could be a consequence of the former, as an increase in microbial cell synthesis offers an alternative hydrogen sink competing with methanogenesis. To test this assumption in live animals, we applied a saliva stimulant, pilocarpine, to modify liquid flow rate in cattle. Four non-lactating cows (750 ± 71 kg) were fed forage only (restricted to constant intake) in a 4 × 4 Latin square design with oral doses of 0, 1, 2.5 and 5mg pilocarpine/kg body weight and day. We quantified feed and water intake, ruminal and total tract mean retention time (MRT) of solute and particle markers, ruminal microbial yield (via urinary purine bases or metabolic faecal nitrogen), CH₄ emission, digestibility, chewing behaviour, reticular motility and rumen fluid parameters. The effect of induced saliva flow was evident by visibly increased salivation and water intake. Increasing the pilocarpine dosages resulted in a linearly decreased MRT of fluid and small particles (p < 0.001 and p< 0.05, respectively) and methane yield as related to digested DM (p < 0.05), the latter at a magnitude of 5%. No effect of treatment was found on ruminal microbial yield estimated via purine derivates. Metabolic faecal N as an indicator of microbial growth linearly correlated with pilocarpine dosages (p < 0.05). No significant relationship was found between pilocarpine dosages and large particle MRT, nutrient digestibility, ruminal pH and short-chain fatty acids. In conclusion, different from some in vitro studies, there was little indication of a reciprocal effect of CH₄ and microbial biomass production in cows fed a forage-only diet.

Dietary Choices of a Foregut-Fermenting Primate, Colobus guereza: A Comprehensive Approach Including Leaf Chemical and Mechanical Properties, Digestibility and Abundance

Free-ranging animals make dietary choices that affect their nutritional status and, ultimately, their health and fitness. We investigated food selection by a leaf-eating foregut-fermenting primate, the guereza (Colobus guereza), using multiple criteria, including chemical and mechanical properties, in vitro digestibility and leaf abundance, on the basis of 30 consecutive months of behavioral observations (4308 h in total) of a family group in the Kalinzu Forest, Uganda, as well as vegetation surveys. We noted that leaf toughness may be a proximate cue for the chemical properties of plant foods, especially for protein, which is an important selection factor used by primates. We also found that the in vitro digestibility of plant foods was greatly influenced by the concentrations of fiber and secondary compounds. At a broad level, none of the studied factors, including leaf chemical and mechanical properties, digestibility and abundance, affected whether guerezas consumed specific leaf items. At a more detailed level, however, protein content, digestibility and toughness were related to the percentage of foraging effort that guerezas devoted to specific items in our study site.

Fermentation of liquid feed with lactic acid bacteria reduces dry matter losses, lysine breakdown, formation of biogenic amines and phytate-phosphorus

This study investigated the fermentation of liquid feed for pigs and the effect of lactic acid bacteria (LAB) supplementation on fermentation rate, dry matter losses (DML), formation of biogenic amines, and degradation of phytate-P. The basal substrate in all three in vitro batch experiments consisted of 50% canola meal, 25% wheat, and 25% barley. The mixed substrates were adjusted to a dry matter (DM) content of 28.4% and fermented in 1-liter vessels at 37 °C for 24 h. Experiment 1 focused on changes in pH profiles over time. Treatments were as follows: 1) liquid feed without additive (control) and 2) liquid feed supplemented with a mixture of Lactobacillus plantarum, Pediococcus pentosaceus, and Lactobacillus lactis (adLAB) at 2.0 × 10⁵ CFU/g liquid feed (wet wt.; n = 8). Substrate pH was measured every 2 h. Experiment 2 focused on DML and the impact of fermentation on phytate-P. Treatments were identical to experiment 1 (control and adLAB; n = 8). Measured parameters included concentration of lactic acid, acetic acid, ethanol, and phytate-P, and DML after 24 h of fermentation. Counts of molds, Enterobobacteriaceae, yeasts, and LAB were determined in one combined sample of all replicates. Dry matter losses were lower in LAB-supplemented fermentations (5.89%) compared to the control (11.8%; P < 0.001). Supplementation with LAB reduced the phytate-P content (2.66 g/kg DM) compared to the control (3.07 g/kg DM; P = 0.002). Experiment 3 evaluated DML and the impact of fermentation on formation of biogenic amines. Treatments were as follows: 1) control, 2) adLAB (2.0 × 10⁵ CFU LAB/g liquid feed), 3) adLys (0.60% DM supplemented lysine), and 4) adLAB+Lys (combination of adLAB and adLys; n = 8). The fermentation of adLys resulted in a nearly complete breakdown of supplemented lysine, whereas only 10% of supplemented lysine was lost in adLAB+Lys. Furthermore, all adLys samples tested positive for cadaverine (mean concentration 0.89% DM), whereas no adLAB samples contained cadaverine above the detection limit (P < 0.001). Results indicate that DML is reduced in fermentations supplemented with homofermentative LAB. Fermentation of liquid feed with homofermentative LAB can effectively reduce the degradation of supplemental lysine and has the potential to further improve P availability.

Sand accumulation in the digestive tract of rabbits (Oryctolagus cuniculus) and guinea pigs (Cavia porcellus): The role of the appendix

We determined location and amount of accumulated sand in the gastrointestinal tract (GIT) of rabbits (Oryctolagus cuniculus) and guinea pigs (Cavia porcellus) fed diets containing external (silicate) abrasives. Computed tomographic abdominal images of rabbits (n = 44) and guinea pigs (n = 16) that each received varying numbers (4–7) of different diets for 14 days each (total n = 311 computed tomographs), and radiographs of dissected GIT and presence of silica in GIT content (n = 46 animals) were evaluated. In rabbits, the majority of accumulated sand was located in the caecal appendix, an elongated, intestinal structure in the left side of the abdomen. The ‘wash‐back’ colonic separation mechanism in rabbits may be partly responsible for a retrograde transport of sand back to the caecum, where dense, small particles accumulate in the appendix. The appendix likely acted as a reservoir of these particles, leading to significant effects not only of the momentary but also of the previous diet on recorded sand volumes in the rabbits. Guinea pigs have no caecal appendix and a colonic separation mechanism not based on a ‘wash‐back’. Less sand accumulation was found in their GIT without a specific location pattern, and there were less previous diet effects in this species. None of the rabbits or guinea pigs developed clinical signs of obstruction during the study, and the recorded sand volumes represented 1.0 ± 1.2% of the 14‐d sand intake in rabbits and 0.2 ± 0.2% in guinea pigs. Accumulation of sand in volumes up to 10 cm³ in the GIT of rabbits does not seem to cause clinical health impairment. Large inter‐individual differences in rabbits indicate inter‐individual variation in proneness to sand accumulation. The reason for the presence of a sand‐trapping caecal appendix in animals that are, due to their burrowing lifestyle and feeding close to the ground, predestined for accidental sand ingestion, remains to be unveiled.

Effects of Dilution Rate on Fermentation Characteristics of Feeds With Different Carbohydrate Composition Incubated in the Rumen Simulation Technique (RUSITEC)

This study investigated the impact of carbohydrate source and fluid passage rate (dilution rate) on ruminal fermentation characteristics and microbial crude protein (MCP) formation. Three commonly used feeds (barley grain [BG], beet pulp [BP], and soybean hulls [SBH]), which differ considerably in their carbohydrate composition, were incubated together with a mixture of grass hay and rapeseed meal in two identical Rusitec apparatuses (each 6 vessels). Differences in fluid passage rate were simulated by infusing artificial saliva at two different rates (1.5% [low] and 3.0% [high] of fermenter volume per h). This resulted in six treatments (tested in 3 runs): BGhigh, BGlow, BPhigh, BPlow, SBHhigh and SBHlow. The system was adapted for 7 d, followed by 4 d of sampling. Production of MCP (mg/g degraded organic matter [dOM]; estimated by 15N analysis) was greater with high dilution rate (DL; p &lt; 0.001) and was higher for SBH compared to both BG and BP (p &lt; 0.001). High DL reduced OM degradability (OMD) compared to low DL (p &lt; 0.001), whereas incubation of BG resulted in higher OMD compared to SBH (p &lt; 0.002). Acetate:propionate ratio decreased in response to high DL (p &lt; 0.001). Total gas and methane production (both /d and /g dOM) were lower with high DL (p &lt; 0.001). In our study increasing liquid passage rate showed the potential to increase MCP and decrease methane production simultaneously. Results encourage further studies investigating these effects on the rumen microbial population.

Digestion of bamboo compared to grass and lucerne in a small hindgut fermenting herbivore, the guinea pig (Cavia porcellus)

Bamboo is an enigmatic forage, representing a niche food for pandas and bamboo lemurs. Bamboo might not represent a suitable forage for herbivores relying on fermentative digestion, potentially due to its low fermentability. To test this hypothesis, guinea pigs (n = 36) were used as model species and fed ad libitum with one of three forages (bamboo, lucerne, or timothy grass) in a fresh or dried state, with six individuals per group, for 3 weeks. The nutrient composition and in vitro fermentation profile of bamboo displayed low fermentation potential, i.e. high lignin and silica levels together with a gas production (Hohenheim gas test) at 12 h of only 36% of that of lucerne and grass. Although silica levels were more abundant in the leftovers of (almost) all groups, guinea pigs did not select against lignin on bamboo. Dry matter (DM) intake was highest and DM digestibility lowest on the bamboo forage. Total short-chain fatty acid levels in caecal content were highest for lucerne and lowest for grass and bamboo. Bamboo-fed guinea pigs had a lower body weight gain than the grass and lucerne group. The forage hydration state did not substantially affect digestion, but dry forage led to a numerically higher total wet gut fill. Although guinea pigs increased DM intake on the bamboo diet, the negative effects on fermentation of lignin and silica in bamboo seemed overriding. For herbivores that did not evolutionary adapt, bamboo as an exclusive food resource can be considered as inadequate.

Increasing food intake affects digesta retention, digestibility and gut fill but not chewing efficiency in domestic rabbits (Oryctolagus cuniculus)

In ruminants, the level of food intake affects net chewing efficiency and hence faecal particle size. For nonruminants, corresponding data are lacking. Here, we report the effect of an increased food intake of a mixed diet in four domestic rabbit does due to lactation, and assess changes in particle size (as determined by wet sieving analysis) along the rabbit digestive tract. During lactation, rabbits achieved a distinctively higher dry matter intake than at maintenance, with a concomitant reduction in mean retention times of solute and particle markers, an increase in dry matter gut fill, a reduction in apparent digestibility of dry matter, and an overall increase in digestible dry matter intake. By contrast, there was no change in faecal mean particle size (mean ± SD: 0.58 ± 0.02 vs. 0.56 ± 0.01 mm). A comparison of diet, stomach content and faecal mean particle size suggested that 98% of particle size reduction occurred due to ingestive mastication and 2% due to digestive processes. Very fine particles passing the finest sieve, putatively not only of dietary but mainly of microbial origin, were particularly concentrated in caecum contents, which corresponds to retention of microbes via a 'wash-back' colonic separation mechanism, to concentrate them in caecotrophs that are re-ingested. This study gives rise to the hypothesis that chewing efficiency on a consistent diet is not impaired by intake level in nonruminant mammals.

Preliminary evidence for a forestomach washing mechanism in llamas (Lama glama)

Dust and grit are ingested by herbivores in their natural habitats along with the plants that represent their selected diet. Among the functions of the rumen, a washing of ingesta from adhering dust and grit has recently been demonstrated. The putative consequence is a less strenuous wear on ruminant teeth by external abrasives during rumination. The same function should theoretically apply to camelids, but has not been investigated so far. We fed six llamas (Lama glama) a diet of grass hay and a lucerne-based pelleted food in which fine sand had been included at about 8% of ingredients, for ad libitum consumption for 6 weeks. Subsequently, animals were slaughtered and content of the different sections of the gastrointestinal tract was sampled for the analysis of dry matter (DM), total ash, and acid detergent insoluble ash (ADIA, a measure for silica). Additionally, two of the animals were subjected to whole-body computer tomography (CT) after death in the natural sternal resting position. No clinical problems or macroscopic changes in the faeces were observed during the experimental period. The results indicate an accumulation of ADIA in the C3 compartment of the stomach complex, in particular in the posterior portion that is the equivalent of the abomasum in ruminants. By contrast, contents of the C1, from which material is recruited for regurgitation and rumination, were depleted of ADIA, indicating that the contents had largely been washed free of sand. The washing effect is an unavoidable side effect of the flotation- and sedimentation-based sorting mechanisms in the ruminant and the camelid forestomachs. In theory, this should allow ruminants and camelids to live in similar habitats as nonruminant herbivores at lower degrees of hypsodonty.

Tooth wear, growth and height in rabbits (Oryctolagus cuniculus) fed pelleted or extruded diets with or without added abrasives

Among the different factors thought to affect dental wear, dietary consistency is possibly the least investigated. To understand tooth wear of herbivorous animals consuming different dietary consistencies with different abrasive potential, we fed 14 rabbits (Oryctolagus cuniculus) exclusively with a timothy grassmeal-based diet in either pelleted or extruded form, or the same diets with an addition of 5% fine sand abrasives (mean size 130 µm). First, we offered the rabbits the pelleted and extruded diets as well as the pelleted control and pelleted abrasive diet in a two-stage preference experiment. Then, the rabbits received each diet for 2 weeks in a randomised serial feeding experiment, where each animal served as its own control. Tooth measurements for wear, growth and height were achieved using a manual calliper, endoscopic examination and CT scans. The analysis of the diets as fed showed almost identical mean particle size, but the extruded diet had a lower density (volume/mass) and softer consistency compared to the pelleted one and was favoured by most rabbits. The rabbits selected against the diet with sand during the preference experiment, possibly because it caused more tooth wear, especially on the teeth most exposed to wear along the upper tooth row (upper P4 and M1). The maxillary teeth also showed evidence of an increased chewing laterality by the end of the experiment. The extruded diet led to a significantly lower cheek teeth height than the pelleted diet, potentially due to the higher chewing effort needed for a similar dry matter intake. The results suggest that dietary hardness alone is a poor predictor of dental wear. The regrowth of the teeth matched wear consistently.

Increasing feed intake in domestic goats (Capra hircus): Measured effects on chewing intensity are probably driven by escape of few, large particles from the forestomach

On the one hand, oral processing - mastication - is considered a relatively inflexible component of mammalian feed acquisition that constrains instantaneous intake rates. On the other hand, experimental data shows that the level of feed intake affects faecal particle size and hence net chewing efficiency in ruminants, with larger particles occurring in the faeces at higher intakes. Here, we report the effect of an increased feed intake during maintenance (L1), late (200% of L1) and peak lactation (300% of L1) of a consistent diet (hay:concentrates 50:50) in eight domestic goats on various measures of digestive physiology including faecal mean particle size (MPS). Increasing intake led to an increased gut fill, a reduction in digesta retention times, and an increase in faecal MPS (from 0.57 to 0.72 mm). However, this was an effect of the large particle fraction (>2 mm) being disproportionately excreted at higher intakes; if MPS was assessed on the basis of particles below the typical escape threshold (≤1 mm), there was no difference between intake levels. These findings suggest that the effect of intake on the calculated net chewing efficiency in ruminants may rather be an effect of increased large particle escape from the forestomach than a reduced chewing intensity per bolus during ingestion or rumination.

Development of a subacute ruminal acidosis risk score and its prediction using milk mid-infrared spectra in early-lactation cows

A routine monitoring for subacute ruminal acidosis (SARA) on the individual level could support the minimization of economic losses and the ensuring of animal welfare in dairy cows. The objectives of this study were (1) to develop a SARA risk score (SRS) by combining information from different data acquisition systems to generate an integrative indicator trait, (2) the investigation of associations of the SRS with feed analysis data, blood characteristics, performance data, and milk composition, including the fatty acid (FA) profile, (3) the development of a milk mid-infrared (MIR) spectra-based prediction equation for this novel reference trait SRS, and (4) its application to an external data set consisting of MIR data of test day records to investigate the association between the MIR-based predictions of the SRS and the milk FA profile. The primary data set, which was used for the objectives (1) to (3), consisted of data collected from 10 commercial farms with a total of 100 Holstein cows in early lactation. The data comprised barn climate parameters, pH and temperature logging from intrareticular measurement boluses, as well as jaw movement and locomotion behavior recordings of noseband-sensor halters and pedometers. Further sampling and data collection included feed samples, blood samples, milk performance, and milk samples, whereof the latter were used to get the milk MIR spectra and to estimate the main milk components, the milk FA profile, and the lactoferrin content. Because all measurements were characterized by different temporal resolutions, the data preparation consisted of an aggregation into values on a daily basis and merging it into one data set. For the development of the SRS, a total of 7 traits were selected, which were derived from measurements of pH and temperature in the reticulum, chewing behavior, and milk yield. After adjustment for fixed effects and standardization, these 7 traits were combined into the SRS using a linear combination and directional weights based on current knowledge derived from literature studies. The secondary data set was used for objective (4) and consisted of test day records of the entire herds, including performance data, milk MIR spectra and MIR-predicted FA. At farm level, it could be shown that diets with higher proportions of concentrated feed resulted in both lower daily mean pH and higher SRS values. On the individual level, an increased SRS could be associated with a modified FA profile (e.g., lower levels of short- and medium-chain FA, higher levels of C17:0, odd- and branched-chain FA). Furthermore, a milk MIR-based partial least squares regression model with a moderate predictability was established for the SRS. This work provides the basis for the development of routine SARA monitoring and demonstrates the high potential of milk composition-based assessment of the health status of lactating cows.

Effects of Pre-Calving Body Condition and Different post partum Concentrate Feed Proportions on Immune-Associated and Hematological Parameters in Pluriparous Dairy Cows

Simple Summary

Dairy cows have to cope with physiological, metabolic and endocrine challenges during the transition from late gestation to lactation. This period is characterized by a negative energy balance. Concentrate feed proportion of the rations is often increased to compensate the energy deficit. This can lead to acidotic conditions in the rumen, which might trigger the release of lipopolysaccharides from bacteria and result in inflammatory responses. An unfavorable pre-calving body condition is known to cause health problems after calving. Cows with a higher body condition (expressed as score, BCS, at a five-point scale) prior to calving might respond differently to either low or high concentrate feed proportions after calving with regard to hematological traits as indicators for possible interactions between nutritional status and immune system. For testing this hypothesis, cows were split into two classes (higher and adequate BCS) six weeks prior to calving according to their actual BCS and fed either a low- or high-energy-dense diet after calving. Neither BCS class nor dietary energy concentration influenced markedly hematological traits, including immune cell phenotypes, and inflammatory markers, such as haptoglobin. The overall covered individual BCS range and the post partum concentrate feed challenge did not overstress physiological adaptability.

Abstract

The present study aimed at evaluating the influences of different concentrate feed proportions in the ration offered to dairy cows post partum with different body condition scores (BCS) before calving. Therefore, 60 pluriparous cows were divided 42 days before expected calving into two groups with a higher or an adequate BCS. After calving, both groups were further subdivided into a group fed a ration with either a low concentrate feed proportion (C, 35% at dry matter basis) or a high (60% at dry matter basis) one. It was hypothesized that different BCS would lead to different reactions concerning varying concentrate feed proportions. Isolated BCS effects were detected in the white blood profile only before calving. Neither low nor high concentrate feed proportions affected hematological, blood immune cell phenotypes and inflammatory markers consistently irrespective of BCS group. It was concluded, that the assessed BCS span covered a range in which the capability of cows to cope with different dietary post partum energy supply remained unchanged.

Dietary phosphorus restriction affects bone metabolism, vitamin D metabolism and rumen fermentation traits in sheep

Homeostasis of calcium (Ca) and phosphate (P_i ) is maintained by a concerted interplay of absorption and reabsorption via the gastrointestinal tract and the kidney and by storage and mobilization from the bone regulated mainly by parathyroid hormone (PTH), 1,25-dihydroxycholecalciferol and calcitonin. The present study aimed at characterizing the effects of dietary P restriction on bone, vitamin D metabolism and rumen fermentation traits reflecting the endogenous P cycle maintaining the ruminal P supply for microbial metabolism. The experiments were done in eleven female, non-pregnant, non-lactating four- to nine-year-old Black Headed Mutton sheep allotted to two feeding groups: "P-restricted" (0.11% P/kg DM and 0.88% Ca/kg DM) and "Control" (0.38% P/kg DM and 0.88% Ca/kg DM). Dietary P restriction did not lead to hypophosphataemia, probably due to a compensation by bone mobilization, demonstrated by increased serum concentrations of a resorption marker and altered gene expression in bone tissue. In addition, the RNA expression of fibroblast growth factor 23, a bone-derived factor involved in the regulation of vitamin D metabolism, was significantly reduced with dietary P restriction. Furthermore, several genes related to vitamin D metabolism and plasma concentrations of 1,25-(OH)₂ D were associated with serum concentrations of phosphate (P_i ). In the parotid gland, the expression of the P_i transporter NaPi2b was negatively associated with serum P_i and positively with parathyroid PTH expression. Although P_i concentrations in saliva and the gastrointestinal tract were significantly reduced, we found no adverse effects of the P-restricted ration on the production of short chain fatty acids, but slight differences in the production of butyrate as well as its relationship to rumen P_i and ammonia concentrations that might indicate an impact on ruminal fermentation.

Modeling reticular and ventral ruminal pH of lactating dairy cows using ingestion and rumination behavior

The prevention and control of metabolic and digestive diseases is an enormous challenge in dairy farming. Subacute ruminal acidosis (SARA) is assumed to be the most severe feed-related disorder and it impairs both animal health and economic efficiency. Currently, ruminal pH as well as variables derived from the daily pH curve are the main indicators for SARA. The objective of this study was to explain the daily pH course in the ventral rumen and reticulum of dairy cows using ingestion pattern and rumination behavior data gathered by automated data recording systems. The data of 13 ruminally fistulated lactating cows were collected at the experimental station of the Friedrich-Loeffler-Institut (Brunswick, Germany). The data included continuous pH measurements, which were recorded simultaneously in the reticulum by pH-measuring boluses and in the ventral rumen by a separate data logger. In addition, rumination behavior was measured using jaw movement sensors, and feed and water intakes were recorded by transponder-assisted systems. Milk yield and body weight were determined during and after each milking, respectively. For statistical evaluation, the data were analyzed using time-series modeling with multiple linear mixed regressions. Before applying the developed mathematical statistical modeling, we performed a plausibility assessment to ensure data quality. The major part of the mathematical statistical modeling consisted of data preparation, where all variables were transformed into a uniform 1-min resolution. Signal transformations were used to model individual feed and water intakes as well as rumination behavior events over time. Our results indicated that diurnal pH curves of both the reticulum and ventral rumen could be predicted by the transformed feed and water intake rates. Rumination events were associated with a marginal temporal increase in pH. We observed that the pH of the ventral rumen was delayed by approximately 37 min compared with that of the reticulum, which was therefore considered in the modeling. With the models developed in this study, 67.0% of the variance of the reticular pH curves and 37.8% of the variance of the ruminal pH curves could be explained by fixed effects. We deduced that the diurnal pH course is, to a large extent, associated with the animal's individual feed intake and rumination behavior.

Effects of Different Concentrate Feed Proportions on Ruminal Ph Parameters, Duodenal Nutrient Flows and Efficiency of Microbial Crude Protein Synthesis in Dairy Cows During Early Lactation

The aim of the study was to examine different pH parameters, such as variations throughout the day, depending on differing concentrate feed proportions. Moreover, special attention was payed to individual variation in microbial efficiencies (microbial crude protein/fermented organic matter) and their relation to ruminal pH, nutrient flows and digestibilities. For this, cows were grouped according to microbial efficiency (more, n = 5, vs. less efficient cows, n = 4). After calving, thirteen ruminally cannulated pluriparous cows, including nine duodenally cannulated animals, were divided into groups offered rations with a lower (35% on dry matter basis, n = 7) or a higher (60% on dry matter basis, n = 6) concentrate feed proportion. Ruminal pH parameters were assessed continuously by using intraruminal probes. Nutrient flows, nutrient digestibility and microbial efficiency were determined for duodenally cannulated cows. For most ruminal pH parameters it seemed that individual variability was higher than the treatment effect. However, a positive relationship between actual concentrate intake and diurnal pH fluctuations was found. Besides, the effect of individually different microbial efficiencies was assessed. Again, there were no group differences for pH parameters. However, nutrient flows were significantly higher in more efficient cows, whereas digestibilities were lower in in more efficient cows.

Validation of the RumiWatch Converter V0.7.4.5 classification accuracy for the automatic monitoring of behavioural characteristics in dairy cows

The objective of the present study was to validate the accuracy of algorithms, implemented in the currently available RumiWatch Converter (RWC) version V0.7.4.5 of the RumiWatch System (RWS), for the classification of behavioural characteristics from jaw and head movements which are monitored by a noseband halter comprising a pressure sensor and a triaxial accelerometer. The accurate classification of behavioural characteristics in different time resolutions is critical for the usage of the RWS for scientific and practical purposes as chewing behaviour provides essential indicators for the assessment of diet adequacy in dairy cows. To validate the RWC V0.7.4.5 classification accuracy for behavioural characteristics of rumination, eating, drinking, other activity and ruminating chews per bolus by direct observation as reference method, 14 dairy cows participated in the trial. Concordance between the consolidated 1-min and 1-h classification results was assessed. The RWC V0.7.4.5 classified only rumination and ruminating chews per bolus precisely, whereas an algorithm optimisation for the classification of eating, drinking and other activity is required. Additionally, classification results from the 1-min and 1-h time summaries were not in agreement with each other except for rumination.

Statistical modeling of ruminal pH parameters from dairy cows based on a meta-analysis

Adequate feeding of high-performance dairy cows is extremely important to avoid the digestive disorder subacute ruminal acidosis. Subacute ruminal acidosis is defined as a status with a below-average ruminal pH that does not cause direct clinical symptoms at the individual level but is relevant for animal welfare due to a higher risk of secondary health problems at the herd level. The main objective of this study was to apply meta-analytical methods in an exploratory approach to investigate the association between pH parameters of the ventral rumen with milk and diet parameters. Data from 32 studies using continuous pH measurement in the ventral rumen of lactating cows were included in the meta-analysis. Available information extracted from all studies was categorized into parameters associated with management, cow, diet, milk, and pH. The statistical analysis was divided into 4 sections. First, a multiple imputation procedure based on a principal component model was applied, since approximately 19% of the data set consisted of missing values due to heterogeneity in provided information between the studies included in the analysis. In a second step, all potential predictors for the pH parameters, including the daily mean pH, the time with a pH below 5.8, and the pH range, were examined for their prediction suitability using multi-level mixed effects meta-regression models. These analyses were performed on the raw and the imputed data. Because the results of both approaches were consistent, the imputing procedure was considered to be appropriate. Third, automated variable selection was applied to all 3 pH parameters separately for the predictor groups milk and diet using the imputed data set. Thereby, multi-model inference was used to estimate the relative importance of the selected variables. Finally, a functional relationship between the 3 pH parameters was established. The fat to protein ratio of milk, milk fat, and milk protein showed significant associations in meta-regression analysis for all 3 pH parameters when used as a single predictor. Out of the group of diet-specific variables, the acid detergent fiber, neutral detergent fiber, nonfiber carbohydrate, starch content, as well as the forage to concentrate ratio, showed the highest significance in the models. In particular, the multi-model inference showed that the protein, fat, and lactose content of the milk can best quantify the association to the daily mean pH and the time with a pH below 5.8 in a multiple regression model.

Microbial protein formation of different carbohydrates in vitro

The aim of this study was to investigate the microbial protein yield of different pure carbohydrates to contribute to a more precise prediction of the microbial protein formed in the rumen. In a first experiment, sucrose, wheat starch, microcrystalline cellulose and citrus pectin were incubated for 8 and 24 hr in the modified Hohenheim gas test (HGT) system (3 runs × 2 syringes) including gas production, ammonia and short-chain fatty acid concentration measurements. Ammonia values were used for estimation of the microbial protein formation. In a second experiment, the same substrates were incubated for 96 hr in the HGT system (2 runs × 3 syringes) and gas production was measured after 2, 4, 6, 8, 12, 16, 24, 30, 36, 48, 60, 72 and 96 hr of incubation to obtain the fermentation kinetics and the time of half-maximal gas production (t_1/2 ) of the substrates. The substrates differed considerably in their fermentation kinetics, and therefore, comparison on the basis of t_1/2 was chosen as the most meaningful. At t_1/2 , microbial protein yield [g/kg dry matter] was higher for cellulose than for sucrose and pectin and higher for starch than for sucrose. The microbial protein expressed in g/L gas production was higher for starch and cellulose than for sucrose and pectin at t_1/2 . Effects of carbohydrates related to ruminal pH may remain undetected in in vitro trials.

Digesta passage in nondomestic ruminants: Separation mechanisms in 'moose-type' and 'cattle-type' species, and seemingly atypical browsers

Ruminants have been classified as having a 'moose-type' or 'cattle-type' digestive physiology. 'Cattle-type' ruminants have a clear difference in the mean retention time (MRT) of fluid vs. small particles in the reticulorumen (RR), with a high 'selectivity factor' (SF = MRT_particle/ MRT_fluid, >1.80), and are typically grazers and intermediate feeders. 'Moose-type' ruminants have lower SF (<1.80), possibly because of defensive salivary proteins that constrain amounts of (high-viscosity) saliva, and are typically restricted to browsing. To further contribute to testing this physiology-diet correlation, we performed 55 individual passage measurements in 4/6 species that have/have not been investigated previously, respectively. Co-EDTA was used as a solute (fluid) and Cr-mordanted hay particles (<2 mm) as particle markers. Results are related to the percentage of grass in the natural diet taken from the literature. Moose (Alces alces, n = 4 on 4 to 5 diets each and n = 2 on a single diet, 5% grass, SF 1.46 ± 0.22) and giraffe (Giraffa camelopardalis, n = 3 on 3 to 5 diets each, 1%, 1.42 ± 0.23) as classical 'moose-type', and cattle (Bos taurus, n = 2, 70%, 2.04) as classical 'cattle-type' ruminants yielded results similar to those previously published, as did waterbuck (Kobus ellipsiprymnus, n = 5, 84%, 2.46 ± 0.49), corroborating that the SF represents, to a large extent, a species-specific characteristic. Results in oryx (Oryx leucoryx, n = 1, 75%, 2.60) and sitatunga (Tragelaphus spekii, n = 4, 68%, 1.81 ± 0.21) correspond to the concept of 'cattle-type' ruminants being grazers or intermediate feeders. However, European bison (Bison bonasus, n = 1, 10%, 2.74), nyala (T. angasii, n = 6, 20%, 1.95 ± 0.25), bongo (T. eurycerus, n = 3, 13%, 2.39 ± 0.54) and gerenuk (Litocranius walleri, n = 1, 0%, 2.25) appear as 'cattle-type' ruminants, yet have a browse-dominated diet. While the results do not challenge the view that a 'moose-type' digestive physiology is an adaptation to browse diets, they indicate that it may not be the only adaptation that enables ruminants to use browse. Apparently, a 'cattle-type' digestive physiology with a high SF does not necessarily preclude a browsing diet niche. High-SF browsers might have the benefit of an increased harvest of RR microbiota and grit removal prior to rumination; how they defend themselves against secondary plant compounds in browse remains to be investigated.

Effects of Body Condition and Concentrate Proportion of the Ration on Mobilization of Fat Depots and Energetic Condition in Dairy Cows during Early Lactation Based on Ultrasonic Measurements

Simple Summary

During early lactation, cows face metabolic challenges. They experience a negative energy balance as energy intake increases more slowly than energy output with milk rises. To compensate for that energy deficit, higher amounts of concentrate are offered. Additionally, cows are able to extract energy from body fat by lipid mobilization. Excessive body fat mobilization, however, leads to metabolic disorders. Therefore, high-conditioned cows are suggested to have a more pronounced lipid mobilization. The intention of the present study was to examine the change of various fat depots during the transition period depending on body condition and energy supply with ultrasonic measurements. Body condition loss after calving usually interpreted as mobilization of subcutaneous adipose tissue was not different between cows with a higher or lower body condition score. However, ultrasonic measurements detected a more pronounced mobilization of subcutaneous adipose tissue in higher conditioned animals. In contrast, inner fat depots were mobilized similarly between cows. Higher concentrate feed proportions led to a less pronounced negative energy balance. A less pronounced negative energy balance would have been expected to decrease lipid mobilization. However, this relation could not be verified in the present study. This demonstrates that sonography-based methods provide a clearer picture of metabolic conditions.

Abstract

The aim of this study was to evaluate energy metabolism and lipid mobilization via ultrasonic measurements (USM), considering inner fat depots, in lactating dairy cows differing in body condition score (BCS) and fed rations with low (35% at dry matter basis; C₃₅) or high (60% at dry matter basis; C₆₀) concentrate feed proportions postpartum. Sixty pluriparous German Holstein cows were arranged in a 2 × 2 factorial design from d 42 antepartum (relative to calculated calving) until d 120 postpartum. Animals were divided into a group with a lower (initial BCS = 3.1 ± 0.38 SD; BCS_L) and a group with a higher (initial BCS = 3.83 ± 0.41 SD; BCS_H) BCS. Due to higher dry matter intake C₆₀ groups reached the positive energy balance earlier, whereas C₃₅ groups had a more pronounced negative energy balance. Although this would suggest a more pronounced mobilization of C₃₅ groups the USM revealed no differences between feeding groups. Differences in BCS between both BCS groups remained almost the same over the trial. This was not reflected in ultrasonic data, as lipid mobilization was higher in higher conditioned cows. These findings demonstrate the extended possibilities of USM to depict metabolic processes.

Root growth compensates for molar wear in adult goats (Capra aegagrus hircus)

One reason for the mammalian clade's success is the evolutionary diversity of their teeth. In herbivores, this is represented by high-crowned teeth evolved to compensate for wear caused by dietary abrasives like phytoliths and grit. Exactly how dietary abrasives wear teeth is still not understood completely. We fed four different pelleted diets of increasing abrasiveness (L: Lucerne; G: grass; GR: grass and rice husks; GRS: grass, rice husks, and sand) to four groups of a total of 28 adult goats, all with completely erupted third molars, over a six-month period. Tooth morphology was captured by medical computed tomography scans at the beginning and end of the controlled feeding experiment, and separation lines between the crown and root segments were defined in the upper right second molar (M2), to gauge absolute wear. Using bootstrapping, significant differences in volume loss between diets L/G and GR/GRS were detected. A small but nevertheless consistent volume gain was noted in the roots, and there was a significant, positive correlation between crown volume loss and root volume gain. This growth could possibly be attributed to the well-known process of cementum deposition and its relation with a putative feedback mechanism, in place to attenuate wear caused by abrasive diets.

Controlled feeding experiments with diets of different abrasiveness reveal slow development of mesowear signal in goats (Capra aegagrus hircus)

Dental mesowear is applied as a proxy to determine the general diet of mammalian herbivores based on tooth-cusp shape and occlusal relief. Low, blunt cusps are considered typical of grazers and high, sharp cusps typical of browsers. However, how internal or external abrasives impact mesowear, and the time frame the wear signature takes to develop, still need to be explored. Four different pelleted diets of increasing abrasiveness (lucerne, grass, grass and rice husks, and grass, rice husks and sand) were fed to four groups of a total of 28 adult goats in a controlled feeding experiment over a 6-month period. Tooth morphology was captured by medical CT scans at the beginning and end of the experiment. These scans, as well as the crania obtained post mortem, were scored using the mesowear method. Comparisons between diet groups showed few significant differences after 6 months, irrespective of whether CT scans or the real teeth were scored. Only when assessing the difference in signal between the beginning and the end of the experiment did relevant, significant diet-specific effects emerge. Diets containing lower phytolith content caused a more pronounced change in mesowear towards sharper cusps/higher reliefs, while the feed containing sand did not result in more extreme changes in mesowear when compared with the same feed without sand. Our experiment suggests that the formation of a stable and hence reliable mesowear signal requires more time to develop than 6 months.

Contribution of different rumen microbial groups to gas, short-chain fatty acid and ammonium production from different diets-an approach in an in vitro fermentation system

In this study, the relative contribution of different microbial groups to ruminal metabolism was investigated for different diets. The rumen microbial cultures included whole rumen fluid, fungi + protozoa, bacteria + protozoa, protozoa and bacteria + fungi and were established by physical and chemical methods. Gas production, short-chain fatty acid (SCFA) and ammonium production were measured at 24 hr in in vitro incubations using the Hohenheim gas test (HGT) procedure. Seven donor animal diets with different concentrate-to-roughage ratios (C:R: 10:90, 30:70, 50:50, 70:30, 70:30BC (BC = NaHCO₃ ), 90:10 and 90:10BC) and five HGT diets (C:R: 10:90, 30:70, 50:50, 70:30 and 90:10) were formulated. Incubations in the HGT were always based on inoculum from sheep diets with the respective C:R ratio. Gas and ammonium production increased (p < 0.001) as a result of a gradual increase in concentrate proportion of the diets. In general, SCFA production followed the same trend. Whole rumen fluid and bacteria + fungi produced approximately 50% higher gas volume than protozoa and fungi + protozoa fractions, whereas gas production with bacteria + protozoa was at an intermediate level. Coculture of protozoa either with bacteria or with fungi produced more ammonium. Populations without bacteria were characterized by a particularly high acetate/propionate ratio. Although an interaction between microbial group and diet was observed for several variables, no clear direction could be established. Manipulating rumen fluid by selectively suppressing specific rumen microbial groups may be a helpful tool in elucidating their role in nutrient degradation and turnover in vitro.

Hallux valgus and metatarsus adductus measurements: inter-reader reliability and correlations on radiographs and MRI

AIM

To assess inter-reader reliability of metatarsus adductus (MA) using the traditional method and Engel's angle (EA) on radiography and magnetic resonance imaging (MRI) and assess correlations with hallux valgus (HV).

METHODS AND MATERIALS

Ninety consecutive patients with radiographs and MRI of the foot were included. Two readers measured HV angle (HVA), traditional metatarsus adductus angle (MAA), and EA on radiographs and HVA and EA on MRI. Three- and two-way mixed model analyses were used for reader agreements. Ninety-five percent bootstrap confidence intervals were calculated. The linear mixed model was used for association between HVA and EA/MAA.

RESULTS

Mean age and male to female ratio was 54.2±15.4 and 0.4:1, respectively. Mean HVA and EA were 20.6±9.4 and 21.2±8, 21.2±8.3 and 22.4±7.5 on radiographs and MRI, respectively. Mean MAA was 18.5±5.7 on radiographs. Inter-reader agreement was good for EA (ICC=0.73, 0.6) and moderate for MAA (ICC=0.41). Positive correlations between HVA, MAA, and EA on radiographs and MRI were found, but none were statistically significant (p=0.44 and 0.87).

CONCLUSION

Engel's angle is more reproducible. Although positive correlations exist between the degrees of HV and MA, they are not statistically significant.

Diets of giants: the nutritional value of sauropod diet during the Mesozoic

A major uncertainty in estimating energy budgets and population densities of extinct animals is the carrying capacity of their ecosystems, constrained by net primary productivity (NPP) and its digestible energy content. The hypothesis that increases in NPP due to elevated atmospheric CO 2 contributed to the unparalleled size of the sauropods has recently been rejected, based on modern studies on herbivorous insects that imply a general, negative correlation of diet quality and increasing CO 2. However, the nutritional value of plants grown under elevated CO 2 levels might be very different for vertebrate megaherbivores than for insects. Here we show plant species-specific responses in metabolizable energy and nitrogen content, equivalent to a two-fold variation in daily food intake estimates for a typical sauropod, for dinosaur food plant analogues grown under CO 2 concentrations spanning estimates for Mesozoic atmospheric concentrations. Our results potentially rebut the hypothesis that constraints on sauropod diet quality were driven by Mesozoic CO 2 concentration.

Comparative selective retention of particle size classes in the gastrointestinal tract of ponies and goats

There is a discrepancy in the literature on potential digesta separation mechanisms in horses, with both a selective retention of fine and of large particles postulated in different publications. To assess the net effect of such mechanisms, we fed ponies on a hay-only diet a pulse dose of whole (unchopped) marked hay together with a solute marker, collected faeces on a regular basis, measured marker concentrations in whole faeces and in their large (2.0-16 mm), medium (0.5-1.0 mm) and small (0.063-0.25 mm) particle fraction, and calculated the corresponding mean retention times (MRTs). For comparison, the same experiment was performed in goats. In goats, as expected, MRT_solute (35 hr) was significantly shorter than MRT_particle (51 hr); only a very small fraction of particle marker was excreted as large particles (2%); and the MRT of these large particles was significantly shorter than that of small particles (with a relevant difference of 8.6 hr), indicating that those few large particles that escape the rumen do so mostly soon after ingestion. In ponies, MRT_solute (24 hr) did not differ from MRT_particle (24 hr); a higher fraction of particle marker was excreted as large particles (5%); and the MRT of these large particles was longer than that of small particles (but with a non-relevant difference of less than 1 hr). These results indicate that no relevant net separation of digesta phases occurs in horses and that selective particle retention mechanisms in the large intestine are unlikely to represent important characteristics of the horse's digestive physiology.

Alterations in the Rumen Liquid-, Particle- and Epithelium-Associated Microbiota of Dairy Cows during the Transition from a Silage- and Concentrate-Based Ration to Pasture in Spring

In spring dairy cows are often gradually transitioned from a silage- and concentrate-based ration (total mixed ration, TMR) to pasture. Rumen microbiota adaptability is a key feature of ruminant survival strategy. However, only little is known on the temporal and spatial microbial alterations involved. This study aims to investigate how the rumen liquid (LAAB), particle (PAAB), and epithelium (EAAB) associated archaea and bacteria are influenced by this nutritional change. A 10-wk trial was performed, including 10 rumen-fistulated dairy cows, equally divided into a pasture- and a confinement- group (PG and CG). The CG stayed on a TMR-based ration, while the PG was gradually transitioned from TMR to pasture (wk 1: TMR-only, wk 2: 3 h/day on pasture, wk 3 & 4: 12 h/day on pasture, wk 5-10: pasture-only). In wk 1, wk 5, and wk 10 samples of solid and liquid rumen contents, and papillae biopsies were collected. The DNA was isolated, and PCR-SSCP and 16S rRNA gene amplicon sequencing analysis were performed. Cluster analysis revealed a higher similarity between LAAB and PAAB, compared to the EAAB, characterized by higher species diversity. At all three locations the microbiota was significantly influenced by the ration change, opposite the generally acknowledged hypothesis that the EAAB remain more consistent throughout dietary changes. Even though the animals in the PG were already on a full-grazing ration for 4-6 days in wk 5, the microbiota at all three locations was significantly different compared to wk 10, suggesting an adaptation period of several days to weeks. This is in line with observations made on animal level, showing a required time for adaptation of 2-3 weeks for production and metabolic variables. A large part of the rumen prokaryote species remained unaltered upon transition to pasture and exhibited a strong host influence, supporting the hypothesis that the rumen microbiota consists of a core and a variable microbiota. For the effect of the location as well as the ration change either very similar or opposite trends among member species of common taxa were observed, demonstrating that microbes that are phylogenetically close may still exhibit substantially different phenotypes and functions.