The functional significance of the browser-grazer dichotomy in African ruminants

The allometric relationships for the fermentation rate of dry matter, the total energy concentration of volatile fatty acids (VFAs), the energy supplied from VFA production and the mass of the digesta contents within the rumen or caecum and proximal colon (hindgut) were used to test whether the digestive strategies of grazing and browsing African ruminants differ. The wet and dry mass of the contents of the rumen and hindgut were allometrically related to body mass (BM). These relationships did not differ between browsing and grazing ruminants. The fermentation rates in the rumen were strongly allometric and the intercepts of the relationships did not differ between browsers and grazers. The fermentation rates in the hindgut were not allometrically related to BM and did not differ between ruminants with different feeding habits. Likewise, the total energy concentration of the VFAs in the rumen and hindgut showed no allometric scaling and did not differ between browsing and grazing ruminants. The energy supplied by VFA production in both the rumen and hindgut of African ruminants scaled at around 0.8 with BM. Only in the case of the energy supplied by VFAs in the rumen were there significantly different intercepts for browsing and grazing ruminants. The energy supplied by VFA production in the rumen was inadequate to meet the energy requirements for maintenance of browsers and small grazers. The retention time of digesta in the alimentary tract was positively related to BM although there was no difference in the allometric relationships for grazers and browsers. The results of these analyses suggest that, after controlling for the effects of body mass, there is little difference in digestive strategy between African ruminants with different morphological adaptations of the gut.     

Dietary selection of metabolically distinct microorganisms drives hydrogen metabolism in ruminants

Ruminants are important for global food security but emit the greenhouse gas methane. Rumen microorganisms break down complex carbohydrates to produce volatile fatty acids and molecular hydrogen. This hydrogen is mainly converted into methane by archaea, but can also be used by hydrogenotrophic acetogenic and respiratory bacteria to produce useful metabolites. A better mechanistic understanding is needed on how dietary carbohydrates influence hydrogen metabolism and methanogenesis. We profiled the composition, metabolic pathways, and activities of rumen microbiota in 24 beef cattle adapted to either fiber-rich or starch-rich diets. The fiber-rich diet selected for fibrolytic bacteria and methanogens resulting in increased fiber utilization, while the starch-rich diet selected for amylolytic bacteria and lactate utilizers, allowing the maintenance of a healthy rumen and decreasing methane production (p < 0.05). Furthermore, the fiber-rich diet enriched for hydrogenotrophic methanogens and acetogens leading to increased electron-bifurcating [FeFe]-hydrogenases, methanogenic [NiFe]- and [Fe]-hydrogenases and acetyl-CoA synthase, with lower dissolved hydrogen (42%, p < 0.001). In contrast, the starch-rich diet enriched for respiratory hydrogenotrophs with greater hydrogen-producing group B [FeFe]-hydrogenases and respiratory group 1d [NiFe]-hydrogenases. Parallel in vitro experiments showed that the fiber-rich selected microbiome enhanced acetate and butyrate production while decreasing methane production (p < 0.05), suggesting that the enriched hydrogenotrophic acetogens converted some hydrogen that would otherwise be used by methanogenesis. These insights into hydrogen metabolism and methanogenesis improve understanding of energy harvesting strategies, healthy rumen maintenance, and methane mitigation in ruminants.Subject terms: Metagenomics, Metagenomics     

Mixing and propulsion of the contents of the reticulo-rumen]

Roughage intake and digestion by ruminants involve complex interactions between the roughage constituents, the microorganisms in the reticulo-rumen (RR) and its motility. Ruminal digestion requires intense activity, ie comminution of feed particles and mixing and propulsion of digesta. The regular repetition of the contraction sequences in the RR every 50 to 70 s subjects the digesta to a consistent pattern of movements. The particles are distributed according to their functional density which depends on the density of the plant structure of the particle, the liquid inside the particle and also the gas, ie on the degree of particle fermentation. An interwoven mat of large low-density particles fills the dorsal sac and the top of the ventral sac of rumen. This mat traps part of the small high density particles. Squeezed by the contractions, the interwoven mat acts like a filter and lets a liquid containing small particles of high density pass into the bottom of the ventral sac. This liquid then flows into the reticulum and passes through the reticulo-omasal orifice (ROO). Chewing during rumination reduces particle size, eliminates particle gas and aids in separating the low-density particles, which are less fermented, from the heavy residues. The outflow of digesta, made possible by the opening of the ROO during the second phase of the reticular contraction, is highly selective. The effluent does not contain particles greater than 2 mm in size in sheep and 4 mm in cattle. This is due to the buoyancy of the large particles in the reticulum, to the self-filtration of the digesta during the passage through the ROO and possibly to backflow from the omasum to the reticulum. Finally, RR motor activity, ie continuously mixing the digesta and monitoring the evacuation of gas and outflow of digesta, allows the homeostasis in the rumen necessary to microbial fermentation. The characteristics of the ingested particles, their rates of size reduction and density increase, the consistency of digesta and the intensity of the rumen wall stimulations are all factors which depend on the nature of feed and intake level. Via mechanisms which are not yet all well known and/or quantified, these factors act upon the efficiency of the mixing and propulsion of the reticulo-ruminal content and thus upon the retention time of the feed in the RR as well as its digestive utilisation.(ABSTRACT TRUNCATED AT 400 WORDS)     

异构前列腺素及其意义

异构前列腺素是花生四烯酸经氧自由基催化的代谢产物,不依赖于环氧化酶,在体内外脂质过氧化试验中均有大量的ｉｓｏ－ＰＧｓ生成,抗氧化剂有抑制作用。ｉｓｏ－ＰＧｓ可做为脂质过氧化的一个新的特异的指标用于临床、病理与药理研究。     

Ontogenesis of muscle and adipose tissues and their interactions in ruminants and other species

The lean-to-fat ratio, that is, the relative masses of muscle and adipose tissue, is a criterion for the yield and quality of bovine carcasses and meat. This review describes the interactions between muscle and adipose tissue (AT) that may regulate the dynamic balance between the number and size of muscle v. adipose cells. Muscle and adipose tissue in cattle grow by an increase in the number of cells (hyperplasia), mainly during foetal life. The total number of muscle fibres is set by the end of the second trimester of gestation. By contrast, the number of adipocytes is never set. Number of adipocytes increases mainly before birth until 1 year of age, depending on the anatomical location of the adipose tissue. Hyperplasia concerns brown pre-adipocytes during foetal life and white pre-adipocytes from a few weeks after birth. A decrease in the number of secondary myofibres and an increase in adiposity in lambs born from mothers severely underfed during early pregnancy suggest a balance in the commitment of a common progenitor into the myogenic or adipogenic lineages, or a reciprocal regulation of the commitment of two distinct progenitors. The developmental origin of white adipocytes is a subject of debate. Molecular and histological data suggested a possible transdifferentiation of brown into white adipocytes, but this hypothesis has now been challenged by the characterization of distinct precursor cells for brown and white adipocytes in mice. Increased nutrient storage in fully differentiated muscle fibres and adipocytes, resulting in cell enlargement (hypertrophy), is thought to be the main mechanism, whereby muscle and fat masses increase in growing cattle. Competition or prioritization between adipose and muscle cells for the uptake and metabolism of nutrients is suggested, besides the successive waves of growth of muscle v. adipose tissue, by the inhibited or delayed adipose tissue growth in bovine genotypes exhibiting strong muscular development. This competition or prioritization occurs through cellular signalling pathways and the secretion of proteins by adipose tissue (adipokines) and muscle (myokines), putatively regulating their hypertrophy in a reciprocal manner. Further work on the mechanisms underlying cross-talk between brown or white adipocytes and muscle fibres will help to achieve better understanding as a prerequisite to improving the control of body growth and composition in cattle.     

Spontaneous level of sister chromosome exchanges and their distribution in human cells]

Blood of practically healthy donors of both sexes (27 females and 23 males) was cultured under the standard conditions during 96 hours. Bromodeoxyuridine (BUdR) was added at the final concentration of 10 mkg/ml 28 hours before harvesting. The slides were stained with acridine orange and Giemsa for differential staining of chromatids. In each culture sister chromatid exchanges (SCE) were analysed in 50 cells, and the part of cells undergoing the first, second and third mitoses at the time of harvesting, was calculated. According to the mean number of SCE per cell, the distribution of individuals was consistent with the normal law, the mean being 6.525 and standard deviation--0.956. A significant heterogeneity in the speed of cell cycle of cultures was observed. The coefficient of variation for the part of cells undergoing the first mitosis was 50%, for the cells in the second mitosis--15%, and for the cells in the third mitosis--154%. Correlation analysis showed a positive dependence of the mean level of SCF upon the age of a donor and upon the part of cells in the second mitosis in this individual. No reliable correlation of the SCE level with the donor's sex was observed. The distribution of cells, obtained from the culture of one individual, was best approximated by beta-distribution, and the distribution of cells obtained from the cultures of different individuals--by gamma-distribution. In both there was obtained a satisfactory approximation by Pearson's distribution of the 1 type, and significant deviations were found from the normal, Poison's and the negative binomial distribution. The conditions were found of similarity of empirical distribution of SCE in cells to the normal one. For that, it is not the value of SCE for a separate cell that should be used as a unit of measurement, but the mean from the values of frequencies for 5-10 cells. Hence, it was shown that for the evaluation of the mean frequency of SCE with the precision of 1 exchange in separate individuals it is necessary to analyse 40 cells, and to observe the 15% increase of spontaneous SCE level under the action of deleterious factors--8 individuals are enough to analyse.     

Food sensory characteristics: their unconsidered roles in the feeding behaviour of domestic ruminants

When domestic ruminants are faced with food diversity, they can use pre-ingestive information (i.e. food sensory characteristics perceived by the animal before swallowing the food) and post-ingestive information (i.e. digestive and metabolic consequences, experienced by the animal after swallowing the food) to evaluate the food and make decisions to select a suitable diet. The concept of palatability is essential to understand how pre- and post-ingestive information are interrelated. It refers to the hedonic value of the food without any immediate effect of post-ingestive consequences and environmental factors, but with the influence of individual characteristics, such as animal's genetic background, internal state and previous experiences. In the literature, the post-ingestive consequences are commonly considered as the main force that influences feeding behaviour whereas food sensory characteristics are only used as discriminatory agents. This discriminatory role is indeed important for animals to be aware of their feeding environment, and ruminants are able to use their different senses either singly or in combination to discriminate between different foods. However, numerous studies on ruminants’ feeding behaviour demonstrate that the role of food sensory characteristics has been underestimated or simplified; they could play at least two other roles. First, some sensory characteristics also possess a hedonic value which influences ruminants’ intake, preferences and food learning independently of any immediate post-ingestive consequences. Further, diversity of food sensory characteristics has a hedonic value, as animals prefer an absence of monotony in food sensory characteristics at similar post-ingestive consequences. Second, some of these food sensory characteristics become an indicator of post-ingestive consequences after their initial hedonic value has acquired a positive or a negative value via previous individual food learning or evolutionary processes. These food sensory characteristics thus represent cues that could help ruminants to anticipate the post-ingestive consequences of a food and to improve their learning efficiency, especially in complex environments. This review then suggests that food sensory characteristics could be of importance to provide pleasure to animals, to increase palatability of a food and to help them learn in complex feeding situations which could improve animal welfare and productivity.     

天然沸石的交换性阳离子类型与农业适用性

天然沸石有良好的离子交换和吸附特性,因此,它在农业上的应用也越来越受到人们的重视,但据我们发现,不同产地沸石,占主导地位的交换性阳离子种类大不相同,如果盲目应用,就会产生相反的结果。通过实验证实,天然沸石的阳离子类型,特别是含交换性Na~ 较高的一类沸石与土壤、肥料相互作用后,对植物生长有很大影响。     

Chromosome numbers in the Aphididae and their taxonomic significance

Abstract. Diploid female chromosome numbers are listed for 180 aphid species not previously karyotyped. The list includes the first chromosome records for several aphid tribes (Tramini, Greenideini, Anomalaphidini, Nippon-aphidini). Variation in chromosome number at different systematic levels is discussed. Usually the karyotype is particularly stable within a genus, but there are notable exceptions (e.g. Amphorophora ) where considerable evolutionary increase in chromosome number has occurred by autosome dissociation with little accompanying morphological change. In several genera differences in gross chromosome morphology can be useful to the taxonomist. Within-species karyotype variation is relatively common in aphids, and instances of structural heterozygosity are particularly numerous in species and groups which have partially or completely abandoned the sexual phase of the life cycle in favour of permanent thelytoky.     

Mechanisms for sister chromatid exchanges and their relation to the production of chromosomal aberrations

By taking advantage of the fact that fluorescent light (FL) induces strand breaks only in bromodeoxyuridine(BrdU)-substituted DNA, and that those breaks eventually lead to the formation of sister chromatid exchanges (SCEs), the response of SCEs to FL was studied carefully in Chinese hamster chromosomes in which, out of four DNA strands, BrdU-substitution had occurred either in one or three strands. The FL-induced SCE frequency did not differ greatly between these two types of chromosomes. However, when they were submitted to caffeine treatment, a drastic increase in the frequency was detected in the trifilarly-substituted chromosomes while a significant decrease occurred in the unifilarly-substituted chromosomes. Based on these results, a working hypothesis was developed that the SCE can arise by at least two different mechanisms, one operating at replicating points probably utilizing the machinery of DNA replication, and the other acting only in the post-replicational DNA portion, probably in a similar fashion as assumed in a general model of crossing over in the eukaryote. These dual mechanisms may account for the discrepancy encountered in the explanations of the induction of SCEs by various exogenous agents as well as spontaneous SCEs. The present study also showed that some, but clearly not all, of chromatid deletions are the outcome of the failure to complete SCEs arising through these mechanisms.     

Composition of by-products of the essential-oil industry and their potential as feeds for ruminants

Eight plant-residues from the essential-oil industry were assayed for chemical composition. Digestibility of the plant residues was determined by rumen fermentation in vitro and in vivo. Dry-matter digestibility of plant residues from black pepper, vanilla bean, ginger root, cocoa bean and celery seed ranged from 43–65%. Only 15–30% of the residues from nutmeg hulls and cinnamon bark were degraded. These data indicate that anaerobic microbes are capable of degrading significant quantities of the plant residues without further processing of these materials. Long-term feeding studies need to be conducted to determine if ruminants will consume these plant materials, and to investigate the effect of these plant residues on rumen microbial- and host cellular-metabolism.     

Vertical distribution of gas exchanges and their integration throughout the entire canopy in a maize field

Photosynthesis Research - Fluxes of carbon and water along a vertical profile within a canopy, particularly the associations between canopy and ecosystem levels, are not well studied. In this...