The role of propionate and acetate in the control of food intake in sheep

The anorectic and thermogenic effects of pharmacological lactate in male mice are confounded by treatment osmolarity and co-administered counterions

Lactate is a circulating metabolite and a signalling molecule with pleiotropic physiological effects. Studies suggest that lactate modulates energy balance by lowering food intake, inducing adipose browning and increasing whole-body thermogenesis. Yet, like many other metabolites, lactate is often commercially produced as a counterion-bound salt and typically administered in vivo through hypertonic aqueous solutions of sodium L-lactate. Most studies have not controlled for injection osmolarity and the co-injected sodium ions. Here, we show that the anorectic and thermogenic effects of exogenous sodium L-lactate in male mice are confounded by the hypertonicity of the injected solutions. Our data reveal that this is in contrast to the antiobesity effect of orally administered disodium succinate, which is uncoupled from these confounders. Further, our studies with other counterions indicate that counterions can have confounding effects beyond lactate pharmacology. Together, these findings underscore the importance of controlling for osmotic load and counterions in metabolite research.

Spineless Cactus plus Urea and Tifton-85 Hay: Maximizing the Digestible Organic Matter Intake, Ruminal Fermentation and Nitrogen Utilization of Wethers in Semi-Arid Regions

The aim of this study was to evaluate the effect of replacing Tifton-85 hay (Cynodon spp. cv. Tifton 85) with 0, 150, 300, 450 and 600 g/kg dry matter (DM) of spineless cactus (SC, Nopalea cochenilifera Salm-Dyck) plus urea and ammonium sulfate (UAS; 9:1) on DM, digestible organic matter (DOM) and indigestible neutral detergent fiber (iNDF) intakes, as well as ruminal fermentation, N-balance, and microbial protein supply (MPS). Five rumen-fistulated and cannulated crossbred wethers, weighing 43.8 ± 5.80 kg, were randomized in a 5 × 5 Latin square design. Isonitrogenous diets (14% crude protein) were supplied with a roughage/concentrate ratio of 70:30. The DOM intake, N-retained, and MPS showed quadratic responses (p < 0.05), with maximum values estimated at the levels of SC+UAS of 414, 438 and 418 g/kg DM, respectively. Rumen pH and ammonia nitrogen, iNDF intake, N-urinary excretion, and serum urea and plasma ammonia reduced linearly (p < 0.05) with increasing SC+UAS inclusion. Ruminal acetate and propionate concentrations increased linearly with increasing SC+UAS inclusion. In wethers fed diets with a roughage/concentrate ratio of 70:30, roughage constituted of a SC+UAS/hay (Tifton-85) ratio of 41:29 is recommended in order to maximize the DOM intake, N-retention, and MPS.

A method of assessing essential amino acid availability from microbial and ruminally undegraded protein in lactating dairy cows

The objective of this study was to extend a stable isotope-based assessment of AA absorption from rumen-degradable protein (RDP) sources to include determination of essential AA (EAA) availability from microbial protein (MCP). To demonstrate the technique, a study using a 2 × 2 factorial arrangement of treatments applied in a repeated 4 × 4 Latin square design was undertaken. Factors were high and low rumen-degradable protein and high and low starch. Twelve lactating cows were blocked into 3 groups according to days in milk and randomly assigned to the 4 treatment sequences. Each period was 14 d in length with 10 d of adaption followed by 4 d of ruminal infusions of ¹⁵N-labeled ammonium sulfate. On the last day of each period, a ¹³C-labeled AA mixture was infused into the jugular vein over a 6-h period to assess total AA entry. Rumen, blood, urine, and milk samples were collected during the infusions. Ruminal bacteria and blood samples were assessed for AA enrichment. Total plasma AA absorption rates were derived for 6 EAA from plasma ¹³C AA enrichment. Absorption of 6 EAA from MCP was calculated from total AA absorption based on ¹⁵N enrichment in blood and rumen bacteria. Essential AA absorption rates from total protein, MCP, and rumen-undegradable protein were derived with standard errors of the mean of 6, 14, and 14%, respectively. An average of 45% of absorbed EAA were from MCP, which varied among 6 EAA and was interactively affected by starch and RDP in diets. Microbial AA availability measured by isotope dilution method increased with the high RDP diets and was unaffected by starch level, except for Met, which decreased with high starch. Microbial protein outflow, estimated from urinary purine derivatives, increased with RDP and was not significantly affected by starch. This was consistent with measurements from the isotope dilution method. Total AA absorption rates measured from isotope dilution were similar to estimates from CNCPS (v. 6.55), but a lower proportion of absorbed AA was derived from MCP for the former method. Compared with the isotope and CNCPS estimates, the Fleming model underestimated microbial EAA and total EAA availability. An average of 58% of the absorbed EAA was converted into milk, which varied among individual AA and was interactively affected by starch and RDP in diets. The isotope dilution approach is advantageous because it provides estimates of EAA availability for individual EAA from rumen-undegradable protein and MCP directly with fewer errors of measurement than can be achieved with intestinal disappearance methods.

The assessment of supplementation requirements of grazing ruminants using nutrition models

This paper was aimed to summarize known concepts needed to comprehend the intricate interface between the ruminant animal and the pasture when predicting animal performance, acknowledge current efforts in the mathematical modeling domain of grazing ruminants, and highlight current thinking and technologies that can guide the development of advanced mathematical modeling tools for grazing ruminants. The scientific knowledge of factors that affect intake of ruminants is broad and rich, and decision-support tools (DST) for modeling energy expenditure and feed intake of grazing animals abound in the literature but the adequate predictability of forage intake is still lacking, remaining a major challenge that has been deceiving at times. Despite the mathematical advancements in translating experimental research of grazing ruminants into DST, numerous shortages have been identified in current models designed to predict intake of forages by grazing ruminants. Many of which are mechanistic models that rely heavily on preceding mathematical constructions that were developed to predict energy and nutrient requirements and feed intake of confined animals. The data collection of grazing (forage selection, grazing behavior, pasture growth/regrowth, pasture quality) and animal (nutrient digestion and absorption, volatile fatty acids production and profile, energy requirement) components remains a critical bottleneck for adequate modeling of forage intake by ruminants. An unresolved question that has impeded DST is how to assess the quantity and quality, ideally simultaneously, of pasture forages given that ruminant animals can be selective. The inadequate assessment of quantity and quality has been a hindrance in assessing energy expenditure of grazing animals for physical activities such as walking, grazing, and forage selection of grazing animals. The advancement of sensors might provide some insights that will likely enhance our understanding and assist in determining key variables that control forage intake and animal activity. Sensors might provide additional insights to improve the quantification of individual animal variation as the sensor data are collected on each subject over time. As a group of scientists, however, despite many obstacles in animal and forage science research, we have thrived, and progress has been made. The scientific community may need to change the angle of which the problem has been attacked, and focus more on holistic approaches.

Variation in animal performance explained by the rumen microbiome or by diet composition

The central aim of this meta-analysis was to determine whether the rumen microbiome can serve as an accurate predictor of performance in beef and dairy cattle compared with predictions based on diet composition. To support this comparison, a set of models was derived and compared. Models predicted milk yield (MY), average daily gain (ADG), dry matter intake (DMI), dairy feed efficiency (FE), and beef FE using different sets of independent variables: diet (D), microbial (M), and experimental (E). Diet variables included dry matter, organic matter, neutral detergent fiber, acid detergent fiber, crude protein, ether extract, nonfiber carbohydrate, starch, and forage percentages. Microbiome variables included relative abundance of 3 major rumen bacterial phyla, species richness, and species diversity. Experimental variables included publication year, breed type (dairy, beef, or Bos indicus), and rumen sampling fraction (fluid or solid). A second set of models used D and E variables as predictors for the microbiome. For both the production and microbiome model sets, predictor variable sets were used individually and in combination. Linear mixed-effects regression, weighted by 1/standard error of the mean, was used to derive models using data from 51 peer-reviewed publications. Models for the same response variable were compared on the basis of concordance correlation coefficient with study effects removed (uCCC), root-estimated variance associated with study and error, and corrected Akaike information criterion values, wherever appropriate. The MY model using D + M + E predictors outperformed all other MY models (uCCC = 0.71). ADG was most accurately predicted by D alone (uCCC = 0.92). Interestingly, M + E was more successful at predicting DMI than any model using D variables. Similarly, dairy FE was more accurately predicted by M + E than D, albeit only slightly (uCCC = 0.69 vs. 0.65). Beef FE could only be modeled using D variables. Overall, breed type proved a better predictor of relative abundances of most rumen bacterial phyla than D. Conversely, species richness and diversity indicators were unaffected by breed type, but could be predicted by D with moderate precision and accuracy (uCCC = 0.63 to 0.69). This analysis suggests that diet and the microbiome may exert independent effects on various aspects of performance. Further research is necessary to determine the reasons for these independent influences.

Butyrate reduces appetite and activates brown adipose tissue via the gut-brain neural circuit

OBJECTIVE

Butyrate exerts metabolic benefits in mice and humans, the underlying mechanisms being still unclear. We aimed to investigate the effect of butyrate on appetite and energy expenditure, and to what extent these two components contribute to the beneficial metabolic effects of butyrate.

DESIGN

Acute effects of butyrate on appetite and its method of action were investigated in mice following an intragastric gavage or intravenous injection of butyrate. To study the contribution of satiety to the metabolic benefits of butyrate, mice were fed a high-fat diet with butyrate, and an additional pair-fed group was included. Mechanistic involvement of the gut-brain neural circuit was investigated in vagotomised mice.

RESULTS

Acute oral, but not intravenous, butyrate administration decreased food intake, suppressed the activity of orexigenic neurons that express neuropeptide Y in the hypothalamus, and decreased neuronal activity within the nucleus tractus solitarius and dorsal vagal complex in the brainstem. Chronic butyrate supplementation prevented diet-induced obesity, hyperinsulinaemia, hypertriglyceridaemia and hepatic steatosis, largely attributed to a reduction in food intake. Butyrate also modestly promoted fat oxidation and activated brown adipose tissue (BAT), evident from increased utilisation of plasma triglyceride-derived fatty acids. This effect was not due to the reduced food intake, but explained by an increased sympathetic outflow to BAT. Subdiaphragmatic vagotomy abolished the effects of butyrate on food intake as well as the stimulation of metabolic activity in BAT.

CONCLUSION

Butyrate acts on the gut-brain neural circuit to improve energy metabolism via reducing energy intake and enhancing fat oxidation by activating BAT.

Amino acid supplements and metabolic health: a potential interplay between intestinal microbiota and systems control

Dietary supplementation of essential amino acids (EAAs) has been shown to promote healthspan. EAAs regulate, in fact, glucose and lipid metabolism and energy balance, increase mitochondrial biogenesis, and maintain immune homeostasis. Basic science and epidemiological results indicate that dietary macronutrient composition affects healthspan through multiple and integrated mechanisms, and their effects are closely related to the metabolic status to which they act. In particular, EAA supplementation can trigger different and even opposite effects depending on the catabolic and anabolic states of the organisms. Among others, gut-associated microbial communities (referred to as gut microbiota) emerged as a major regulator of the host metabolism. Diet and host health influence gut microbiota, and composition of gut microbiota, in turn, controls many aspects of host health, including nutrient metabolism, resistance to infection, and immune signals. Altered communication between the innate immune system and the gut microbiota might contribute to complex diseases. Furthermore, gut microbiota and its impact to host health change largely during different life phases such as lactation, weaning, and aging. Here we will review the accumulating body of knowledge on the impact of dietary EAA supplementation on the host metabolic health and healthspan from a holistic perspective. Moreover, we will focus on the current efforts to establish causal relationships among dietary EAAs, gut microbiota, and health during human development.

Control of appetite and energy intake by SCFA: what are the potential underlying mechanisms?

In recent years, there has been a renewed interest in the role of dietary fibre in obesity management. Much of this interest stems from animal and human studies which suggest that an increased intake of fermentable fibre can suppress appetite and improve weight management. A growing number of reports have demonstrated that the principal products of colonic fermentation of dietary fibre, SCFA, contribute to energy homeostasis via effects on multiple cellular metabolic pathways and receptor-mediated mechanisms. In particular, over the past decade it has been identified that a widespread receptor system exists for SCFA. These G-protein-coupled receptors, free fatty acid receptor (FFAR) 2 and FFAR3 are expressed in numerous tissue sites, including the gut epithelium and adipose tissue. Investigations using FFAR2- or FFAR3-deficient animal models suggest that SCFA-mediated stimulation of these receptors enhances the release of the anorectic hormones peptide tyrosine tyrosine and glucagon-like peptide-1 from colonic L cells and leptin from adipocytes. In addition, the SCFA acetate has recently been shown to have a direct role in central appetite regulation. Furthermore, the SCFA propionate is a known precursor for hepatic glucose production, which has been reported to suppress feeding behaviour in ruminant studies through the stimulation of hepatic vagal afferents. The present review therefore proposes that an elevated colonic production of SCFA could stimulate numerous hormonal and neural signals at different organ and tissue sites that would cumulatively suppress short-term appetite and energy intake.

Nutritional regulation of glucokinase: a cross-species story

The glucokinase (GK) enzyme (EC 2.7.1.1.) is essential for the use of dietary glucose because it is the first enzyme to phosphorylate glucose in excess in different key tissues such as the pancreas and liver. The objective of the present review is not to fully describe the biochemical characteristics and the genetics of this enzyme but to detail its nutritional regulation in different vertebrates from fish to human. Indeed, the present review will describe the existence of the GK enzyme in different animal species that have naturally different levels of carbohydrate in their diets. Thus, some studies have been performed to analyse the nutritional regulation of the GK enzyme in humans and rodents (having high levels of dietary carbohydrates in their diets), in the chicken (moderate level of carbohydrates in its diet) and rainbow trout (no carbohydrate intake in its diet). All these data illustrate the nutritional importance of the GK enzyme irrespective of feeding habits, even in animals known to poorly use dietary carbohydrates (carnivorous species).

Identification of the porcine G protein-coupled receptor 41 and 43 genes and their expression pattern in different tissues and development stages

Short-chain fatty acids (SCFAs) are not only an important energy source, but they also play a regulatory role in various physiological processes in humans and rodents. Current studies, mostly in humans and rodents, have revealed that SCFAs acted as endogenous ligands for G protein-coupled receptor GPR41 and GPR43. Whether proteins similar to human GPR41 and GPR43 mediate the regulatory effects of SCFAs in swine remains unclear to date. The aims of this study were to determine whether GPR41 and GPR43 genes are expressed in porcine different tissues; and whether the expression of GPR41 and GPR43 is tissue-specific and/or time-associated. The alignment results showed that pig chromosome 6 contained GPR41 and GPR43 genes. Reverse transcription polymerase chain reaction (RT-PCR) indicated that GPR41 and GPR43 were expressed in porcine various tissues. The 2218 bp and 1908 bp nucleotide sequence representing the full-length cDNA sequence of porcine GPR41 and GPR43 was obtained from the ileum and spleen using rapid amplification of cDNA ends (RACE), which were capable of encoding 335 and 329 amino acid sequences, respectively. The structure prediction revealed that porcine GPR41 and GPR43 proteins had seven putative trans-membrane domains. The real-time PCR results indicated that GPR41 and GPR43 were expressed throughout the developmental stages in a tissue-specific and time-associated manner. GPR41 and GPR43 were most highly expressed in the ileum (P<0.01) and the spleen (P<0.01), respectively. Western blot results showed that porcine GPR41 and GPR43 proteins were expressed in a variety of porcine tissues, including the spleen, ileum, colon, and adipose tissue. In situ GPR41 and GPR43 immunoreactivities were observed through immunohistochemistry in the spleen, ileum, colon, and adipose tissue. In conclusion, the pig genome encoded GPR41 and GPR43 genes, and these two genes were detected in a variety of porcine tissues and expressed in tissue-specific and time-associated manner.

Fibre digestibility, abundance of faecal bacteria and plasma acetate concentrations in overweight adult mares

The purpose of the present study was to compare digestibility of grass hay, faecal and plasma volatile fatty acid (VFA) concentrations, and faecal bacterial abundance in overweight and moderate-condition mares. Five overweight adult mixed-breed mares and five adult mixed-breed mares in moderate condition were housed individually and limit-fed orchard grass (Dactylis glomerata) hay at 20 g/kg body weight (as fed) daily for 14 d. Forage DM and fibre digestibility were determined using AOAC methods; digestible energy was measured using bomb calorimetry; plasma and faecal VFA concentrations were determined by use of GC and MS; faecal Firmicutes, Bacteroidetes, Fibrobacter succinogenes, Ruminococcus flavefaciens and total bacteria abundance was determined by quantitative real-time PCR using previously designed phylum-specific 16S ribosomal RNA gene primers. No differences in hay digestibility, faecal VFA concentrations or faecal bacterial abundance were detected between overweight and moderate-condition mares. Mean plasma acetate concentrations were higher (P = 0·03) in overweight (1·55 (range 1·43-1·65) mmol/l) v. moderate-condition (1·39 (range 1·22-1·47) mmol/l) mares. We conclude that the higher plasma acetate in overweight mares should be further investigated as a potential link between gut microbes and obesity in horses.

Carbohydrate supplements and their effects on pasture dry matter intake, feeding behavior, and blood factors associated with intake regulation

Supplementary feeds are offered to grazing dairy cows to increase dry matter (DM) and metabolizable energy (ME) intakes; however, offering feed supplements reduces pasture DM intake, a phenomenon known as substitution. The objective of the study was to investigate changes in blood factors associated with intake regulation in monogastric species in pasture-fed dairy cows supplemented with either a starch- or nonforage fiber-based concentrate. Fifteen multiparous Friesian × Jersey cross cows were assigned to 1 of 3 treatments at calving. Measurements were undertaken in wk 8 of lactation. Treatments were pasture only, pasture plus a starch-based concentrate (3.5 kg of DM/cow per day; STA), and pasture plus a nonforage fiber-based concentrate (4.4 kg of DM/cow per day). Pelleted concentrates were fed at an isoenergetic rate in 2 equal portions at a.m. and p.m. milkings. Measurements were undertaken to investigate differences in pasture DM intake, feeding behavior, and profiles of blood factors for 4h after a.m. and p.m. milkings, the periods of intensive feeding in grazing cows. Supplementing cows with STA concentrate reduced pasture DM intake to a greater extent than the fiber concentrate, although time spent eating did not differ between treatments. The blood factor response to feeding differed between the a.m. and p.m. feeding events. Blood factors associated with a preprandial or fasted state were elevated prefeeding in the a.m. and declined following feeding, whereas satiety factors increased. In comparison, the blood factor response to feeding in the p.m. differed, with responses to feeding delayed for most factors. Plasma ghrelin concentration increased during the p.m. feeding event, despite the consumption of feed and the positive energy state remaining from the previous a.m. feeding, indicating that environmental factors (e.g., sunset) supersede physiological cues in regulating feeding behavior. The greater reduction in pasture DM intake for the STA treatment in the p.m. may be related to the level of hunger or satiety before the feeding event and not solely to the consumption of supplement. Data indicate that neuroendocrine factors are, at least in part, responsible for the substitution of pasture for supplementary feeds.

Intestinal health functions of colonic microbial metabolites: a review

This review tries to find a scientific answer on the following two questions: (1) to what extent do we understand the specific role of colonic microbial metabolites, especially short-chain fatty acids (SCFA), in maintaining the health status and prevention of diseases of the colon and the host; (2) to what extent can we influence or even control the formation of colonic microbial metabolites which are beneficial for the health status. The review focuses on the following topics: energy source, intestinal motility, defence barrier, oxidative stress with special attention for antiinflammatory and anti-carcinogen functions, and satiety. Also the risk of overproduction of SCFA is discussed. Reviewing the literature as present today, it can be concluded that physiological levels of SCFA are vital for the health and well-being of the host and that the presence of carbohydrates (dietary fibre, prebiotics) is essential to favour the metabolic activity in the direction of carbohydrate fermentation. For optimal motor activity of the ileum and colon, to regulate the physiological intestinal mobility, steadily fermentable dietary fibres or prebiotics are crucial. The formation of SCFA, especially propionate and butyrate, up to high physiological levels in the colon, much likely also contributes to the defence mechanisms of the intestinal wall. No final answer can be given yet about the role of SCFA in anti-inflammation and anti-carcinogenicity, but recently published research shows possible mechanisms in this field. The intake of prebiotics or specific dietary fibres promotes the formation of SCFA within the physiological range, and more or less specifically increases the levels of propionate and butyrate. In this way, they provide benefit to the host, especially the natural regulation of the digestive system.

Control of food intake by metabolism of fuels: a comparison across species

Research with laboratory species suggests that meals can be terminated by peripheral signals carried to brain feeding centres via hepatic vagal afferents, and that these signals are affected by oxidation of fuels. Pre-gastric fermentation in ruminants greatly alters fuels, allowing mechanisms conserved across species to be studied with different types and temporal absorption of fuels. These fuels include SCFA, glucose, lactate, amino acids and long-chain fatty acid (FA) isomers, all of which are absorbed and metabolised by different tissues at different rates. Propionate is produced by rumen microbes, absorbed within the timeframe of meals, and quickly cleared by the liver. Its hypophagic effects are variable, likely due to its fate; propionate is utilised for gluconeogenesis or oxidised and also stimulates oxidation of acetyl-CoA by anapleurosis. In contrast, acetate has little effect on food intake, likely because its uptake by the ruminant liver is negligible. Glucose is hypophagic in non-ruminants but not ruminants and unlike non-ruminant species, uptake of glucose by ruminant liver is negligible, consistent with the differences in hypophagic effects between them. Inhibition of FA oxidation increases food intake, whereas promotion of FA oxidation suppresses food intake. Hypophagic effects of fuel oxidation also vary with changes in metabolic state. The objective of this paper is to compare the type and utilisation of fuels and their effects on feeding across species. We believe that the hepatic oxidation theory allows insight into mechanisms controlling feeding behaviour that can be used to formulate diets to optimise energy balance in multiple species.

Systemic treatment with the enteric bacterial fermentation product, propionic acid, produces both conditioned taste avoidance and conditioned place avoidance in rats

Propionic acid, an enteric bacterial fermentation product, has received recent attention in regards to satiety and obesity in humans. The possibility that propionic acid might produce internal aversive cues was investigated in two experiments using conditioned taste avoidance and place avoidance procedures to index the potential aversive nature of systemic treatment with propionic acid in male rats. Experiment 1 examined the effect of systemic treatment with propionic acid (500 mg/kg), LiCl (95 mg/kg) or vehicle (all corrected to pH 7.5) on the formation of conditioned taste avoidance using a lickometer procedure. On 3 acquisition days three groups of rats were injected with propionic acid, LiCl or vehicle, following 30 min access to 0.3M sucrose solution. Both the Propionic acid group and the LiCl group evidenced a conditioned taste avoidance by the end of the acquisition period. During a drug free extinction phase the Propionic acid group showed extinction of the taste avoidance whereas the LiCl group did not. Experiment 2 involved place preference conditioning with propionic acid treatment associated with one novel context and vehicle with a different novel context on 6 conditioning trials for each type of injection. Place avoidance was assessed on two drug free extinction trials. Multi-variable assessment of the unconditioned (Acquisition Trials) and conditioned effects (Extinction Trials) of propionic acid on locomotor activity was quantified as was chamber choice time on the extinction trials. Propionic acid induced a significant place avoidance and significantly reduced locomotor activity on some acquisition trials. During the extinction trials rats exhibited enhanced locomotor activity levels in the propionic acid associated chamber, likely due to the conditioned aversive nature of this chamber.

Propionate. Anti-obesity and satiety enhancing factor?

Propionate is produced along with acetate and butyrate as a result of fermentative activity of gut microflora on dietary fiber. It has long been known to exhibit hypophagic effects in ruminants, however, its potential physiological roles in non-ruminants as well as humans remained unnoticed over the years. In view of various studies pointing towards the hypophagic as well as hypocholesterolemic effects of propionate in humans, it may act as an important factor in amelioration of obesity, a lifestyle disease arising due to energy imbalance and growing at a startling rate globally. Short chain fatty acids have recently been ascribed as ligands to G-protein coupled receptors (GPRs) 41 and 43. Thus, propionate along with acetate may also be involved in the regulation of adipogenesis and adipokine release mediated via GPRs. The present review summarizes the evidence which collectively raise the possibility of propionate as a dietary factor to depress appetite and combat the obesity epidemic.

The effect of dietary inclusion of sugar-beet pulp on the feeding behaviour of dry sows

Feeding behaviour of six sows receiving a diet with a high inclusion (500 g/kg) of sugar-beet pulp (SBP) was compared with that of six sows receiving a conventional cereal-based diet (control). The feeding rate was determined for both the rate of consumption of the daily food allowance (SBP or control diet) and of a test portion (of control diet) offered at different intervals after the daily food allowance. SBP sows consumed their daily food allowance more slowly than control sows, SBP sows also consumed the test portion more slowly than control sows, when this was offered immediately after the daily food allowance. Prolonging the time taken to eat the control diet, by presenting it in meal form, did not change the feeding rate of the test diet. Offering the test portion 2 h after the daily food allowance, increased the feeding rate of the test portion for both control and SBP sows, with a smaller but still significant treatment difference. Gastric distension appeared to be a major factor in regulating intake when feeding a diet containing SBP. The extent to which feeding rate could be used as an index of feeding motivation and the welfare consequences of using bulky diets for sows are discussed.

The patho-physiology ofTrypanosoma congolensein Scottish Blackface sheep: influence of diet on digestive function

The influence of types of roughage, barley straw (diet B) versus lucerne hay (diet L), on the patho-physiology of a T. congolense infection was compared in eight pairs of Scottish Blackface male twin lambs. One animal of each twin pair was infected and the other used as a pair-fed control. Voluntary food intake, body weight, digestive function, various blood haematological and biochemical measurements were made.

Voluntary organic matter intake decreased significantly after the T. congolense infection, the decrease being greater in the diet L group than in the diet B group lambs (P < 0·01). The apparent digestibility coefficients of crude protein and organic matter were significantly lower in the infected lambs (P < 0·01). Mean retention time of the roughage through the digestive tract in the animals given barley straw was significantly longer (P < 0·05) due to a lower rumen outflow rate constant (P < 0·01). Infection resulted in longer mean retention times (P < 0·01).

Packed cell volume (PCV) was significantly lower before infection in the animals given diet B (P < 0·01). After infection, diet (P < 0·01) and infection (P < 0·01) had an additive effect on PCV. The anaemia was both macrocytic (P < 0·05) and hypochromic (P < 0·01).

Diet B resulted in higher plasma cholesterol (P < 0·05), but lower plasma urea (P < 0·01) and albumin (P < 0·01) concentrations before infection than diet L. The T. congolense infection significantly lowered plasma cholesterol (P < 0·01) and increased plasma urea (P < 0·01) concentrations compared with the uninfected controls. Plasma albumin concentrations decreased, but were more affected by nutrition (P < 0·01) than by infection (P < 0·05).

It ivas concluded that the patho-physiological effects of the T. congolense infection in the Scottish Blackface lambs were affected by the type of roughage offered, but that these effects were additive rather than interactive to the effects of infection.

Biological effects of propionic acid in humans; metabolism, potential applications and underlying mechanisms

Undigested food is fermented in the colon by the microbiota and gives rise to various microbial metabolites. Short-chain fatty acids (SCFA), including acetic, propionic and butyric acid, are the principal metabolites produced. However, most of the literature focuses on butyrate and to a lesser extent on acetate; consequently, potential effects of propionic acid (PA) on physiology and pathology have long been underestimated. It has been demonstrated that PA lowers fatty acids content in liver and plasma, reduces food intake, exerts immunosuppressive actions and probably improves tissue insulin sensitivity. Thus increased production of PA by the microbiota might be considered beneficial in the context of prevention of obesity and diabetes type 2. The molecular mechanisms by which PA may exert this plethora of physiological effects are slowly being elucidated and include intestinal cyclooxygenase enzyme, the G-protein coupled receptors 41 and 43 and activation of the peroxisome proliferator-activated receptor γ, in turn inhibiting the sentinel transcription factor NF-κB and thus increasing the threshold for inflammatory responses in general. Taken together, PA emerges as a major mediator in the link between nutrition, gut microbiota and physiology.

Regulation of adipokine production in human adipose tissue by propionic acid

BACKGROUND

Dietary fibre (DF) has been shown to be protective for the development of obesity, insulin resistance and type 2 diabetes. Short-chain fatty acids, produced by colonic fermentation of DF might mediate this beneficial effect. Adipose tissue plays a key role in the regulation of energy homeostasis, therefore, we investigated the influence of the short-chain fatty acid propionic acid (PA) on leptin, adiponectin and resistin production by human omental (OAT) and subcutaneous adipose tissue (SAT). As PA has been shown to be a ligand for G-protein coupled receptor (GPCR) 41 and 43, we investigated the role of GPCR's in PA signalling.

MATERIALS AND METHODS

Human OAT and SAT explants were obtained from gynaecological patients who underwent surgery. Explants were incubated for 24 h with PA. Adipokine secretion and mRNA expression were determined using ELISA and RT-PCR respectively.

RESULTS

We found that PA significantly stimulated leptin mRNA expression and secretion by OAT and SAT, whereas it had no effect on adiponectin. Furthermore, PA reduced resistin mRNA expression. Leptin induction, but not resistin reduction, was abolished by inhibition of Gi/o-coupled GPCR signalling. Moreover, GPCR41 and GPCR43 mRNA levels were considerably higher in SAT than in OAT.

CONCLUSIONS

We demonstrate that PA stimulates expression of the anorexigenic hormone leptin and reduces the pro-inflammatory factor resistin in human adipose tissue depots. This suggests that PA is involved in regulation of human energy metabolism and inflammation and in this way may influence the development of obesity and type 2 diabetes.

Neuroendocrine and physiological regulation of intake with particular reference to domesticated ruminant animals

The central nervous system undertakes the homeostatic role of sensing nutrient intake and body reserves, integrating the information, and regulating energy intake and/or energy expenditure. Few tasks regulated by the brain hold greater survival value, particularly important in farmed ruminant species, where the demands of pregnancy, lactation and/or growth are not easily met by often bulky plant-based and sometimes nutrient-sparse diets. Information regarding metabolic state can be transmitted to the appetite control centres of the brain by a diverse array of signals, such as stimulation of the vagus nerve, or metabolic 'feedback' factors derived from the pituitary gland, adipose tissue, stomach/abomasum, intestine, pancreas and/or muscle. These signals act directly on the neurons located in the arcuate nucleus of the medio-basal hypothalamus, a key integration, and hunger (orexigenic) and satiety (anorexigenic) control centre of the brain. Interest in human obesity and associated disorders has fuelled considerable research effort in this area, resulting in increased understanding of chronic and acute factors influencing feed intake. In recent years, research has demonstrated that these results have relevance to animal production, with genetic selection for production found to affect orexigenic hormones, feeding found to reduce the concentration of acute controllers of orexigenic signals, and exogenous administration of orexigenic hormones (i.e. growth hormone or ghrelin) reportedly increasing DM intake in ruminant animals as well as single-stomached species. The current state of knowledge on factors influencing the hypothalamic orexigenic and anorexigenic control centres is reviewed, particularly as it relates to domesticated ruminant animals, and potential avenues for future research are identified.

Characterization of feed efficiency traits and relationships with feeding behavior and ultrasound carcass traits in growing bulls

The objectives of this study were to characterize feed efficiency traits and to examine phenotypic correlations between performance and feeding behavior traits, and ultrasound measurements of carcass composition in growing bulls. Individual DMI and feeding behavior traits were measured in Angus bulls (n=341; initial BW=371.1+/-50.8 kg) fed a corn silage-based diet (ME=2.77 Mcal/kg of DM) for 84 d in trials 1 and 2 and for 70 d in trials 3 and 4 by using a GrowSafe feeding system. Meal duration (min/d) and meal frequency (events/d) were calculated for each bull from feeding behavior recorded by the GrowSafe system. Ultrasound measures of carcass 12th-rib fat thickness (BF) and LM area (LMA) were obtained at the start and end of each trial. Residual feed intake (RFIp) was computed from the linear regression of DMI on ADG and midtest BW(0.75) (metabolic BW, MBW), with trial, trial by ADG, and trial by midtest BW(0.75) as random effects (base model). Overall ADG, DMI, and RFIp were 1.44 (SD=0.29), 9.46 (SD=1.31), and 0.00 (SD=0.78) kg/d, respectively. Stepwise regression analysis revealed that inclusion of BW gain in BF and LMA in the base model increased R(2) (0.76 vs. 0.78) and accounted for 9% of the variation in DMI not explained by MBW and ADG (RFIp). Residual feed intake and carcass-adjusted residual feed intake (RFIc) were moderately correlated with DMI (0.60 and 0.55, respectively) and feed conversion ratio (FCR; 0.49 and 0.45, respectively), and strongly correlated with partial efficiency of growth (PEG; -0.84 and -0.78, respectively), but not with ADG or MBW. Gain in BF was weakly correlated with RFIp (0.30), FCR (-0.15), and PEG (-0.11), but not with RFIc. Gain in LMA was weakly correlated with RFIp (0.17) and FCR (-0.19), but not with PEG or RFIc. The Spearman rank correlation between RFIp and RFIc was high (0.91). Meal duration (0.41), head-down duration (0.38), and meal frequency (0.26) were correlated with RFIp and accounted for 35% of the variation in DMI not explained by MBW, ADG, and ultrasound traits (RFIc). These results suggest that adjusting residual feed intake for carcass composition will facilitate selection to reduce feed intake in cattle without affecting rate or composition of gain.

Plasma metabolite concentrations and hepatic enzyme activities in pregnant Romney ewes with restricted feeding

Plasma metabolite concentrations and activities of enzymes related to energy metabolism in plasma, peripheral leukocytes and liver of pregnant Romney ewes with restricted feeding were measured to assess those metabolites and enzymes as indicators for evaluating metabolic conditions in the ewes. The body weights and plasma lactate concentrations of the low-feeding ewes (about 1.0 times maintenance) were significantly lower than those of the high-feeding ewes (about 1.5 times maintenance). There were no significant differences in plasma protein, glucose, triglyceride, cholesterol, pyruvate and immunoreactive insulin concentrations and plasma and leukocyte enzyme activities between both groups. Hepatic malate dehydrogenase activities were significantly higher and hexokinase activities were significantly lower in the low-feeding ewes than in the high-feeding ewes. Restricted feeding could maintain pregnancy and some plasma metabolites and peripheral leukocyte enzymes may be useful indicators for evaluating metabolic changes in ewes.

Comparison of Plasma Metabolite Concentrations and Enzyme Activities in Beef Cattle Raised by Different Feeding Systems in Korea, Japan and New Zealand

Concentrations of metabolites and immunoreactive insulin (IRI) and activities of enzymes related to energy metabolism were measured in plasma of Korean and Japanese beef cattle, which were raised by the indoor feeding system programmed to feed larger amount of roughage in their growing periods and larger amount of concentrate diet in their finishing periods (Japanese feeding system), and grazing New Zealand beef cattle. By the Japanese beef grading system, Korean and Japanese beef cattle showed high beef quality score, average grade 3.3 and 3.6, respectively. The plasma free fatty acid and lactate concentrations and lactate dehydrogenase (LDH), malate dehydrogenase (MDH) and aspartate aminotransferase (AST) activities in Korean beef cattle were significantly higher than those in Japanese beef cattle. The plasma lactate concentration in Korean beef cattle was 8.40 mmol/l, which was similar to the values observed in lactic acidosis. The higher activities of plasma LDH, MDH and AST may indicate slight liver damage by slightly acidotic conditions in Korean beef cattle. New Zealand beef cattle fed on pasture which they harvest by grazing showed significantly lower plasma glucose, cholesterol, lactate and IRI concentrations and enzyme activities than those in Korean and Japanese beef cattle fed on larger amount of concentrate diets. Plasma metabolite concentrations and energy metabolism-related enzyme activities may be good indicators for evaluating metabolic conditions of beef cattle raised by different feeding systems.

Phlorizin administration does not attenuate hypophagia induced by intraruminal propionate infusion in lactating dairy cattle

Infusion data from ruminants has shown that propionate stimulates satiety and decreases meal size, possibly because of increased propionate oxidation in the liver. In this experiment, phlorizin was used to increase glucose demand, which was expected to decrease propionate oxidation and attenuate the decrease in dry matter intake (DMI) caused by propionate infusion. Twelve multiparous, ruminally-cannulated Holstein cows (49+/-33 d in milk, 40+/-7 kg/d milk; mean+/-SD) were randomly assigned to square and treatment sequence in a replicated 4x4 Latin square experiment with a 2x2 factorial arrangement of treatments. Treatments were subcutaneous injection of phlorizin or propylene glycol in combination with intraruminal infusion of either Na acetate or Na propionate. Following a 7-d adaptation period, phlorizin (4 g/d) and control injections were administered every 6 h for 7 d. During the final 2 d of injections, Na acetate or Na propionate solutions (1 mol/L, pH 6.0) were infused continuously at the rate of 0.80 L/h. Feeding behavior data were collected during the final 2 d of treatment. Phlorizin caused urinary excretion of 400+/-40 g glucose/d across infusion treatments. Phlorizin tended to increase plasma free fatty acid and beta-hydroxybutyrate concentrations to a greater extent with Na acetate compared to Na propionate infusion (both interactions P<0.15). Phlorizin decreased and Na propionate increased plasma insulin and glucose concentrations. Infusion of Na propionate decreased DMI (18.4 vs. 21.1+/-1.4 kg/d, P<0.001) through an increase in intermeal interval (89.2 vs. 77.3+/-6.6 min, P=0.03), resulting in fewer meals per day (11.6 vs. 13.7+/-0.7, P<0.001). Phlorizin did not alter DMI (P=0.39) or measures of feeding behavior, nor were there interactions with infusion type. Increasing glucose demand does not limit the extent to which propionate decreases DMI in lactating dairy cows.

The G-protein-coupled receptor 40 family (GPR40–GPR43) and its role in nutrient sensing

Recent deorphanization efforts have paired the G-protein-coupled receptors GPR40, GPR41 and GPR43 with fatty acids as endogenous ligands. While carboxylic acids have been historically known to serve as fuel sources and biomarkers of disease, these studies demonstrate that fatty acids can act as signalling molecules at the cell-surface level. This receptor subfamily shares approx. 30% identity among members, with some limited cross-over between ligand activities. Generalized expression patterns within the pancreatic β-cell, adipose depots and the gastrointestinal tract infer involvement in energy source recognition, absorption, storage and/or metabolism. GPR40, activated by medium and long-chain fatty acids, has been shown to potentiate insulin secretion at the β-cell, and has been hypothesized to participate in the detrimental effects of chronic fatty acid exposure on β-cell function. GPR41 and GPR43 have been reported to stimulate leptin release and adipogenesis respectively via activation by short-chain fatty acids. These common themes implicate GPR40, GPR41 and GPR43 in playing significant roles in metabolic diseases, such as diabetes, obesity and the metabolic syndrome.

Comparison of Activities of Enzymes Related to Energy Metabolism in Peripheral Leukocytes and Livers between Holstein Dairy Cows and ICR Mice

Activities of enzymes related to energy metabolism and isoenzyme patterns of lactate dehydrogenase (LDH) were determined in peripheral leukocytes and livers of Holstein dairy cows and Institute of Cancer Research (ICR) mice. In dairy cow liver, activities of enzymes in glycolysis, malate-aspartate shuttle and lipogenesis were lower, but activities of glucose-6-phosphatase in gluconeogenesis were higher than those in mouse liver. Glucokinase activities were below detection limit in leukocytes and liver of the cows. Dairy cow leukocytes and liver showed the isoenzyme patterns with dominance of LDH-1, -2 and-3, whereas mouse leukocytes and liver showed that LDH-5 was dominant. The LDH isoenzyme patterns were very similar between leukocytes and liver in each animal species. Some enzymes in leukocytes may reflect those enzymes activities in liver and be a useful indicator for energy metabolism in animals.

THE COW AS A MODEL TO STUDY FOOD INTAKE REGULATION

Animal models have been invaluable for studying aspects of food intake regulation that for various reasons cannot be observed in humans. The dairy cow is a unique animal model because of an unrivaled energy requirement; its great drive to eat results in feeding behavior responses to treatments within the physiological range. Cows' docile nature and large size make them ideal for measuring temporal treatment effects because digestion and absorption kinetics and responses in endocrine systems, gene expression, metabolite pools and fluxes, and feeding behavior can be measured simultaneously. Thus, cows are important models to investigate interactions of short-term signals regulating food intake. Furthermore, different physiological states throughout the lactation cycle provide powerful models to study how short- and long-term signals interact to affect long-term energy status. The use of the cow as a model can lead to breakthroughs in understanding the complex interactions of signals regulating food intake.

A family of fatty acid binding receptors

The family of G protein-coupled receptors (GPCRs) serves as the target for almost a third of currently marketed drugs, and provides the predominant mechanism through which extracellular factors transmit signals to the cell. The discovery of GPCRs with no known ligand has initiated a frenzy of research, with the aim of elucidating the physiological ligands for these "orphan" receptors and revealing new drug targets. The GPR40 family of receptors, tandemly located on chromosome 19q13.1, exhibit 30-40% homology to one another and diverse tissue distribution, yet all are activated by fatty acids. Since agonists of GPR40 are medium to longchain fatty acids and those for GPR41 and 43 are short-chain fatty acids, the family clearly provides an intriguing example of how the ligand specificity, patterns of expression, and function of GPCRs can diverge through evolution. Here we summarize the identification, structure, and pharmacology of the receptors and speculate on the respective physiological roles that the GPR40 family members may play.

A glance at G-protein-coupled receptors for lipid mediators: a growing receptor family with remarkably diverse ligands

A plethora of lipid-like molecules known to act as intracellular second messengers are now recognized to signal cells through plasma membrane 7 transmembrane G-protein-coupled receptors (GPCRs). This has been the result of a decade-long genetic hunt for novel sequences encoding 7 transmembrane receptor proteins and the efforts to pair novel sequences with biologically active substances of (partly) unknown molecular mechanism of action. Identification of novel GPCR ligand pairs represents the first step to shed more light into the mode of action of novel cellular signaling molecules in human health and disease and might represent a fruitful source for the development of new drugs, judged on the successful history of GPCR as drug targets. Since 2000, more than 16 reports became available on lipid mediators--as diverse as lysophospholipids, arachidonic acid metabolites, short-, medium-, and long-chain fatty acids as well as steroid-like molecules--exerting their effects as extracellular mediators via rhodopsin-like family GPCRs. These reports have opened new avenues for research in human lipid receptor physiology and pharmacology. Here, the current knowledge on the recently deorphanized lipid receptors, including their isolation, expression pattern, function, and possible physiological or pathological roles will be reviewed.

Short-chain fatty acids stimulate leptin production in adipocytes through the G protein-coupled receptor GPR41

Leptin is an adipose-derived hormone that regulates a wide variety of physiological processes, including feeding behavior, metabolic rate, sympathetic nerve activity, reproduction, and immune response. Circulating leptin levels are tightly regulated according to energy homeostasis in vivo. Although mechanisms for the regulation of leptin production in adipocytes are not well understood, G protein-coupled receptors may play an important role in this adipocyte function. Here we report that C2-C6 short-chain fatty acids, ligands of an orphan G protein-coupled receptor GPR41, stimulate leptin expression in both a mouse adipocyte cell line and mouse adipose tissue in primary culture. Acute oral administration of propionate increases circulating leptin levels in mice. The concentrations of short-chain fatty acids required to stimulate leptin production are within physiological ranges, suggesting the relevance of this pathway in vivo.

Intraruminal infusion of propionate alters feeding behavior and decreases energy intake of lactating dairy cows

The dose-response effects of intraruminal infusion of propionate on feeding behavior of lactating dairy cows were evaluated with eight ruminally cannulated Holstein cows past peak lactation. Treatments were mixtures of propionic acid and acetic acid containing propionic acid at eight different concentrations in Experiment 1, and mixtures of sodium propionate and sodium acetate containing sodium propionate at 4 different concentrations in Experiment 2. Experimental designs were an 8 x 8 and duplicated 4 x 4 Latin squares, respectively, for Experiments 1 and 2. Treatment solutions were infused into the rumen continuously for 14 h at a rate of 16.7 and 25 mmol/min, respectively, for Experiments 1 and 2. Infusion started 2 h before feeding and ended 12 h after feeding; feeding behavior was monitored for 12 h after feeding using a computerized data acquisition system. Total metabolizable energy (ME) intake was calculated by adding the energy of infusates to dietary energy intake. In both experiments, as the proportion of propionate of the infusates increased, total ME intake and dry matter intake decreased linearly. As infusion of propionate increased, meal size tended (P < 0.09) to decrease linearly and intermeal interval tended (P < 0.07) to increase linearly in Experiment 1; meal size decreased linearly and number of meal bouts tended (P < 0.08) to decrease linearly in Experiment 2. These observations indicate that the reduction in dietary energy intake from propionate infusion was greater than the energy supplied from infusates, and that propionate plays an important role in feed intake regulation by affecting both satiety and hunger.

Extent of hypophagia caused by propionate infusion is related to plasma glucose concentration in lactating dairy cows

Two experiments were conducted to evaluate how dose-response effects of intraruminal infusion of propionate on feeding behavior and plasma metabolites are altered by diets differing in fermentability. Twelve ruminally cannulated Holstein cows were used in each experiment. Cows were fed diets containing either steam flaked corn or dry cracked corn (30% of dietary dry matter) in expt. 1, and diets differing in forage-to-concentrate ratio (66:34 vs. 36:64) in expt. 2. For both experiments, the experimental design was a crossover for dietary treatment, and a 6 x 6 Latin square for infusion treatment within a diet for each period. Infusion treatments were mixtures of sodium propionate and sodium acetate, containing propionate at 0, 0.2, 0.4, 0.6, 0.8 and 1.0 as a fraction of total volatile fatty acids infused. Treatment solutions were infused into the rumen continuously for 18 h starting 6 h before feeding at a rate of 23.1 mmol/min. Although propionate production from ruminal fermentation was expected to be different, dietary treatments did not affect dry matter intake (DMI) responses to propionate infusion for either experiment. However, propionate infusion decreased DMI linearly in expt. 1, but did not decrease DMI at lower rates of propionate infusion, which were much more effective at increasing plasma glucose concentration in expt. 2. Propionate had a smaller hypophagic effect at low concentrations of plasma glucose and had a greater hypophagic effect at elevated concentrations of plasma glucose, which could be explained by changes in the metabolism of propionate in the liver.

Effects of corn grain conservation method on feeding behavior and productivity of lactating dairy cows at two dietary starch concentrations

Effects of conservation method of corn grain and dietary starch concentration on dry matter intake (DMI) and productivity of lactating dairy cows were evaluated. Eight ruminally and duodenally cannulated Holstein cows (55 +/- 15.9 d in milk; mean +/- SD) were used in a duplicated 4 x 4 Latin square design with a 2 x 2 factorial arrangement of treatments. Experimental diets contained either ground high-moisture corn (HM) or dry ground corn (DG) at two dietary starch concentrations (32 vs 21%). Mean particle size and dry matter (DM) concentration of corn grain were 1863 pm and 63.2%, and 885 microm and 89.7%, for HM and DG, respectively. DMI was lower for HM compared to DG treatment in high-starch diets (20.8 vs 22.5 kg/d), but similar for the HM and DG treatments in low-starch diets (19.7 vs 19.6 kg/d). This reduction in DMI is attributed to smaller meal size for HM compared to DG in high-starch diets (1.9 vs 2.3 kg of DM for high-starch diets; 2.1 vs 2.0 kg of DM for low-starch diets). Faster starch fermentation for HM in high-starch diets might result in satiety with smaller meal size. Milk yield was greater when cows were fed high-starch diets compared to low-starch diets (38.6 vs 33.9 kg/d) regardless of corn grain treatment. High-starch diets increased solids-corrected milk yield by 3.3 kg (35.2 vs 31.9 kg/d) compared to low-starch diets for cows fed DG, but did not increase for cows fed HM. This was because of a lower milk fat concentration for cows fed HM in high-starch diets. Reducing ruminal starch fermentation by substituting DG for HM can increase the productivity of lactating cows fed high-starch diets.

Preovulatory follicular status and diet affect the insulin and glucose content of follicles in high-yielding dairy cows

Insulin and glucose may be limiting factors for ovarian function in dairy cows genetically selected for high milk yield. The effects of nutrition on the intrafollicular content of insulin and glucose were investigated in Israeli Holstein dairy cattle fed a basic total mixed ration and producing 34-39kg of milk daily. In experiment 1, carried out in 11 oestrus-synchronised cows, little variation in insulin concentration was found in plasma sampled during the luteal phase, but high variation was found in plasma sampled during the follicular phase. Therefore, in order to prevent confounding the effects of diet and of phase in cycle in the following experiments, experimental diets were fed during the luteal phase of synchronised oestrus cycles. In experiment 2, designed as Latin-Square, six cows received sequentially diets containing 17.1 (control) or 19.7% of crude protein, using two sources of supplementary protein, i.e. soyabean meal (SBM) and corn gluten meal (CGM), differing in ruminal degradability and leucine content. When dry matter intake was used as covariant, plasma insulin on day 16 was 29.5 and 26.4% higher in cows fed diets containing SBM and CGM than in the control (P<0.05). In experiment 3, 17 cows were individually fed the basic diet and then switched to isoenergetic diets containing SBM (n=5), CGM (n=6) or corn grain (CG, n=6) given from day 10 to 16 of the synchronised oestrus cycle. On the eve of day 16, and in the morning of day 17, they were administered PGF(2alpha) and the content of 26 largest follicles was aspirated by using the transvaginal ovum pick-up technique. Follicles were sorted into two classes (preovulatory and subordinate) according to oestradiol concentration and the progesterone:oestradiol ratio in follicular fluid (FF). Higher concentrations of insulin (0.282 versus 0.127ng/ml, P<0.0001) and of glucose (0.614 versus 0.386g/l, P<0.002), were found in FF from preovulatory follicles. The insulin concentration in the FF of cows fed the CG diet was 26% higher than in their counterparts fed CGM (P<0.04), SBM being intermediate. Dietary effects did not reach significance in subordinate follicles. The finding that preovulatory follicular status is associated with increased intrafollicular insulin and glucose suggests that insulin is involved in follicular maturation. The nutritional effect on intrafollicular glucose and insulin may have practical implications to optimise feeding in dairy cows during phases of the oestrus cycle.

Effects of diet on short-term regulation of feed intake by lactating dairy cattle

Physical and chemical characteristics of dietary ingredients and their interactions can have a large effect on dry matter intake (DMI) of lactating cows. Physical limitations caused by distension of the reticulo-rumen or other compartments of the gastrointestinal tract often limit DMI of high producing cows or cows fed high forage diets. Fermentation acids also limit DMI from a combination of increased osmolality in the reticulo-rumen and specific effects of propionate, although the mechanisms are not clear. The specific physical and chemical characteristics of diets that can affect DMI include fiber content, ease of hydrolysis of starch and fiber, particle size, particle fragility, silage fermentation products, concentration and characteristics of fat, and the amount and ruminal degradation of protein. Site of starch digestion affects the form of metabolic fuel absorbed, which can affect DMI because absorbed propionate appears to be more hypophagic than lactate or absorbed glucose. Dry matter intake is likely determined by integration of signals in brain satiety centers. Difficulty in measurement and extensive interactions among the variables make it challenging to account for dietary effects when predicting DMI. However, a greater understanding of the mechanisms along with evaluation of animal responses to diet changes allows diet adjustments to be made to optimize DMI as well as to optimize allocation of diet ingredients to animals. This paper discusses some of the characteristics of dietary ingredients that should be considered when formulating diets for lactating dairy cows and when allocating feeds to different groups of animals on the farm.

The effect of nutrients on feed intake in ruminants

The purpose of the present review is to examine the role played by nutrients in controlling feed intake in ruminants, in light of their particular anatomical, physiological, nutritional and behavioural characteristics. The ration is first digested in the rumen for several hours by microbial fermentation. Volatile fatty acids, which constitute 50-75% of a ruminant's energy supply, considerably depress feed intake when administered by short-term infusion into the rumen. However, this effect seems to be largely due to osmolarity problems. Only propionate seems to have a specific action, unrelated to osmolarity, in the mesenteric or portal veins. Nitrogenous nutrients have little short-term effect on feed intake, except when there is excess NH3 in the rumen. Metabolic cues from intestinal digestion, particularly of glucose and starch, have very little short- or long-term influence in controlling feed intake, in comparison with rumen digestion cues. However, the short-term responses in feeding behaviour do not always reflect longer-term effects on feed intake control. The effects of volatile fatty acid infusion on feed intake are much less significant over the long term, except in the case of propionate. The nutrients required for good microbial activity (proteins in the rumen) generally promote feed intake, whereas nutrients that disrupt rumen functioning (lipids) reduce feed intake. After a learning period, preferences are always governed by a tendency toward optimum rumen functioning, rather than by animal nutritional requirements, although the two factors are not independent. Ruminants, due to their particular anatomical and nutritional characteristics, have, in the course of their evolution, developed specific feed intake control mechanisms based on nutritional cues.

Influence of feed intake and source of dietary carbohydrate on the metabolic response to propionate and glucose challenges in lactating goats

The influence of type of nutrients in the diet (rapidly degraded starch plus rapidly degraded N or highly digestible fiber plus slowly degraded N) and amount of feed offered (2.40 +/- 0.10 or 2.00 +/- 0.10 kg of dry matter/d) on plasma constituents after a glucose tolerance test or a propionate challenge test were studied using 12 multiparous dairy goats. Type of diet and interaction between type of diet and amount of feed offered had no effect on the concentrations of any plasma metabolite measured during propionate challenge. During propionate challenge, goats fed at the high dry matter intake (DMI) had a higher clearance of propionate and glucose and a higher ratio of plasma insulin to glucose. During glucose challenges, goats fed diets that were rich in highly digestible fiber tended to have lower peak concentrations of glucose, and goats fed at the high DMI had a higher clearance of glucose. The plasma insulin response to the glucose test was not altered by treatment. The ratio of plasma insulin to glucose was numerically, although nonsignificantly, higher for goats fed at the high rate of DMI. Most of the differences concerning glucose metabolism, insulin response, and tissue responsiveness to insulin appeared to be primarily due to the amount of feed offered and not to the type of diets fed to dairy goats in midlactation.

Preference for wheat straw by lambs conditioned with intraruminal infusions of starch

We hypothesized that feed preference depends on the interplay between flavour and postingestive effects, and we tested two predictions based on this hypothesis: (1) lambs acquire preferences for poorly nutritious feeds paired with starch; and (2) preferences persist when starch is no longer administered. Twenty lambs were randomly allocated to two groups and conditioned as follows: on odd-numbered days, lambs in group 1 received onion-flavoured wheat straw and lambs in group 2 received oregano-flavoured wheat straw. On even-numbered days, the flavours were switched and starch (2.5-9.4% of the digestible energy received/d) was infused into the rumen of all animals during straw consumption. Four periods of 8 d of conditioning were performed and on the 9th day of each period all animals were offered a choice between onion- and oregano-flavoured straw. After conditioning, starch administration was suspended and lambs were offered onion- and oregano-flavoured straw at weekly intervals for 8 weeks (extinction). Lambs strongly preferred the flavoured straw paired with starch, and this preference persisted during extinction. Thus, these results suggest that the postingestive effects of energy play an important role in the development of feed preferences of ruminants.

Inhibitory effects of short intravascular infusions of propionate on reticulo-rumen motility in the sheep

The effect of short infusions into the hepatic portal vein of propionate on reticulo-rumen motility was examined in conscious sheep. Infusions of 10 min duration of propionate at 1-6 mmol.min-1 into the portal vein reduced the frequency and amplitude of reticulum and rumen contractions, especially the amplitude of rumen contractions. Inhibitory effects were not confined to the portal route and were also obtained via the jugular vein, carotid artery, coeliac artery and anterior mesenteric artery. Butyrate was also effective, but acetate much less so and NaCl almost without effect. The inhibitory responses remained after section of nerves to the liver. It appears unlikely the effects reflexly originate from the liver or are derived centrally.