Changes in portal blood metabolites and insulin with feeding steers twice daily

Immune and metabolic effects of rumen-protected methionine during a heat stress challenge in lactating Holstein cows

Multiparous, lactating Holstein cows (n = 32) were randomly assigned to one of two dietary treatments [TMR with rumen-protected Met (RPM) or TMR without RPM (CON)], and within each dietary treatment group cows were randomly assigned to one of two environmental treatment groups in a split-plot crossover design. In phase 1 (9 d), all cows were fed ad libitum and in thermoneutral conditions (TN). In phase 2 (9 d), group 1 (n = 16) was exposed to a heat stress (HS) challenge (HSC). Group 2 cows (n = 16) were pair-fed (PFTN) to HSC counterparts and remained in TN. After a 21-d washout period, the study was repeated (period 2) and the environmental treatments were inverted relative to treatments from phase 2 of period 1, while dietary treatments remained the same for each cow. During phase 1, cows in RPM had greater plasma Met concentration compared with cows in CON (59 and 30 µM, respectively; P < 0.001). Cows in PFTN had a greater decrease (P < 0.05) in plasma insulin than cows in HSC at 4 h (-2.7 µIU/mL vs. -0.7 µIU/mL) and 8 h (-7.7 µIU/mL vs. -0.4 µIU/mL) during phase 2. Compared with cows in PFTN, cows in HSC had an increase (P < 0.05) in plasma serum amyloid A (-59 µg/mL vs. +58 µg/mL), serum haptoglobin (-3 µg/mL vs. +33 µg/mL), plasma lipopolysaccharide binding protein (-0.27 and +0.11 µg/mL), and plasma interleukin-1β (-1.9 and +3.9 pg/mL) during phase 2. In conclusion, HSC elicited immunometabolic alterations; however, there were limited effects of RPM on cows in HSC.

Self-organization of foraging behaviour: From simplicity to complexity without goals

A herbivore faces challenges while foraging—ongoing changes in its physiological condition along with variation in the nutrient and toxin concentrations of foods, spatially and temporally—that make selecting a nutritious diet a vital affair. Foraging behaviours arise from simple rules that operate across levels of resolution from cells and organs to individuals and their interactions with social and physical environments. At all these levels, behaviour is a function of its consequences: a behaviour operating on the environment to induce changes is itself changed by those events. Thus, behaviour emerges from its own functioning—behaviour self-organizes-not from that of its surroundings. This ostensible autonomy notwith-standing, no self-organizing system (cell, organ, or individual) is independent of its environs because existence consists of an ongoing exchange of energy and matter. According to this view, the notion of cause and effect is replaced with functional relationships between behaviours and environmental consequences. Changes in physical environments alter the distribution, abundance, nutritional, and toxicological characteristics of plants, which affect food preference. Social interactions early in life influence behaviour in various ways: animals prefer familiar foods and environments, and they prefer to be with companions. Animals in unfamiliar environments often walk farther, ingest less food, and suffer more from malnutrition and toxicity than animals in familiar environments. An individual's food preferences—and its ability to discriminate familiar from novel foods—arise from the functional integration of sensory (smell, taste, texture) and postingestive (effects of nutrients and toxins on chemo-, osmo-, and mechano-receptors) effects. The ability to discriminate among foods is critical for survival: all problems with poisonous plants are due to an inability to discriminate or a lack of alternatives. Animals eat a variety of foods as a result of nearing or exceeding tolerance limits for sensory and postingestive effects unique to each food. After eating any food too frequently or excessively, the likelihood increases that animals will eat alternative foods owing to exceeding sensory-, nutrient-, and toxin-specific tolerance limits. Cyclic patterns of intake of a variety of foods reflect seemingly chaotic interactions among flavours, nutrients, and toxins interacting along continua.

How does pattern of feeding and rate of nutrient delivery influence conditioned food preferences?

Ruminant herbivores have been shown to learn about food properties by associating food flavours with the food's post-ingestive consequences. Previous experimentation supporting the conditioned food aversion/preference hypothesis has generally employed very simple diet learning tasks which do not effectively represent the wide range of foods selected within single bouts typical of wild, free-ranging ruminant herbivores. We tested the ability of a ruminant herbivore to associate a food with artificially administered nutrient rewards in a designed experiment where we altered the temporal pattern of encounter with the food as well as the nature (fast or slow reward) of the post-ingestive outcome. Twenty-four goats were offered branches of Sitka spruce (SS) and Norway spruce (NS) for 4 h per day on two days per week for five weeks. The pattern of feeding varied with treatment such that the species on offer changed every hour (short) or every 2 h (long). The energy treatment altered the reward delivered during Sitka consumption so that animals were dosed either with predominantly sugar (rapidly fermented), predominantly starch (slower fermentation rate), or with water (placebo). Preference was measured on the day following each learning day. We expected that goats would find it easier to associate SS with post-ingestive rewards when the duration of encounter was longest, and that associations would be stronger with the most rapidly digested post-ingestive reward. In the event, goats did not alter their consumption of SS in response to the treatments. Our results suggest that at the scale of temporal resolution of encounters with different plant species (1-2 h), and at the different rates of experiencing post-ingestive consequences tested in this experiment, ruminants do not appear to discriminate the nutritive properties of foods predominantly through a post-ingestive feedback mechanism. They must, instead, use a range of cues-including post-ingestive consequences-to assess food properties.

Ultrasound-guided percutaneous portocentesis in 21 cows

An ultrasound-guided portocentesis was performed in 21 clinically healthy cows, and blood was collected for haematological, biochemical and blood-gas analyses. At the same time blood samples were collected from the left jugular vein of each cow for the same analyses. Immediately after the centesis, portal blood pressure was measured. The cows were examined daily thereafter for eight days and then slaughtered for postmortem examination of the internal organs. The mean (sd) portal blood pressure was 37.1 (5.47) mmHg, and ranged from 24 to 49 mmHg. There were small but significant differences between many of the haematological and biochemical parameters in jugular and portal blood, and the concentration of bile acids was on average 2.7 times higher, and the concentration of ammonia was 19.3 times higher in portal blood. The demeanour and behaviour of the cows, and their appetite and rectal temperature remained normal during the eight-day observation period. The haematocrit, total and differential leucocyte counts, and the concentrations of total solids and fibrinogen were not affected by portocentesis. On postmortem examination, no lesions were apparent in the peritoneum, liver and portal vein.

Opioid-mediated responses of dietary protein on reticular motility and plasma insulin

Four ruminally and abomasally cannulated steers (603 +/- 22.7 kg of body weight) were used to determine whether ruminally undegradable protein (RUP) would exert opioid-mediated effects on reticuloruminal motility or circulating concentrations of insulin. Steers were fed isonitrogenous diets (16% crude protein) containing either 30 or 40% RUP. The low RUP diet was supplemented with urea and soybean meal, and the high RUP diet was supplemented with blood meal, fish meal, corn gluten meal, and meat and bone meal. Diets contained 57% wheat silage and were fed twice daily at 0800 and 1600 h. Experimental periods were 10 d in length. Blood samples were taken from jugular catheters, and reticular motility was measured at hourly intervals on d 10 over a 16-h period. Either naltrexone (0.5 mg/kg of body weight) or saline was infused into the abomasum at the second feeding (9 h). Naltrexone reduced the frequency of reticular contractions by 16.5% for steers fed the low RUP diet. Naltrexone decreased the duration of reticular contractions by 9.3% for steers fed the low RUP diet and increased duration by 8.7% for steers fed the high RUP diet. Naltrexone decreased the opening time of the reticuloomasal orifice, expressed as a percentage of predose measurements, by 16.3% for steers fed the high RUP diet. Insulin was 21.3% higher with the high RUP diet. The postprandial rise in insulin decreased 36.7% with naltrexone. Dietary protein can exert effects mediated by opioids in ruminants.

Insulin response to glucose and glucose tolerance following feeding in sheep

Sheep offered a roughage diet for 4 h daily were injected intravenously with glucose before and at various times after feeding. The insulin secretory response to glucose and the rate of disappearance of injected glucose were determined. While the basal concentration of plasma insulin was unchanged, the base-line plasma glucose concentration tended to decrease during the meal. The glucose load brought about an increase in the plasma insulin concentration at each injection, but the insulin response to glucose and the rate of glucose disposal were increased during the meal. On varying the time of feeding between 08.00 and 16.00 hours, the increase in the insulin response to glucose and in the rate of glucose disposal always appeared to be related to the giving of food, independent of the time food was offered. It is concluded that feeding increases the insulin response to an intravenous glucose load even when the increase in the basal level of plasma insulin on feeding is very modest in sheep given a roughage diet. The increased insulin response and glucose disposal rate following feeding did not appear to be related to diurnal rhythms in insulin secretory activity or glucose metabolism.

Regulation of volatile fatty acid uptake by mitochondrial acyl CoA synthetases of bovine liver

Mitochondria of bovine liver contain acyl CoA synthetases necessary for the uptake of propionate, butyrate, and valerate whereas acetate is bound only weakly. Purification of these enzymes separated a distinct propionyl CoA synthetase highly specific for propionate and acrylate and a butyrate-activating fraction with broad substrate specificity for short and medium chain fatty acids. Evidence from kinetic studies and sucrose density centrifugation suggested that this latter fraction was composed of two enzymes, a butyryl CoA synthetase and a valeryl CoA synthetase. The apparent molecular weights of the propionyl, butyryl, and valeryl CoA synthetases were 72,000, 67,000, and 65,000. The Michaelis-Menten constants of propionyl CoA synthetase for propionate, adenosine 5'-triphosphate, and coenzyme A were 1.3 x 10(-3)M, 1.3 x 10(-3)M, and 6.3 x 10(-4)M. Enzyme activity is regulated by the concentration of propionate in portal blood. Relative to propionyl, butyryl, or valeryl CoA synthetases little acetyl CoA synthetase could be demonstrated. In ruminants hepatic metabolism is such that use of acetate as an energy source is minimum. This ensures that an alternative energy source to glucose, as acetate units, will reach the extrahepatic tissues. Separation of a distinct propionyl CoA synthetase regulated by the concentration of propionate in portal blood is significant because a primary role of ruminant liver is to synthesize glucose from ruminally derived propionate.

Addition of sodium bicarbonate to complete pelleted diets fed to dairy calves

During two trials, 35 and 27 Holstein calves were fed ad libitum complete, pelleted diets containing either 35% alfalfa (Trial 1) or 35% grass (Trial 2) hay from birth to 12 wk of age. Calves in Trial 1 were fed one of the following diets: control, control + 3.5% sodium chloride, or control + 5% sodium bicarbonate. In Trial 2, diets were: control, control + 5% sodium bicarbonate, or control + 5% sodium bicarbonate + loose, chopped grass hay. Intake of dry matter, gain in body weight, ruminal pH, or fecal starch did not differ. Calves fed sodium bicarbonate in Trial 1 but not 2 had a reduced feed efficiency compared with control and supplemented diets. In Trial 1 added sodium bicarbonate did not alter intake or digestible energy. Addition of sodium bicarbonate increased concentration of ruminal acetate and butyrate and decreased propionate in both trials. Fecal pH was elevated in calves fed sodium bicarbonate diets during both trials. Sodium chloride increased water intake in Trial 1, and sodium bicarbonate increased water indigestible energy. Addition of sodium bicarbonate increased concentration of ruminal acetate and butyrate and decreased propionate in both trials. Fecal pH was elevated in calves fed sodium bicarbonate diets during both trials. Sodium chloride increased water intake in Trial 1, and sodium bicarbonate increased water indigestible energy. Addition of sodium bicarbonate increased concentration of ruminal acetate and butyrate and decreased propionate in both trials. Fecal pH was elevated in calves fed sodium bicarbonate diets during both trials. Sodium chloride increased water intake in Trial 1, and sodium bicarbonate increased water intake in Trial 2. Incidence of free-gas bloat was higher in calves fed sodium bicarbonate in both trials. Addition of sodium bicarbonate to complete pelleted diets containing 35% alfalfa or 35% grass hay appeared to have no benefit for young, growing dairy calves in performance and health.

Portal blood insulin and metabolite changes with spontaneous feeding in steers

Four Holstein steers surgically prepared with a device for sampling blood from the portal vein were used to study changes in metabolites and insulin of portal blood associated with spontaneous meal feeding. The animals were fed a complete mixed ration (3.4 kcal/g digestible energy) in individual, electronically controlled feeding units. Blood was sampled before, during, and after meals. During the meal, blood samples were at 2-min intervals. Blood was sampled at 50 individual meals. Average meal length was 15.0 min and average consumption per meal was 631.7 g. Portal insulin increased within 2 min of meal initiation and remained elevated for the first 14 min of meals. Free fatty acids also increased at 8, 10, 12, 16, and 18 min after meal initiation. There were no consistent changes in packed cell volume, glucose, beta-hydroxybutyrate, or volatile fatty acids during this time. On control days when no feed was consumed, there were no significant changes in concentrations of metabolites or insulin. The increase in insulin of portal blood, which occurs upon meal initiation, preceded changes in metabolites. Therefore, the rapid change in insulin may be the result of a reflex neural stimulation rather than the result of a metabolite stimulating release of insulin.