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

Propionate challenge tests have limited value for investigating bovine metabolism

Two experiments were designed to assess the potential utility of the propionate challenge test (PCT) as an index of gluconeogenic capacity. In Expt. 1, the dose-response to jugular propionate infusion was assessed in a duplicated 4 x 4 Latin square experiment with 8 lactating dairy cows. Sodium propionate (4.5 mol/L, pH 7.4) was infused in an intrajugular bolus at 0 (saline), 0.52, 1.04, or 1.56 mmol/kg body weight (BW), and jugular blood was sampled over the following 2 h. Peak propionate concentration in plasma and area under the curve for plasma glucose both increased linearly with increasing propionate dose (P < 0.01). Plasma free fatty acid (FFA) concentration was elevated by all propionate treatments at 20 min postinfusion (P = 0.03), and plasma cortisol concentration tended to increase (P < 0.10) after propionate infusions. Experiment 2 was designed to study the effect of short-term differences in fed state on responses to propionate infusion. Lactating dairy cows (n = 8) were included in a duplicated 4 x 4 Latin square design with a 2 x 2 factorial arrangement of treatments. Sodium propionate (1.04 mmol/kg BW) or saline was infused either before feeding (0900) or 2 h after feeding (1300). Fed cows consumed 4.4 +/- 1.4 kg dry matter before the PCT. Although fed cows had a significantly higher preinfusion plasma propionate concentration, fed state did not influence postinfusion changes in plasma propionate, glucose, insulin, glucagon, or FFA concentrations. Liver glycogen concentration decreased significantly after propionate, but not saline infusion (P < 0.05). Short-term differences in fed state do not affect the physiological responses to PCT. However, glucagon release after jugular administration of propionate is likely supraphysiologic, and postinfusion lipolysis and glycogenolysis suggest that stress responses may alter PCT measurements. Although the PCT may help to diagnose liver dysfunction, it is not a useful index with which to assess differences in gluconeogenic capacity.

Phlorizin administration increases hepatic gluconeogenic enzyme mRNA abundance but not feed intake in late-lactation dairy cows

Gluconeogenic capacity may be an important factor regulating dry matter intake (DMI) in lactating dairy cows. To determine whether increased glucose demand affects feed intake and hepatic gene expression, lactating Holstein cows were treated with phlorizin or vehicle (propylene glycol) for 7 d. Multiparous cows (n = 12; 269 +/- 65 d in milk, mean +/- SD) were randomly assigned to treatment sequence in a crossover design and were adapted to a common diet for 7 d before the beginning of the experiment. Phlorizin injected s.c. at 4 g/d caused glucose excretion in urine at the rate of 474 g/d. Although phlorizin decreased lactose synthesis and milk production (both P < 0.01), DMI and 3.5% fat-corrected milk production were not altered by treatment. A net deficit of 383 g glucose/d in milk and urine for phlorizin (relative to control) was likely replaced partially through increased gluconeogenesis. The molar insulin:glucagon ratio was decreased 17% by phlorizin (P < 0.001) and hepatic phosphoenolpyruvate carboxykinase, glucose-6-phosphatase, and pyruvate carboxylase mRNA abundance increased (all P < 0.05). Late-lactation dairy cows adapted quickly to an increase in peripheral glucose demand; adaptation mechanisms likely included enhanced gluconeogenic capacity, whereas DMI was not altered.

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.

Varying protein and starch in the diet of dairy cows. II. Effects on performance and nitrogen utilization for milk production

The main objective of this experiment was to examine the effects of the percentage and source of crude protein (CP) and the amount of starch in the diet of dairy cows on the lactational performance and use of N for milk production. Sixty multiparous Holstein cows were used in a 210-d lactational trial with a completely randomized design with a 2 x 3 factorial arrangement of treatments. Two sources of CP [solvent-extracted soybean meal (SBM) and a mixture of SBM and a blend of animal-marine protein supplements plus ruminally protected Met (AMB)] and 3 levels of dietary CP (means = 14.8, 16.8, and 18.7%) were combined into 6 treatments. On a dry matter (DM) basis, diets contained 25.0% corn silage, 20.0% alfalfa silage, 10.0% cottonseed, 26.7 to 37.0% corn grain, and 4.8 to 13.5% protein supplement, plus minerals and vitamins. Across the 210 d of lactation, the productive response of dairy cows to the source of supplemental CP depended on the concentration of CP in the diet. At 18.7% CP, cows fed SBM consumed more DM and produced more milk, 3.5% fat-corrected milk, fat, and true protein, but had lower efficiency of feed use and body condition score than cows fed AMB. At 16.8% CP, cows fed AMB produced more 3.5% fat-corrected milk, fat, and true protein than cows fed SBM. At 14.8% CP, cows fed SBM consumed more DM but produced less true protein and had lower feed efficiency than cows fed AMB. Across CP sources, cows fed 14.8% CP produced less fat-corrected milk and true protein than cows fed 16.8 and 18.7% CP. Across CP percentages, cows fed AMB produced more fat-corrected milk per kilogram of DM consumed than cows fed SBM. Despite these interactions, improvements in the gross efficiency of N use for milk production were achieved through reductions in the intake of N independently of the source of CP. Data suggest that the intake of N by high-producing dairy cows that consume sufficient energy and other nutrients to meet their requirements can be decreased to about 600 to 650 g daily if the source of RDP and RUP are properly matched with the source and amount of carbohydrate in the diet.

Effects of Feeding Propionate and Calcium Salts of Long-Chain Fatty Acids on Transition Dairy Cow Performance

Multiparous Holstein cows (n = 40) were used in a randomized complete block design to determine the effects of feeding Ca and Na salts (1:1, wt/wt) of propionate and Ca salts of long-chain fatty acids (LCFA) on transition cow performance. All cows were fed the same basal diet once daily for ad libitum intake. Treatments (g/d) were 320 cornstarch (CS) as a control, 120 propionate (PRO), 120 propionate and 93 LCFA (PF1), and 178 propionate and 154 LCFA (PF2). Treatments were hand-mixed into the upper one-third of the TMR from 2 wk pre- through 3 wk postpartum. Intakes were recorded from 21 d pre- through 21 d postpartum. Energy density and crude protein were 1.54 and 1.65 Mcal/kg and 14.4 and 18.8% for pre- and postpartum diets, respectively. All cows received a common diet from 22 to 70 days in milk (DIM). Milk composition was analyzed on d 7, 14, and 21. Blood was sampled at 14, 7, and 2 d prepartum and 2, 7, 14, and 21 DIM. Pre- and postpartal dry matter intake (DMI) averaged 11.9 and 16.4 kg/d, respectively, and did not differ among treatments. A diet x week interaction for postpartal DMI was observed as cows fed PF2 consumed 2 kg/d less DM during wk 2 relative to other treatments. Milk yields from 22 to 70 DIM were 48.8, 48.5, 47.8, and 51.3 kg/d for CS, PRO, PF1, and PF2, respectively, and were not significantly affected by treatments. Milk true protein (3.32 vs. 3.16%) was increased and MUN (12.5 vs. 14.4 mg/dL) was decreased for CS relative to other treatments. Milk fat yield from cows fed PRO tended to be greater than those fed PF1 (1.58 vs. 1.29 kg/d). Plasma glucose, insulin, and beta-hydroxybutyrate were not affected by treatments. The PF2 treatment tended to decrease NEFA in plasma relative to PF1 over all times measured (492 and 670 muEq/L) and significantly decreased plasma NEFA relative to those fed PF1 postpartum (623 and 875 muEq/L). Relative to PF1, feeding propionate and LCFA at the higher level in this experiment improved energy balance postpartum as evidenced by decreased concentrations of plasma NEFA.

Effects of intraruminal infusion of sodium, potassium, and ammonium on hypophagia from propionate in lactating dairy cows

The objective of this experiment was to evaluate effects of salt type on hypophagic effects of intraruminal infusion of propionate in lactating dairy cows. Our working hypothesis is that oxidative metabolism of propionate causes satiety by increasing hepatic ATP concentration and decreasing the discharge rate of the hepatic vagus. We hypothesized that hypophagic effects of propionate are reduced by ammonium and potassium. We speculated that ammonium infusion lowers hepatic ATP concentration because ATP is used for urea synthesis and potassium increases the discharge rate of the hepatic vagus. Eight ruminally cannulated Holstein cows in midlactation were used in a duplicated 4 x 4 Latin square design experiment. Treatments were intraruminal infusion of propionic acid, ammonium propionate, sodium propionate, and potassium propionate. Treatment solutions were 0.93 M for propionate and 0.67 M for salts among the treatments except for propionic acid. Treatment solutions were infused over 14 h starting 2 h before feeding at 17.9 ml/min, which is equivalent to 16.7 and 11.9 mmol/min for propionate and salts, respectively. Infusion of ammonium propionate decreased dry matter intake compared with sodium propionate and potassium propionate (P < 0.04; 11.0 vs. 14.0 and 13.9 kg/12 h) by decreasing meal frequency without affecting meal size, indicating that ammonium delayed the sense of hunger. No difference in DMI and feeding behavior was observed between infusion of sodium and potassium propionate. Contrary to the hypothesis, ammonium infusion did not reduce hypophagic effects of propionate, possibly because the urea cycle indirectly stimulated oxidative metabolism in the liver by generating oxidizable carbon from amino acid catabolism.

Hypophagic effects of ammonium are greater when infused with propionate compared with acetate in lactating dairy cows

The objective of this experiment was to determine interactions between hypophagic effects of propionate and ammonium in lactating dairy cows. Eight ruminally cannulated Holstein cows in mid-lactation were used in a duplicated 4 x 4 Latin square design experiment with a 2 x 2 factorial arrangement of treatments. Factors evaluated were type of volatile fatty acid (VFA; acetate vs. propionate) and type of salt (sodium vs. ammonium). Treatment solutions were infused continuously into the rumen at a rate of 16.7 mmol of VFA salts/min starting 2 h before feeding and ending 12 h after feeding. Hypophagic effects of ammonium were significantly greater for cows infused with propionate (4.3 vs. 12.1 kg/12 h; SEM = 1.3) compared with acetate (13.5 vs. 15.3 kg/12 h; SEM = 1.3; interaction P < 0.01). This interaction was attributed to a greater reduction in meal frequency for ammonium treatment compared with sodium treatment when infused with propionate (3.9 vs. 7.2/12 h; SEM = 0.8) compared with acetate (6.6 vs. 7.0/12 h; SEM = 0.8), indicating that infusion of ammonium propionate reduced hunger. Meal size was decreased by infusion of propionate compared with acetate, but was not affected by ammonium compared with sodium, indicating that ammonium did not affect satiety. Mechanisms to explain the interactions between ammonium and propionate on meal frequency and feed intake warrant further investigation.

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.