Effect of ruminal infusion of glucose, volatile fatty acids and hydrochloric acid on mineral metabolism in sheep

Two experiments were conducted to study the effects of alterations in ruminal pH and volatile fatty acid (VFA) concentrations on utilization of Mg and other minerals. In Exp. 1, two metabolism trials were conducted with 12 ruminally cannulated crossbred wethers fed 800 g/d of orchard-grass (Dactylis glomerata, L.) hay. After each feeding, wethers were ruminally infused with 500 ml (4.2 ml/min) or either 1) deionized water, 2) 40% (w/v) glucose solution, 3) .26 M propionic and .17 M butyric acid solution or 4) .35 M HCl. The pH of the VFA solution was adjusted to 6.8 with 10N NaOH. In Exp. 2, a metabolism trial was conducted with 12 ruminally cannulated crossbred wethers fed 600 g of orchard-grass hay and infused with a buffered VFA solution prepared as in Exp. 1 or with an unbuffered solution. In both experiments each trial consisted of a 5-d adaption period followed by four 5-d collections of feed, feces and urine. Compared with the glucose treatment, infusion of the buffered VFA solution produced similar acetic and propionic and higher (P less than .05) butyric acid concentrations (Exp. 1). The HCl solution produced changes in ruminal and pH values similar to those of the glucose infusion. In Exp. 1, apparent absorption of Mg was increased over twofold by the glucose infusion (P less than .05), but the other infusions had no effect. Apparent absorption of P was decreased (P less than .05) by HCl infusion, and K absorption was decreased by HCl and glucose infusions. In Exp. 2, infusion of the unbuffered VFA solution decreased apparent Mg absorption by 15.7%, compared with infusion of the buffered solution. These experiments suggest that the increased Mg absorption observed with carbohydrate supplementation is not due to alterations in ruminal pH or VFA levels.     

Effects of chlorpromazine on plasma concentrations of long chain fatty acids and glucose in sheep

Intravenous chlorpromazine was found to cause rapid increases in plasma concentrations of glucose and long chain fatty acids in adult sheep of both sexes. α-adrenergic blockade with phentolamine suppressed the increase in glucose concentration but not the increase in concentration of long chain fatty acids caused by chlorpromazine. β-adrenergic blockade with propranolol suppressed the increase in concentration of long chain fatty acids but not the increase in glucose concentration caused by chlorpromazine. These results were consistent with the hypothesis that chlorpromazine caused a systemic release of epinephrine.     

Effects of naloxone on ad libitum intake and plasma insulin, glucose, and free fatty acids in maintenance-fed sheep

The dose-dependent effects of naloxone on feed intake, and plasma chemicals (insulin, glucose, FFA) purportedly involved in feed intake regulation, were determined in 16-hr fasted sheep that were lean and chronically fed maintenance. Dorset ewes (n = 5) were treated with 0 (saline), 0.3, 1 or 3 mg/kg of naloxone in a generalized randomized block experiment with at least 7 d between successive doses. Feed intakes and plasma insulin, glucose and FFA were determined frequently during 24 hr of ad libitum intake after each naloxone treatment. The 0.3, 1 and 3 mg/kg doses of naloxone reduced (P less than 0.01) the 4-hr feed intake by 30, 40, and 60% respectively, whereas the initial feed intake (10 min) was decreased (P less than 0.05) 45% only by 3 mg/kg naloxone. However, total 24-hr intakes were similar across all doses because intakes between 4 and 24 hr of feeding in sheep treated with 0.3 (839 g), 1.0 (802 g) and 3.0 (1330 g) mg/kg naloxone exceeded (P less than 0.01) that in saline-treated sheep (391 g). Feeding-induced changes in plasma insulin, glucose and FFA concentrations were independent of naloxone treatment, suggesting that endorphinergic control of feed intake may not involve coincidental changes in plasma insulin, glucose and FFA levels which are thought to play a role in systemic regulation of appetite in animals. The endorphinergic regulation of appetite in sheep may involve the central nervous system, rather than peripheral opiate mechanisms that utilize blood-borne signals. Further, the ability of naloxone to suppress appetite in sheep appears inversely related to the duration of fasting or severity of negative energy balance.     

Effects of ruminal infusion of volatile fatty acids on plasma concentration of growth hormone and insulin in sheep.

In an initial experiment we observed postprandial changes in plasma concentrations of growth hormone (GH), insulin, glucagon, and somatostatin (SRIF) in sheep. We then examined whether increasing the rumen concentration of volatile fatty acids (VFA) by infusing a VFA mixture at three rates (53.5, 107, and 214 micromol/kg/min for 4 hr) mimicked the postprandial changes in hormone secretion. Feeding significantly (P < 0.05) suppressed the plasma GH concentration for 6 hr, whereas it significantly (P < 0.05) increased plasma concentrations of insulin, glucagon, and SRIF. Plasma glucose levels tended to decrease after feeding but then gradually increased over the prefeeding level (P < 0.05). Intraruminal infusion of the VFA mixture at 107 micromol/kg/min caused similar changes in ruminal VFA concentrations to those seen after feeding. The infusion significantly (P < 0.05) suppressed GH secretion in a dose-dependent manner, whereas it caused a significant (P < 0.05) increase in insulin and glucose concentrations without changing glucagon concentrations. From these results, we conclude that the postprandial change in ruminal VFA concentration may be a physiological signal which modifies GH and insulin secretion in sheep.     

Effect of wood waste on the digestibility of glycides and level of volatile fatty acids in sheep]

Sheep were subject to an experiment concerning the effect of treated beech sawdust and thickened aqueous hydrolyzate of beech wood (xylocel) on the digestibility of glycides and on the level of volatile fatty acids (VFA) in the rumen content. The results prove that the use of treated beech sawdust as a replacer for ground barley straw favourably influenced the digestibility of monosaccharides, cellulose, lignin and total dry matter of the diet. Sawdust reduced the concentration of total VFA in the rumen content but the ratio of acetic acid to propionic acid (A:P) was lower and the energetic efficiency of the VFA produced was higher in the diet containing sawdust. The addition of urea to the diet with beech sawdust conditioned less effectively, as distinct from the case mentioned above, did not give a clear effect. Urea encouraged the digestibility of pentosanes, glucose and cellulose, but reduced the energetic efficiency of the VFA produced. Xylocel had no clear effect on the digestibility of sugars either. The higher A:P ratio and the lower energetic efficiency of the VFA produced testify to the fact that xylocel in combination with beet molasses was not a sufficient replacer of sugar-beet glycides.     

Net portal appearance of volatile fatty acids in sheep intraruminally infused with mixtures of acetate, propionate, isobutyrate, butyrate, and valerate

The net portal appearance of volatile fatty acids (VFA) was investigated in four ruminally fistulated and multicatheterized sheep. During the experiments, the sheep were fed once every hour for 14 h and intraruminally infused with mixtures of VFA for the 12 h commencing 2 h after the initiation of the hourly feeding protocol. Paired arterial and portal blood samples were obtained hourly during the last 6 h of the experiments. In the control treatment (1), only water was infused intraruminally. In Treatments 2 through 4, the intraruminal infusion rates of propionate (40 mmol/h), isobutyrate (5 mmol/h), and valerate (5 mmol/h) were unchanged. In Treatments 2, 3, and 4, the acetate infusion rate was 100, 60, and 20 mmol/h, respectively, and the butyrate infusion rate was 10, 30, and 50 mmol/h, respectively. Thus, the infusion rate of VFA carbon was constant across Treatments 2 through 4. Portal recovery estimated from the increased net portal appearance in Treatments 2 through 4 compared to the control treatment was 85% for propionate and 60% for isobutyrate, and these recoveries were unaffected by treatment. The portal recovery of butyrate increased (from 21 to 32%) with increasing infusion rate of butyrate and decreasing infusion rate of acetate, as did the portal recovery of valerate (from 14 to 31%). The portal recovery of acetate was 55%, when measured as net portal appearance. Thus, it seems that the capacity for beta-oxidation in ruminal epithelium is limited, which would explain the increasing portal recovery of butyrate and valerate with increasing infusion rate of butyrate, when infusion rate of VFA carbon is unchanged.     

Response of plasma glucose, free fatty acids and triglycerides to starving and re-feeding in cockerels and geese

The effect of starving cockerels and geese for 8 d followed by re‐feeding on plasma glucose, FFA and triglycerides has been studied. In both species plasma glucose concentration fell while FFA concentration rose during starvation. The fall in plasma glucose was followed by a secondary gradual increase. Re‐feeding caused a rebound in plasma glucose, and restored the FFA to its initial concentration. Plasma triglycerides were not affected by starvation in either species. Re‐feeding was followed by a rise in plasma triglycerides in geese only.     

Forestomach epithelial receptor activation by rumen fluids from sheep given intraruminal infusions of volatile fatty acids

Forty-four reticuloruminal epithelial receptors were tested with rumen fluids obtained from 12 sheep before they were intraruminally infused with 4.0M acetic acid (8 sheep) or 4.0M butyric acid (4 sheep; preinfusion rumen fluid) and with rumen fluids obtained at the onset of ruminal stasis (abolition rumen fluid). The preinfusion rumen fluids from the 8 acetic acid-infused sheep (mean pH, 6.55) contained 1.7 mM nondissociated volatile fatty acids (VFA)/L and excited none of the 25 receptors tested. Preinfusion rumen fluids from the 4 butyric acid-infused sheep (mean pH, 6.98) contained 0.3 mM nondissociated VFA/L and also did not evoke responses in any of the 19 receptors tested. Abolition rumen fluids from sheep treated with acetic acid excited 17 of the 25 receptors tested and contained 89.4 mM nondissociated VFA/L, of which nondissociated acetic acid comprised 85.0 mM/L. Abolition rumen fluids from sheep treated with butyric acid activated 14 of the 19 receptors tested and contained 61.1 mM nondissociated VFA/L, of which 38.7 mM/L was nondissociated butyric acid. Preinfusion rumen fluids whose pH values were adjusted to that of abolition rumen fluids with HCl contained nondissociated VFA levels ranging from 16.3 mM/L (acetic acid-treated sheep) to 20.6 mM/L (butyric acid-treated sheep) and elicited responses in 4 of 30 receptors tested. Preinfusion rumen fluids whose pH values were adjusted to the pH value of abolition rumen fluid with acetic acid contained 29.5 mM nondissociated VFA/L and excited 7 of 13 tested receptors.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effects of estrogen and progesterone on the blood levels of glucose, non-esterified fatty acids and cholesterol in ovariectomized sheep

The effects of estrogen and progesterone on the blood levels of glucose, non-esterified fatty acids and cholesterol in ovariectomized sheep.The effects of estradiol benzoate and progesterone on blood glucose, NEFA and cholesterol were studied in ovariectomized sheep. Intramuscular injection of 2.5 mg estradiol benzoate gave biphasic changes in NEFA. After 2 hrs. NEFA was decreased, but thereafter an increase occurred and maximum levels were reached after 24 hrs. Blood glucose was significantly increased from 12 to 48 hrs. after the injection. Serum cholesterol was lowered after 24 hrs., but thereafter the level increased. Maximum values were obtained after 120 hrs. Progesterone at the same dose did not change any of the measured parameters. Simultaneous administration of estradiol benzoate and progesterone gave similar responses as estradiol benzoate alone.Blood glucose and NEFA were followed during heat in a lactating cow. Both parameters increased after ovulation.Since NEFA was increased during so long time after the injection of estradiol benzoate, the mechanism behind this effect was discussed. No lipolytic hormone has been reported to give a response of this duration. Estrogen is known to increase plasma GH, and since GH is strongly lipolytic in sheep it seemed possible that the elevated NEFA levels were caused by increased GH secretion. There is now evidence that also estrogen-induced changes in serum cholesterol are pituitary dependant. It was therefore considered possible that all the noted metabolic changes were mediated by the pituitary.