Estimation of lysine and methionine requirements of growing steers fed corn silage-based or corn-based diets.

Methionine and lysine requirements of growing steers were studied. Steers (Experiment 1, 313 kg) fed 6.4 kg of an 80% corn silage diet (1.38% N) had duodenal flows of methionine, cysteine, and lysine of 9.7, 10.7, and 40.2 g/d. Linear increases in plasma methionine and plasma lysine in response to abomasal infusions of DL-methionine and L-lysine indicated that requirements for methionine and lysine were met by basal flows or that neither lysine nor methionine was the first or sole limiting amino acid. Steers (Experiment 2, 383 kg) fed 7.5 kg of a 75% corn diet (1.55% N) had methionine, cysteine, and lysine flows at the duodenum of 13.8, 16.1, and 52.9 g/d. Abomasal infusions of DL-methionine resulted in linear increases in plasma methionine, but abomasal infusions of L-lysine resulted in two-phase broken line plasma amino acid response curves. For steers infused with lysine alone, the breakpoint occurred at 4 g/d infused lysine, whereas steers receiving 9 g/d DL-methionine had a breakpoint at 8 g/d infused lysine. The total absorbable lysine requirement was estimated to be 44 to 48 g/d, depending upon methionine status. Rumen-protected amino acids fed to steers on both dietary regimens were effective in supplying methionine and lysine postruminally.

Effects of rumen-protected methionine and lysine on ruminant performance and nutrient metabolism.

Four trials were conducted to determine the effects of supplemental rumen-protected methionine (RPMet) and lysine (RPLys) on lamb N metabolism and steer feedlot performance. In trial 1, 20 Suffolk-sired, crossbred lambs (avg weight 32 kg) were fed diets containing no supplemental methionine (Met) and lysine (Lys), .03% RPMet, .05% RPLys or .03% RPMet + .05% RPLys. Lambs fed .03% RPMet + .05% RPLys had a 33% increase in N retention compared with lambs fed no supplemental Met and Lys. In trial 2, to verify the protection and availability of these amino acids, five Targhee lambs (avg weight 35 kg) were fed corn-soybran flake diets supplemented with urea and were assigned in a 5 X 5 Latin square to one of the following treatments: 1) control; 2) .03% RPMet + .05% RPLys offered in the diet; 3) .03% RPMet + .05% RPLys abomassally infused; 4) .03% non-protected Met + .05% non-protected Lys offered in the diet and 5) .03% Met + .05% Lys abomasally infused. Treatments 2, 3 and 5 decreased (P less than .05) urinary N (g/d) and increased N retention (P less than .05) compared with the control diet (treatment 1). Increases (P less than .05) in plasma Met and Lys concentrations indicated that the amino acids were protected and available for animals at the site of absorption. In trial 3, 40 crossbred Angus steers (avg weight 247 kg) were fed diets composed of 53% corn silage and 47% concentrate and supplemented with soybean meal to 11.3% crude protein. Steers that were fed diets containing .19% RPMet + .11% RPLys had greater daily gain (P less than .05) than those fed diets containing no supplemental amino acids, .11% RPMet + .01% RPLys, and .15% RPMet + .06% RPLys (1.39 vs 1.23, 1.22 and 1.20 kg/d, respectively). Similar improvements in feed conversion resulted and increases in plasma Met concentrations followed the same trend. In trial 4, 40 crossbred Angus steers (avg weight 368 kg) were fed corn grain-corn silage diets supplemented with urea. Treatments were: no supplemental amino acids; .05% RPMet + .01% RPLys; .10% RPMet + .04% RPLys; and .15% RPMet + .07% RPLys. No differences in steer performance resulted due to supplemental RPMet and RPLys (P greater than .05). The results of these trials suggest that the RPMet and RPLys used in this study are protected from ruminal degradation, are available post-ruminally and can improve lamb N balance and growing steer performance.

Feedlot performance and carcass characteristics of steers fed diets containing ammonium salts of the branched-chain fatty acids and valeric acid.

Two trials were conducted to study the effects of feeding a mixture of ammonium salts of isovaleric, 2-methylbutyric, isobutyric and valeric acids (AS-VFA) on feedlot performance and carcass characteristics of growing and finishing Angus, Hereford and Angus X Hereford steers. In trial 1,192 steers (8 steers/pen, 6 pen/treatment) averaging 251 kg body weight and in trial 2, 240 steers (8 steer/pen, 7 pens/treatment, 9 pens/control treatment) averaging 216 kg body weight were randomly assigned to four anhydrous ammonium salt-volatile fatty acid (AS-VFA) treatment levels: 0 (control), .14, .28 and .42% of the diet dry matter (DM). In each trial, the growing and finishing diets were isocaloric, isonitrogenous and supplemented with monensin (26 mg/kg diet). In both trials, steers received implants of 200 mg progesterone and 20 mg estradiol benzoate. Combined data from the trials confirmed the absence of average daily gain and feed conversion responses during the growing period. During the finishing period, the combined data for gain and feed conversion for the control steers and the steers fed .14, .28 and .42% AS-VFA were 1.43, 7.09; 1.43, 6.99; 1.48, 6.67 and 1.45, 6.80, respectively. Gains increased 3.5% (P less than .10) and feed conversion improved 5.9% (P less than .07) in steers fed .28% AS-VFA compared with gain and feed conversion of the control steers. At the end of the growing period in the first trial, a urea dilution technique was used to estimate the body composition of 12 steers from each treatment. Estimates of percent body fat and percent body protein were similar (P greater than .20) for all steers, irrespective of treatment. At the end of the trials, carcass yield grades for the combined data were 2.6 and 2.8 (P less than .10) for steers fed .28% AS-VFA and for the control steers, respectively. Carcass weight, dressing percentage and marbling score were lower (P less than .10) in steers fed AS-VFA than for steers fed the control. However, in general, carcass characteristics were not greatly influenced by AS-VFA. A possible use for a supplement containing branched-chain fatty acids and valeric acid in finishing steer diets is suggested by the improvement in feedlot performance and by the slight increase in carcass yield.

Plasma magnesium levels as influenced by cold exposure in fed or fasted sheep.

Eight ewes weighing about 52 kg were used in a 2 X 2 factorial arrangement of treatments replicated with temperature reversal to determine the effect of cold exposure on plasma Mg, Ca, free fatty acids (FFA), glucose and insulin concentrations and on renal clearance of Mg and Ca. Closely sheared ewes were fed a complete mixed diet at either 1.5% of body weight with no pretreatment fast or fed ad libitum followed by fasting 3 days before initiation of temperature treatments. Fasting superimposed on cold exposure reduced (P less than 0.01) plasma Mg at 1 hour after exposure to cold, and this effect continued during the cold treatment period, whereas Mg concentration was not significantly affected in fed sheep. Plasma FFA measured across temperature treatments was increased (P less than 0.01) by fasting. FFA measured across dietary treatments was only slightly increased by cold exposure. Plasma glucose levels of fasting sheep were lower (P less than 0.05) than those of fed sheep; however, levels rose (P less than 0.05) after exposure to cold. A tendency for plasma insulin to increase after cold stress was observed. Renal clearances of Mg and Ca were markedly reduced (P less than 0.01) by fasting, but clearance was not changed by cold stress. These results suggest that exposure to cold (2-5 degrees) and a deficient dietary intake synergistically reduce plasma Mg in sheep.

Renal function and magnesium clearance in young and old cows given potassium chloride and sodium citrate.

Six young (3 yr old) and six old (8 to 11 yr old) cows were used to examine renal function, KCl and sodium citrate effects on Mg clearance rate and the relation of parathyroid hormone (PTH) to Mg reabsorption. The treatments were 1.5 g KCl/kg body weight (BW) and 1.5 g Na citrate/kg BW. Inulin and p-aminohippuric acid (PAH) clearance rates were used as measures of glomerular filtration rate (GFR) and effective renal plasma flow (ERPF), respectively, in control cows on each treatment day. Creatinine clearance rate was also used as a measure of GFR in all cows. Magnesium loading (2.4 mg/kg BW) through continuous intrajugular infusion of MgCl2 facilitated the measurement of changes in Mg clearance rate and reabsorption due to treatment. Inulin and creatinine clearance rates were not different as measures of GFR, and there were no differences in ERPF between young and old cows. Old cows had lower (P less than .05) GFR, creatinine to PAH clearance ratios and tubular reabsorption of Mg than young cows. Intraruminal infusion of KCl and Na citrate increased (P less than .05) the GFR. Potassium chloride increased plasma K concentration (P less than .001), plasma K clearance rate (P less than .002), plasma Na clearance rate (P less than .03), plasma Mg concentration (P less than .05), net tubular reabsorption of Mg (P less than .02), maximum tubular reabsorption of Mg (P less than .002) and plasma PTH concentration (P less than .03). Plasma Mg clearance rate was increased only by Na citrate (P less than .05). These results suggest a possible relationship between age, renal function, Mg antagonists and PTH in Mg homeostasis and in the etiology of hypomagnesemic tetany.

Plasma parathyroid hormone and insulin concentrations in cows administered potassium chloride and sodium citrate.

Two age group of nonpregnant cows were used to study plasma changes in parathyroid hormone, insulin, and glucose, and renal clearance rates of magnesium, calcium, and inorganic phosphorus after intraruminal administration of 1.5 g potassium chloride (KCl)/kg body weight (BW) or 1.5 g sodium citrate/kg BW. Magnesium (2.4 mg/kg BW) was simultaneously infused intravenously for 120 minutes to facilitate the measurement of changes in magnesium clearance rate and kidney tubular resorption due to the treatments. Elevated plasma concentrations of potassium from intraruminal infusion of KCl increased plasma parathyroid hormone, insulin glucose, and magnesium levels. Net tubular resorption of magnesium (TMg) was also increased after potassium dosing, and the old cows had lower TMg values compared with the young cows. Plasma magnesium and calcium clearance rates were increased only by citrate, while phosphorous was not influenced by either treatment. These results provide evidence for a relationship between potassium and the endocrine factors, parathyroid hormone, and insulin; citrate appears to antagonize tubular resorption of magnesium and calcium.

Influence of intrajugular administration of insulin, glucagon and propionate on voluntary feed intake of sheep.

The effect of intrajugular injections of insulin, glucagon and propionate, administered singly and in combination, as possible peripheral feedbacks in the control of feed intake in wethers was studied. A complete mixed diet (25% chopped hay: 75% cracked corn) was fed ad libitum. The treatments were saline, 6 mU insulin/kg body weight (BW), 9 ng glucagon/kg BW and 1.3 mg propionate/kg BW. In Exp. 1, five wethers were given the treatments at the beginning of each spontaneous meal over a 24-hr period, and total daily feed intakes were measured. The average number of injections per sheep for a 24-hr period was eight. In Exp. 2, the effects of the treatments on plasma concentrations of insulin, glucagon, propionate and glucose at 15, 30, 60 and 120 min after injection were measured in six other wethers. In Exp. 1, insulin (P less than .01), glucagon (P less than .01), insulin plus propionate (P less than .05) and glucagon plus propionate (P less than .05) decreased 24-hr feed intake by 18.5, 15.8, 11.0 and 11.8%, respectively, compared to the saline control. In Exp. 2, plasma insulin concentrations were increased (P less than .05) at 15 min after administration of insulin and insulin plus propionate, to 2.0 and 2.1 times the preinjection levels, respectively. Glucagon concentrations in plasma were increased (P less than .01) at 15 min after the injection of glucagon, to 2.0 times the pretreatment values. Insulin and glucagon concentrations in plasma were increased only slightly (P less than .10) after administration of glucagon plus propionate. No treatments affected glucose or propionate concentrations in the plasma. Increases in plasma concentrations of insulin, glucagon and propionate may interact directly or initiate other mechanisms involved in the short-term control of feed intake by sheep on a concentrate diet.

Effect of intrajugular administration of insulin on feed intake, plasma glucose and plasma insulin of sheep.

The effect of intrajugular administration of insulin on feed intake, plasma glucose and plasma insulin of 16 wether sheep was studied. A concentrate ration was fed ad libitum to eight wethers, and a forage ration fed to eight different wethers. For each ration, feed intake of four of the eight wethers was measured in one experiment and blood was sampled from the other four wethers at 15, 30, 60 and 120 minutes after injection in a second experiment. The four treatments were saline, 1 mU, 6 mU and 2,000 mU insulin/kg body weight. The highest insulin dose did not affect feed intake of either ration despite producing a marked hypoglycemia, whereas the 6 mU insulin treatment depressed feed intake 1 hour after injection with small changes in concentration of plasma glucose in sheep fed either the concentrate or forage ration. Concentration of plasma insulin was elevated 15 minutes following the 6 mU insulin treatment for the concentrate and forage ration, while 1 mU insulin did not affect plasma insulin. The results of this study suggest a possible role for insulin in the short-term control of feeding in sheep fed either a concentrate or forage ration.

Effect of intraportal and continuous intrajugular administration of insulin on feeding in sheep.

The effect of intraportal and intrajugular administration of insulin on feed intake and on glucose and insulin of jugular blood was studied. Ad libitum intake of four wethers was measured and jugular blood was sampled at various times after intraportal administration of the treatments and meal initiation. The treatments injected in the first experiment were saline, 2 mU, 4 mU and 6 mU insulin/kg body weight (BW), and in a second experiment were saline, 2 mU, 6 mU and 12 mU insulin/kg BW/minute infused over a 15-minute period. Feed intake was depressed only by 15-minute intraportal infusion of the 2 mU and 6 mU doses. Plasma insulin was elevated at 5 minutes after injection of 4 mU and 6 mU insulin/kg BW, and elevated at 5 and 15 minutes after 15-minute infusion of all three treatments; plasma glucose was not affected. Two additional experiments used four wethers in which jugular blood was sampled during a 24-hour intrajugular infusion of insulin. The combined treatments were saline, 0.02 mU, 0.2 mU, 2 mU and 6 mU insulin/kg BW/minute. The 6 mU dose stimulated feed intake, 2 mU increased plasma insulin and both 2 and 6 mU depressed plasma glucose. Thus, the site, timing and amount of exogeneous insulin administration may cause varying feed intake responses. The results are discussed with respect to a possible role of insulin in appetite control in sheep.

Effect of heat stress on the potassium requirement of the hen.

Four diets were formulated with potassium levels ranging from 0.4 to 1.0% and each diet was fed to laying hens at temperatures of 26.7%, 32.2, and 37.8 degrees C. Analyses for potassium in the plasma, egg, and excreta and potassium retained were used to determine the effects of heat stress on the potassium balance of laying hens. Urine potassium data from a surgically-altered hen provided insight into urinary excretion of potassium under conditions of heat stress. Regression analyses of the data obtained indicated that temperature significantly influenced plasma potassium concentrations, while egg and excreta potassium concentrations and the amount of potassium retained were not significantly influenced by temperature. The data suggest that 0.4% potassium in the diet is adequate for meeting potassium requirements under conditions of heat stress. However, 0.6% dietary potassium may be a more suitable level for assurance against a potassium imbalance at elevated temperatures. One percent dietary potassium appears to be an excessive level.