Effect of water restriction and dietary potassium on nutrient metabolism in lambs

Twenty-four Hampshire X Suffolk wether lambs (40 kg) were used in a 2 X 2 factorial arrangement of treatments to study the influence of water restriction and high levels of dietary K on nutrient utilization. Lambs were offered either a normal K diet (1.86% K) or a high K diet (3.66% K). Additionally, the lambs were offered either a normal quantity of water (previously determined voluntary intake of lambs fed normal K levels) or were restricted to a water intake 80% of normal. Each lamb received 800 g/d of a fescue hay-corn diet (77.5% fescue hay) with an additional 20 g of KCl offered to lambs on high K treatments. The experiment consisted of 14 d of adjustment and 7 d of total collection with blood and ruminal parameters measured on the last day of collection. Both acid detergent fiber digestibility and N balance were reduced (P less than .05) by high K intake. Urinary Mg excretion tended (P greater than .05) to be decreased by water restriction. Plasma Mg concentrations at 2 h post-feeding (PF) tended (P greater than .05) to be reduced by a high K intake at a normal level of water consumption but increased at high K intake when water intake was restricted. A similar pattern was observed for plasma K concentrations. Although high K intake resulted in elevated (P less than .05) ruminal K concentrations both at 2 and 6 h PF, ruminal concentrations of ammonia-N and volatile fatty acids were not affected (P greater than .05) by treatment. These data suggest that nutrient utilization in both the digestive tract and tissues is altered by level of K and modest water restriction.     

Nutrient utilization in lambs fed diets high in sodium or potassium

Twenty-four wether lambs averaging 47 kg were used to study the effects of dietary K and Na additions on metabolism of lambs. Lambs were randomly allotted to four treatments and fed 900 g/d of the following: control diet consisting of 50% ground tall fescue hay and 50% concentrate; K diet calculated to contain 4% K with K added as KCl; Na diet calculated to contain 4% Na with Na added as NaCl, and K-Na diet containing 2% K and 2% Na with K and Na added from the same sources as in the K and Na diets. Water intake and urine excretion were highest for lambs fed the Na diet. Dry matter (DM) and crude protein (CP) digestibilities were similar among treatments. The K-Na diet resulted in decreased (P less than .05) acid detergent fiber (ADF) digestibility compared with lambs fed the Na diet. Nitrogen (N) retention was highest (P less than .05) in lambs fed the K diet and lowest in those fed the Na diet. Rumen NH3-N was lower (P less than .05) in lambs fed the Na diet compared with controls. Rumen K at 2 and 6 h postfeeding was highest (P less than .05) and rumen Na at 6 h lowest (P less than .05) for lambs fed the K diet. Plasma K values at both sampling times were highest (P less than .05) in lambs fed the K diet. At 6 h postfeeding, plasma Mg was higher in control lambs compared with those fed the K-Na diet.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of dietary sewage solids on feedlot performance, carcass characteristics, serum constituents and tissue elements of growing lambs

Twenty fine-wool wether lambs were allotted randomly at weaning to be fed a conventional diet (CD) formulated for growing lambs, or the same basal mixture plus dried gamma-irradiated solids from primary sewage sludge (SS) incorporated as 7% of the dry matter. Feedlot performance and chemical elements in whole blood were monitored during 90 d, after which lambs were slaughtered and carcass data were collected. Concentrations of Ag, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, Pb and Zn were measured in livers, kidneys, bones, spleens and muscles. Sewage solids in the diet did not affect performance appreciably, although dressing percentages from lambs fed SS were 4% lower than CD-fed animals (P less than .05). Rib eye areas, fat thicknesses, quality and yield grades were similar (P greater than .05). Element concentrations in whole blood at weaning, after 56 d of the feeding trial and at slaughter did not differ (P greater than .05) between dietary groups. Serum chemistry determinations showed no biologically meaningful patterns related to diets. Lambs fed SS had higher (P less than .05) concentrations of Cu in livers (51.1 vs 34.3 +/- 3.8 micrograms/g, mean +/- SE) and Pb in kidneys (4.0 vs 2.2 +/- .3 micrograms/g) and lower (P less than .05) Mg in kidneys (.69 vs .72 +/- .01 mg/g). None of the elements in spleen and muscle tissue differed (P greater than .05) between diet groups. Lambs fed SS had elevated (P less than .05) bone Co, Cu, Fe, K and Na compared with those of CD.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of dietary protein level on nitrogen metabolism in lambs: studies using 15N-nitrogen

Six wether lambs (31 kg) were randomly assigned to two treatments (three lambs/treatment): a high protein intake (HP; 21 g N/d) or a low protein intake (LP; 12 g N/d). Each lamb received 860 g/d dry matter (DM) of a pelleted diet (75% corn-soybean meal, 25% cottonseed hulls) offered hourly in 24 equal portions. Single injections of 15N-labelled compounds were made into the ruminal NH3-N and blood urea-N pools to measure the rate of flux through, and transfer of N between, these and the bacterial N pool. Total tract digestibilities of DM and N were lower (P less than .05) for the LP than the HP treatment. Abomasal flows of total, feed or bacterial N tended to be greater (P greater than .05) in lambs fed HP than LP. Lambs fed HP excreted more (P less than .01) urinary N, yet retained a greater (P less than .01) amount of N than lambs fed LP (6.2 vs 1.8 and 9.7 vs 4.1 g N/d, respectively). Pool size and production rate for both ruminal NH3-N and blood urea-N were greater (P less than .05) for the HP than LP treatment. Lambs consuming HP degraded more (P less than .05) blood urea-N in the gastro-intestinal tract (13.4 vs 6.9 g N/d); however, lambs fed LP degraded a greater (P less than .05) percentage of synthesized body urea-N (88.7 vs 71.8%). Ruminal NH3-N absorption was greater (P less than .01) for the HP than LP treatment (3.1 vs .5 g N/d). Although the percentage of bacterial N derived from ruminal NH3-N was similar (P greater than .05) between diets (51.1 vs 63.9), a greater (P less than .05) percentage of bacterial N was derived from blood urea-N in lambs fed LP than HP (77.1 vs 30.2%). Lambs fed LP incorporated a greater (P less than .10) amount of blood urea-N into bacterial N than lambs fed HP (5.5 vs 2.6 g N/d). These data are interpreted to suggest that blood urea-N may provide a substantial quantity of N for bacterial protein synthesis and, thus, may be an important source of protein in the deficient animal. In addition, urea recycling may play an important role in the recovery of ruminal NH3-N lost through absorption in animals fed a high level of protein.     

Influence of limestone level in high concentrate and high roughage diets on site and extent of digestion in lambs

Two digestion and slaughter trials were conducted to evaluate the influence of limestone level on site and extent of digestion and rumen fermentation in lambs. In trial 1, 11 wether lambs (avg wt 40.7 kg) were fed 75% concentrate diets supplemented with .6, 1.5 or 3.0% limestone (.6,1.2,1.7% dietary Ca, respectively) in a completely randomized design. Dry matter intake increased linearly (P less than .10) with limestone level; therefore, other data were analyzed with dry matter intake as a covariate. Total tract organic matter digestion decreased linearly (P less than .05) with increasing limestone but dry matter and fiber digestion were not affected by limestone. Ruminal digestion of dry matter and organic matter declined linearly (P less than .05) with increasing limestone. Ruminal neutral detergent fiber (NDF) digestion was higher with the 1.5 than the .6 and 3.0% limestone diets (quadratic effect, P less than .05) but ruminal digestion of other fiber components was not affected by limestone. Ruminal volatile fatty acids were not affected by limestone level; however, rumen ammonia concentrations decreased linearly (P less than .05) with increasing limestone level. In trial 2, 12 wether lambs (avg wt 43.3 kg) were fed a 35% concentrate diet with .1, 1.5 or 3.0% limestone (.5, 1.2 and 1.6% dietary Ca, respectively) in a completely randomized design. Dry matter intake was not affected by limestone level, but digestibility of dry matter, organic matter and starch (P less than .10), energy, crude protein, acid detergent fiber (ADF) and cellulose (P less than .05) responded quadratically to limestone level, with increases at the 1.5% limestone level. Ruminal dry and organic matter (P less than .05), NDF (P less than .10), ADF (P less than .01), cellulose (P less than .05) and starch (P less than .05) digestion responded quadratically to limestone level with higher values at the 1.5% limestone level. Proportions of ruminal propionate increased linearly (P less than .01) with increasing limestone level and acetate: propionate ratio declined linearly (P less than .01) with limestone level.     

Growth performance, serum hormones, and metabolite responses before and after weaning in lambs weaned at 42 days of age: effect of preweaning milk and postweaning alfalfa or grass hay diets.

Fourteen fall-born lambs were used to determine the effects of diet before and after weaning on intake, growth, serum hormones, and metabolite profiles. Before weaning, lambs were intensively sampled for 6 h at 35 and 42 d of age. Before sample collection, lambs were allowed to suckle, and milk intake was recorded. At 42 d of age, lambs were weaned and randomly allotted to ad libitum access to either alfalfa or grass hay. Blood samples were collected at 49 and 56 d of age for 6 h. Milk intake did not differ (P greater than .10) between groups. After weaning, lambs fed alfalfa hay consumed more (P less than .05) hay and had greater (P less than .05) ADG than lambs fed grass hay. Postweaning diet had no effect (P greater than .10) on serum insulin, growth hormone (GH), insulin:GH ratio, prolactin, cortisol, glucose, or nonesterified fatty acids (NE-FA) concentrations. Lambs consuming alfalfa had higher (P less than .05) serum urea nitrogen (SUN) at 49 and 56 d of age than lambs consuming grass. At 35 and 42 d of age, (P less than .05) serum insulin and insulin:GH ratio were higher (P less than .05) after milk intake than at 49 and 56 d of age after hay intake. Serum GH was higher (P less than .05) in lambs at 35 and 42 d of age for 2 h postfeeding, but by h 3 through 5, lambs consuming milk had lower (P less than .05) values than lambs consuming hay.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of supplemented magnesium from magnesium oxide or dolomitic limestone upon digestion and absorption of minerals in sheep

Three metabolism trials were conducted with six lambs fitted with abomasal and ileal cannulae to determine the site of supplemental Mg absorption when supplied as dolomitic limestone or magnesium oxide. Magnesium intake was 1.09 g/d for the lambs fed the control diet and 2.21 and 2.10 g for those fed the dolomitic limestone and magnesium oxide supplemented diets, respectively. Irrespective of its source, the major site of Mg absorption was the preintestinal region. Magnesium was secreted in the small intestine in lambs fed all three diets. Magnesium supplementation resulted in an increase (P less than .05) in preintestinal Mg absorption, with magnesium oxide having the highest value. Supplementation had no effect (P greater than .05) on secretion or absorption of Mg from the small and large intestines or total retention of Mg. With all three diets, the major site of Ca absorption was the stomach region with additional absorption taking place in the large intestine. Calcium was secreted in the small intestine of lambs fed all treatments. Generally, K, Na and P were secreted in the preintestinal region and absorbed from the small and large intestines. The major site of K and P absorption appeared to be the small intestine and for Na, the large intestine. Serum minerals were unchanged (P greater than .05) due to treatment, but the levels of Mg, K and inorganic P tended to be higher in lambs supplemented with either of the Mg sources. It appears that the greater utilization of Mg from magnesium oxide vs dolomitic limestone is due to greater absorption of Mg from the forestomach region.     

Effect of diet composition and feed intake level on diet digestibility and ruminal metabolism in growing lambs.

Lambs (29 +/- 2.5 kg) were fed three diets at various intakes to determine whether diet composition or level of intake was reflected in changes in diet digestibility or ruminal fluid characteristics. In Exp. 1, a 90% concentrated, pelleted diet or a whole shelled corn diet with a pelleted protein supplement was fed at three levels of intake: ad libitum and 92.5 and 85% of ad libitum (n = 15). Exp. 2 compared the 90% concentrate diet with diets in which the energy density was diluted to 55 or 72.5% concentrate by including alfalfa hay as a possible method of restricting energy intake (n = 6). Lambs were adapted to diets for 13 d; feces were collected for 6 d and ruminal fluid was collected 0, 3, and 6 h after feeding on the day following fecal collection. Restricting intake in Exp. 1 did not affect DM digestibility or digestibility of CP or starch. Digestibility of ADF was increased (P less than .10) by restricting intake. Ruminal fluid pH, ammonia concentration and VFA concentrations were affected little by either restricted intake level. Digestibility of DM was 4% higher (P less than .001) and starch 5% higher (P less than .001) for the whole shelled corn diet than for the pelleted, high-concentrate diet. Ruminal pH of lambs fed the whole shelled corn diet was higher and fluctuated less than the ruminal pH of lambs fed the high-concentrate, pelleted diet. In Exp. 2, diet digestibility was reduced (P less than .01) and ruminal pH was increased (P less than .002) by addition of hay. Restricted feeding of lambs did not seem to increase diet digestibility or alter ruminal conditions.     

Influence of postfast dietary crude protein and phosphorus content on nitrogen, phosphorus, calcium, and magnesium repletion in sheep.

An experiment was conducted to determine the influence of postfast dietary CP and P concentration on the repletion of N, P, Ca, and Mg lost during a 3-d fast in sheep. Four Suffolk wether lambs averaging 35 kg were used in a 4 x 4 Latin square design. Lambs were fed a control diet (700 g/d; as-fed basis) for 14 d and were then deprived of feed and water for 3 d. Lambs were then fed one of four isoenergetic realimentation diets: 1) low CP/low P, 2) low CP/high P, 3) high CP/high P, and 4) high CP/very high P. Realimentation N and Mg intakes were 9.8 and 1.1 g/d for lambs fed the low-CP diet and 18.1 and 1.7 g/d for lambs fed the high-CP diets, respectively. Realimentation P intakes were 1.40, 2.36, 2.66, and 3.82 g/d for lambs fed Diets 1, 2, 3, and 4, respectively. Nitrogen, P, Ca, and Mg apparent digestibility and balance and serum urea N, free fatty acids, P, Ca, Mg, and alkaline phosphatase were determined during the prefast, fast, and realimentation periods. Lambs fed the high-CP diets had higher (P less than .05) N and P digestibility and balance than lambs fed the low-CP diet. Increasing the dietary P content did not affect (P greater than .15) P balance or digestibility. In general, the realimentation diet fed did not affect (P greater than .15) serum concentrations of free fatty acids, alkaline phosphatase, inorganic P, Ca, or Mg.     

Absorption of magnesium and other macrominerals in sheep infused with potassium in different parts of the digestive tract

Two metabolism trials were conducted with 12 crossbred wether lambs, each surgically equipped with a ruminal catheter and abomasal and ileal cannulae, to study the effect of K infusion in different sites of the digestive tract on site of absorption and flow of minerals. The treatments consisted of the infusion of 33.6, 12.0 or 12.0 g K/d as bicarbonate into either the rumen, abomasum or ileum, respectively. Each trial consisted of a minimum 5-d preliminary period, five 3-d collection periods to determine mineral balance and a 6-d sampling period to determine mineral flow and site of absorption. Chromic oxide was incorporated into the diet for use as a marker. Magnesium was absorbed primarily from the preintestinal region. Ruminal infusion of K tended to decrease preintestinal Mg absorption. Absorption of Mg in the entire tract was decreased (P less than .05) 43% when K was infused into the rumen. There was a slight absorption of Mg in the small intestine, followed by a net secretion into the large intestine. Serum Mg levels tended to be depressed in lambs infused with K intraruminally. Calcium flow from the preintestinal region was decreased (P less than .05) by infusion of K into the rumen. Only lambs infused with K in the rumen had a net secretion of Na into the small intestine. The large intestine was the primary site of net Na absorption for ruminal-infused lambs. Phosphorus flow from the preintestinal region was decreased (P less than .05) by infusion of K into the rumen. Potassium flow from both the preintestine and small intestine was increased (P less than .05) by ruminal K infusion. The infusion of K into the rumen, abomasum or ileum increased (P less than .05) the total absorption of K, with the small intestine being the major absorptive site. The infusion of potassium bicarbonate into the rumen of sheep raised (P less than .05) the pH of the ruminal contents 15%. Ruminal infusion of K depresses Mg absorption, while the infusion of K into the abomasum or ileum does not affect Mg absorption. Therefore, the role of K in grass tetany may be via this depression of Mg absorption.     

Effects of dietary monensin and potassium on apparent absorption of magnesium and other macroelements in sheep

Twelve ruminally cannulated lambs (average weight, 31.1 kg) were used to determine the effects of monensin and K on apparent absorption of Mg in lambs. Lambs were assigned randomly to two groups and fed a basal high concentrate diet containing .44% K with or without 20 mg/kg monensin for 19 d of dietary adjustment. During adjustment, lambs were housed by treatment group and given ad libitum access to their diets. Following dietary adjustment, lambs were placed in individual metabolism stalls and fed 450 g of their respective diet twice daily. Within each monensin group, lambs were infused ruminally with 0, 7.6 or 31.6 g K/d (equal amounts at each feeding in 158 ml of distilled-deionized water) during three periods in a 3 X 3 Latin-square arrangement of K treatments. Each period consisted of a 10-d preliminary phase and a 7-d collection phase followed by a 3-d D2O infusion phase to determine water turnover. Addition of monensin to the diet decreased (P less than .05) fecal Mg excretion 15.9%. Apparent absorption and retention of Mg were increased (P less than .05) with the addition of monensin. Increasing K level increased (P less than .05) fecal Mg excretion. Apparent absorption of Mg decreased (P less than .05) from .93 to .80 g/d when either level of K was infused into the rumen. Monensin decreased the acetate:propionate (A:P) ratio. There was a significant interaction between monensin and K level for acetate and propionate (molar %), and A:P ratio. In the presence of higher K concentrations, monensin appears to be more effective in decreasing the A:P ratio.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of feeding frequency on forage fiber and nitrogen utilization in sheep

Four crossbred wether lambs (38 kg) with permanent ruminal and abomasal cannulae were used in a 4 X 4 Latin square arrangement of treatments to determine the effect of feeding frequency (FF) on forage fiber and N utilization. Lambs were offered 900 g of good quality (vegetative) Kentucky-31 tall fescue hay in equal portions either 2, 4, 8 or 16 times daily. Water consumption increased (P less than .05; linear) with increased FF. Apparent total tract digestibilities of dry matter, organic matter and cell wall constituents were not affected (P greater than .05) by FF, but apparent total tract digestibility of crude protein decreased (P less than .05; linear) with increased FF. Ruminal and post-ruminal digestion of acid detergent fiber (percent of total tract digestion) differed (P less than .05; cubic) among FF treatments. Although N retention was not affected (P greater than .05) by FF, increased FF decreased (P less than .05; linear) mean ruminal ammonia-N concentrations. Both the quantity of total N reaching the abomasum and the efficiency of microbial crude protein synthesis tended to increase (P greater than .05) with increased FF. In addition, the daily quantity of microbial N reaching the abomasum was affected (P less than .05; cubic) by FF. Ruminal pH was not affected (P greater than .05) by FF, whereas total volatile fatty acid concentrations (VFA) decreased (P less than .05; linear) with increased FF. Responses in molar proportions of individual VFA to FF were variable, and suggest that increasing FF elicits significant changes in the distribution of fermentation end-products.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of pre-fast dietary roughage content on recovery from feed and water deprivation in beef steers

Sixty steer calves of mixed British breeding averaging 268 kg were randomly assigned to four treatment groups of 15 calves each to determine the influence of pre-fast dietary roughage content on recovery from feed and water deprivation. Three groups were fed diets containing either 84 (HR), 60 (MR) or 35% (LR) roughage at 1.75% of body weight for 3 d. Calves in these three groups were deprived of feed and water for 24 h, limit-refed and watered for 24 h, and deprived of feed and water for 48 h (deprivation). Calves were then fed the MR diet ad libitum for 2 wk. The fourth group of control steers was continuously fed the MR diet throughout the experiment. Realimentation weight gains and feed intakes were not affected by pre-fast diet roughage content. Blood packed cell volume increased (P less than .05) during deprivation. Blood potassium was not affected by deprivation but declined (P less than .05) upon refeeding. Plasma urea-N increased (P less than .05) during deprivation but returned to pre-fast concentrations by d 3 of realimentation. Ruminal volume was not significantly affected by deprivation but increased (P less than .05) by 50 to 100% upon refeeding. Ruminal fluid total volatile fatty acid (VFA) concentrations declined (P less than .05) during deprivation. On d 3 of realimentation, a linear contrast (P less than .05) was observed between total VFA concentrations and the pre-fast diet roughage content.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of monensin on Mg, Ca, P and Zn metabolism and tissue concentrations in lambs

A study consisting of two trials was conducted to determine the effects of monensin on the apparent absorption and retention of magnesium (Mg), phosphorus (P), calcium (Ca) and zinc (Zn) and to determine mineral changes in tissue and ruminal fluid. Eight lambs (39 kg) were used in trial 1, and 10 lambs (37 kg) were used in trial 2. Animals were blocked by weight and fed a high concentrate diet with or without 20 mg/kg monensin. Trials began with a dietary adjustment period lasting 18 d in trial 1 and 21 d in trial 2. Animals were then placed in metabolism stalls for a 10-d stall adjustment period followed by a 12-d collection period. Collections to determine mineral balance were made during the first 10 d of the collection period. Blood and ruminal fluid samples were taken on d 11 of the collection period. Lambs were slaughtered on d 12 of the collection period and tissue samples were collected. Monensin supplementation increased (P less than .05) Mg retention 42.0%. Urinary Ca excretion decreased (P less than .05) 60.0% when monensin was fed. Monensin supplementation decreased (P less than .05) liver Ca and bone Ca, 45.5 and 2.9%, respectively. Apparent P digestibility increased (P less than .05) 40.0% and P retention increased (P less than .10) 26.8% due to monensin supplementation. Both apparent absorption and retention of Zn increased (P less than .01) 50.0 and 45.0%, respectively, with monensin supplementation. Ruminal fluid Zn concentrations decreased (P less than .05) 33.0% with the addition of monensin.(ABSTRACT TRUNCATED AT 250 WORDS)     

Physiological effects of feeding high levels of magnesium to sheep

The effects of feeding high levels of Mg to sheep on animal health, nutrient digestibility, metabolism of macro-minerals, blood and tissue mineral concentrations and hematological and histological tissue changes were evaluated. Six lambs were allotted to each of four diets supplemented with MgO to attain .2, .6, 1.2 or 2.4% Mg. Total fecal and urinary collections were made for the initial 20 d and last 10 d of a 50 d study. Diarrhea was noted in lambs fed the two highest Mg levels. Apparent digestibility of DM, ADF and CP decreased linearly (P less than .01) with increasing Mg levels. Dietary Mg levels did not affect (P greater than .05) rectal temperature, respiration rate or pulse rate. Apparent absorption and retention of Mg (g/d) were lowest in lambs fed 2.4% Mg until 15 d on trial, after which values increased linearly (P less than .01) with dietary Mg. Phosphorus absorption and retention decreased linearly (P less than .01) with increasing Mg levels. Increasing dietary Mg resulted in a linear increase (P less than .01) in serum Mg and variable increases (P less than .05) in erythrocyte Mg. Serum Ca was decreased linearly (P less than .05) and quadratically (P less than .05) by added Mg during the d 1 to 30 and 40 to 50 periods, respectively. Serum inorganic P was elevated consistently in lambs fed 2.4% Mg. A linear response to increasing dietary Mg (P less than .05) occurred in the Mg content of liver, kidney, rib bone and femur bone. Dietary Mg did not alter (P greater than .05) other criteria.(ABSTRACT TRUNCATED AT 250 WORDS)     

Low-quality roughages in high-concentrate pelleted diets for sheep: digestion and metabolism of nitrogen and energy as affected by dietary fiber concentration

Two trials were conducted to evaluate effects of, and interactions between, level and source of fiber in the diet on ruminal environment, microbial protein synthesis, nutrient digestion and flow of digesta through the gastrointestinal tract of multiple-fistulated sheep (trial 1; 4 X 4 Latin square design) and on ruminal, digestive and metabolic characteristics of early-weaned lambs (trial 2; randomized complete block design; 3 periods). All diets tested were pelleted and were formulated to contain either 39% or 25% neutral detergent fiber (NDF), with corncobs or cottonseed hulls (CSH) as the major NDF (roughage) sources. In trial 1, dry-matter (DM) and organic-matter (OM) digestibilities were not different (P greater than .05) among treatments. Digestibility of NDF was higher (P less than .05) with high-fiber. Bacterial N synthesis (g N/kg OM truly digested) was not different (P greater than .05) among treatments. Molar proportion acetate was higher (P less than .05) and molar proportion propionate lower (P less than .05) when sheep were fed high-fiber diets. In trial 2, apparent DM digestibility was higher (P less than .05) for lambs fed diets containing corncobs. Energy digestibility was higher (P less than .05) at the low-fiber level and for lambs fed diets containing corncobs. Apparent NDF digestibility by lambs was higher (P less than .05) at the high-fiber level and for lambs fed diets containing corncobs. Nitrogen retained (percentage of N intake) was higher (P less than .05) for lambs fed diets containing CSH. Ruminal pH and molar proportion acetate were higher (P less than .05) and molar proportion propionate lower (P less than .05) for lambs fed high-fiber diets. Although responses to corncob vs CSH inclusion in high-energy pelleted diets differ, both roughages are effective as fiber sources in sheep diets.     

Effects of dietary potassium and sodium on magnesium utilization in sheep

Two metabolism trials were conducted to determine the effect of altering dietary Na and K on Mg availability. Three dietary treatments (normal K-normal Na, high K-normal Na and high K-high Na) were imposed upon nine crossbred wether lambs in a randomized block design. Each trial consisted of a 5-d diet adjustment, a 10-d preliminary period and a 5-d collection of feed, feces and urine. Increasing K and Na intake increased the percentage of Mg excreted in feces. Both elevated K and K-Na depressed (P less than .10) urinary Mg excretion, primarily a reflection of depressed Mg absorption in animals fed these diets. Apparent K absorption and retention increased when animals were supplemented with K. Addition of Na to the diet did not alter absorption or retention of K. Apparent K and Na availability increased when K and Na supplements were included in the diet. This increased availability resulted from increased total absorbed K and Na compared with a fixed endogenous excretion. Calcium balance in lambs was not affected by addition of K or Na. Lambs were able to absorb enough Mg from their respective diet to maintain normal serum Mg levels. Addition of Na to a diet high in K did not enhance Mg absorption in lambs.     

Feed intake and digestion by beef cows fed prairie hay with different levels of soybean meal and receiving post-ruminal administration of antibiotics

Six cannulated beef cows (one Angus, two Hereford and three Angus x Hereford; 405 kg) were used in a 6 x 6 latin square experiment with a 2 x 3 factorial arrangement of treatments. Prairie hay (.77% N, 73% neutral detergent fiber [NDF] and 7% acid detergent lignin) was fed ad libitum from d 1 through 14 and at 90% of ad libitum intake from d 15 through 21 during digesta collection. Periods lasted 21 d. Soybean meal (SBM) was offered at 0 (control, C), .12 (low, L) or .24% of body weight (high, H; dry matter basis). Cows received daily doses of an antibiotic mixture (1 g neomycin and .125 g bacitracin) or saline in the duodenum. Prairie hay dry matter (DM) intake increased (P less than .05) linearly with SBM supplementation, being 25 and 40% greater for L and H than for C, respectively. Ruminal fluid concentrations of NH3-N and total volatile fatty acids increased (P less than .05) linearly as SBM was added to the diet. Ruminal fluid dilution rate increased linearly and particulate passage rate increased (P less than .05) quadratically with increasing SBM. True ruminal digestibilities of organic matter, NDF and N increased (P less than .10) quadratically with increasing SBM (organic matter; 50.3, 57.9 and 58.3%; NDF: 54.7, 60.4 and 59.8%; N: 17.5, 45.1 and 51.4% for C, L and H, respectively). Main effects of antibiotic administration were not significant. Increases in DM intake when SBM was given were large compared with the small elevations in ruminal digestion, implying that metabolic regulation was modifying intake of low-quality forage.     

Growth and carcass characteristics and serum growth hormone, prolactin and insulin profiles in Debouillet lambs treated with ovine growth hormone and(or) zeranol

Sixteen Debouillet wether lambs (approximately 3 mo old) were placed indoors in 1.5- x 3-m pens (14 h light:10 h dark) 28 d after weaning. Lambs received no implant or a 12-mg zeranol implant on d-2 (eight lambs/group). Two days later (d 0), animals received either 0 or 2.5 mg ovine growth hormone (oGH, eight lambs/group) s.c. on alternate days for 42 d. Animals had ad libitum access to water, salt, mineral and a pelleted alfalfa diet (16% CP). After 42 d, lambs were slaughtered to evaluate carcass traits, organ weights and femur characteristics. Zeranol by oGH interactions were not detected (P greater than .20). Zeranol increased (P less than .05) BW, improved (P less than .05) feed:gain during the first 20 d and increased (P less than .10) feed intake during the last 22 d of the 42-d trial compared with controls. Carcass characteristics were not altered (P greater than .10) by 12 mg zeranol. Serum insulin and prolactin were elevated (P less than .05), but serum GH was not influenced by zeranol compared with controls. Exogenous oGH decreased feed intake (P less than .10) and improved feed:gain (P less than .05) during the initial 20 d compared with controls, but did not influence (P greater than .20) these variables during the last 22 d of the study. Carcass traits were not influenced (P greater than .10) by oGH. Exogenous ovine GH dramatically elevated (P less than .05) serum GH, but did not affect serum insulin or prolactin (P greater than .10).(ABSTRACT TRUNCATED AT 250 WORDS)     

Mineral status of beef cows and sheep on spring pasture fertilized with kieserite

The utilization of minerals in orchardgrass (Dactylis glomerata L.) fertilized with kieserite (2,240 kg/ha) was examined in spring with lactating beef cows and wether lambs. Kieserite increased the concentration of Mg in vegetative herbage from .22 to .29% ( P less than .01) and of S from .20 to .29% (P less than .01), with little effect on other minerals. Fertilization also increased (P less than .01) apparent absorptions of Mg and S by lambs fed cut orchardgrass, from 24.5 to 36.5% and from 58.6 to 66.9%, respectively, and increased (P less than .01) apparent Mg retention from +.16 to +.33 g/day. Fertilization did not affect dry matter digestibility or apparent absorption of N, Ca or P by lambs. composition of blood and saliva of beef cows grazing fertilized and unfertilized pastures was determined during a 2-week period in early spring. Cows grazing kieserite-treated pastures showed a small increase (P greater than .05) in serum Mg, ultrafiltrable Mg and red blood cell (RBC) Mg, and fewer cows on the fertilized pastures showed severe hypomagnesemia (less than 1.0 mg/100 ml) after the first day of grazing. The decline in blood Mg concentrations was not accompanied by hypocalcemia or by changes in serum Na or K concentrations, but serum inorganic P decreased (P less than .01) markedly during the first 10 days of grazing. Ultrafiltrable Ca in blood was affected by fertilizer and period, but it is questionable whether either ultrafiltrable Mg or Ca would provide a more sensitive index of mineral status than serum concentrations. Concentrations of K, NA and P in saliva were more susceptible to fertilizer and period effects than were concentrations in blood, although all values fell within a normal range. There was no evidence of an inverse relationship between serum Mg and concentration of K in saliva of cows after a change from a winter-type diet to spring herbage containing high levels of N and K.