Effects of supplemental protein source and level of urea on intestinal amino acid supply and feedlot performance of lambs fed diets based on alkaline hydrogen peroxide-treated wheat straw.

Two experiments were conducted to determine the effects of supplemental CP source and level of urea on intestinal amino acid (AA) supply and feedlot performance of lambs fed diets based on alkaline hydrogen peroxide-treated wheat straw (AHPWS). In Exp. 1, five cannulated (ruminal, duodenal, and ileal) crossbred wethers (61 kg) were used in a 5 x 5 Latin square design. Treatments consisted of different sources of CP and included soybean meal (SBM), a combination of urea, distillers dried grains (DDG), and fish meal, each provided an equal portion of supplemental CP (UDF), and three levels of urea (17, 33, and 50% of supplemental CP) fed in combination with DDG (U17, U33, and U50). Organic matter and N digestibilities decreased (P less than .05) when lambs were fed U17 compared with those fed SBM. There were no differences (P greater than .05) in bacterial N or AA flows to the duodenum due to CP source despite large differences in ruminal NH3 N concentrations and lower ruminal OM digestion when lambs were fed U17. Duodenal nonbacterial N and AA flows were highest (P less than .05) in lambs fed U17 and UDF and lowest when lambs were fed U50 and SBM. Lysine concentration in duodenal digesta decreased with incremental increases in DDG. In Exp. 2, 30 individually penned ram lambs (33 kg) were allotted to five CP treatments in a randomized complete block design. Treatments were similar to those of Exp. 1, with the exception that U17 was replaced by a 14% CP diet with SBM as the supplemental CP source; all other diets were formulated to contain 12% CP. Lambs fed U50 had decreased (P less than .08) ADG and gain/feed compared with all other treatments, and lambs fed UDF had greater (P less than .05) ADG and gain/feed than lambs fed U33. It was concluded that 17% of the supplemental CP from urea seems adequate to maximize bacterial protein synthesis and that no more than 33% of the supplemental CP should be provided by urea in diets based on AHPWS. Feeding a combination of ruminally resistant protein sources with complementary AA profiles of lysine and methionine (UDF) may enhance quality of protein entering the duodenum and feedlot performance.     

Effects of dietary phosphorus, soil ingestion and dietary intake level on performance, phosphorus utilization and serum and alimentary tract mineral concentrations in lambs

Two experiments were conducted with lambs fed concentrate-based diets to study the effects of dietary P and soil ingestion on performance, P utilization and mineral composition of serum and alimentary tract contents. In Exp. 1, 20 wether lambs were fed diets for 21 d in a 2 X 2 factorial arrangement of treatments with .2 or .3% total dietary P and O or 9% added Florida Ultisol (highly weathered soil with high P-fixation capacity) containing 4,600 and 6,400 mg/kg total Al and Fe, respectively. True P absorption increased (P less than .05) from 30 to 42% and from 37 to 54% when soil was added to the basal and high P diets, respectively. In Exp. 2, 24 wether lambs were assigned randomly to a 2 X 2 X 2 factorial arrangement of treatments. Lambs were fed during a 70-d period using diets described previously on either a restricted or an ad libitum basis. Soil increased Fe concentration in ruminal fluid (P less than .05) and ash percentage (P less than .001) in ruminal solids and feces. Aluminum concentration in ruminal solids and feces and Fe in ruminal solids were increased (P less than .001) by soil addition, whereas concentrations of Ca, Mg, P, Zn, Cu and Mn in ruminal solids and feces were decreased (P less than .01) by soil addition. There were time X P interactions on serum inorganic P (P less than .01) and Mg (P less than .05) concentrations. Although high in P-fixing capacity, soil fed to lambs in these experiments improved P utilization. Lambs appeared to be able to adapt to changes in intake of dietary minerals in soil, possibly through adaptation of ruminal microflora or a redistribution of body mineral pools.     

Effect of ruminal escape protein and fat on nitrogen utilization in lambs exposed to elevated ambient temperatures.

Eight wether lambs (mean BW = 28.8 kg) with ruminal and abomasal cannulas were assigned to either thermally neutral or high ambient temperature treatments. Within each temperature, lambs were randomly allotted to dietary treatments consisting of a basal diet (60% corn and 24% cottonseed hulls) either with (high; 11.4% CP) or without (control; 10.1% CP) added ruminal escape CP as fish meal and with (high) or without (control) 5% added ruminally inert fat in a 2 x 2 factorial treatment arrangement using a Latin square design. Lambs were fed 606 g of DM/d in each period, which consisted of a 10-d adjustment followed by 6 d of sample collection. High temperature increased (P less than .05) respiration rate, evaporative water loss, and rectal temperature. When compared with controls, lambs fed high escape CP retained more N when exposed to high temperatures (2.8 vs 3.6 g of N/d) and less N at neutral temperatures (3.3 vs 3.1 g of N/d; temperature x escape CP; P less than .05). Retention of N was greater (P less than .05) in lambs fed high than in those fed control fat (3.8 vs 2.7 g/d). Lambs fed high vs control escape CP had greater abomasal feed N flow (percentage of intake) when fed high-fat diets (77.3 vs 56.1%) but similar dietary N flow when fed control fat diets (55.8 vs 54.3%; fat x escape CP; P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of increasing crude protein level on nitrogen retention and intestinal supply of amino acids in lambs fed diets based on alkaline hydrogen peroxide-treated wheat straw.

The effects of increasing dietary CP level on N retention (Exp. 1) and intestinal supply of amino acids (AA; Exp. 2) were studied in lambs fed diets based on alkaline hydrogen peroxide-treated wheat straw (AHPWS). Soybean meal (SBM) was substituted for corn to increase CP level in both experiments. In Exp. 1, an incomplete design for the two-way elimination of error was used to allot 24 ram lambs (mean BW = 25 kg) within breed to six CP levels (6, 8, 10, 12, 14, and 16% of DM). Neutral detergent fiber digestibility and N retention increased quadratically (P = .06 and P less than .01, respectively) with increasing CP level. Nitrogen retention, expressed as a percentage of N intake, was greatest for lambs fed 12% CP (20.7%) but was greatest for lambs fed 14% CP when expressed as grams per day (4.0 g/d). In Exp. 2, five multicannulated St. Croix lambs (34 kg) were used in a 5 x 5 Latin square design. Treatments were 8.5, 11, 13.5, 16, and 18.5% dietary CP. Chromic oxide was used as a digesta flow marker and purines were used as a bacterial marker. Protein level had no effect on extent of dietary CP degradation in the rumen (69 +/- 3.2%). True ruminal OM digestibility increased (P less than .01) linearly and ruminal fluid NH3 N concentration increased (P less than .01) quadratically with increasing CP level. Total, bacterial, and nonbacterial N and AA flows to the duodenum increased (P less than .05) linearly with increasing CP level. Duodenal AA profile (g/100 g total AA) was altered slightly. The essential AA valine, isoleucine, phenylalanine, lysine, and arginine increased (P less than .05) and methionine decreased (P less than .05) in proportion to other AA with increasing CP level. Flows of all essential AA increased with increasing CP level. Apparent small intestinal N and AA disappearance increased linearly (P less than .05) and apparent total tract N digestibility increased (P less than .01) quadratically with increasing CP level. These data are interpreted to indicate that maximal N retention and fiber digestibility in diets based on AHPWS are obtained at 12% CP, even though the intestinal supply of AA continues to increase with increasing CP level. Supplementation of diets based on AHPWS with an extensively degraded protein source (SBM) does not substantially alter the profile of AA entering the duodenum compared to the AA profile of bacterial protein.     

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.     

Effect of protein supplementation on expression and distribution of urea transporter-B in lambs fed low-quality forage

Two experiments were conducted to determine the effects of ruminal protein degradability, supplementation frequency, and increasing dietary protein on the expression and distribution of urea transporter-B (UT-B) in lambs fed low-quality forage (mature crested wheatgrass hay; 4.2 to 4.7% CP). In Exp. 1, 15 Dorset wether lambs (initial BW=45.8+/-1.3 kg) were blocked by initial BW and assigned to 1 of 3 treatments within a randomized complete block design for 28 d, with supplements fed to achieve 7, 10, or 13% total dietary CP. In Exp. 2, 13 Dorset wether lambs (initial BW=34+/-4 kg) were used in a completely randomized design and given 1 of 4 isonitrogenous supplements: 1) ruminally degradable protein (RDP) fed daily (n=3), 2) RDP fed on alternate days (n=3), 3) ruminally undegradable protein (RUP) fed on alternate days (n=3), or 4) a 50:50 mixture of RDP and RUP fed on alternate days (n=4) for 18 d. Alternate-day treatments were fed at twice that of daily supplementation. On the last day of both experiments, lambs were killed and samples taken for Western blot analyses for UT-B. Immunoblotting using a rabbit polyclonal antibody to UT-B confirmed the presence of distinct 32-kDa (consistent with a nonglycosylated UT-B protein) and 47-kDa (probable N-glycosylated form of UT-B) protein bands in all 9 tissues analyzed. In both experiments, the liver, dorsal rumen, reticulum, and ventral rumen displayed strong bands at 32 kDa and lighter bands at 47 kDa, whereas the cecum, large colon, spiral colon, and parotid salivary gland displayed slight 32-kDa bands and stronger, more visible bands at 47 kDa. Both protein bands were apparent in the kidney at similar visual intensities in Exp. 1, whereas the relative intensities of the 2 UT-B bands in the kidney were variable, and appeared somewhat reciprocal among animals in Exp. 2. Although the abundance of the 47-kDa UT-B band in the ventral rumen was greater (P=0.03) in lambs fed RDP daily in Exp. 2, no other treatment differences (P >or= 0.15 to 0.99) in the abundance of the 32- or 47-kDa UT-B proteins within tissues were observed in either experiment. Although protein supplementation strategy had little effect on UT-B expression in tissues other than the ventral rumen, differences in the degree of glycosylation of UT-B across tissues may provide insight into its regulation.     

Effects of dairy biomass protein on ruminal fermentation and site and extent of nutrient digestion by lambs

Twelve ruminally and abomasally cannulated lambs (27 +/- 1.16 kg) and 16 intact lambs (28 +/- 1.49 kg) were used in two trials to study the influence of dairy biomass (a cheese processing wash water sludge) as a protein source in medium-concentrate diets. In Trials 1 and 2, lambs were assigned to one of three concentrate diets containing 0, 10 or 20% biomass with an additional positive control diet in Trial 2. Biomass provided 27.4 and 52.7% of the CP in 10 and 20% biomass treatments, respectively. Diets were similar in N content and were fed at 3.5% of initial BW (as fed). Apparent ruminal OM and N digestibilities were lower (P less than .10) in lambs receiving 20% biomass than in lambs fed 0 or 10% biomass. Postruminal N digestibility was higher (P less than .10) for lambs fed 20% biomass. Apparent OM and N digestibilities in both trials were reduced (P less than .10) in lambs fed 20% biomass. Apparent OM and N digestibilities in both trials were reduced (P less than .10) in lambs receiving 10% biomass compared to lambs fed other treatments. Plasma urea N concentration (mg/dl) was higher (P less than .10) at 3 and 9 h after feeding in lambs receiving 10 and 20% biomass compared with control lambs. Although N retention was unchanged, fecal N excretion was higher (P less than .10) and urinary N excretion was lower (P less than .10) in lambs consuming 10 and 20% biomass treatments. Non-ammonia N and feed N flow (g/d) were higher (P less than .10) in abomasal contents of lambs consuming 20% biomass vs other dietary treatments but N digestibility was decreased. In conclusion, digestibility was decreased and site of N digestion was altered by feeding biomass.     

Influence of L-Carnitine on Performance and Ruminal and Blood Metabolites of Grazing Calves and Finishing Lambs

Three experiments were conducted to study the influence of level and type of L-carnitine (LC) on performance and rumiasl and plasma metabolites of weanling calves and finishing lambs. Weanling calves (84) grazing dormant dallisgrass-bermudagrass forage were fed a 20% CP supplement to provide 0, 0.5, 1, or 2 g of ruminally unprotected (RUP) LC per calf daily in Exp. 1. There was a linear increase (P=0.01) and cubic response (P=0.03) to RUP LC in growth rate and quadratic changes (P=0.01) in plasma ammonia N (PAN) and plasma urea N (PUN). In Exp. 2, 32 lambs were individually fed 14% CP diets containing 0, 50, 100, or 200 ppm RUP LC or ruminally protected (RP) LC in a 2 × 4 arrangement of treatments. Lambs gained BW faster (P=0.03) and more efficiently (P=0.07) as the LC level increased to 100 ppm and then declined at 200 ppm (quadratic response). Longissimus area decreased (P=0.03), and fat cover tended (P=0.15) to decline, at 50 and 100 ppm LC and increased at 200 ppm (linear and quadratic response). Ruminal ammonia N levels were reduced at 50 ppm LC but increased at greater LC levels (linear, quadratic, and cubic response, P=0.02). Plasma carnitine concentrations increased (P=0.01) as the dietary level of LC increased. Protected LC was more effective than RUP LC in increasing growth rate (P=0.06) and reducing PAN (P=0.1). In Exp. 3, 16 wether and 16 ewe lambs were individually fed corn-based or soybean hull-based diets with 0 or 100 ppm RP LC in a 2 × 2 arrangement of treatments. Lambs fed RP LC gained BW faster and more efficiently (P=0.04) than lambs that were not fed LC. Lambs fed corn-based and soybean hull-based diets responded similarly to RP LC; however, performance was greater (P=0.03) for lambs fed the corn-based diet. Gender of lambs did not influence the response to diet or RP LC. Supplementing the diet with 100 ppm RP LC reduced (P=0.01) ruminal pH and ammonia N. Plasma carnitine concentrations were increased (P=0.01), and PAN was decreased (P=0.04) by feeding 100 ppm RP LC. Ruminnaly unprotected and RP LC were effective in improving growth rate in ruminants; the latter appeared to be more effective in finishing lambs. L-carnitine reduced ruminal ammonia N and plasma glucose and, in some cases, PAN and PUN.     

Effects of ruminal escape proteins and canola meal on nitrogen utilization by growing lambs

The effects of ruminal escape proteins and canola meal (CM) on N utilization by growing lambs were evaluated in two experiments. In both experiments, seven supplemental dietary protein treatments were fed. For each of these protein treatments a 3 x 3 Latin square metabolism trial was conducted, using two sets of three lambs and three periods. Within square treatments were 1.4, 1.7 and 2.0 times maintenance intake levels. In Exp. 1, protein treatments were control (7.0% CP, DM basis), urea fed at 9.5 or 12% dietary CP, CM fed at 9.5 or 12% dietary CP and a 50:50 (N basis) mixture of blood meal/corn gluten meal (BC) fed at 9.5 or 12% dietary CP. In Exp. 2, protein treatments were urea, 64% urea and 36% BC (all mixtures on a N basis), 36% urea and 64% BC, BC, 50% CM and 50% BC (CM/BC), CM and soybean meal (SBM), all at 10.5% CP. In Exp. 1, apparent N digestibility (AND) was lower for CM diets than for urea (P = .13) and BC (P less than .05) diets (49.0 vs 50.6 and 51.3%, respectively). Absorbed N was utilized with similar efficiencies for all supplemental protein sources. Dietary CP and digestible protein (DP) were closely related (DP = .879[CP%] -3.66; r2 = .91), indicating that for urea, CM and BC total tract N digestibility was not influenced by theoretical ruminal degradability. In Exp. 2, N balance and N utilization efficiency indicated that the optimal extent of ruminal protein degradation was about 50%. Nitrogen balance was similar for the CM, CM/BC and SBM treatments.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of two levels of enzyme preparation on ruminal fermentation, particulate and fluid passage and cell wall digestion in wether lambs consuming either a 10% or 25% grain diet

Effects of a fungal enzyme preparation on ruminal fermentation, digesta kinetics and cell wall digestion were studied. Either 0, 22 or 25 g/d of enzyme preparation was offered to nine ruminally cannulated Rambouillet or Columbia wether lambs (avg wt 28.6 kg) in two randomized complete block experiments. An alfalfa hay-corn mixture at 2.1% of body weight (10% corn) was used in Exp. 1. In Exp. 2, 2.7% of body weight (25% corn; Exp. 2) was fed. Ruminal samples were collected at 0, 4, 8, 12 and 24 h postfeeding on d 17 of each 22-d period to measure fluid dilution rate and fermentation characteristics. An intraruminal dose of Yb-labeled hay followed by fecal sampling on d 19 through 22 was used to estimate particulate passage and fecal output. Ruminal pH, NH3 concentrations, total volatile fatty acid and proportion of individual acids were not influenced (P greater than .10) by the addition of either level of enzyme preparation in either Exp. 1 or 2. Dry matter digestibility also showed no effect (P greater than .10) of enzyme preparation added to either diet. In Exp. 1, wethers receiving 35 g/d of the enzyme preparation had greater cell wall digestion (49.8%; P less than .05) than wethers receiving either 22 g/d or no enzyme preparation (45.7 and 42.9%, respectively). In Exp. 2, with a 25% corn diet, no influence (P greater than .10) of enzyme preparation was noted on cell wall digestibility. Particulate and ruminal fluid passage rate parameters remained unchanged (P greater than .10) by the addition of either level of enzyme preparation, regardless of the diet fed.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of supplemental sodium bicarbonate on nutrient digestibilities and ruminal pH measured continuously

A technique was used to monitor continuously ruminal pH using a strip-chart recording pH meter. Ruminal pH measurements were made in four ruminal-cannulated crossbred wether lambs (ag initial weight, 42.5 kg). For l.5 h daily, lambs were given ad libitum access to 50% concentrate-50% chopped orchardgrass hay diets supplements with 0, l.5, 3.0 and 4.5% sodium bicarbonate (NaHCO3). A split-plot Latin-square design was used to evaluate NaHCO3 level and day of adaptation on the percentage of time (%T) that ruminal pH was less than 6.6, 6.2, 5.8, 5.4 and 5.0. No effect due to day of adaptation existed for ruminal pH measurements (P more than .10), while the effect of dietary NaHCO3 level was quadratic (P more than .01) for the %T that ruminal pH was less than 5.4. To evaluate the effects of NaHCO3 on nutrient digestion, the same diets were fed to eight wether lambs (avg initial weight, 38 kg) at 85% of their ad libitum intake in a replicated 4 x 4 Latin-square digestion trial. Digestibilities of dry matter (DM), organic matter, N and fiber fractions were not different due to level of NaHCO3 (P greater than .10). Ash digestibility increased with increasing levels of dietary NaHCO3 (P less than .01). Four ruminal-cannulated mature Hereford steers were also given ad libitum access to the diets in a split-plot Latin-square trial to evaluate effects of dietary NaHCO3 level on ruminal pH and in situ digestion of soybean meal N and orchardgrass DM. During incubation of the dacron bags for 3, 6, 9, 12, 24 and 36 h also increased linearly with increasing level of NaHCO3. Ruminal solid and liquid dilution rates were not affected by level of supplemental NaHCO3 (P greater than .10). The results of these trials suggest that increasing level of dietary NaHCO3 greatly increases the proportion of time ruminal pH is above critical levels for ruminal protein and dry matter digestion, but does not affect total tract nutrient digestion when 50% concentrate diets are fed.     

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.     

Evaluation of dairy food processing wash water solids as a protein source: III. Nitrogen utilization by heifers fed medium-concentrate diets

Eight multicannulated heifers (average BW 415 +/- 34 kg) were used in a replicated 4 x 4 Latin square to evaluate fluid milk processing wash water solids (WWS) as a dietary N source. Heifers were fed corn/cottonseed hull-based diets containing soybean meal (control, 0% WWS N) or WWS replacing soybean meal at 33, 67, or 100% of supplemental dietary N. Total tract and ruminal DM and OM digestibilities decreased linearly or cubically (P less than .05) as dietary WWS N increased. Total ruminal VFA concentration (P less than .05) and propionic acid molar proportion (P less than .10) were greater in heifers fed 0 vs 100% WWS N. Heifers fed 0% WWS N had the greatest (P less than .05) ruminal ammonia concentration at all sampling times. Dietary WWS did not affect (P greater than .10) ruminal pH, fluid dilution rate, fluid flow, fluid volume, or turnover time. Total tract N digestibility decreased quadratically (P less than .10) with increasing WWS N in the diet. Supplemental WWS N did not affect (P greater than .10) flow of duodenal ammonia N or bacterial N, or efficiency of microbial N synthesis. Diets containing WWS N resulted in a cubic increase (P less than .10) in duodenal flow of essential amino acids compared with 0% WWS N; however, there were no differences in small intestinal amino acid disappearance. Data indicate that WWS can replace 33% of the soybean meal N in a corn/cottonseed hull-based diet without decreasing ruminal fermentation, fluid digesta kinetics, microbial efficiency, or small intestinal amino acid utilization.     

Effects of corn processing and dietary fiber source on feedlot performance, visceral organ weight, diet digestibility, and nitrogen metabolism in lambs

In Exp. 1, early-weaned Targhee and Polypay crossbred lambs (60 ewes and 66 rams; initial BW 24 +/- 1.0 kg) were used in a 2 x 3 factorial experiment to determine the effects of corn processing (whole shelled corn [WSC] or ground and pelleted corn [GC]) in combination with supplemental fiber (none [control]; soybean hulls, SBH [highly digestible]; or peanut hulls, PH [highly indigestible]) on DMI, ADG, feed efficiency, and visceral organ weight. For the total trial, WSC resulted in a 4% increase (P < .01) in ADG vs GC, and supplemental fiber resulted in increased (P < .01) DMI and ADG vs the control diet. Experiment 2 was conducted using 12 Targhee and Polypay crossbred wether lambs (initial BW 25 +/- 7 kg) to determine the effects of corn processing and fiber source in high-concentrate diets on diet digestibility and N retention using the same diets as in Exp. 1. Lambs fed WSC had greater (P < .001) apparent N digestion, true N digestion, and N retention (P < .01) than those fed GC. The apparent digestibilities of DM, OM, and NDF were greater (P < .001) for WSC than for GC diets. Peanut hulls resulted in decreased (P < .01) DM, OM, and NDF apparent digestibilities compared with the control and SBH diets. Starch digestion was not affected (P > .10) by diet. Whole corn resulted in improved DM, OM, NDF, and N digestibility compared with GC. Overall, both the SBH and PH diets resulted in greater DMI and ADG than the control diet, which lacked supplemental fiber.     

Digestibility and dry matter intake of diets containing alfalfa and kenaf

Two experiments were conducted to determine the dietary value of pellets containing kenaf (Hibiscus cannabinus cv. 'Everglade 41') hay. Averaged across both experiments, kenaf pellets contained 82.6% kenaf hay, 16.6% liquid molasses, and 0.8% mineral oil. The chemical composition of the kenaf pellet was 12.6% crude protein (CP), 41.2% neutral detergent fiber (NDF), and 14.4% acid detergent fiber (ADF). In Exp. 1 (digestion and N balance trial), 18 lambs (body weight [BW] = 36.4 kg) were blocked by BW. Lambs were randomly assigned within a block to Diet 1 (59.5% corn and 40.5% alfalfa pellet), Diet 2 (59.7% corn, 28.4% alfalfa pellets, and 11.9% kenaf pellets), or Diet 3 (59.6% corn, 16.5% alfalfa pellets, and 23.9% kenaf pellets). Diets were formulated so that CP was the first-limiting nutrient. Each diet was limit-fed at 2.4% of BW. Replacing alfalfa pellets with kenaf pellets tended to decrease (P = 0.10) CP and ADF intakes, but increased (P = 0.01) DM digestibility. Diet had no effect (P = 0.33) on N balance. In Exp. 2 (dry matter [DM] intake trial), 32 lambs (BW = 30.4 kg) were blocked by gender and BW. Within a block, lambs were randomly assigned to one of four diets in a 2 x 2 factorial arrangement. Main effects were hay (bermudagrass or fescue) and supplemental protein source (kenaf or alfalfa pellets). Lambs were housed in individual pens with ad libitum access to the assigned hay. Supplemental protein was fed (185 g of DM) once daily. Hay intake was measured weekly for 8 wk. Lambs consumed more (P = 0.002) fescue than bermudagrass hay (743 vs 621 g/ d). Lambs fed fescue hay gained weight more rapidly (P = 0.001) than lambs fed bermudagrass hay (120 vs 72 g/d). Hay intake and ADG were similar (P = 0.90) for lambs fed alfalfa or kenaf pellets. Kenaf hay mixed with molasses and mineral oil can be formed into a pellet. In the diets used in this experiments, kenaf pellets can replace alfalfa pellets in diets fed to lambs without altering forage intake, gain, or N retention.     

Body weight and tissue gain in lambs fed an all-concentrate diet and implanted with trenbolone acetate or grazed on alfalfa

Targhee x Hampshire lambs (average BW 23 +/- 1 kg) were used in two experiments to determine the effects of finishing on concentrate with an anabolic implant or forage grazing after concentrate feeding on growth, organ and viscera weights, and carcass tissue accretion. In Exp. 1 and 2 lambs were penned by sex and assigned for slaughter at initial (23 kg), intermediate (37 kg), or end BW (ewes, 47.7; wethers 50.4 kg). From 23 to 37 kg BW, lambs were fed all-concentrate diets in drylot (DL) or grazed on alfalfa (ALF). Experiment 1 was a 2 x 2 factorial with 28 lambs; factors were wether vs ewe lambs and unimplanted vs DL implanted with trenbolone acetate-estradiol benzoate. There were no differences in organ and viscera weights due to implant status. However, ADG (P < .03) and lean gain (P < .02) were greater for implanted than for unimplanted wethers (507 vs 357 g and 1,314 vs 656 g, respectively). Ewes did not respond to the implant. Fat accretion was not affected by implantation. Experiment 2 was a 2 x 3 factorial with 42 lambs; factors were wether vs ewe lambs and drylot during growing and finishing phases (DL-DL) vs drylot during growing and alfalfa grazing during finishing (DL-ALF) vs alfalfa grazing during growing and finishing phases (ALF-ALF). In Exp. 2, ADG of DL-DL lambs was greater (P < .01) than ADG of DL-ALF or ALF-ALF lambs. Lambs on ALF-ALF had smaller (P < .05) livers and rumen/reticulum weights but heavier (P < .04) kidney, omasum, small and large intestine, and cecum weights than those on DL. In Exp. 2, DL-ALF and ALF-ALF lambs had overall hindsaddle lean gain equal to those on DL-DL with less mesenteric fat and 100 g less separable fat. Finishing lambs on alfalfa reduced fat accretion without decreasing lean accretion, whereas trenbolone acetate implants for lambs fed concentrate increased BW gain and lean accretion without affecting fat accretion.     

Effects of animal-to-animal exchange of ruminal contents on the feed intake and ruminal characteristics of fed and fasted lambs

Four Suffolk x Hampshire wether lambs averaging 55 kg with permanent ruminal cannulas were used in a 4 x 4 Latin square design to determine the effects of exchange of ruminal contents between fed and fasted lambs on subsequent DMI and ruminal characteristics. Lambs were fed a pelleted 70% roughage diet at 2% of BW for 17 d. During each period of the Latin square two lambs were deprived of feed and water for 3 d. At the end of the fasting period ruminal contents from one fed and one fasted lamb were exchanged. Lambs were then given ad libitum access to feed for 8 d, during which DMI, feeding pattern, and ruminal characteristics were monitored. Measurements of ruminal volume determined by total collection and indigestible marker (lithium sulfate) suggested that only about 50% of total ruminal contents were actually exchanged. Fasted lambs had lower (P less than .05) DMI, ruminal fermentative capacity, ruminal DM weight, and ruminal DM percentage than fed lambs during the first 4 d of realimentation. Exchange of ruminal contents did not (P greater than .10) affect DMI, feeding pattern, ruminal fluid pH, ruminal fermentative capacity, ruminal contents DM percentage, ruminal nucleic acid concentration, or VFA. Dosing fasted lambs with ruminal contents from nonfasted lambs reduced (P less than .05) ruminal liquid volume, dry weight of ruminal contents, and propionate concentration. Results of this trial are interpreted to indicate that although decreased ruminal function is a factor in the low feed intakes of fasted ruminants, the possibility of increasing postfast feed intake via improved ruminal function is limited because other metabolic factors may play a more important role.     

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 the novel urease inhibitor N-(n-butyl) thiophosphoric triamide on ruminant nitrogen metabolism: II. Ruminal nitrogen metabolism, diet digestibility, and nitrogen balance in lambs

Three lamb metabolism experiments were conducted to investigate the effects of chronic administration of the novel urease inhibitor N (n-butyl) thiophosphoric triamide (NBPT) on ruminal N metabolism, fermentation, and N balance. In Exp. 1, ruminally cannulated wethers (n = 28; 45.0 +/- .9 kg) were administered one of seven doses of NBPT (0 [control], .125, .25, .5, 1, 2, or 4 g of NBPT daily) and fed a common cracked corn/cottonseed hull-based diet twice daily containing 2% urea at 2.5% of initial BW for the duration of the 15-d experiment. Overall, NBPT decreased (linear P < .0001; quadratic P < .001) ruminal urease activity, resulting in linear increases (P < .0001) in ruminal urea and decreases in ruminal NH3 N concentrations. However, the detection of an NBPT x day interaction (d 2 vs 15; P < .01) indicated that this depression in urea degradation diminished as the experiment progressed. Increasing NBPT linearly decreased (P < .01) total VFA concentrations on d 2 of the experiment, but it had no effect (P > .10) on d 15. Increasing NBPT had no effect (P > .10) on DM or ADF digestibilities, but it linearly decreased (P < .01) N digestibility. Supplementing NBPT produced a linear increase (P < .05) in urinary N excretion and a linear decrease (P < .01) in N retention. In Exp. 2, ruminally cannulated wethers (n = 30; 46.8 +/- .6 kg) were fed one of two basal diets (2.0 vs 1.1% dietary urea) at 2.5% of initial BW and dosed with either 0 (control), .25, or 2 g of NBPT daily for the duration of the 15-d experiment. There were no NBPT x dietary urea interactions (P > .10) for Exp. 2. Increasing NBPT depressed (linear and quadratic P < .0001) ruminal urease activity, producing linear (P < .0001) increases in urea N and linear decreases in NH3 N in the rumen. As in Exp. 1, an NBPT x day interaction (P < .05) was noted for urea, NH3 N, and total VFA concentrations; the maximum response to NBPT occurred on d 2 but diminished by d 15 of the experiment. Administration of NBPT did not influence (P > .10) DM, ADF, or N digestibilities in Exp. 2. In Exp. 3, wether lambs (n = 30; 26.4 +/- .7 kg) were subjected to the same treatment regimen as in Exp. 2 for a 14-d N balance experiment. Although several NBPT x dietary urea interactions (P < .05) were noted, increasing NBPT did not affect (P > .10) N digestibility. Administration of NBPT quadratically increased (P < .10) urinary N excretion, producing a linear decrease (P < .05) in N retention. These results suggest that although NBPT is capable of inhibiting ruminal urease short-term, the ruminal microflora may be capable of adapting to chronic NBPT administration, thereby limiting its practical use in improving the utilization of dietary urea.     

Basal and hormone-stimulated metabolism in lambs varies with breed and diet quality

The present study investigated the effects of breed and diet quality on basal and hormone-stimulated energy metabolism in lambs. Twenty-four 7-mo-old merino (MM; n = 12) and second-cross (2X; n = 12) lambs were maintained indoors and fed ad libitum either a low-quality (7.8% crude protein [CP] and 8.1 MJ metabolizable energy [ME]/kg dry matter [DM]) or a moderate-quality (17.6% CP and 9.1 MJ ME/kg DM) diet in a crossover design. After 3 wk of feeding, lambs were injected intravenously with insulin (10 μg/kg body weight [BW]) and epinephrine (0.8 μg/kg BW) on consecutive days and blood samples were collected at -30, -15, -1, 3, 6, 10, 15, 20, 30, 45, 60, 90, and 120 min relative to time of injection. Lambs fed the low-quality diet had lower DM (P < 0.001), CP (P < 0.01), and ME (P < 0.001) intakes than lambs fed the moderate-quality diet. Baseline nonesterified fatty acid (NEFA) concentrations were higher (P < 0.001) in lambs fed a low-quality diet than in those fed a moderate-quality diet but there were no breed differences. Second-cross lambs had higher basal plasma concentrations of glucose (P < 0.001), lactate (P < 0.001), and cortisol (P < 0.02) than the MM lambs, although there was no effect of diet on any of these plasma variables. Insulin injection caused a rapid hypoglycemic response in all lambs but the response was more pronounced (P < 0.01) in MM lambs compared with 2X lambs. The cortisol response to insulin was twice as great (P < 0.05) in MM lambs compared with 2X lambs. There was a rebound in plasma NEFA concentrations after approximately 30 min postinjection that was most pronounced (P < 0.01) in MM lambs. Epinephrine injection caused a rapid increase in plasma NEFA, which tended to be lower in lambs fed the moderate-quality diet (P = 0.07) than in those fed the low-quality diet, but did not differ between breeds. Epinephrine injection caused rapid hyperglycemia, with the response being lower (P < 0.006) in lambs fed the moderate-quality diet compared with those fed the low-quality diet and greater (P < 0.050) in 2X than in MM lambs. Epinephrine injection caused a rapid increase in plasma lactate that tended to be greater (P = 0.07) in 2X lambs compared with MM lambs. The present study demonstrated clear breed differences in basal and hormone-stimulated metabolism, such that the 2X lambs appeared to be less sensitive to insulin and more sensitive to epinephrine than the MM lambs. These metabolic differences may be related to the fundamental differences in physiology that are associated with meat and wool production from 2X and MM breeds, respectively. They may also be related to adaptation of the MM breed to harsh environments through the ability of the body to metabolize fat resources, which are an efficient source of energy for survival.