Effects of zinc and sodium monensin on ruminal degradation of lysine-HCl and liquid 2-hydroxy-4-methylthiobutanoic acid.

Four nonlactating, mature, Holstein cows were fitted with ruminal cannula and used in a 4 x 4 Latin square-designed experiment to evaluate the impact of supplemental Zn and monensin on ruminal degradation of Lys and liquid 2-hydroxy-4-methylthiobutanoic acid (HMB). Cows were fed 4.54 kg (as fed) of alfalfa hay top-dressed with 4.54 kg (as fed) concentrate once daily. Concentrates were formulated to provide 0 or 500 mg/kg of Zn as ZnSO4 and 0 or 40 mg/kg of monensin in the total diet. Zinc supplementation provided approximately 22-fold greater dietary Zn than estimated by NRC requirements. On d 14 of each period, cows were dosed via the rumen cannula with 50 g of HMB and 100 g of Lys-HCl, and the concentrations of Lys and HMB were monitored every 0.5 h for 8 h. Supplemental Zn tended to decrease the proportion of acetate in ruminal fluid postfeeding and increased the proportion of propionate in ruminal fluid postfeeding. Supplemental Zn increased mean fluid passage rate from the rumen. Monensin decreased the proportion of acetate and increased the mean proportion of propionate in ruminal fluid, resulting in a decrease in the ratio of acetate to propionate. Monensin also increased the mean fluid passage rate from the rumen. Neither Zn nor monensin affected the apparent rate of ruminal disappearance of HMB or Lys. However, Zn and monensin interacted to alter the ruminal degradability of free Lys but not HMB. These data indicate that Zn and monensin may interact to alter ruminal degradability of free amino acids.

Effect of phytase addition and dietary calcium and phosphorus levels on plasma metabolites and ileal and total-tract nutrient digestibility in pigs.

Two experiments were conducted to determine the effect of phytase on plasma metabolites and AA and energy digestibility in swine. In Exp. 1, eight barrows (surgery BW = 52 kg) were fitted with steered ileocecal cannulas. The experiment was a Latin rectangle and the treatments were 1) corn-soybean meal diet adequate in Ca and P (0.5% Ca, 0.19% available P [aP]), 2) corn-soybean meal diet with reduced Ca and P (0.4% Ca, 0.09% aP), 3) Diet 1 with 500 phytase units/kg, or 4) Diet 2 with 500 phytase units/kg. Pigs were fed twice daily to a total daily energy intake of 2.6 x maintenance (106 kcal of ME/kg of BW(0.75)). For each ileal digesta sample, digesta samples were collected for two 24-h periods and combined for each pig. The combination of supplementing with phytase and decreasing the concentration of dietary Ca and P increased average ileal AA (P < 0.02), starch (P < 0.02), GE (P < 0.04), and DM (P < 0.03) digestibilities. In Exp. 2, a feeding challenge was conducted with barrows (eight per treatment; average BW of 53 kg). The treatments consisted of a corn-soybean meal diet or corn-soybean meal diet + 500 phytase units per kilogram of diet. In the diet with no phytase, Ca and aP were at 0.50% and 0.19%, respectively, and, in the diet with phytase, Ca and aP were each decreased by 0.12%. A catheter was surgically inserted into the anterior vena cava of each pig 6 d before the start of the feeding challenge. The barrows were penned individually, and the diets were fed for 3 d before the challenge. The pigs were held without feed for 16 h, and blood samples were obtained at -60, -30, and 0 min before the pigs were fed (2% of BW). Blood samples were then collected at 10, 20, 30, 40, 50, 60, 75, 90, 105, 120, 150, 180, 210, 240, 270, and 300 min after feeding. Glucose area under the response curve and plasma glucose, insulin, urea N, and total alpha-amino N concentrations were increased (P < 0.05) in pigs fed the diet with reduced Ca and P and the phytase addition. Area under the response curve for insulin, urea N, and total alpha-amino N; insulin:glucose; and plasma NEFA concentration, clearance, and half-life were not affected by diet. In conclusion, the combination of Ca and P reduction and phytase addition increased nutrient and energy digestibility in diets for pigs and increased plasma concentrations of glucose, insulin, urea N, and alpha-amino N.

Influence of dietary carnitine in growing sheep fed diets containing non-protein nitrogen.

The influence of supplemental L-carnitine was investigated in growing sheep fed rations containing non-protein nitrogen (NPN). The experiment was conducted as a randomized block design with a 2x2 factorial arrangement of treatments. Lambs (77.4kg BW, n=24) were fed a total mixed ration (12.1-13.6% CP) with two levels of L-carnitine (0 or 250ppm) and two levels of NPN (urea contributing 0 or 50% of total dietary N) for a 50-day period. Jugular blood samples were collected at 0, 1, and 3h post-feeding, and ruminal fluid samples were collected at 1h post-feeding, during days 1, 8, 29, and 50 of the experiment. Average daily gain (121 versus 214g) was lower (P<0.0001) in lambs fed the NPN diets. Lambs consuming diets containing NPN had higher (P<0.0001) ruminal fluid pH (6.6 versus 5.9), ruminal ammonia N (4.8 versus 2.8mmol/l), and plasma ammonia N (177.1 versus 49.5µmol/l) than lambs not fed NPN. Additionally, lambs fed the NPN diets had lower plasma urea N (14.5 versus 17.5mmol/l; P<0.003) and thyroxine (T(4)) concentrations (65.8 versus 78.4ng/ml; P<0.02), and lower T(4):triiodothyronine (T(3)) ratio (37.9 versus 43.9; P<0.02). Plasma glucose concentrations were higher (P<0.05) in lambs fed L-carnitine (3.83 versus 3.70mmol/l). Two oral urea load tests (OULT 1 and OULT 2) were conducted during the 50-day trial. Urea solutions (0.835g/kg(0.75) BW) were administered as oral drenches. During the OULT 1 (day 10), plasma ammonia N and glucose concentrations were highest (P<0.0001) in the lambs fed NPN with L-carnitine compared with lambs fed control, L-carnitine, and NPN diets. During the OULT 2 (day 50), plasma ammonia N was highest (P<0.0001) in the NPN and NPN with L-carnitine groups compared with the control and L-carnitine groups. Plasma glucose was lowest (P<0.04) in the NPN with L-carnitine group compared with the NPN and L-carnitine groups, but did not differ (P>0.10) from the control group. Plasma urea N levels in both OULT 1 and OULT 2 were lower (P<0.0001) in the NPN and NPN with L-carnitine groups compared with the control and L-carnitine groups. In the present experiment, production and plasma criteria were affected by NPN incorporation in the diets. Production criteria were not affected by inclusion of L-carnitine in the diet, however, L-carnitine reduced experimentally induced hyperammonemia by day 50 of the trial.

Effects of dietary inclusion of chromium propionate and calcium propionate on glucose disposal and gastrointestinal development in dairy calves.

In experiment 1, 21 male Holstein calves (43.9 kg) were fed only milk replacer at 1.4% of their body weight as dry matter for 6 wk. Dietary treatments included a commercial milk replacer (22% protein, 15% fat) containing (dry basis) either 6.4% Ca propionate or 6.4% dextrose (control) and either 0 or 0.5 mg/kg of supplemental Cr as Cr propionate. Neither Cr nor Ca propionate affected body weight gain; however, Ca propionate tended to increase the growth of the entire foregut measured after slaughter at 6 wk of age. A Minimal Model glucose tolerance test indicated that insulin sensitivity was not affected by treatment. However, calves fed Cr had higher glucose disappearance indexes than controls when propionate was not fed (0.013 vs. 0.019 units) but similar clearance when propionate was included (0.018 vs. 0.018 units, Cr x P interaction). The area under the glucose response curves after propionate-loading tests was much greater for calves fed the Cr versus control replacer when propionate was not present; however, when propionate was included, the response was less dramatic. In experiment 2, 25 Holstein calves were used to study performance and metabolic responses when milk replacer, and then postweaning starter, were supplemented with 0.5 mg/kg of Cr as Cr propionate. The metabolic responses of these calves were not affected by treatment. Overall, combined data suggested that supplemental Cr may improve glucose effectiveness; however, these responses seemed to be attenuated by supplemental propionate.

Influence of intravenous L-carnitine administration in sheep preceding an oral urea drench.

Two experiments were conducted to investigate the effect of i.v. administration of L-carnitine on selected metabolites in sheep and to determine the feasibility of using L-carnitine to ameliorate the deleterious effects of hyperammonemia in sheep. In Exp. 1, i.v. L-carnitine solutions were administered at three levels in a replicated Latin square: 0 (CONT), 6.36 (CAR 1), and 12.72 (CAR 2) mmol L-carnitine/kg x (75) BW using Suffolk ewes (n = 6; average BW 75+/-3 kg). Plasma L-carnitine concentration was increased (P<.05) by treatment (51.9 vs 102.3, and 96.4 micromol/L in CONT, CAR 1, and CAR 2, respectively). Plasma glucose concentration was elevated (P<.05) in CAR 2 and CAR 1. Plasma NEFA concentration was highest (P<.05) in CAR 2. Area under the response curve for glucose was greater (P<.02) in CAR 2. In Exp. 2, Suffolk ewes (n = 16; average BW 48+/-2 kg) were used in a randomized complete block design with a 2x2 factorial treatment arrangement to determine the effects of i.v. L-carnitine administration during an oral urea load test (OULT). L-Carnitine (0 and 6.36 mmol/kg x (75) BW) was administered i.v. at 30 min, and an oral urea drench (50% wt/vol; 0 and 300 mg/kg BW) was administered at 60 min. Plasma L-carnitine was increased (P<.0001) by i.v. L-carnitine. Plasma ammonia N was highest (P<.0001) in the UREA treatment compared with the CONT, CARN, and CARN + UREA treatments (148 vs 95, 101, and 108 micromol/L, respectively). Intravenous L-carnitine administration influenced plasma glucose and NEFA concentrations in sheep and, when administered 30 min preceding an OULT, prevented the development of subclinical hyperammonemia in sheep.

Performance and metabolic responses of young dairy calves fed diets supplemented with chromium tripicolinate.

Forty-two Holstein calves were used to study performance and metabolic responses when milk replacer and then postweaning starter were supplemented with 1 ppm of Cr as Cr-tripicolinate. From birth through 8 wk of age, supplemental Cr tended to improve the growth performance of bull calves but not of heifer calves. Starter intake and feed efficiency were not affected by supplemental Cr. From 1 to 5 wk of age, plasma cortisol concentrations sampled just prior to feeding decreased, and concentrations of insulin-like growth factor-I increased. All calves appeared to become less sensitive to insulin as they aged. From 1 to 5 wk of age, plasma glucose and insulin concentrations gradually diverged for all calves; glucose concentrations decreased, and insulin concentrations increased. In addition, glucose clearance rate, measured by i.v. glucose tolerance tests, was more rapid when calves were 2 wk of age than when calves were 8 wk of age. The glucose clearance rate was greater in heifer calves than in bull calves but was not affected by supplemental Cr. Entry of plasma glucose following an i.v. propionate load was also greater in heifer calves than in bull calves but was not affected by supplemental Cr. Plasma nonesterified fatty acids were lower in calves fed milk replacer or starter supplemented with Cr than in control calves, although this effect diminished as calves aged. This finding was considered to be indirect evidence of enhanced insulin sensitivity in calves fed milk replacer or starter supplemented with Cr. Overall, data suggested that supplemental Cr-tripicolinate had minor effects on the metabolism and growth performance of conventionally managed dairy calves. The most notable effects occurred during the initial few weeks of life.

Seasonal effects of supplemental fat or undegradable protein on the growth and metabolism of Holstein calves.

One summer (heat stress) and one winter (neutral conditions) trial were conducted to assess the effects of varied amounts of RUP and fat on the growth and metabolic responses of calves. In each trial, 190-kg Holstein calves (n = 45) were fed a basal diet of corn and cottonseed hulls supplemented with soybean meal (control) or supplemented with raw or roasted whole soybeans or the basal ration plus prilled hydrogenated tallow either with or without a mixture of feather meal and blood meal. Prilled tallow was more detrimental to fiber digestion and growth performance than were whole soybeans, especially during summer. During winter, calves fed a high (49%) percentage of the dietary CP as RUP had similar BW gain and efficiency of feed usage as did calves fed a moderate percentage (39%), but, during summer, calves fed the high percentage of RUP had greater BW gain and efficiency than did calves fed moderate percentages of RUP. Ruminal concentrations of VFA were parallel to digestibilities of fiber in the total tract. Ruminal concentrations of ammonia or blood concentrations of urea were not consistent with the concentrations of RDP fed. Concentrations of glucose, NEFA, insulin, and thyroid hormones in the blood were primarily affected by season. Data suggested that a higher percentage and AA quality of RUP improved the growth of calves during summer but not during winter.

Dietary protein and energy restriction in mares: rapid changes in plasma metabolite and hormone concentrations during dietary alteration.

Two diets consisting of bermudagrass hay and a corn-cottonseed hull-based supplement were formulated to provide either 100% (control) or 50% (restricted) of the protein and energy requirements for maintenance for mature mares. Twelve light horse mares were fed the control diet for 7 d, and then at 0800 on d 0, six mares were switched to the restricted diet. All diets were fed as two equally sized meals at 0800 and 1600. At 0800 on d 7, mares receiving the restricted diet were switched back to the control diet. Relative to control mares, mares switched to the restricted diet had reduced plasma concentrations of glucose (P = .005) and insulin (P = .09) in response to the two restricted meals on d 0. However, concentrations of both glucose and insulin returned to control levels (P > .1) within 1 h after the consumption of the control diet on d 7. Dietary restriction increased (P = .009) plasma NEFA concentrations within the first 24 h, and NEFA concentrations remained elevated (P < .001) in restricted mares until the mares were returned to the control diet on d 7. Meal-induced increases (P < .05) in plasma concentrations of glucose, insulin, urea N, glucagon, and thyroxine were observed. These results emphasize the importance of early sampling when monitoring plasma constituents during nutrient alterations and indicate that prefeeding responses of plasma constituents alone may not fully explain the metabolic consequences of nutrient restriction.

Feed deprivation of mares: plasma metabolite and hormonal concentrations and responses to exercise.

Twelve light horse mares were fed a control diet that provided 100% of their maintenance protein and energy requirements for 7 d and were then either continued on the control diet or totally deprived of feed (with access to water) for 3 d . Plasma samples were drawn twice daily throughout the experiment, at 15-min intervals for 9 h beginning 45 h after feed removal, and at 10-min intervals around an exercise bout beginning 73 h after feed removal. Feed deprivation increased (P < or = .06) whole blood beta-hydroxybutyrate and plasma NEFA, urea N, L-lactate, and glucagon concentrations, decreased (P = .02) IGF-I concentrations, and did not change (P > .1) plasma glucose insulin, prolactin, triiodothyronine, and thyroxine concentrations. Exercise increased (P < .05) plasma NEFA, prolactin, and growth hormone (GH) concentrations in all mares. Plasma NEFA concentrations increased (P < .001) after exercise and remained increased in fed mares, but rapidly decreased in deprived mares (time x diet interaction, P = .006). Plasma glucose concentrations following exercise increased in deprived mares but decreased in fed mares (time x diet interaction, P = .07). The plasma prolactin response after exercise also differed between groups (P = .09). Feed-deprived mares had greater (P = .02) plasma GH concentrations before exercise (73 h after feed withdrawal) and had a greater (P < .001) GH peak at 10 min after initiation of exercise. The increase in secretion rate o GH due to feed deprivation in these mares was similar to that reported for other domestic species but was not nearly as great in magnitude.

Influence of chromium tripicolinate on glucose metabolism and nutrient partitioning in growing lambs.

Twenty-four Suffolk lambs (average BW 38 +/- 2.7 kg; 16 ewes and 8 wethers) were fed either a corn-cottonseed hull-based control diet (CON) or CON plus 250 ppb of Cr as chromium tripicolinate (CrPic). Lambs were penned in groups of three and ADG and DMI were measured through d 85 of the experiment. Jugular blood samples were obtained during wk 2, 7, and 11. An i.v. glucose tolerance test (IVGTT; 500 mg of glucose/kg BW) and an i.v. insulin challenge test (IVICT; .1 IU of ovine insulin/kg BW) were performed during wk 2 and 10 of the trial. This was followed by a N balance trial during wk 3 and 11. Wethers were slaughtered at the end of the experiment and carcass characteristics determined. No differences (P > .10) were observed between dietary treatments in DMI, ADG, or N balance; however, the CrPic-fed wethers had 18% less fat over the 10th rib (P = .082) and a lower yield grade (P = .014). Plasma NEFA was lower throughout the trial (P < .03) and cholesterol was 17% lower during wk 2 (P < .02) in lambs fed CrPic. There were no differences due to diet (P > .10) in plasma concentrations of urea N, glucose, albumin, total protein, insulin, glucagon, triiodothyronine, or thyroxine. Glucose clearance rate and half-life during the IVGTT and IVICT did not differ (P > .10) between CON and CrPic groups; however, during the IVGTT on wk 2, plasma insulin was elevated (P < .05) and glucose reduced (P = .067) in the lambs fed CrPic. Supplemental CrPic seems to influence metabolic measurements that may affect performance of growing lambs.

Influence of nitrogen fertilization and defoliation frequency on nitrogen constituents and feeding value of annual ryegrass.

Two experiments were conducted to determine the seasonal effects of N fertilizer (NF) and defoliation interval (DI) on specific N fractions within annual ryegrass (AR) and overall usage of AR N by growing lambs. In Exp. 1, NF (0, 112, 224, and 336 kg of N/ha) and DI of 2, 4, or 6 wk were factorially applied to AR plots. Both decreasing DI and increasing NF increased N levels in AR in a manner that depended on harvest date (NF or DI x harvest date interaction, P < .05). The proportions of .2% NaOH soluble N or soluble protein N were not affected (P > .05) by NF or DI. Although NF had no effect (P > .05) on in situ disappearance of DM, decreasing the DI seemed to reduce the severity of the season-induced reduction in DM disappearance (DI x harvest date interaction, P = .04). In Exp. 2, NF (0 or 224 kg of N/ha) and a DI of 2 or 6 wk were factorially applied to AR plots. Fresh, frozen AR was fed in semipurified diets (48% of DM as AR) to four wether lambs (23 +/- 1.3 kg) using a 4 x 4 Latin square. Diets including AR had greater ruminal DM and plant N digestibilities when AR had a 2-wk vs a 6-wk DI with NF but had reduced digestibilities when AR had a 2-wk vs a 6-wk DI without NF.(ABSTRACT TRUNCATED AT 250 WORDS)

Dietary protein and(or) energy restriction in mares: plasma growth hormone, IGF-I, prolactin, cortisol, and thyroid hormone responses to feeding, glucose, and epinephrine.

Sixteen light horse mares were fed diets of bermudagrass hay and a corn/cottonseed hull-based supplement formulated to contain either 100% (control) or 50% (restricted) of the protein and(or) energy requirements for maintenance in a 2 x 2 factorial arrangement of treatments. Plasma IGF-I, prolactin, cortisol, triiodothyronine, and thyroxine were monitored for 33 d. On the 27th d, frequent blood samples were drawn throughout the day for the measurement of growth hormone (GH), and on the 29th d, an epinephrine challenge and an i.v. glucose tolerance test (IVGTT) were performed in the morning and afternoon, respectively. Restriction of protein and(or) energy reduced (P < .001) plasma IGF-I concentrations within 24 h, and the effect persisted through the 24th d. Energy restriction decreased (P = .01) plasma cortisol concentrations, whereas thyroid hormones were not influenced (P > .1) by restriction of protein and(or) energy. Plasma prolactin concentrations were low throughout the experiment and after the IVGTT, but they increased (P = .003) after feeding. Protein restriction increased (P = .09) the occurrence of GH episodes during the 14-h feeding period on d 27; the greatest effect occurred in the mares restricted in both nutrients. In contrast, energy restriction reduced (P = .05) the GH response to epinephrine injection. We conclude that 1) protein deficiency in mares increases GH secretion, whereas energy restriction alone does not, 2) a deficiency in energy and(or) protein reduces IGF-I secretion, and 3) prolactin concentrations increase after feeding, even at a time of year when secretion rates are naturally low.

Dietary protein and(or) energy restriction in mares: plasma glucose, insulin, nonesterified fatty acid, and urea nitrogen responses to feeding, glucose, and epinephrine.

Sixteen light horse mares (8 to 9 yr of age; 457 to 579 kg BW) were fed Bermudagrass hay and a corn/cottonseed hull-based supplement formulated to contain either 100% (control) or 50% (restricted) of the protein and(or) energy requirements for maintenance in a 2 x 2 factorial arrangement of treatments. Daily measurements of intake, BW, and plasma hormones and metabolites were made for 33 d. Plasma glucose, insulin, NEFA, and urea N were measured in hourly samples drawn on d 27, and parallel with an i.v. glucose tolerance test (IVGTT) and epinephrine challenge on d 29. Energy restriction increased daily NEFA concentrations (P < .001) and urea N (P = .013), whereas protein restriction decreased (P = .002) urea N concentrations. These effects of protein and energy restriction occurred within 24 h and were consistent (day effect, P > .1) throughout the remaining 24 d. Normal meal consumption elevated plasma glucose, insulin, and urea N concentrations (time effect, P < .08). Plasma NEFA concentrations did not change after feeding in mares fed control energy, but decreased in mares fed restricted energy (energy x time interaction, P = .005). After IVGTT, areas under the curve for plasma glucose and insulin were smaller in mares fed restricted protein (P < .05), whereas glucose area was larger in mares fed restricted energy (P = .009). After epinephrine injection, energy restriction increased the initial magnitude of the NEFA response, but after 50 min, reduced plasma NEFA below pre-injection concentrations (energy x time interaction, P = .06).(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of chromium picolinate on glucose usage and metabolic criteria in growing Holstein calves.

Holstein calves, 10 steers (98 +/- 16 kg; Exp. 1) and 14 heifers (122 +/- 7 kg; Exp. 2), were fed either corn-cottonseed hull basal diets (CON; 15.1 and 13.2% CP, respectively) or CON plus 370 micrograms/kg of Cr as Cr-tripicolinate (CrP). After either 58 (Exp. 1) or 56 (Exp. 2) days of ADG and DMI measurement, calves were individually fed 1.4% of their BW every 12 h through the end of each experiment. Nitrogen balance, i.v. glucose tolerance tests (IVGTT), i.v. insulin challenge tests (IVICT), baseline growth hormone (GH) measurements, and GH-releasing hormone challenges were then performed on calves in split groups on d 70 through 87 in Exp. 1. In Exp. 2, all challenges began on d 78 and N balance was not determined. Inclusion of CrP did not affect (P > .10) ADG, DMI, or ADG/DMI of pooled data from Exp. 1 and 2 or N balance criteria in Exp. 1. Plasma glucose, insulin, and NEFA concentrations were not affected (P > .10) by CrP. Total plasma cholesterol was lower (P < .05) for CrP- than for CON-fed calves at wk 4 in Exp. 1 and wk 6 in Exp. 2. During IVGTT, calves fed CrP vs CON had higher (P < .05) clearance rates for glucose in Exp. 1 (2.68 vs 1.88%/min) and in Exp. 2 (2.64 vs 2.08%/min). During IVICT, calves fed CrP vs CON had higher clearance rates for glucose in Exp. 1 (2.98 vs 2.34%/min; P = .12) and in Exp. 2 (2.89 vs 2.00%/min; P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of protein quality in heat-treated soybean products using the growth responses of lambs and calves and a nylon bag-rooster assay.

Three studies were conducted to evaluate N and amino acid (AA) availability from processed soybean (SB) products. In Exp. 1 and 2, treatments consisted of corn-cottonseed hull basal diets plus SB products including SB meal (SBM); ground, raw SB (RSB); or extruded SB (ESB). In Exp. 1, 15 Suffolk (28.6 kg) and 15 Louisiana native breed (16.3 kg) ewe lambs were used in a 35-d growth trial. Although breed affected (P < .10) DMI and ADG of lambs, the diets did not (P > .10). In Exp. 2, 12 Suffolk wether lambs (34.0 kg) were used in a 3 x 3 multiple-square Latin square design N metabolism trial. Lambs fed RSB tended (P = .13) to retain more N than those fed ESB, but N retained by lambs fed RSB and ESB was similar (P > .10) to that of lambs fed SBM. In Exp. 3, four crossbred steer calves (240 kg) were used in a 4 x 4 Latin square design N metabolism trial with the above treatments plus heat-damaged SB (HDSB). Calves fed RSB and ESB retained similar (P > .10) amounts of N. Compared with calves fed RSB and ESB, calves fed SBM retained more (P < .10) N. Calves fed HDSB retained less (P < .10) N than those fed other diets. The individual SB products and the total mixed diets used in Exp. 3 were incubated intraruminally in nylon bags and the residual DM recovered and precision-fed to cecectomized roosters to estimate its intestinal AA digestibility. Digestibility of residual AA seemed to be relatively uniform across AA.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of fish meal and supplemental fat on performance of finishing steers exposed to moderate or high ambient temperatures.

Ninety-six Hereford x Angus steers (mean initial BW = 295 kg) were used in two growth experiments conducted at moderate and high ambient temperatures (AT), 48 steers per AT. Within each AT, calves were assigned to six dietary treatments consisting of a basal diet (approximately 60% corn and 20% grass hay) supplemented with either 0, 2.5, or 5% fat and with either soybean meal (SBM) or Menhaden fish meal (FM) included at levels such that a ratio of 16.3 kcal of NEm per kilogram of CP was maintained. Blood and ruminal fluid were collected 40 d before slaughter. During the final 28 d of the moderate AT experiment, apparent digestibility of dietary components was measured in four individually fed steers from each dietary treatment. Steer ADG was not affected by fat, and DMI and efficiency of gain were not affected (P > .10) by treatment. Average daily gain was lower for steers fed FM than for those fed SBM at moderate AT but higher at high AT (CP source x AT interaction; P < .05). Ruminal ratio of acetate to propionate declined linearly with increasing fat at moderate AT but was not affected by fat at high AT (fat x AT interaction trend; P = .08). Plasma urea N concentration increased linearly (P < .05) with increasing fat and was higher (P < .05) in steers kept at high than in those kept at moderate AT. Although apparent digestibility was not altered in steers fed FM, DM and NDF (P < .05) and ADF (P = .07) digestibility decreased with increasing fat in steers fed SBM (CP source x fat interaction).(ABSTRACT TRUNCATED AT 250 WORDS)

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)

Effect of supplemental lysocellin and tetronasin on growth, ruminal and blood metabolites, and ruminal proteolytic activity in steers grazing ryegrass.

Forty-eight Angus and Brangus steers (249 kg initial BW) were used in a randomized complete block design. Steers grazed annual ryegrass (Lolium multiflorum [L.] Lam.) for 107 d and were sampled at 35 and 70 d. Treatments consisted of a corn supplement (C) or corn supplement plus either 80 mg.steer-1.d-1 of lysocellin (L) or 60 mg.steer-1.d-1 of tetronasin (T). When compared with C, ADG of L- and T-fed steers was higher (P less than .05) for the complete 107-d study (1.15 vs 1.25 kg/d). At 35 d, ruminal acetate:propionate ratio tended (P = .07) to be higher for C than for L- and T-fed steers (4.6 vs 3.8). When compared with T, steers fed L tended (P = .11) to have higher acetate:propionate ratios. Ruminal concentrations of ammonia and free amino acids were not affected (P greater than .05) by treatment, but ruminal proteolytic activity tended (P = .13) to be lower for L- and T-fed than for C steers at 70 d. Ionophores did not alter (P greater than .05) ruminal mineral concentrations, but ruminal Mg concentration tended (P = .14) to be higher for T- than for L-fed steers at 70 d. When compared with L- and T-fed steers, C steers had lower (P less than .05) plasma concentrations of Mg (23.7 vs 21.9 mg/liter) and Ca (113.0 vs 104.2 mg/liter) at 35 d. Plasma mineral concentrations were similar (P greater than .05) for L- and T-fed steers. Data are interpreted to indicate that L and T may improve ADG, decrease ruminal acetate:propionate ratio, and alter mineral metabolism.

Metabolic and endocrine responses of lambs fed Acremonium coenophialum-infected or noninfected tall fescue hay at equivalent nutrient intake.

Ten Hampshire x Western wether lambs (means weight = 30.1 kg) equipped with ruminal and abomasal cannulas were fed either low-Acremonium coenophialum (AC) Kentucky-31 (less than 1% infected) or high-AC G1-307 (greater than 95% infected) varieties of tall-fescue (TF) hay of similar nutrient composition in a completely randomized design. Lambs were housed in metabolism crates at 21 +/- 1 degrees C and fed 552 g DM/d of ground hay at 0800 and 2000. A 10-d adaptation preceded 7 d of sample collection. Levels of water and DM voluntarily consumed by the low-AC group during the adjustment period were held constant for both treatment groups throughout the collection period by intraruminal insertion of unconsumed DM and water. Fixed water intake markedly reduced voluntary water intake but it alleviated previous depressions in voluntary DM intake in lambs fed high-AC. Mean daily respiration and heart rates, rectal temperature and hematocrit were not affected (P greater than .10) by treatment. Compared with high-AC, lambs fed low-AC retained a greater (P less than .10) amount of N (1.8 vs 1.1 g/d) and a greater (P less than .10) percentage of their N intake (16.4 vs 9.9%). Abomasal total and bacterial N flow and ruminal digestion of cell wall components were not affected (P greater than .10) by treatment. Total tract digestion of DM, NDF and ADF was lower (P less than .01) for high- than for low-AC. Serum prolactin concentration was higher (P less than .10) for lambs fed low- than for those fed high-AC TF, but serum cortisol and thyroxine concentrations were not affected (P greater than .10) by treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Alterations in ruminal utilization of magnesium and zinc in lambs fed different ratios of concentrate: forage.

Twelve wether lambs were used to study the effects of concentrate level on ruminal utilization of Mg and Zn. Treatments consisted of concentrate: forage ratios (C:F) of 10:90, 40:60, and 70:30. Ruminal pH.hours (pH x hours area below 6.7 in 24-hour period) increased (P less than .01; linear) with increasing C:F. Bacterial intestinal Mg flow increased (P less than .01; linear) with increasing C:F and was strongly correlated with pH.hours (r = .75, P = .008). Ruminal Mg absorption was not affected (P greater than .05) by C:F, but correlated well with bacterial intestinal Mg flow (r = .66; P = .026). As with Mg, intestinal flow of bacterial Zn increased (P less than .01; linear) with increasing C:F and was highly correlated with pH.hours (r = .76, P = .006). Ruminal Zn absorption declined (P less than .05; linear) with increasing C:F and correlated well with bacterial Zn flow (r = -.82, P = .002). Data suggest that ruminal pH and (or) bacterial accumulation of Mg and Zn may compromise ruminal absorption of these minerals.