Performance of feedlot steers fed diets containing laidlomycin propionate or monensin plus tylosin, and effects of laidlomycin propionate concentration on intake patterns and ruminal fermentation in beef steers during adaptation to a high-concentrate diet.

Two hundred eighty-eight beef steers (British x Continental x Brahman) were fed a 90% concentrate diet containing either no ionophore (control), laidlomycin propionate at either 6 or 12 mg/kg of dietary DM, or monensin plus tylosin (31 and 12 mg/kg of DM, respectively). Neither of the two levels of laidlomycin propionate nor monensin plus tylosin affected (P greater than .10) ADG or feed:gain ratio. Monensin plus tylosin reduced (P less than .01) daily DMI for the 161-d trial period compared with the other three treatments. Laidlomycin propionate at 6 mg/kg increased (P less than .05) DMI relative to the control, laidlomycin propionate at 12 mg/kg, and monensin plus tylosin diets during the 2nd wk of the trial and from d 57 to 84. Treatments did not affect carcass measurements. In a second experiment, 12 ruminally cannulated steers were fed diets containing no ionophore or laidlomycin propionate at either 6 or 12 mg/kg of DM. Samples were obtained for two consecutive days while the dietary concentrate level was 75%, after which the diet was switched abruptly to 90% concentrate, and samples were collected on several days during a 21-d period. The rate at which steers consumed their daily allotment of feed was not altered markedly by laidlomycin propionate. Likewise, laidlomycin propionate did not affect total ruminal VFA concentrations or proportions. Ruminal concentrations of D-lactate were reduced (P less than .10) by 6 but not by 12 mg/kg of laidlomycin propionate.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of feeding growing cattle high-concentrate diets at a restricted intake on feedlot performance

Three trials were conducted to compare effects of restricted intake of high-concentrate diets vs ad libitum intake of corn silage diets during the growing phase on feedlot cattle performance. In Trial 1, 120 steers (initial BW, 246 kg) were fed 1) a corn silage-based diet ad libitum, 2) a high-moisture corn-corn silage-based diet with intake restricted to a level 20% less than that of the corn silage diet or 3) a high-moisture corn-based diet with intake restricted to a level 30% less than that of the corn silage diet. Steers fed the 20% restricted corn-corn silage-based diet tended (P = .07) to gain slower than those fed the corn silage or 30% restricted high-concentrate diet. Feed efficiency and diet digestibility were greatest for steers fed the 30% restricted-intake, high-concentrate diet (P less than .01). Performance of steers during the subsequent 118-d finishing period was not affected (P greater than .65) by source of energy during the growing period. In Trial 2, ADG of steers fed the 30% intake-restricted, high-concentrate diet was lower (P less than .01) than that of steers with ad libitum access to corn silage. During the 84-d growing period, steers fed supplemental blood meal had 8.3% greater gains and a 6% greater efficiency of feed use than those fed supplemental soybean meal (P less than .01). Monensin did not affect (P = .82) performance of steers fed 30% restricted-intake diets. During the 76-d finishing period, gains and feed conversion were improved (P less than .01) for steers fed the restricted-intake diet in the growing period compared with those given ad libitum access to corn silage. During the growing period in Trial 3, ADG of steers restricted-fed an all-concentrate diet were slightly greater (P less than .10) than ADG of those given ad libitum access to corn silage. Gains did not differ (P = .37) during the subsequent finishing period when steers were switched to 85 or 100% concentrate diets. We concluded that intake of all concentrate diets can be restricted to achieve gains equal to those of steers given ad libitum access to corn silage-based diets without detrimental effects on finishing performance.     

Influence of lysocellin and monensin on mineral metabolism of steers fed forage-based diets

Studies were conducted to determine the effects of lysocellin and monensin on mineral metabolism of steers fed forage-based diets. In each study treatments consisted of 1) control, 2) 100 mg lysocellin/d, 3) 200 mg lysocellin/d and 4) 200 mg monensin/d. Twenty-four growing Hereford steers were used in each of two experiments to evaluate the effects of ionophore feeding on plasma and ruminal soluble mineral concentrations. Steers were fed individually greenchop (tall fescue and bermudagrass) ad libitum and .91 kg/d of a corn-trace mineral salt-ionophore supplement. Plasma and ruminal fluid samples were obtained on d 28 and 84 in both studies. Ruminal concentrations of soluble phosphorus (P) and iron (Fe) were higher (P less than .05), whereas soluble manganese (Mn) was lower (P less than .01), in steers fed lysocellin than in controls. Steers fed lysocellin had higher (P less than .05) plasma magnesium (Mg) concentrations than control steers. Plasma and ruminal soluble mineral concentrations generally were similar for the monensin and 200 mg lysocellin treatments. Two additional studies were conducted to determine the effects of lysocellin and monensin on macromineral apparent absorption and retention in steers fed tall fescue greenchop. Steers were adjusted to their diets for 28 d and then placed in metabolism crates for a 6-d acclimation followed by a 5-d collection of urine and feces. Percent apparent absorption of calcium (Ca), potassium (K), Mg and P was higher (P less than .05), whereas sodium (Na) absorption was lower (P less than .05), in steers fed lysocellin than in controls. Mineral absorption was similar in steers fed 200 mg lysocellin or monensin. Calcium (P less than .05) and K (P less than .10) retention (percent of intake) was increased by ionophore feeding. Results indicate that lysocellin and monensin alter apparent absorption and retention of certain minerals in steers fed forage-based diets.     

Effects of lysocellin on performance, ruminal and plasma characteristics of growing cattle

Twenty-four Hereford steers averaging 228 kg initially were used to evaluate four levels of lysocellin (0, 11, 22 and 33 mg/kg diet) when individually fed a corn silage-based diet. Gains were similar for all lysocellin levels over the 112-d study. As lysocellin level increased, there was a linear decrease in dry matter intake and an improvement in feed conversion (P less than .05). Feed to gain ratios were 6.27, 6.14, 5.67 and 5.59 for the 0, 11, 22 and 33 mg/kg of lysocellin treatments, respectively. Molar proportion of acetate was lower (P less than .05) and propionate was higher (P less than .05) for steers fed lysocellin than for controls at d 84. Ruminal fluid concentrations of soluble Cu and Zn were higher (P less than .05) in steers fed lysocellin at 28 and 84 d and increased as lysocellin level increased. Plasma Zn was lower (P less than .05) at both 28 and 84 d in steers fed lysocellin, whereas plasma Cu concentrations were similar for controls and for those fed lysocellin. Both ruminal fluid soluble P and plasma P concentrations were higher (P less than .05) in steers fed lysocellin than in controls at d 84. These results are interpreted to indicate that feed conversion of growing cattle is improved by lysocellin and that metabolism of certain minerals is affected by this ionophore.     

Effects of dietary zilpaterol hydrochloride on feedlot performance and carcass characteristics of beef steers fed with and without monensin and tylosin

A feedlot experiment was conducted under commercial conditions in the Texas Panhandle using 3,757 feedlot steers (average of 94 steers/pen) to evaluate the effects of feeding zilpaterol hydrochloride with or without monensin and tylosin on feedlot performance and carcass characteristics. The experiment was conducted using a randomized complete block design. Treatments were arranged as a 2 (no zilpaterol vs. zilpaterol) x 2 (monensin and tylosin withdrawn vs. monensin and tylosin fed during the final 35 d on feed) factorial. Steers were fed for a total of 161 to 167 d, and treatments were administered during the final 35 d that cattle were on feed. When included in the diet, zilpaterol, monensin, and tylosin were supplemented at 8.3, 33.1, and 12.2 mg/kg (DM basis), respectively. Zilpaterol was included in the diet for 30 d at the end of the finishing period and withdrawn from the diet for the last 5 or 6 d cattle were on feed. Cattle were harvested and carcass data collected. There were no zilpaterol x monensin/tylosin interactions (P >or= 0.12) for ADG or G:F. Feeding zilpaterol increased ADG (P < 0.001) by 0.20 kg and G:F (P < 0.001) by 0.029 kg/kg during the last 35 d on feed. Likewise, when feedlot variables were measured throughout the entire 161- to 167-d feeding trial, ADG (3.4%; P < 0.001) and G:F (3.9%; P < 0.001) were increased. Feeding zilpaterol increased (P < 0.001) dressing percent and HCW and decreased (P < 0.001) total liver abscess rate compared with controls. In addition, zilpaterol increased (P < 0.001) LM area by an average of 8.0 cm(2). There was a zilpaterol x monensin/tylosin interaction (P = 0.03) for marbling score. Zilpaterol decreased (P < 0.001) marbling score regardless of monensin and tylosin treatment, although withdrawal of monensin and tylosin for 35 d decreased marbling to a greater extent (31 vs. 17 degrees). Zilpaterol decreased (i.e., improved; P < 0.001) calculated yield grade regardless of monensin and tylosin treatment, but feeding zilpaterol in combination with the withdrawal of monensin and tylosin for 35 d decreased calculated yield grade to a greater extent (0.49 vs. 0.29) compared with the zilpaterol, monensin, and tylosin combination treatment (zilpaterol x monensin/tylosin interaction, P = 0.03). Results suggest that monensin and tylosin can be withdrawn from the diet during the zilpaterol feeding period (final 35 d on feed) with minimal effect on animal performance, although feeding zilpaterol in combination with monensin and tylosin seemed to moderate effects on carcass quality.     

Nitrogen utilization and digestibility by growing steers and goats of diets that contain monensin and low crude protein

Two digestion and metabolism experiments were conducted to determine effects of monensin in low-protein diets. Monensin supplementation (27 mg/kg of diet dry matter) of steers (303 kg) fed 8.7% crude protein increased (P less than .01) apparent N digestibility and N retention and decreased (P less than .01) percentage of N apparently absorbed lost in urine. Apparent digestibilities of dry matter, gross energy and acid detergent lignin were increased (P less than .05). Digestibilities of neutral detergent and acid detergent fibers were not affected by monensin. In growing wether goats (15 kg) fed 8.5% crude protein, monensin (23 mg/kg of diet dry matter) improved (P less than .01) apparent N digestibility and apparent N absorption. However, urinary N excretion also increased (P less than .05), resulting in no difference in N retention. Monensin did not affect digestibilities of dry matter or gross energy. Efficiency of feed conversion and average daily gain were improved with monensin supplementation of growing goats fed a low-protein, high-roughage diet. Monensin resulted in typical shift of acetate-to-propionate ratio in both experiments. Results suggest that improved N utilization may account for some benefits of feeding monensin.     

Nitrogen utilization by ruminants during restricted intake of high-concentrate diets

A series of experiments was conducted to determine the effects of limit-feeding high-concentrate (LFHC) diets on dietary CP requirements of steer calves. When steer calves were fed 80% concentrate diets at 78 g/kg of BW.75, increasing dietary CP resulted in increased ADG (P less than .001). Average daily gain was increased in steers as daily monensin dosage increased from 120 to 180 mg (P less than .05). Increasing the daily monensin dosage to 240 mg did not increase ADG further. There were no (P greater than .10) CP X monensin interactions, suggesting that the monensin response was caused by improved energy utilization and not be the possible protein-sparing effects of ionophores. Steer calves in the second feedyard experiment expressed similar ADG when provided equal NEg as limit-fed, high-moisture ear corn (HMEC) or when given ad libitum access to corn silage. The basal diet did not affect the steers' daily N requirement for growth. Gain per unit of protein intake declined quadratically (P less than .05) with increasing CP intake, indicating that CP requirements were near NRC estimates on both diets. The corn silage-based diet was less digestible (70.3 vs 77.4%; P less than .01) than the HMEC diet when fed to lambs. Fecal output differed (P less than .10) substantially (342 g/d of corn silage vs 205 g/d of HMEC), whereas fecal N output was only slightly higher (6.97 vs 6.34 g/d, respectively; P less than .10). Limited feeding of higher-concentrate diets to steer calves seemed to be an effective management procedure and did not cause acute digestion upset.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of salinomycin level on nutrient digestibility and ruminal characteristics of sheep and feedlot performance of cattle

A sheep digestion trial and two feedlot trials with cattle were conducted to study effects of an ionophore, salinomycin, on nutrient digestibility, ruminal metabolism and cattle performance. In trial 1, addition of salinomycin at 5.5, 11 or 22 ppm to 60% concentrate diets fed to ruminal-cannulated rams had no effect (P greater than .05) on apparent digestibility of dry matter (DM), organic matter (OM), neutral detergent fiber (NDF), acid detergent fiber (ADF) or starch in comparison with control diets. Apparent nitrogen (N) digestibility was increased (P less than .05) in animals fed salinomycin. Salinomycin did not affect total volatile fatty acid (VFA) concentrations in the rumen, but resulted in a linear (P less than .05) increase in molar proportion of propionate and a linear (P less than .05) decrease in molar proportions of acetate and butyrate and in acetate:propionate ratios. Shifts in VFA proportions were fully expressed within 4 d after salinomycin was added to the diet. In trial 2, salinomycin was added at 5.5, 11, 22 or 33 ppm to 85% concentrate diets fed to finishing steers. Salinomycin level had a quadratic effect (P less than .05) on daily weight gain and resulted in a quadratic (P less than .05) decrease in feed intake with a resultant average improvement of 10.3% in feed efficiency. Salinomycin (5.5, 11, 16.5 or 22 ppm) and monensin (22 ppm) were added to 90% concentrate diets in trial 3 and produced increased rates of gain without affecting feed intake.(ABSTRACT TRUNCATED AT 250 WORDS)     

Dietary roughage regimen for feedlot steers: reduced roughage level (2%) during the mid-finishing period.

Because roughage in feedlot diets is one of the most expensive ingredients on an energy basis, regimens that minimize roughage usage are of interest. Crossbred steers of British breeds (n = 112, initial BW = 405 kg) were used to compare the feeding of diets containing 2% roughage from d 22 through 84 and 10% roughage from d 85 to finish (d 133; 2/10%) to the feeding of 10% roughage throughout the finishing period (10/10%); all diets were based on steam-flaked sorghum grain and contained monensin and tylosin. When the 2% roughage diet was fed, steers consumed less feed (6.8 vs 7.8 kg/d, P less than .01), tended to gain less (1.11 vs 1.20 kg/d, P = .13), and were numerically more efficient (16.5 vs 15.5 kg of gain/100 kg of DMI, P greater than .2) than steers fed the 10% roughage diet (10/10%). After the roughage content was increased from 2 to 10% on d 85 (all steers fed 10% roughage), steers fed the 2/10% regimen had greater DMI (8.4 vs 8.0 kg/d, P = .08) and ADG (1.29 vs 1.09 kg, P = .06), and tended to be more efficient (15.4 vs 13.6 kg of gain/100 kg of DMI, P = .10) than steers fed the 10/10% regimen. Steers fed the two regimens had similar (P greater than .2) overall gain performance. The 2/10% regimen tended to have a greater percentage of Choice carcasses (58 vs 42%, P = .14) and numerically more liver abscesses (24 vs 15%, P greater than .2) than the 10/10% regimen.(ABSTRACT TRUNCATED AT 250 WORDS)     

Site and extent of apparent magnesium and calcium absorption in steers fed monensin

Eight crossbred steers (avg wt, 350 kg) with duodenal and ileal cannulas were used in two experimental periods in a single-reversal design to determine the effects of monensin on site and extent of apparent absorption of Mg and Ca. Steers were fed a cottonseed hull:concentrate diet (30:70) with or without 25 mg monensin/kg. The diet contained .20% Mg and .38% Ca. Each diet contained .25% Cr2O3 as a digesta marker. During each period, steers were fed the control diet for 10 d before allotment to treatments. Each period consisted of 17 d for diet adjustment and 6 d for collection. During the collection phase, fecal samples were obtained beginning on d 1 and continuing through d 6 at 12-h intervals progressing 2 h each day. Apparent Mg availability (grams apparently absorbed expressed as a percentage of grams of intake) increased (P less than .05) from 18.4 to 32.5% when monensin was fed. Feeding monensin increased (P less than .05) the apparent Mg availability and amount of Mg absorbed in the preintestinal region (47.7 vs 29.8% and 8.5 vs 5.1 g/d, respectively). Larger quantities (P less than .05) of Mg were secreted into the small intestine when monensin was fed. Monensin did not alter (P less than .05) apparent Ca availability or absorption in any segment of the digestive tract. These data indicate that monensin increased Mg and did not change Ca availability in the preintestinal region.     

Influence of decoquinate on ruminal fermentation, diet digestibility and cattle performance

Three experiments utilizing three Holstein steers (235 and 299 kg avg body weight for Exp. 1 and 2, respectively) were conducted to evaluate the effects of decoquinate, a synthetic coccidiostat, on ruminal fermentation, diet digestibility and performance of steers fed a finishing diet containing monensin and tylosin. Experiment 1 utilized a 70% forage diet, whereas Exp. 2 utilized a 20% forage diet. Each experiment was a 3 X 3 Latin-square design with treatments being 0, .5 and 5 mg decoquinate/kg body weight. Ruminal fermentation characteristics, water kinetics and blood constituents were measured on d 11 of each period, and zero-time volatile fatty acid (VFA) production was measured at 3 and 6 h post-feeding on d 12 to 14. No changes were seen in plasma glucose or L-lactate, ruminal pH, NH3-N or ruminal L-lactate for either experiment. Dry matter digestibility was depressed (P less than .05) at the .5- and 5-mg levels of decoquinate in Exp. 1, but dry matter digestibility was not affected in Exp. 2. No changes were seen in ruminal volume, outflow or total VFA concentration for either experiment. Molar proportions of VFA were not affected in Exp. 1, but the proportions of isobutyrate and butyrate decreased (P less than .05) at the 5-mg level of decoquinate in Exp. 2. Volatile fatty acid production was not changed in Exp. 1, but butyrate production was decreased (P less than .05) at the 5-mg level in Exp. 2. Experiment 3 involved 135 crossbred steers (259 kg avg initial wt), which were stratified by weight into 12 pens.(ABSTRACT TRUNCATED AT 250 WORDS)     

Salinomycin and lasalocid effects on growth rate, mineral metabolism and ruminal fermentation in steers

Two experiments were conducted to determine the effects of salinomycin and lasalocid on metabolism and growth of growing steers. In Exp. 1, 80 Angus steers (228 kg) were assigned to the following treatments: 1) control, 2) 50 mg salinomycin.hd-1.d-1, 3) 100 mg salinomycin.hd-1.d-1 and 4) 250 mg lasalocid.hd-1.d-1. Steers were fed corn silage once daily with allotments based on the amount of silage that each pen of five steers would consume in a 24-h period. In addition, .81 kg/hd of a corn-soybean meal supplement was fed daily during the 112-d study. Daily gains were similar across treatments, but feed intake was lower (P less than .05) for steers fed ionophores. Molar proportions of ruminal acetate were lower (P less than .05) in steers fed ionophores at 28 and 90 d. Ruminal propionate was lower (P less than .05) in control steers at 28 d, but values were similar across treatments on d 90. Plasma copper (Cu) was lower (P less than .05) in control steers on both sampling days. In Exp. 2, 16 Hereford steers were allotted to two blocks of eight animals each and assigned to one of three treatments: 1) control (n = 6), 2) 11 mg salinomycin/kg diet (n = 6) and 3) 33 mg lasalocid/kg diet (n = 4). Following a 28-d adjustment period, apparent absorption and retention of macrominerals and nitrogen (N) were determined during a 5-d collection period. Apparent absorption and retention of N did not differ among treatments when data were analyzed using N intake as a covariate.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of breed and diet on growth, nutrient digestibility, body composition and plasma hormones of Brangus and Angus steers

Two split-plot designed experiments were conducted to determine the effects of breed (Angus, A, or Brangus, B) and diet (fescue hay, FH; corn silage, CS; or concentrate) on composition and rate of growth, diet digestibility and plasma hormones of steers. In Exp. 1, 10 steers (five of each breed) were fed a CS-based diet followed by a FH-based diet for two consecutive 60-d periods. Both breeds had lower (P less than .01) DM intake and digestibility when fed FH than when fed CS diets. The B steers had higher (P less than .01) plasma insulin concentrations than A steers when fed the CS diet. In Exp. 2, during two consecutive years, 10 steers previously fed CS- and FH-based diets were finished with a corn silage-whole shelled corn-based diet. During yr 1, A steers had higher (P less than .01) DM intake and plasma triiodothyronine (T3) and thyroxine (T4) concentrations (P less than .05) than B steers did. Although final weights were similar (P greater than .10), A steers had heavier (P less than .05) carcass weights than B steers did. During yr 2, A steers had higher (P less than .07) DM and starch digestibilities and higher (P less than .01) plasma T4 concentrations than B steers did. The greater (P less than .01) energetic efficiency of A steers was attributed to the greater rates of fat deposition during yr 2. Regardless of type of diet fed, A steers were more efficient at depositing energy. Higher circulating T4 concentrations of A than B steers may explain some of the physiological differences between these breeds.     

Steam-rolled wheat diets for finishing cattle: effects of dietary roughage and feed intake on finishing steer performance and ruminal metabolism

Two experiments were conducted to determine the influence of dietary roughage concentration and feed intake on finishing steer performance and ruminal metabolism. In Exp. 1, 126 steers (334 kg) were used in a completely randomized design and fed (120 d) diets of steam-rolled wheat without roughage or containing 5, 10 or 15% roughage (50% alfalfa hay:50% corn silage). Steers fed 5 or 10% roughage gained faster (quadratic, P less than .05) and were more efficient (quadratic, P less than .05) than steers fed 15% or no roughage. In Exp. 2, six ruminally cannulated steers (447 kg) were used in a 6 x 6 latin square design and fed (twice daily) diets of steam-rolled wheat without roughage or containing 5 or 15% alfalfa hay at twice or three times NE required for maintenance. Increasing dietary roughage increased (linear, P less than .01) ruminal liquid passage 38%, indigestible ADF passage 63%, Yb-labeled wheat passage 75% and fiber fill 31%. The rate of in situ starch digestion tended to increase (linear, P = .16), and ruminal VFA concentration was 40 mM higher (P less than .01) at 4 h after feeding with increased roughage. Increased feed intake increased (P less than .05) ruminal starch fill, fiber fill, liquid fill and liquid passage 23%, Yb-labeled wheat passage 50% and Dry-labeled hay passage 20%. It reduced protozoa five- to sixfold (P less than .01) but doubled total bacterial counts (P less than .01). Ruminal NH3N was lower (P less than .01) and total VFA concentration was 50 mM higher (P less than .01) at 4 h after feeding. The acetate:propionate ratio was reduced from 2.3 to 1.3 (P less than .01) with increased intake. Adding roughage to a steam-rolled wheat diet increased passage and tended to increase rate of starch digestion; increased feed intake with its associated effects on ruminal fill and passage dramatically shifted the microbial population and fermentation end products.     

Performance, methanogenesis and nitrogen metabolism of finishing steers fed monensin and nickel

Sixty-four Angus steers initially averaging 354 kg were allotted to a 2 X 2 factorial arrangement of treatments to determine the effects of dietary Ni (0 or 5 mg/kg supplemental), monensin (0 or 33 mg/kg) and their possible interaction on performance, methane production and N metabolism. The basal diet was a high energy, corn-cottonseed hull based diet containing 10.2% crude protein and .30 mg/kg Ni on a dry matter basis. Monensin reduced (P less than .05) feed intake, did not affect average daily gain and improved (P less than .05) feed conversion over the 102-d study. Nickel supplementation did not significantly alter or interact with monensin to affect steer performance. However, steers fed Ni tended to have higher average daily gains and improved feed conversions. Monensin decreased (P less than .05) in vitro methane production, altered several carcass traits, increased (P less than .05) molar proportion of ruminal propionate and decreased (P less than .05) molar proportion of ruminal acetate. Nickel did not alter methane production, carcass characteristics or ruminal volatile fatty acid proportions. Both monensin and Ni increased (P less than .05) ruminal fluid urease activity when samples were obtained before feeding. A significant monensin X Ni interaction was found to affect ruminal epithelial urease activity. Monensin increased ruminal epithelial urease in steers not receiving supplemental Ni, but had no effect on ruminal epithelial urease activity in steers fed supplemental Ni. Ruminal fluid protein and ammonia-N were decreased (P less than .05) by monensin. Results of this study indicate that Ni may interact with monensin to affect ruminal epithelial urease activity but not performance or methane production in finishing steers.     

Effect of rotating monensin plus tylosin and lasalocid on performance, ruminal fermentation, and site and extent of digestion in feedlot cattle

Two trials were conducted to evaluate the effects of ionophore rotation programs on performance and digestion by feedlot cattle. A 90% concentrate diet was fed with treatments of no ionophore (C), 33 mg lasalocid/kg diet daily (L), 29 mg monensin plus 11 mg tylosin/kg diet daily (MT), and daily (D) and weekly (W) rotation of L and MT. In Trial 1, feedlot performance of 200 crossbred steers (average initial BW 296 kg) was evaluated during a 133-d period. In Trial 2, four crossbred steers (average initial BW 376 kg) fitted with ruminal, duodenal and ileal cannulas were used in a 4 x 4 Latin square design to evaluate treatment effects (excluding W) on ruminal fermentation and site and extent of digestion. In Trial 1, daily rotation of L and MT improved (P less than .10) feed:gain ratio compared with other treatment groups, but daily feed intake did not differ (P greater than .10) among treatments. Daily gain was greater (P less than .10) for steers fed D than for those fed C or MT, but not different from that of steers fed L or W. Carcass measurements did not differ (P greater than .10) among treatments. In Trial 2, ruminal molar proportions of butyrate and valerate were decreased (P less than .07) by MT and D compared with C and L. Proportions of other VFA, ammonia concentrations and ruminal pH did not differ among treatments. Ionophore treatments did not affect site or extent of digestion of OM, starch or N; no differences among treatments were observed for efficiency of microbial protein synthesis. Although daily rotation of L and MT improved performance of growing-finishing feedlot steers, this improvement was not attributable to alterations in ruminal fermentation, or in site or extent of nutrient digestion.     

Energy value of corn wet milling by-product feeds for finishing ruminants

Five trials were conducted to evaluate the energy value of corn wet milling by-products in finishing diets. In trials 1 (45 finishing lambs, 34 kg) and 2 (70 digestion wethers, 32 kg), Rambouillet X Suffolk lambs fed corn gained faster (P less than .10), more efficiently (P less than .10) and had higher (P less than .01) digestibilities of neutral and acid detergent fiber (NDF, ADF) and starch than lambs fed dry corn gluten feed (DCGF). Lambs fed wet corn gluten feed (WCGF) consumed less feed (trial 1, P less than .05; trial 2, P less than .01), were more efficient (P less than .01) NDF and ADF digestibilities than lambs fed DCGF. Starch, NDF and ADF digestion were higher (P less than .01) for lambs fed WCGF vs wet corn bran (WCB). Lambs fed WCGF gained faster (P less than .10) and consumed more (trial 1, P = .12; trial 2, P less than .10) feed than lambs fed WCB. Dried corn bran increased (trial 1, P less than .05; trial 2, P less than .01) intake and increased (P less than .01) dry matter digestion (DMD) compared with WCB. In trial 3, rates of in vitro dry matter and NDF disappearance were similar among by-product feeds. In trial 4 (50 individually fed Shorthorn-Hereford-Angus steers, 316 kg), steers fed WCGF tended to consume more (P = .14) feed than steers fed DCGF. Corn gluten feed (CGF) replacing 0 to 46% corn decreased gain (linear, P less than .05) and DMD (linear, P less than .10), while starch digestion was highest for 23% CGF (quadratic, P less than .01). A level X CGF type interaction (P = .15) occurred for efficiency due to the lower gain of steers fed 46% DCGF. The efficiency of CGF utilization was 97% that of corn when WCGF replaced 23 or 46% corn or DCGF replaced 23% corn. Dry CGF replacing 46% corn had 87% the value of corn. In trial 5 (186 Hereford-Angus cattle, 310 kg), DCGF replacing 25 and 50% corn had 97 to 100% the efficiency of corn, while intake and gain were not affected. Dry CGF replacing 25 and 50% corn silage increased (linear, P less than .05) intake 11.3% and gain 13.8%. In ruminants, CGF is highly digestible and feed efficiency is similar to corn when WCGF is fed up to 50% of the grain component or when DCGF is fed up to 25% of the grain component.     

Effect of nutrition, age and size on compensatory growth in two breeds of steers

Compensatory gain in cattle was studied to determine if age, previous rate of gain or size were factors of importance. A factorial experiment was conducted with growing diet regimen (control vs restricted), age [spring-born (older) vs fall-born (younger)] and breed (Angus vs Charolais) as the factors. During a growing phase, the two diets, (control = dehydrated alfalfa pellets; restricted = cubed grass-alfalfa hay, cottonseed hulls and soybean meal) were fed to both the older and younger steers of each breed to provide groups of similar age but different weights (growing regimen within age) and groups of similar weights but different ages (older-restricted vs younger-controls) at the time at which the steers were switched to a high concentrate diet. Interactions of breed with age and previous growing regimen diet on digestibility of some nutrients in the finishing diet were evident. During the growing phase, control steers averaged .72 kg/d gain, whereas the restricted steers averaged .25 kg/d. The older-restricted steers compensated (P less than .05) from 30 to 120 d after the beginning of the feedlot phase compared with older-control steers. Rates of gain of younger steers were intermediate to those of the older steers throughout the finish phase and were not influenced by growing diet, except on d 30. Rate of gain during the growing phase was negatively correlated (P less than .05) with rate of gain during the finishing phase (60 to 120 d). Within breed, weight at the beginning of the feedlot phase also was negatively correlated with gain during the finishing phase. Skeletal growth was reduced (P less than.05) by the restricted diet during the growing phase, and small compensation (P greater than .05) was observed during the finishing phase. Feed/gain for restricted steers was slightly lower (P greater than .05) than control steers. Younger steers were more efficient (P less than .05) overall in converting dry matter to gain, due to the relatively shorter growing phase when compared with the older steers. These data indicate that both previous gain and weight upon realimentation are influential on compensatory growth.     

Ionophores alter hepatic concentrations of intermediary carbohydrate metabolites in steers

The effects of ionophores on liver weight and function were determined in finishing steers (n = 24; avg weight 440 kg). Steers were group-fed one of three treatments (control, lasalocid or monensin at 33 mg/kg feed) for 46 d prior to slaughter. Three days prior to slaughter, blood was collected for the determination of serum Ca and Mg. At slaughter, the liver was removed, weighed, sampled, frozen in liquid nitrogen and subsequently analyzed for concentrations of carbohydrate metabolites and minerals. Liver weight (5.9 kg) was unaffected by treatment. Serum and hepatic Ca and Mg were not affected by ionophore treatment. Hepatic glycogen levels in steers fed ionophores were unaffected by treatment. Fructose 1,6-bisphosphate was 21% lower (P less than .10) in hepatic tissue of steers fed ionophores, whereas dihydroxyacetone phosphate was 15 to 37% greater in hepatic tissue of steers fed monensin (P less than .20) or lasalocid (P less than .10). Glyceraldehyde 3-phosphate was elevated more extensively by lasalocid than by monensin with increases of 72 (P less than .05) and 132% (P less than .001), respectively, over controls. Glycerol 3-phosphate levels were 37% (P less than .05) and 12% (NS) greater with these ionophores. Hepatic levels of pyruvate were elevated 12 (NS) to 36% (P less than .17) for monensin and lasalocid. Fructose 2,6-bisphosphate levels were 25% lower (P less than .25) in hepatic tissue of steers fed ionophores than in hepatic tissue from control steers. Other metabolites of carbohydrate metabolism in hepatic tissue were not altered appreciably. Changes in levels of intermediary metabolites of carbohydrate metabolism suggest alterations in hepatic carbohydrate metabolism favoring gluconeogenesis in steers fed ionophores.     

Performance and carcass traits of early-weaned steers receiving either a pasture growing period or a finishing diet at weaning

A 2-yr study was conducted to evaluate 1) steers fed ad libitum high concentrate after weaning (CONC), or 2) steers grown on pasture for 82 d, followed by high-concentrate finishing (PAST), on the performance and carcass traits of 74 early-weaned (117 d of age) steers. Potential breed differences were evaluated using crossbred steers of three types: 1) 3/4 Angus x 1/4 Simmental (BRI), 2) 3/4 Simmental x 1/4 Angus (CON), and 3) 1/2 Wagyu x 1/4 Angus x 1/4 Simmental (WAG). Steers were randomly assigned within breed to the two treatments. There was no interactions (P > .10), so the data were pooled over years. The CONC steers had an ADG that was .17 kg/d higher (P = .0001), intake 1.09 kg/d lower (P = .0001), and gain:feed ratio .013 unit better (.190 vs .177, P = .008) than PAST steers overall. Growing treatment did not affect total concentrate consumed (P = .97). The BRI steers required 31 d less than did CON steers (P = .008), and 23 d less than WAG steers (P = .05) when fed to a constant fat end point (1.1 cm). The BRI steers exhibited an ADG .16 kg/d higher (P = .0003), tended (P = .07) to have an ADG intake .49 kg/d higher, and exhibited gain:feed .01 unit better (.189 vs 180) than WAG steers. When compared with CON steers, BRI steers consumed 310 kg less total concentrate (P = .0003). No differences (P > .38) were observed between growing treatments for carcass characteristics or sensory attributes except that CONC steers tended (P = .11) to improve percentage of steers grading Average Choice or higher by 47% over PAST steers. The WAG steers had a 76-unit higher marbling score (1,000 = Small00, 1,100 = Modest00) (P = .006) than BRI steers, resulting in 19% more (P = .09) steers grading > or = Choice and 82% more (P = .03) grading > or = Average Choice. Liver (P = .15) and rumen (P = .01) weights as a percentage of hot carcass weight were reduced for CONC steers. The CONC steers had higher gain, lower intake, better efficiency, reduced liver and rumen weights, and consumed the same amount of total concentrate when compared with PAST steers. The BRI steers had less finishing days and lower daily intake compared with CON steers. The WAG steers had more days finishing, lower gain, lower intake, more undesirable efficiencies, consumed the same amount of total concentrate, and improved quality grades compared with BRI steers.