Twenty ruminally fistulated steers (Exp. 1, 448 kg and Exp. 2, 450 kg) were used in two consecutive randomized complete block experiments with five treatments in each experiment. The purpose was to evaluate the impact of feeding different supplemental sugars or starch in combination with supplemental degradable intake protein (DIP) on the utilization of low-quality tallgrass-prairie hay. In Exp. 1, steers were given ad libitum access to forage and, except for the negative control (NC), received a limited supply (insufficient to maximize forage use) of supplemental DIP (.031% BW/d, DM basis). In addition to the NC, this experiment included four supplementation treatments in which one of four carbohydrate (CHO) sources (starch, glucose, fructose, or sucrose) was fed at .30% BW of DM/d. In Exp. 2, the treatment structure was identical except that the supplemental DIP level (.122% BW, DM basis) was near the level needed to maximize forage use. Forage OM intake (FOMI) was not affected (P> or =.26) by supplementation in Exp. 1 but was increased (P = .05) in Exp. 2. However, no difference (P> or =.46) in FOMI occurred among CHO sources in either experiment. Total OM and digestible OM intakes were increased (P<.01) by supplementation in both experiments. In Exp. 1, no difference (P>.26) in OM digestion (OMD) occurred among treatments. In Exp. 2, supplementation increased (P<.01) OMD. Additionally, sugars yielded a higher (P = .04) OMD than starch, and the monosaccharides yielded a higher (P = .02) OMD than sucrose. In Exp. 1, NDF digestion (NDFD) was decreased (P = .02) by supplementation, but no differences (P> or =.21) occurred among CHO sources. In Exp. 2, NDFD was increased (P = .03) by supplementation. Additionally, sugars led to higher (P = .05) NDFD than starch, and the monosaccharides led to higher (P = .03) NDFD than sucrose. In both experiments, discernible patterns were observable with regard to the effects of supplementation and type of supplemental CHO on ruminal fermentation characteristics. In conclusion, even though some consistency in fermentation profiles for different carbohydrate sources was evident in both experiments, forage intake and digestion responses were not consistent across experiments. This raises the possibility that carbohydrate source may interact with the amount of supplemental DIP fed and, as such, deserves additional investigation.

Two experiments were conducted to evaluate L-carnitine supplementation to cattle fed grain-based diets. In Exp. 1, seven Angus-cross steers (216 kg) were used in a 7 x 4 incomplete Latin square experiment to evaluate the effects of supplemental L-carnitine on N balance and blood metabolites. Steers were fed a corn-based diet (17.5% CP) at 2.5% of BW. Treatments were 0, 0.25, 0.5, 1.0, 1.5, 2.0, and 3.0 g/d of supplemental carnitine. The 18-d periods included 13 d for adaptation and 5 d for collection of feces and urine. Blood was collected before feeding and 3 and 6 h after feeding on d 18 of each period. Dry matter intakes tended to be highest when 1.5 g/d of carnitine was supplied, but N retention was not affected by carnitine and averaged 29.3 g/d. Plasma carnitine concentrations and urinary excretion increased with increasing carnitine supply, indicating that at least some of the carnitine escaped ruminal degradation and was absorbed by the steers. Plasma concentrations of NEFA demonstrated a treatment x time interaction; they decreased linearly in response to carnitine before feeding but increased linearly in response to carnitine at 6 h after feeding. Serum insulin and plasma glucagon, IGF-I, cholesterol, triglyceride, and amino acids were not affected by carnitine. Plasma concentrations of glucose, glycerol, urea, and beta-hydroxybutyrate all were increased by some of the levels of carnitine supplementation, but results for these measurements did not follow easily described patterns and seemed to be related to differences in DMI. In Exp. 2, 95 crossbred steers (357 kg initial BW) were fed finishing diets (14.5% CP) for 129 d. Diets were based on steam-flaked corn and contained 6% alfalfa and 4% tallow. Feed intakes, gains, and feed efficiencies were not affected by supplementation with 2 g/d L-carnitine. However, steers receiving L-carnitine tended to have fatter carcasses, as indicated by tendencies (P < 0.2) for thicker backfat, higher marbling scores, and higher yield grades. In conclusion, carnitine supplementation did not alter lean deposition in growing steers but it did alter plasma NEFA concentrations of growing steers fed a corn-based diet and also seemed to increase fat deposition in finishing cattle.

Consumption of monensin-containing feed contaminated with macrolide antibiotic residues resulted in the death of cattle from multiple feedlots in south-central Kansas. Cattle were fed milo dried distiller's grains (DDG) with solubles from a common source in conjunction with the ionophore antibiotic, monensin. Deaths occurred as early as 72-96 hours after feeding and were preceded by either no premonitory signs or 1 or more of the following: anorexia, depression, dyspnea, locomotor deficits, and recumbency. Significant gross lesions were pulmonary and mesenteric edema, hepatomegaly, and generalized myocardial and skeletal muscle pallor that was confirmed histologically as acute myodegeneration and necrosis. Other significant histologic lesions included centrolobular hepatocellular necrosis, congestion, and pulmonary interstitial and alveolar edema with fibrin exudation. Animals that survived beyond 6 weeks had poor weight gain and coalescing foci of myocardial fibrosis with residual myocardial degeneration. Analysis of trace mineral supplements for monensin were within the manufacturer's label range. The DDG samples from affected feedlots had 50-1,500 ppm of erythromycin, clarithromycin, and related macrolide antibiotic analogues, which originated in the alcohol residue. In a preliminary feeding trial, cattle fed this contaminated DDG in combination with monensin had clinical signs and died with gross and histologic findings comparable to those of the field cases. Even though rations supplemented with the contaminated DDG contained approved levels of monensin, the clinical and postmortem findings were consistent with those expected for monensin toxicosis. The presence of macrolide antibiotic residues in the contaminated feed appeared to affect the biotransformation of otherwise nontoxic levels of monensin, leading to clinical ionophore toxicosis.

The effects of supplemental methionine (Met), supplied abomasally, on the activities of methionine synthase (MS), cystathionine synthase (CS) and betaine-homocysteine methyltransferase (BHMT) were studied in growing steers. Six Holstein steers (205 kg) were used in a replicated 3 x 3 Latin square experiment. Steers were fed 2.6 kg dry matter daily of a diet containing 83% soybean hulls and 8% wheat straw. Ruminal infusions of 180 g/d acetate, 180 g/d propionate, 45 g/d butyrate, and abomasal infusion of 300 g/d dextrose provided additional energy. An amino acid mixture (299 g/d) limiting in Met was infused into the abomasum to ensure that nonsulfur amino acids did not limit growth. Treatments were infused abomasally and included 0, 5 or 10 g/d L-Met. Retained N (20.5, 26.9 and 31.6 g/d for 0, 5 and 10 g/d L-Met, respectively) increased (P < 0.01) linearly with increased supplemental Met. Hepatic Met, vitamin B-12, S-adenosylmethionine and S-adenosylhomocysteine were not affected by Met supplementation. Hepatic folates tended (P = 0.07) to decrease linearly with Met supplementation. All three enzymes were detected in hepatic tissue of our steers. Hepatic CS activity was not affected by Met supplementation. Hepatic MS decreased (P < 0.01) linearly with increasing Met supply, and hepatic BHMT activity responded quadratically (P = 0.04), with 0 and 10 g/d Met being higher than the intermediate level. Data from this experiment indicate that sulfur amino acid metabolism may be regulated differently in cattle than in other tested species.

Two experiments were conducted to evaluate the impacts of increasing levels of supplemental soybean meal (SBM) on intake, digestion, and performance of beef cattle consuming low-quality prairie forage. In Exp. 1, ruminally fistulated beef steers (n = 20; 369 kg) were assigned to one of five treatments: control (forage only) and .08, .16, .33, and .50% BW/d of supplemental SBM (DM basis). Prairie hay (5.3% CP; 49% DIP) was offered for ad libitum consumption. Forage OM intake (FOMI) and total OM intake (TOMI) were increased (cubic, P = .01) by level of supplemental SBM, but FOMI reached a plateau when the daily level of SBM supplementation reached .16% BW. The concomitant rises in TOMI and OM digestibility (quadratic, P = .02) resulted in an increase (cubic, P = .03) in total digestible OM intake (TDOMI). In Exp. 2, spring-calving Hereford x Angus cows (n = 120; BW = 518 kg; body condition [BC] = 5.3) grazing low-quality, tall-grass-prairie forage were assigned to one of three pastures and one of eight treatments. The supplemental SBM (DM basis) was fed at .08, .12, .16, .20, .24, .32, .40, and .48% BW/d from December 2, 1996, until February 10, 1997 (beginning of the calving season). Performance seemed to reach a plateau when cows received SBM at approximately .30% BW/d. Below this level, cows lost approximately .5 unit of BC for every .1% BW decrease in the amount of supplemental SBM fed. Providing supplemental SBM is an effective means of improving forage intake, digestion, and performance of beef cattle consuming low-quality forages.