Two experiments were conducted to evaluate digestion, performance, and physiological responses to Acremonium coenophialum-infected tall fescue straw offered to vary ergovaline concentrations. In Exp. 1, 16 Hereford x Angus ruminally cannulated steers (370 +/- 12 kg BW, mean +/- SE) were blocked by age and BW and, within block, randomly assigned to one of four treatments containing graded concentrations of ergovaline in the diet: 1) 0 ppb, 2) 158 ppb, 3) 317 ppb, and 4) 475 ppb. Alkaloid concentrations were produced using various mixtures of two varieties of tall fescue straw that had similar genetic and phenotypic characteristics but differed in degree of endophyte incidence and associated concentrations of alkaloids. In the 36-d digestion study, feed intake, apparent DMD, and total tract NDF digestion were not influenced by alkaloid concentration (P > .10). Differences were observed with digesta kinetics; specifically indigestible ADF (IADF) fill and outflow decreased linearly with increasing alkaloid concentration (P < .10). These differences, however, may be attributed to differences in IADF concentration of the diets. Physiological variables (heart rates, respiration rates, and rectal, ear, and tailhead skin surface temperatures) were not influenced by alkaloid concentration (P > .10). Concentration of serum prolactin measured weekly tended (P < .10) to decrease with increasing alkaloid concentration of the diet. At the conclusion of the study, each steer was injected with 100 micrograms of thyrotropin-releasing hormone (TRH). All steers responded to the TRH challenge (P < .10); however, responses did not differ (P > .10) between alkaloid concentrations of the basal diet (P > .10).(ABSTRACT TRUNCATED AT 250 WORDS)

A.; Maddock, R. J.; Stamm, M. M.; Schauer, C. S.; Rush, Ivan G.; Quinn, S.; and Lardy, G. P., "Growing rate of gain on subsequent feedlot performance, meat, and carcass quality of beef steers" (2009 LG diet consisted of 52.5% barley silage, 39.0% whole shell corn, and 8.5% supplement, whereas the HG diet contained 43.9% barley silage, 47.4% whole shell corn, and 8.7% supplement (DM basis). Initial BW (226 kg) was not different (P = 0.70) between treatments. Steers fed the HG diet had increased ADG (1.67 vs. 1.40 kg/d; P < 0.001) compared with steers fed LG diet. Dry matter intake was greater (9.49 vs. 8.35 kg/d; P < 0.001) for steers fed the HG vs. LG diet. Total backgrounding cost ($/animal) was less (P < 0.001) for those steers fed LG diet compared with HG diet ($126.00 vs. $140.35, respectively); however, total cost per kilogram of BW gain was not different (P = 0.24; $0.485/kg of BW gain). After the backgrounding period, steers were fed a common finishing diet for 135 d. During the finishing period, LG steers had similar (P = 0.12; 10.73 vs. 10.35 kg/d) DMI compared with those fed HG diets; however, ADG was not different (1.55 kg; P = 0.72) among treatments. Hot carcass weight, marbling score, 12th-rib fat, LM area, and USDA yield grade were not different (P > 0.12) between treatments and averaged 363 kg, Sm 30 , 1.33 cm, 83.8 cm 2 , and 2.7, respectively. There were no differences (P = 0.77; 3.63 ± 0.12 kg) in WBSF tenderness of rib-eye steaks. Percent cooking loss was increased in LG diets (P = 0.017). No differences were observed in consumer sensory analysis of tenderness, juiciness, and flavor intensity (P ≥ 0.276; 5.43 ± 0.12, 5.07 ± 0.13, and 5.17 ± 0.05, respectively). These data suggest that feeding steers diets that differ in energy concentration and result in ADG of 1.4 and 1.7 kg/d during the growing period results in minimal changes in subsequent finishing performance and does not affect meat quality.

Two studies were conducted to evaluate high-quality tall fescue hay as a supplement to beef cattle fed low-quality roughages. In Exp. 1, 15 ruminally cannulated Hereford x Angus steers (average weight 390 kg) were blocked by weight and assigned randomly to one of three treatments: 1) tall fescue straw, no supplement; 2) tall fescue straw plus tall fescue hay supplement; 3) tall fescue straw plus alfalfa hay supplement. The 28-d digestion study consisted of 14 d of adaption, 6 d of intake data, and 6 d of collection of feces, respectively, with a 1-d ruminal sampling (d 27) and ruminal evacuations (d 28). In Exp. 2, 90 gestating Hereford x Angus cows were stratified by age and body condition and, within stratum, assigned randomly to three replications of the same treatments as described for Exp. 1. In both studies, a basal diet of tall fescue straw was fed with ad libitum access, alfalfa hay was fed at .4% BW, and tall fescue hay was fed at a level isonitrogenous with the alfalfa hay (.61% BW). In Exp. 1, DMI was at least 13% greater (P < .01) for supplemented steers than for nonsupplemented steers and was 12% greater (P < .10) for steers receiving supplemental tall fescue hay than for alfalfa hay-supplemented steers. Digestibility of DM was greater for supplemented steers than for nonsupplemented steers (P < .05) and, between supplement treatments, greater for tall fescue hay-supplemented steers than for alfalfa hay-supplemented steers (P < .10). Ruminal ammonia values peaked at 3 h after feeding and were higher for steers fed supplement treatments than for those fed the control treatment from just before feeding through 6 h after feeding (P < .10). In Exp. 2, supplemented cows gained more BW than nonsupplemented cows (P < .01), and the tall fescue hay-supplemented cows gained more BW (P < .10) than cows supplemented with alfalfa hay. Likewise, supplemented cows lost less condition (P < .01) than their nonsupplemented counterparts during the 84-d supplementation period, and cows receiving tall fescue hay supplement tended (P = .23) to lose less condition than cows receiving alfalfa hay supplement. No differences in calf growth were noted among treatment groups (P < .10). In conclusion, supplementation of high-quality tall fescue hay to cows fed low-quality forage diets seems to result in performance that is similar to or better than that of cows receiving alfalfa hay supplements when fed on an isonitrogenous basis.