Crossbred steers (n = 252, BW = 379 +/- 28 kg) were allotted to 42 pens in a 2 x 3 factorial arrangement of treatments: control or steroid implant (STR; estradiol benzoate+progesterone [three lighter blocks reimplanted on d 84] and trenbolone acetate [reimplanted on d 63]), and either 0, 80, or 160 mg/wk of recombinant bovine somatotropin (bST). Steers were adapted to the finishing diet (12% roughage equivalent, 13% CP) before the start of the experiment and fed for 84 or 119 d. Blood samples were taken on d 0, 14, 28, 56, and 84 for plasma urea N (PUN), serum somatotropin (ST), plasma insulin-like growth factor I (IGF-I), and plasma amino acid assay. Few interactions were noted (P > .1). Gain was increased by both treatments: 1.30 vs 1.66 kg/d for control vs. STR (P < .001) and 1.44, 1.49, and 1.51 kg/d (linear, P = .07) for 0, 80, and 160 mg of bST/wk, respectively. Gain efficiency was also improved: 169 vs 205 g/kg (P < .001) and 177, 189, and 195 g/kg (linear, P < .001), respectively. Average PUN was decreased (P < .001) 29% by STR and decreased 17 and 29% by 80 and 160 mg of bST/wk, respectively (linear, P < .001). Somatotropin decreased mean serum ST compared with controls; STR increased ST 36% compared with controls. Average plasma IGF-I was increased (P< .001) 12% by STR and 13 and 19% (linear, P < .001) by 80 and 160 mg of bST/wk, respectively. Both STR and bST influenced (P < .05) plasma amino acid profiles. Indicators of carcass fatness were decreased linearly (P < .05) by bST; STR implant tended to decrease carcass fatness and increase longissimus muscle area, which was related to carcass weight. The anabolic effects of STR and bST were found to be additive and possibly independent in feedlot steers.
One-hundred and fifty crossbred yearling-heifers, averaging 264 +/- 17 kg were fed a 77% barley diet for 140 days to evaluate the effect of 0, 33, 49.5 and 66 ppm avoparcin and 33 ppm monensin on growth rate, feed efficiency, carcass quality and ruminal volatile fatty acid (VFA) concentration. Heifers were allotted by weight to 25 pens (six head per pen) in a randomized complete block design of five treatments and five replicates per treatment. On day 140, rumen fluid was obtained from a randomly selected replicate of six heifers from each treatment for VFA analysis. Carcass data and liver samples were obtained at slaughter on day 147. All avoparcin-fed cattle consumed less feed per unit gain (P less than .05) than did those in the control group. Feed intakes of the monensin-fed heifers and the heifers fed 49.5 ppm avoparcin were lower (P less than .05) than those of the control group. There were no differences (P greater than .05) between treatments for measured carcass, liver or rumen parameters.
I . Glucose, and acetic, propionic and butyric acids, the major energy sources available to ruminants, have been comparatively evaluated as energy sources for growth in lambs. The energy sources wcrc administered intravenously at 2.092 and 2 . j 10 MJ metabolizable energy per 24 h for periods of 9-12 d. Nitrogen was given in excess of requirement so that growth rate was limited by energy, as indicated by the increased N retention after intravenous administration of energy.2. The N-balance results from the trials showed that propionic acid promoted a significantly ( P < 0.01) higher N retention than acetic acid. In some of the experiments there were no significant difYerences between propionic and butyric acids, and in others, no significant differences between acetic and butyric acids. Compared with isoenergetic glucose infusion, all volatile fatty acids were less efficiently utilized than glucose. The mean values for N balznce (gjd) were 2.37 during control infusion, 6.53, 571, 5.48 and 4 5 9 during glucose, propionate, butyrate and acetate infusions, respectively.3. All energy sources reduced the faecal N excretion significantly. The greatest reduction was observed during butyrate treatment. The mean values for faccal N excretion (gjd) w-ere 4.24 €or control, 4.00 for acetate, 3.89 for propionate, 3.83 for glucose, and 3.76 for butyrate infusion. The reduced faecal N excretion after hutyrate infusion partly accounts for the increased N retention with that treatment.
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