We measured contractile force of ventricular strips form the turtle Chrysemys picta bellii exposed to 1 h of combined anoxia and acidosis (pH 7.0) at 20 degrees C. Strips either beat spontaneously (self-paced) or in response to electrical stimulation (paced at 12, 24, or 36 beats/min). Tissue [lactate] and intracellular pH (pHi) were measured in control strips and at the end of anoxia-acidosis. In self-paced strips, at normal extracellular Ca2+ concentration ([Ca2+]o) (1 mM), both rate and force fell significantly after 1 h of anoxia-acidosis to 54 and 17.1%, respectively, of control values. Increased [Ca2+]o to 10 mM at 30 min had a small but significant positive effect on both rate and force. Contractile force of paced strips also fell progressively during anoxia-acidosis, but the decrease varied directly with pacing frequency. Under all cases of anoxia-acidosis, pHi fell significantly from the control value of 7.53; in paced strips, acidosis was most severe at 36 beats/min (pHi 6.75), and in self-paced strips, pHi (approximately 6.85) was independent of [Ca2+]o. Based on this and previous work, we conclude that combined anoxia-acidosis, similar to that observed in vivo after prolonged anoxic submergence, profoundly depresses cardiac function. Both hypercalcemia and bradycardia improve performance in this extreme state, but these effects are not as great as when anoxia and acidosis occur alone.
Increased dietary inclusion of rapidly-fermentable carbohydrates and a great proportion of corn-derived CP may result in increased rumen degradable protein (RDP) microbial requirements and reduced RDP supply, respectively. An experiment was conducted to evaluate the effect of processing and moisture content of corn grain in finishing diets concurrently balanced to meet increased RDP requirements on feedlot cattle performance. A semi-dent corn hybrid crop was harvested and stored as dry-whole (DWC), dry-rolled (DRC), whole high-moisture (WHMC), or rolled high-moisture (RHMC) corn (89.3% DM and 32.4% moisture for dry and high-moisture corn, respectively). Four dietary treatments containing 78.8-79.0% corn grain were arranged by adding (DM basis) 0.15, 0.20, 0.0, or 0.0% of urea to DWC, DRC, WHMC, or RHMC-based diets, respectively, to meet RDP requirements, which were measured in previous experiments using the same corn hybrid as in the present experiment. Angus steers (n = 144; 356 ± 2.7 kg initial BW) were group-housed in 24 pens, fed once daily from d 1 to 86, and held off feed and water for 16 h to record initial and final BW. Data were analyzed as a randomized complete block (6) design. Rate of BW gain and HCW increased and DMI decreased (P ≤ 0.02) from dry and whole to moist and rolled corn-fed steers (Table 1). Consequently, steers fed the RHMC-based and 0%-urea diet were finished at heavier BW and were more efficient (P ≤ 0.02) converting feed into BW and carcass compared with steers fed any of the other diets. Feeding high-moisture compared with dry corn led to improved cattle performance and might reduce urea-derived costs. The convenience of using RHMC instead of WHMC may rely upon the balance between improved animal performance and increased feed costs associated with corn processing.
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