Graduate Thesis Or Dissertation
 

In vitro and in vivo evaluations of chemically treated ryegrass straw

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  • Seven in vitro trials were conducted to compare the effects of soaking annual ryegrass straw in solutions of sodium hydroxide (Na₄OH), potassium hydroxide (KOH), ammonium hydroxide (NH₄OH), or sodium formate (NaCHO₂) at varying levels. Dry matter digestibility (DDM) was the criterion used to measure treatment response. A 3 x 3 Latin square designed lamb digestion trial, replicated three times, followed these screening trials. Its purpose was to study the effects that NaOH-treated straw had on animal health, feed and water intake, urine excretion and pH, apparent digestibility, nitrogen and energy utilization and sodium and potassium balances. Three feeding trials were also carried out to measure the performance of heifer calves fed untreated, but supplemented ryegrass straw based rations. A 3 x 3 Latin square designed sheep digestion trail supplied additional data on apparent digestibility and nitrogen and energy utilization for three of these rations. Spraying a two percent NaOH solution on straw did not significantly improve DDM while soaking at the same level produced a significant (P<.01) increase. There was no significant difference among particle sizes or treatment times for straw soaked in two percent NaOH. Two, four, six or eight percent levels of either NaOH₂ or KOH solutions significantly (P<.01) enhanced DDM. No significant improvement was noted above the eight percent level. NaCHO₂ significantly (P<.01) increased DDM above native straw, but higher treatment levels were necessary to achieve an equal magnitude of improvement than for NaOH. NH₄OH treatment produced variable results which could not be consistently repeated, but the crude protein (CP) content of treated straw was consistently increased. This was in contrast to NaOH soaking, which significantly (P< .01) degraded CP, acid detergent fiber (ADF) and acid detergent lignin (ADL) with each increase in level. All treatment combinations also produced significant (P< .01) cell wall constituents (CWC) declines below native straw. Straw treated on a solution basis was significantly (P< .01) higher in DDM than that treated on a dry matter basis. However, treated straw DDM was significantly (P< .01) greater in either case than that recorded for untreated straw. Draining off of the NaOH effluent prior to drying significantly (P< .01) reduced DDM. There was a trend for water soaking to depress DDM, but significance was not reached until samples were drained prior to drying. No detrimental effects were noted when lambs consumed unwashed NaOH-soaked straw. Daily dry matter (DM) intake per kg of body weight was significantly (P< .05) reduced for treated straw when compared to untreated. Increased water consumption and urninary excretion (P< .01) were evident when straw soaked in a one percent NaOH solution (ration three) was fed. Urine pH for sheep consuming straw treated on an eight percent dry matter basis (ration two) was significantly (P< .05) reduced below that recorded for urine from sheep fed the other two rations. However, none of the pH's were outside the normal range for ruminants. Treatment two significantly (P< .05) reduced apparent digestibilities for straw, DM, organic matter (OM), energy, CP, ash and cell contents below that for the other two treatments. Treatment three significantly (P< . 05) increased straw, ash, ADF, hemicellulose and CWC apparent digestibilities when compared to untreated straw (ration one). The digestibility of CP was significantly (P< .01) greater in the untreated straw ration. All sheep were in a positive nitrogen balance for the duration of the trials. There was no significant difference in nitrogen balance for lambs fed rations one and three. However, nitrogen retention for lambs receiving ration two was significantly (P< .05) depressed below the quantity retained by lambs on the other two rations. Ration three was clearly superior in terms of either percent nitrogen intake or percent of digested nitrogen. Untreated straw supported a statistically (P<.05) higher level of digestible energy per g DM intake than did either of the treated straw rations. Utilization of the gross energy of ration two was significantly (P< .05) less than that from the other two rations. Ration three supported lower average daily gains than the other two rations (P< .01). No definite conclusions can be drawn from the sodium and potassium balances. Evidently, sodium residue levels were not large enough to cause any problems as there were no observable side effects and potassium excretion was not increased. A series of feeding trials demonstrated that ryegrass straw can successfully comprise from 45 to 86% of a ration for growing heifers. Feeding value of the straw was improved to support gains from 0.38 kg to 0.80 kg per day by the use of a variety of feed ingredients that corrected the straw's deficiencies. Performance data suggested that the maximum level of urea that can be used in such high roughage rations is about 1.5%. Above this level gains and feed efficiency were depressed. Digestion trial data showed that DDM for untreated, supplemented straw was from 47.5 to 50. 4%. From 61.5 to 67.5% of the CP and 39.9 to 43.2% of the CWC was digestible. The CP was least digestible in the ration containing alfalfa. Nitrogen retention ranged from 6.1 to 7.1 g per day. The superior ration in this respect was ration 5, which contained whey.
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