Ruminal degradation of protein and carbohydrate using a batch culture system, and response to roughage removal, rumen modifier inclusion and postruminal amino acid supply in feedlot cattle
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Three main studies were conducted to characterize protein and carbohydrate ruminal degradation using a batch culture system, demonstrate and responses to roughage removal, rumen modifiers inclusion and postruminal amino acid supply in feedlot cattle. The objective of the first study was to characterize rumen N, starch, and NDF degradation rate (k[subscript d]), and further calculate ruminal degradable, undegradable and extent of digestion of those nutrients using a batch culture system. Nitrogen k[subscript d] experiments (48- h incubation) used soybean meal (SBM), AminoPlus (AP, Ag Processing Inc, Omaha, NE), corn dry distiller's grain solubles (DDGS), porcine blood meal (BM), cottonseed meal (CSM) and fish meal (FM), and ammonia release was used as an indicator of N degradation. Starch experiments (72-h incubation) used ground corn (GC), steam flaked corn (SFC), barley grain (BG) and wheat middlings (WM), and k[subscript d] was determined by DM disappearance and starch analysis. Neutral detergent fiber experiments (72-h incubation) used alfalfa fresh (AF), alfalfa hay (AH), tall fescue fresh (FF) tall fescue hay (FH) and soybean hulls (SH), and k[subscript d] was determined by DM disappearance and NDF analysis. Ruminal degradable protein decreased and undegradable protein increased between SBM, AP, FM, CSM, DDGS and BM for each respective feed (P < 0.01). AminoPlus and SBM did not differ (P = 0.27) on extent of digestion. Linear response contrasts were different (P < 0.05) among all feeds except between CSM compared to AP and FM, and BM compared to DDGS. Ruminal degradable starch was greater, and undegradable was lesser, for BG and WM compared to GC, and SFC did not differ from other feeds (P = 0.055). Quadratic response contrasts were different among all feeds (P < 0.01) except for GC compared to SFC and WM compared to BG (P > 0.05). Ruminal degradable NDF was greater, and undegradable was lesser, for AF, FF and SH compared to AH and FH (P < 0.01). Quadratic response contrasts were different among all feeds (P < 0.05) except for AH compared to AF and FH, and AF compared to FH (P > 0.05). Variance was mostly due to hour differences (93.3, 99.6 and 89.2% for N, starch and NDF, respectively). In conclusion, this study provides estimates of protein and carbohydrate ruminal degradation of feedstuff for use in diet formulation models. Ruminal degradation results observed in this study agree with published data and have been proved to be reproducible, resulting in a viable, and less complex method, to determine ruminal digestion characteristics of feedstuff. The objective of the second study was to determine the effects of roughage removal, ruminal modifiers, and diets balanced to meet effective energy and predicted AA requirement on beef steer growth performance. Crossbred steers (n = 150; 284 ± 23 kg BW) were fed 5 diets. Four diets were balanced to meet effective energy and predicted AA requirement with a traditional feedlot diet used as Control. Two diets contained roughage, with monensin (R-MO) or essential oils (R-EO). Two diets replaced roughage with corn; no-roughage with monensin (NR-MO) or essential oil (NR-EO). Steers fed roughage diets had greater BW (P < 0.01) compared to no-roughage, and final BW was greater (P = 0.004) for R-MO than Control. Average daily gain was greater (P < 0.01) for steers fed roughage diets compared to no-roughage. Steers fed balanced diet (R-MO) had greater ADG (P < 0.01) than Control. Dry matter intake was greater (P < 0.01) for steers fed roughage compared to no-roughage diets. Steers fed R-MO had greater ADG (P = 0.03) than Control. Steers fed no-roughage diets were more feed efficient (P < 0.01) compared to roughage diets. Hot carcass weight and marbling score were greater (P < 0.01) for steers fed roughage compared to no-roughage, and HCW was greater (P = 0.017) for R-MO than Control. Ribeye area was greater (P = 0.02) for steers fed R-EO and other treatments did not differ among each other. Steers fed R-MO had lesser ribeye area[times]cwt [superscript -1] compared to all other diets (P < 0.05). Steers fed R-MO had greater yield grade (P = 0.03) compared to all other diets. In conclusion, roughage removal improved feed efficiency but gain and carcass weight were not optimized. Balancing diets to meet effective energy and predicted AA requirement increased ADG for overall period, and increased carcass weight. Overall steers performance was not affected by ruminal modifiers, monensin or essential oils. The objective of the third study was to determine the effect of roughage removal and ruminal modifiers on ruminal fermentation characteristics in beef steers fed no-roughage diets. Three steers (initial BW 977 [plus or minus] 24.5 kg) were used in a 3 x 3 Latin square. Roughage diet was formulated to meet effective energy and predicted absorbable AA requirement with monensin (R-MO) to achieve an ADG 1.82 kg[times]d[superscript -1] for growing steers (BW 272 kg). No-roughage diets had fescue hay replaced with whole corn. Some ingredient levels in No-roughage diets were adjusted to meet nutrient requirements, and contained monensin (NR-MO) or essential oils (NR-EO). Dry matter intake was controlled at 1.87, 1.48, and 1.52% BW for R-MO, NR-MO and NR-EO, respectively. Daily average ruminal pH (mean, minimum and maximum), ammonia N and VFA did not differ among diets. Ruminal pH was greater (P < 0.04) for R-MO and lesser for NRMO in the initial hours after feeding and did not differ among diets between 8 and 10 h (P > 0.05). Average hourly pH across diets ranged from 6.37 to 5.74. Ammonia N was greater for NR-MO and NR-EO than R-MO during 2 and 10 h after feeding. In conclusion, roughage removal and replacement of monensin by essential oils had no effect on VFA profile, daily average ammonia N concentration and pH (daily average, minimum and maximum).
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