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
Authors:   , Masiero Mariana
   Medeiros 
Published: April 2021

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 less
than 0.01). AminoPlus and SBM did not differ (P = 0.27) on extent of digestion. Linear
response contrasts were different (P less than 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 less than 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 less than
0.01). Quadratic response contrasts were different among all feeds (P less than 0.05)
except for AH compared to AF and FH, and AF compared to FH (P greater than 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 Â± 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 less than 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 less than 0.01) for
steers fed roughage diets compared to no-roughage. Steers fed balanced diet (R-MO) had
greater ADG (P less than 0.01) than Control. Dry matter intake was greater (P less than 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 less than 0.01) compared
to roughage diets. Hot carcass weight and marbling score were greater (P less than 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 less than 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 less than 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 greater than 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).