Effects of feed intake level on efficiency of microbial protein synthesis and nitrogen balance in Boran steers consuming tropical poor-quality forage

Digesta passage and nutrient digestibility in Boran steers at low feed intake levels

“…Live weight changes of the animals were in the range of −1029 to 471 g/d across the four experimental periods. This is in line with the measured N retention of +5.1, −6.0, −6.4 and −8.2 g N/d for MER100, MER80, MER60 and MER40 respectively (Wassie et al, ). Live weight losses and a negative N balance at below MER feeding levels point to the mobilization of protein tissue (Chilliard et al, ) during each five‐week period of adaptation and measurements.…”

“…In the present study, CP digestibility was more strongly correlated with post‐ruminal laminar flow time (TT) than with rumen retention time (CMRT). The higher microbial N flow at MER100 than at MER80 (Wassie et al, ) and the relatively strong correlation of CP digestibility and TT underlined the importance of the lower GIT for CP digestion in the present study. To summarize, by comparing our MER100 and MER80 findings with literature, the higher digestibility of NDF and ADF as passage rate prolonged while feed intake declined are fully confirmed.…”

“…The decreased fibre digestibility was not related to the efficiency of ruminal microbial protein synthesis, which was similar for MER80, MER60 and MER40 (11.9, 11.8, 12.7 g N/kg digestible OM intake; Wassie et al, ). This might indicate that rumen fermentation and microbial growth were little impaired at sub‐maintenance feeding levels (Doreau et al, ; Wassie et al, ). However, apparent digestibility of DM, OM and CP might also be affected by a decline of nutrient absorption in the rumen and lower GIT or by a reduced activity of the animal's enzymatic digestion (Chilliard, Bocquier, & Doreau, ; Ortigues & Doreau, ) due to declining blood and oxygen flow to digestive organs in situations of severe energy deficiency.…”

“…The decreased fibre digestibility was not related to the efficiency of ruminal microbial protein synthesis, which was similar for MER80, MER60 and MER40 (11.9, 11.8, 12.7 g N/kg digestible OM intake; Wassie et al, 2019). This might indicate that rumen fermentation and microbial growth were little impaired at sub-maintenance feeding levels (Doreau et al, 2004;Wassie et al, 2019).…”

“…Supply of easy degradable carbohydrates and N through concentrate feeding is recommended for high fibre diets to improve particle breakdown and digestion (Hristov et al, ; Lazzarini et al, ; McLennan, Bolam, Kidd, Chandra, & Poppi, ; Mlay, Pereka, Weisbjerg, Hvelplund, & Madsen, ). Higher dietary CP and lower fibre concentration at MER100 than at MER80 improved CP digestibility as well as the efficiency of ruminal microbial protein synthesis and N balance (Wassie et al, ). However, higher efficiency of microbial protein synthesis at MER100 than at MER80 (13.7 and 11.9 g N/kg digestible OM intake respectively) did not improve DM and OM digestibility, and NDF and ADF digestibility were lower at MER100 than at MER80, which might be explained by the faster rumen passage of particles at MER100.…”