Kiran, D., Krishnamoorthy, U., Manju, G.L. and Manjunath, V. 2011. Relationship between gas production, true degraded organic matter and microbial biomass synthesis for protein feedstuffs as influenced by incubation time in the in vitro gas production. Animal Nutrition and Feed Technology, 11: 53-62.Five protein feedstuffs, namely ambadi (Hibiscus cantzabinus) cake, cottonseed meal, groundnut meal, rapeseed meal, and sesame meal were evaluated using the in vitro gas production technique, for fermentation stoichiometry, gas production, true digested organic matter (TDOM) and microbial biomass (MB) synthesis at incubation time of half asymptotic gas production (t(1/2)) and 24 h. The mean molar ratio of short chain fatty acids (c2:c3:c4) for the protein supplements at t(1/2) and 24 h were 0.71:0.20:0.09 and 0.72:0.19:0.09, respectively. The mean gas production (ml/g DM) at t(1/2) and 24 h were 101.2 and 196.3 respectively, whereas the TDOM (mg/g DM) at the corresponding incubations were 578.6 and 657.5. Similarly, mean partitioning factor (PF) at t(1/2) (5.87) was significantly (P < 0.0001) higher than at 24 h (3.37). The MB (mg/g DM) in the apparent undigested residue in the incubations was 172.8 and 100.0 at t(1/2) and 24 h, whereas the RNA equivalents (mg/g DM) for the corresponding incubations were 9.69 and 7.45, respectively. However, the ratio of RNA: MB at t(1/2) and 24 h were 0.0581 and 0.0808, respectively (P=0.0257). The disproportionate increase in gas production against the increase in TDOM at 24 h compared to at tin with similar fermentation stoichiometry at both incubations is explainable by the unfermented OM at t(1/2) that is solubilized by the ND extraction, thereby contributing to TDOM. Thus the artifact caused by solubilization of unfermented OM at t(1/2) could equal to or greater than the artifact caused by microbial lysis up to 24 h incubation. It is concluded that, for protein feedstuffs, the t(1/2) may not be the most appropriate time for determination of PF as an index of microbial biomass synthesis efficiency.

Effects of supplementing finger millet straw (FMS) with concentrates differing in partitioning factor (PF) on dry matter (DM) intake, nutrient digestibility and N metabolism were studied in crossbred heifers. The two concentrates, a high PF concentrate (HPFC) and low PF concentrate (LPFC), were formulated to be iso-metabolizable energetic and iso-N, but differ in PF. Eight crossbred heifers were divided into two groups of four based on body weight. Diets consisted of ad libitum FMS and concentrate supplements at the rate of 1kg/heifer/day as fed. The feeding experiment was completed in two periods in a switchover design, with each period lasting for 10 weeks with a 6-day metabolism study at the end of each period. The ME (MJ/kg DM) and CP content (g/kg DM) of HPFC and LPFC were 12.3, 161 and 13.1 and 149, respectively. The PF of the corresponding concentrates was 4.16 and 3.73. The intake (kg/day) of DM, organic matter (OM) and CP for the HPFC and LPFC groups were 4.37, 4.07, 0.27 and 4.35, 4.07, 0.26, respectively, but there were no differences between them. The digestibility (g/kg DM consumed) of OM for the two groups was similar (630.3 versus 650.7), whereas the digestibility of CP in HPFC (450.8) was higher (P=0.015) than in LPFC (396.1). The N retained in HPFC was higher than in LPFC (10.74g/day versus 8.80g/day, P=0.014), and urinary allantoin excretion (UAe, mmol/day) in HPFC was 54.88 versus 47.67 in LPFC (P=0.085). The calculated microbial N supply to the duodenum (g/day) was higher (P=0.098) in HPFC (38.09) versus LPFC (31.37). The microbial N (g/kg of digestible OM intake) for HPFC and LPFC was 14.7 and 11.8, respectively (P=0.023). Body weight gain (g/day) for the corresponding groups was 349 and 311 (P=0.003). The high PF concentrate supplement tended to result in higher efficiency of microbial biomass synthesis with an FMS-based high forage diet.