Fermentation kinetics of stems of sorghum and millet genotypes

Zerbini, E and Sharma, A and Rattunde, H F W (1999) Fermentation kinetics of stems of sorghum and millet genotypes. Animal Feed Science and Technology, 81 (1 - 2). pp. 17-34. ISSN 0377-8401

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Abstract

Gas production profiles were obtained from in vitro fermentation of stems of six genotypes of sorghum and millet grown at the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), India. The ranking of sorghum and millet genotypes by cumulative gas production was consistent throughout the 96-hour fermentation period. However, differences were proportionally greater during the initial 3 and 6 h of fermentation. The multiphase model described by Groot et al. [Groot, J.C.J., Cone, J.W., Williams, B.A., Debersaques, F.M.A., Lantinga, E.A., 1996. Anim. Feed Sci. Technol. 64:77–89] was used to fit the in vitro fermentation gas observations of these substrates, and fermentation kinetics parameters were calculated using the fitted model. The final estimates of the model parameters (A, B, C), tested by varying the initial estimates obtained with the monophasic model by ±50%, were stable, showing no dependence on the starting values of the model parameters. However, in millet stems, the C parameter has shown a tendency to converge near unity. The stability of the final values of the parameters of the model in this study suggests the potential applicability of the multiphase model when only nine gas observations over a period of 96 h were available. However, the indeterminacy in the parameters of phase 1 for some millet stems indicates the need of an intermediate gas value between 0 and 3 h. In both, sorghum and millet the asymptotic gas of the first phase (A1) was negatively correlated with NDF (r = −0.82, p < 0.05; r = −0.80, p < 0.05, respectively) and lignin (r = −0.86, p < 0.05; r = −0.95, p < 0.01, respectively). The estimated maximum fractional rate of substrate digestion in the second phase (Rm2) showed a strong inverse relationship with lignin (r = −0.93, p < 0.01) in millet but not in sorghum. On the other hand, the time at which the rate of fermentation reached its maximum in phase 1 (tmax1) was negatively correlated with ADF and lignin (r = −0.88, p < 0.05 and r = −0.87, p < 0.05, respectively) in sorghum, whereas in millet only tmax2 (phase 2) was negatively correlated with lignin (r = −0.88, p < 0.05). Estimated differences in the contribution from the different phases to similar cumulative gas at 48 h in stems of different sorghum genotypes indicate the need to complement measurements of total gas production with selected kinetics parameters. The degree of variability between genotypes observed for kinetics parameters related to both, phases 1 and 2 suggest that these parameters have potential for discriminating feed quality differences between crop residues or plant parts. These results point out the difficulty in finding a single feed quality parameter to be used to rank different crop residues of different genotypes. Additional studies are needed to associate these parameters with voluntary intake and in vivo rumen outflow rates with which these phases could be associated.

Item Type:	Article
Divisions:	UNSPECIFIED
CRP:	UNSPECIFIED
Uncontrolled Keywords:	Gas production; Genotypes; Millet; Sorghum; Stems; Fermentation models
Subjects:	Mandate crops > Millets Mandate crops > Sorghum
Depositing User:	Library ICRISAT
Date Deposited:	28 Dec 2011 03:34
Last Modified:	28 Dec 2011 03:34
URI:	http://oar.icrisat.org/id/eprint/5104
Official URL:	http://dx.doi.org/10.1016/S0377-8401(99)00081-4
Projects:	ILRI/ICRISAT collaborative project “Genetic enhancement of ruminant quality of crop residues of sorghum and millet"
Funders:	UNSPECIFIED
Acknowledgement:	This research was implemented as part of the ILRI/ICRISAT collaborative project “Genetic enhancement of ruminant quality of crop residues of sorghum and millet”. The authors thank Drs. Paschal Osuji and Harinder Makkar for useful comments during the preparation of the manuscript.
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