Forage quality of irrigated tanzânia grass

Author(s)

Marco Antonio Alvares Balsalobre

• Document type: Doctoral Thesis
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC)
• Defense date: 2002-04-26

Examining board members

Moacyr Corsi; Paulo César de Faccio Carvalho; Luiz Gustavo Nussio; Ricardo Andrade Reis; Flavio Augusto Portela Santos

• Advisor: Moacyr Corsi

Abstract

The objective of this work was to: determine the chemical composition; study DM, NDF, CP and nNDF ruminal kinectics; estimate forage intake by Nellore growing steers of irrigated Tanzania grass (Panicum maximum Jacq.); and validate the Cornell system. Simulated-grazed samples were collected on three periods of the year (spring, summer and fall, totaling 10 grazing cycles) on irrigated paddocks, rotationally grazed to three post grazing green dry matter residues (T1 = low, T2 = medium and T3 = high). Three rumen cannulated animals were used in a 3 x 3 Latin square design to determine the in situ degradability up to 96 hours of incubation. NDF, CP and nNDF were determined through NIRS in the residue remaining in the bags. Although there were no statistical differences imposed by the treatments during the year, the NDF and ADF showed higher values (P <.05) in the spring/summer, and lignin in the winter (P <.05) grazing cycles. Along the year the carbohydrate C fraction, TDN and CP varied from 14.14 to 23.21%, 55.26 to 59.31% and 11.29 to 14.61%, respectively. The Nsol, NNP and nADF (as CP%) varied from 18.23 to 28.77%, 24.97 to 35.97% and 6.48% to 11.94%, respectively. The average nFDN (as CP%) was 49.11%. From July to September forage quality was the lowest, probably due to the slowest tissue replenishment and flowering tillers’ accumulation. The N largest proportion (average of 40% of the CP fraction) was recovered in the cell wall, specifically in the B3 fraction, which should be the most important fraction on ruminal fermentation kinetics studies. Forage quality was the highest in the summer. The low post grazing residue treatment showed the largest increase in digestibility in all fractions from spring (74.96%) to summer (81.41%). The soluble protein fraction showed values up to 40% of the RDP, which varied from 62 to 76% of the CP. The NDF C fraction was underestimated by the CNCPS; our data suggests the %lignin/% NDF should be multiplied by a factor between 2.91 and 3.35. The CNCPS overestimated the nNDF C fraction (12.11 to 17.08%) as compared to the wet lab analysis value, as regarded to be the nADF fraction (6.48 to 10.7%). In general our results showed that the CP digestibility decreased as the CP and nNDF contents increased. The low post grazing residue and the spring time showed the lowest forage intake (65.8 and 61.3 g/kg PM, respectively). On the average the NDF intake was 1.34% of live weight. The post grazing height, leaf allowance and digestible dry matter explained 50% of forage intake. The forage intake increased as both the post grazing and leaf allowance increased during the summer. The estimated maximum forage intake (82.98 g/kg PM) during the summer was obtained with a post-grazing residue of 2,833 kg/ha of GDMR. The estimated range of RDP/RDOM ratio was from 15.02 to 19.18, which indicates an excess of rumen nitrogen of 4 to 29%. Overall the forage intake was overestimated in 3.8 to 55% by the CNCPS. (AU)