Efeito do processamento do milho no desenvolvimento do rúmen, desempenho de bezerros e na digestibilidade in vitro do grão

Abstract

Two experiments were conducted to evaluate the effects of corn processing, fine ground, flaked and broken ( 30 % ) on performance and health of calves (in vivo), and parameters of degradation (in vitro). In the in vivo experiment fifty-four Holstein calves were used from birth to 90 days old. Six animals from each group were euthanized at 30, 60 and 90 days for weighing organs and collect a fragment of the ventral sac epithelium of the rumen for histological and morphometric analysis. The concentrate intake from 5th to 8th weeks of life was lower in fine ground group (p<0,06) and similar between groups from the 9th week (p>0,06). Fine ground group had the lower body weight (p<0,06). Acetate, propionate and butyrate concentrations were different between groups (p < 0.06). The organs weights did not differ between groups (p>0,06) except reticulorumen which was heavier in the cracked corn group (p<0,06). There were no histological changes in ruminal epithelium between different groups. To perform the second experiment was necessary to develop an equation to estimate the volume of gas produced from pressure data (P) and volume (V) obtained by the fermentation of sorghum incubated in F57 bags (Ankom ®). 474 simultaneous P and V data were quantified, which varied from 0 to 4670 psi and the volume between 0 and 38 mL. The equation relating V and P obtained was: V ( ml) = 0.747 (where 0.0733 ) + 7.23 P (where 0.1165 ) + 0.101 P2 (where 0.0372 ) (R2 = 0.99 ) . The development of this equation allowed the use of F57 bags (Ankom ®) for the in vitro semi - automatic gas production technique. The second in vitro experiment was conducted to evaluate the dry matter degradability (DMD) and gas production of different corn processing : finely ground, flaked , cracked corn silage and rehydrated. Seven fistulated Holstein calves were used at 30 days of age as rumen inoculum donors. The evaluations were performed at 22 , 42 , 64 and 84 days of life. Three moments were used to evaluate the DMS and gas production: Six , 12 and 48 hours after ruminal fluid inoculation. The greatest gas production and DMS were, in descending scale, rehydrated corn, finely ground, flaked and broken. DMS and gas production were higher (p<0,05) at 42 days (39,19% and 108,87 mL) compared to 22 days (30,13% and 85,61 mL). Analyses with rumen innocuous of calves with 64 and 84 days were similar to those of 42 days (p>0,05). This indicates that after 22 days of microbial degradation maize with less efficiency than from 42 days of age. The grinding and processing of rehydrated corn silage were similar for the production of gases and DMS, indicating that both have the potential to produce the same performance in calves when the evaluated only available energy, however, the effects on ruminal environment should be considered.