Partial replacement of ground corn by citrus pulp or steam-flaked corn fed at two concentrate Levels on rumen parameters and kinetics

Abstract Text:

The objective of this study was to evaluate three nonstructural carbohydrate (NSC) sources and two levels of concentrate on rumen parameters and kinetic of beef steers, having sugarcane silage as roughage source. Six rumen-cannulated Nellore steers, initial BW 345.10 ± 14 kg, 20 mo old, were individually fed and assigned to 2 non-contemporary 6 × 6 Latin squares (LS) in a 3 × 2 factorial arrangement of treatments. Treatments consisted of three sources of NSC: ground corn (GC), 70% of GC replaced by pelleted citrus pulp (PCP) or by steam-flaked corn (SFC), and 2 levels of concentrate in diet (CONC): either 60% (60C) or 80% (80C) on DM basis. The experiment had 6 periods of 14 d. Samples of ingredients, orts, and rumen contents were analyzed for chemical composition. Rumen fluid was collected for rumen pH, short chain fatty acids (SCFA), and ammonia nitrogen (N-NH₃) analyses. Statistical analysis was conducted using PROC MIXED procedure of SAS and model included fixed effects of CONC, NSC, and interaction (CONC×NSC); as well as random effects of period, animal(LS) and LS. Treatment effects were considered significant at P ≤ 0.05. Increasing concentrate from 60C to 80C decreased NDF turnover rate (P < 0.01) and rate of passage (k_p) (P < 0.01). It also decreased DM and NDF intake (P < 0.01). Partial replacement of GC by either SFC or PCP decreased DM and CP intake (P < 0.01). The PCP increased NDF turnover rate (P = 0.02) and decreased k_p (P < 0.01), compared to GC. There was a CONC×NSC effect (P < 0.05) on rumen mass of OM, DM, and FDN; where PCP with 60C decreased these parameters. Rumen mass of iNDF was not influenced by any treatment (P > 0.05). PCP increased rumen pH (P <0.01), acetic acid (P < 0.01), decreased propionic acid (P < 0.01) and, consequently, increased A:P ratio (P < 0.01). The PCP increased total tract digestibility of DM (P = 0.01) and NDF (P < 0.01), compared to GC. Partial replacement of GC by SFC decreased acetic acid (P < 0.01), increased starch digestibility (P = 0.05), and decreased rumen N-NH₃ (P = 0.03). In conclusion, replacing GC by PCP in sugarcane silage based diets reduced intake and rate of passage, but increased rumen pH and digestibility. Replacing GC by SFC increased starch digestibility and reduced rumen N-NH₃.

Keywords: carbohydrate source, concentrate levels, sugarcane silage