Effect of corn and beet pulp based concentrate on ruminal parameters in wethers fed with fresh forage

Abstract

Four wethers housed in individual pens and fitted with ruminal cannulae were grouped (two wethers per group) and fed fresh forage (Italian ryegrass, Lolium multiflorum) with either beet pulp (BP) or corn based concentrate (C) as supplements, using a crossover experimental design. The experiment was carried out during two experimental periods: the growing phase (early spring, G) and the reproductive phase (late spring, R) of the ryegrass. The diet of each animal was changed as the grass moved from the vegetative phase to the reproductive phase. The intake, the chemical composition of the diet and ruminal parameters such as pH, ammonia and volatile fatty acid were determined. Total dry matter intake (DMI) decreased from early to late spring (1081 vs 767 g/d; P<0.0001). Herbage DMI in particular decreased more (811 vs 543 g/d; P<0.05) than concentrate DMI (271 vs 224 g/d; P<0.054). There were marked differences in the chemical composition of the diet in wethers fed with the forage from early or late spring. This was because of changes in the characteristics of the forage. In detail, DM, NDF and ADF increased from early to late spring while CP, and EE decreased (P<0.05). Ruminal pH was lower in G than in R (6.24 vs 6.57, P<0.05). The concentrate used had no effect on the pH value. The ammonia concentration in the rumen fluid decreased from early to late spring (10.79 vs 6.68 mg/100 ml, P<0.05) and it was not influenced by the source of carbohydrates from the concentrate. VFA rumen fluid concentration increased (P<0.05) after feeding and decreased before the second meal. In the rumen fluid, the maximum total VFA concentration and the lowest pH were observed 2 h after the morning meal. Acetate and butyrate concentrations in the rumen fluid were influenced by the period (P<0.05) but not by the concentrate source. By contrast, the concentrate source significantly influenced the rumen fermentation patterns of propionate and VFA ratios, with higher propionic acid and lower acetate to propionate ratios in C than BP. This highlights the importance of the carbohydrate source in supplements for pasture based rations which varied according to the proportion of beet pulp and corn in the ingested diet.

Keywords

• Ryegrass, Concentrate, pH, Volatile fatty acid, Ammonia.