Effect of application rate of a nitrite-hexamine containing additive on the fermentation and nutritional composition of direct-cut or wilted ruzi grass silage

Abstract

The objective of this study was to verify whether the application rate of a chemical additive based on sodium nitrite (300 g/L) and hexamine (200 g/L) interacts with the dry matter (DM) content, manipulated by wilting, to change the fermentation and nutritional composition of ruzi grass silage. Treatments were a factorial combination of two forage DM levels (direct-cut and wilted up to 426 g/kg DM) and four doses of additive (0, 1, 2 and 3 L/t), with four replicates per treatment. After 60 d of regrowth, a field of ruzi grass (0.2 ha) was cut with a pull-type rotating disc mower at 10 cm above the ground. The forage from half of the harvested area was immediately collected manually (206 ± 2.4 g/kg of DM) and chopped by a stationary forage chopper (10-mm theoretical length of cut). Another half of the harvested area was wilted for 4 h till reaching 426 ± 9.2 g/kg of DM before harvesting and chopping. Each forage source was divided into 16 piles (2 kg/pile) to receive the additives (4 piles per treatment), resulting in a total of 32 piles (i.e., replicates). Afterwards, 1 kg of treated forages were ensiled in nylon-polyethylene bags (33 × 45 cm, 160 µm thick) and vacuum-sealed. After 60 d of storage, the silos were opened and silages were sampled to determine: DM loss, microbial counts, fermentation end-products, chemical composition and in vitro DM digestibility. There was an interaction between additive dose and DM content for several silage characteristics, including DM loss during fermentation (P < 0.001). Within each DM level, the fermentation-end products associated with Clostridium metabolism (e.g. n-butyric acid, propionic acid, i-butyric acid, i-valeric acid, n-valeric acid, ammonia and 2,3-butanediol) reduced linearly as the additive dose increased. The DM loss of direct-cut (134, 117, 106, 85 g/kg) and wilted (77, 68, 50, 46 g/kg) silages were linearly reduced with the increasing additive application rate, whereas DM loss was lower for the wilted forage. The content of soluble carbohydrates, crude protein, rumen undegraded protein, and in vitro DM digestibility increased linearly as additive dose increased in each DM condition (direct-cut and wilted), indicating that the treated silages were better preserved. In conclusion, both wilting and application of additive based on sodium nitrite and hexamine were able to restrict the development of clostridia and nutrient losses during the fermentation of ruzi grass silage, whereas the dose of additive required to curtail butyric fermentation interacted with DM content. Assuming linearity of response, each 1 L/t of additive was able to replace approximately 60 g/kg of crop DM as a strategy to reduce DM loss.