Effect of extent and rate of wilting on nitrogen components of grass silage

Abstract

Wilting grass prior to ensiling generally increases the dry matter (DM) intake but the effect of wilting on animal performance is still poorly understood. There is a need to improve understanding of the effects of wilting on the nutritional components and chemical composition of grass silage. This study focused on the effects of the extent and rate of wilting on N components of grass silage. Meadow grass was wilted to four DM contents (200, 350, 500, 650 g kg−1) at two different rates (fast, slow), creating a total of eight silages. Crude protein (CP) fractions were measured using the Cornell Net Carbohydrate and Protein System. Utilizable CP at the duodenum (uCP), a measure of feed protein value, was estimated using the modified Hohenheim gas test. Ruminally insoluble, undegraded feed CP (RUP) was measured using an in situ technique. Amino acid (AA) composition prior to and after rumen incubation was also investigated. Utilizable CP at the duodenum, RUP and true protein fractions B2 and B3 were increased by rapid wilting and high DM content (DM > 500 g kg−1), although the increase with DM was only mild for uCP, probably due to lower ME content in the DM‐650 silages. Non‐protein‐N decreased with increasing DM and rapid wilting. The higher RUP content from both DM‐650 silages leads to a higher total AA content after rumen incubation. Treatment also influenced the AA composition of the ensiled material, but the AA composition after rumen incubation was similar across treatments. Rapid and extensive wilting (DM > 500 g kg−1) improved protein value and reduced CP degradability. Increased uCP may result in higher milk protein yield, while reduced degradability may reduce N lost from urinary excretion. The primary effect of wilting on post‐ruminal AA supply from RUP appeared to be quantitative, rather than qualitative.

Protein characteristics in grass–clover silages according to wilting rate and fermentation pattern

“…Nevertheless, the analytical variation and errors were about the same in the two studies, and the concentration of uCP 0·04 was within the same range for quite similar forages (120–140 g kg −1 DM in the study of Edmunds et al . (), and 120–150 g kg −1 DM in the present study).…”

“…Our results were in agreement with the findings of Edmunds et al . () who found a lower non‐protein nitrogen concentration in rapidly wilted than in slowly wilted silages. They explained the difference by differing duration of exposure to proteolytic plant enzymes.…”

“…Edmunds et al . () evaluated the effect of wilting on grass silage using the same in vitro technique in combination with an in situ method and the Cornell system for protein evaluation of forages (Sniffen et al ., ). They concluded that the degree and rate of wilting influenced the concentration of uCP 04 and rumen‐undegraded protein in grass silage and that the method may be a useful tool in predicting animal response to the forage because it considers the interaction of energy and protein metabolism.…”

“…As mentioned above, the estimated concentrations of uCP 04 in the present study covered about the same range as in the silage analyses performed by Edmunds et al . (, ). This fact indicates reproducibility of the method between laboratories but, as Edmunds et al .…”

“…These compounds may reduce the exposure of the protein to rumen degradation (Lee et al ., ; Eickler et al ., ; Coblentz and Grabber, ) and increase the flow of feed protein from the rumen (Vanhatalo et al ., ). A second option is to increase the wilting rate during preservation and thereby inhibit the natural proteolysis that is induced in plant cells after harvest (Verbič et al ., ; Edmunds et al ., ). A third option is the use of additives to achieve a rapid lowering of pH and to regulate or prevent proteolysis and fermentation of easily degradable carbohydrates (McDonald et al ., ; Van Soest, ; Jatkauskas and Vrotniakiene, ).…”