The influence of associative effects on thein vitro-estimated utilizable crude protein (uCP) of feeds for ruminants

Abstract

Nineteen feed mixtures, formulated with 16 single feeds, were used to study the influence of associative effects on utilizable crude protein (uCP) of feed mixtures. The in vitro incubation technique of Zhao and Lebzien (2000) was used for uCP determination. It was found that the in vitro-determined uCP (D-uCP) was significantly higher than the weighted uCP (W-uCP) of feed mixtures and there was a significant regressive relationship between W-uCP (x) [g x kg(-1)DM] and D-uCP (y) [g x kg(-1)DM]: y=(0.94 +/- 0.23)x + (18.78 +/- 35.58), r2=0.49, n=19, p < 0.01. It was concluded that there exist significant associative effects of feed mixtures on uCP. In formulation of rations for ruminants the D-uCP should be used instead of W-uCP. Because of the low regression coefficient of the equation above, the D-uCP cannot be estimated from the W-uCP.

Ruminal fermentation characteristics and related feeding values of compound feeds and their constituting single feeds studied by using in vitrotechniques

“…Due to the small variability between feeds and only eight data points for regression analysis, this systematical overestimation should be interpreted with caution and reference to their biological and practical relevance, which seems negligible. This contrasts with the findings of Zhao et al (2005), who reported higher differences between calculated and observed uCP values in an experiment using 16 single feeds and 19 mixtures. They noted statistically significant and nonsystematic differences between calculated and observed uCP values.…”

“…They noted statistically significant and nonsystematic differences between calculated and observed uCP values. However, the authors mentioned the possibility of incomplete incubation of some feeds due to incomplete mixing with the incubation liquid (Zhao et al, 2005). Such an effect was avoided in the present study by the constant motion of the rotary incubator.…”

“…The CP fractions can be used to estimate ED values, which were found to correlate well with the ED values determined in situ (Shannak et al, 2000). Additivity of feeding values of forages or mixes of forages and concentrates has been investigated utilising GP (Sandoval-Castro et al, 2002;Robinson et al, 2009;Niderkorn et al, 2011) and uCP (Zhao et al, 2005). However, to our knowledge, there has been no research on the additivity of ID RUP .…”