Comparison of in situ degradation kinetics of lucerne germplasm by ANOVA of non-linear models

Abstract

The ANOVA of non-linear models was used to evaluate the in situ degradation of five lucerne germplasm grown in the Po Valley of Italy during the growing seasons of 1987–1989. The germplasm included one North American synthetic cultivar, three Italian synthetic cultivars and one local Italian ecotype. The degradation kinetics of dry matter (DM), neutral detergent fibre (NDF), acid detergent fibre (ADF) and cellulose were measured using the nylon bag technique. Forage samples, cut at 10% bloom, were wilted, oven dried, ground (5-mm screen) and incubated for 0, 2, 4, 8, 12, 24, 48, 72, 120 and 168 h in the rumen of two dry Holstein cows fitted with ruminal cannula. The significance of two contrasts was tested: Contrast 1: ecotype versus synthetic cultivars and Contrast 2: North American versus Italian synthetic cultivars. Total DM yield of the ecotype showed no significant difference from the synthetic cultivars, while in Contrast 2, the North American synthetic showed greater DM yield (83.5 vs. 72.5 metric tonnes (MT) ha −1, P < 0.05). Chemical composition data showed the ecotype having greater ( P < 0.10) NDF and cellulose content relative to the synthetic cultivars. The North American synthetic cultivar showed greater ( P < 0.10) crude protein content than the Italian synthetic cultivars. Effective DM degradability, at a ruminal turnover rate of 8% h −1, was higher ( P < 0.05) for the synthetic cultivars (48.6%) compared with the ecotype (46.1%). This advantage for the synthetic cultivars may have resulted from greater content of non-cell-wall constituents and by the presence of cell wall constituents available to ruminal microorganisms. ANOVA of non-linear models showed higher DM and NDF degradability for synthetic cultivars from 0 to 168 h and from 13 to 168 h at P < 0.05, respectively. Therefore, cultivar selection significantly influenced the nutritive properties of lucerne forage. The application of ANOVA of non-linear models for Contrast 2 showed a generally greater ( P < 0.05) availability for the fibre fraction for the North American synthetic cultivar. These important nutritional differences could not have been detected using the traditional statistical analysis of single degradation parameters.