The aim of this study is to evaluate the behavior of the parameters of the degradation model proposed by Mertens & Loften (1980) fitted to the results of a rehearsal of degradability in situ. In the experiment, we evaluate the potentially degradable residue of neutral detergent fiber (NDF) of coastcross grass (Cynodon dactylon x Cynodon nlemfunensis) cut at 60 days, with three replications. The potentially degradable residue of NDF is studied using fifteen incubation times (0; 0.5; 1; 3; 6; 9; 12; 18; 24; 36; 48; 56; 72; 96 and 120 hours). The experimental plot is comprised of a non-lactating cow with a permanent ruminal fistula. It is obtained mean and individual fits for the animals. Variances of parameter estimators is also obtained through both the covariance matrix of the parameters and the jackknife method, then resulting expressions for the estimate of the confidence interval for the parameters of the model. The results shows that the jackknife method presents larger variance estimate for the parameters of the model of Mertens & Loften (1980), resulting in confidence intervals of greater amplitude and less precise parameter estimates for both the individual and mean fits.
Nonlinear regression; ruminal degradability; jackknife method; coast-cross grass
