Methods for determination of passage rates of, fibre in tropical forages in mature non-pregnant dairy heifers

Abstract

Passage rates were estimated in vivo using five rumen fistulated non-pregnant dairy heifers. Rumen evacuation technique (RET), and chromium mordanted fibre (CR-MF) method were used to estimate passage rates in 5 x 5 Latin Square experiment. Passage rates measured using CR-MF and RET showed high variabiltiy between forages and between the two methods., The passage rates derived from parameters obtained from RET differed (P<0.03) between the forage diets. The values were 1.78-1. 63, 1 .54 and. 1. 36 % h^-1 for urea treated rice straw (UTRS), Lucerne/(Medicago: sativa) grass, mixture hay, Brachiaria bnzantha hay (BH), Lucerne alone (LH) and maize (Zea mays) silage (MS) respectively. The passage rates obtained from CR-MF method were also different (P< 0.42) between the forage diets and were 3.24, 2.98, 2.79, 2.56 and 2.26% h^-1 for MS, LH, UTRS, LGH and BH respectively. The values were higher in CR-MF method ranging from 2,26-3. 24 h^-1 compared to those obtained from RET which ranged from 1.36-1.78 h^-1. The results further showed that the passage rates were estimated with different accuracy when compared with the precision with which the passage rates were used to calculate fill values for prediction of dry matter intake (DMI). Fil values, calculated from RET predicted DMI with a precision of R² = 0.70 compared to R² = 0.46 obtained from CR-MF. It was conclued that CR-MF give higher values of passage rates  in tropical forages than RET method of estimating passage rates and the later method is recommended as it predicted DMI with higher precision.

Keywords: Rumen evacuation technique (RET), chromium, mordanted fibre (CR-MF), flow rate

Tanzania J Agri. SC. (2002) Vol. 5. No.1, 1l-20