Estimation of feed intake and digestibility in Zebu type Arsi steers fed natural pasture using the n-alkane technique

Abstract

An experiment was conducted to validate the use of n-alkanes technique to estimate feed intake and digestibility in cattle under the sub-humid tropical conditions. The experiment was conducted using Zebu type Arsi steers fed natural pasture at different levels of dry matter (DM) intake (DMI). Eight steers, blocked into four groups based on body weight (BW), were used for the experiment. The steers in each group were randomly assigned to either low intake (11 g DM/kg BW) or high intake (ad libitum at 50 g refusal per kg diet offered) diet. The steers were housed in individual pens, and each steer was dosed twice daily with paper bung containing 400 mg C32 alkane using a balling gun for 15 days. Steers received pasture diets twice a day (at 8:00 and 16:00 h) with half of the daily allocation offered at each feeding. Feed intake, refusal, and total fecal outputs were recorded, weighed and sub sampled for proximate and n-alkane concentrations analysis. The odd-chain n-alkanes comprised the highest percentage during both wet and dry seasons. The alkanes C29, C31 and C33 were present in concentrations greater than 59 mg/kg DM in the two seasons. The mean fecal recovery rates ranged from 0.49 to 0.79 for low and 0.62 to 0.99 for high intake group, respectively during the wet season, whereas 0.68 to –1.05 for low and 0.61 to 0.9 for high intake group during the dry season, respectively. The DMI predictions using the double n-alkane technique were affected by season (P < 0.05) after fecal recovery correction. The C31/C32 and C33/C32 pairs accurately estimated the DMI regardless of intake levels during the wet season. During the dry season, the prediction for the low intake level improved after feacal recovery corrections, whereas that for the high intake level was accurate both with and without fecal recovery corrections. Moreover, using C35 alkane as internal marker provided an accurate estimate of DM digestibility (DMD) during both seasons for low intake group. The results obtained in this study confirm the accuracy of the n-alkane markers to estimate DMI and DMD in cattle consuming different levels of wet and dried pasture. However, accuracy can be reduced for digestibility estimation at higher levels of intake which need further validation.