Prediction of Feed Intake and Its Relationships with Chemical Composition of Diets in Goats Consuming Concentrate, Bahiagrass Pasture and Mimosa Browse

Abstract

An indoor and a grazing experiment was conducted to determine how estimated feed intake and digestion by grazing goats consuming concentrate, bahaigrass pasture, and mimosa browse changed with body weight (BW), level of supplementation, and forage chemical composition. Twenty four Boer wether goats were assigned in a completely randomized design with repeated measures on the following 3 treatments: concentrate, mimosa browse, and bahiagrass pasture. Internal markers used to estimate both dry matter (DM) digestibility (DMD) and DM intake (DMI) included acid detergent lignin (ADL) and acid insoluble ash (AIA). Marker-derived estimates of DMD and DMI were compared with DMD measured by total fecal collection or directly measured by in vivo feed intake rate. Both ADL and AIA-based markers in mimosa and bahiagrass diets were similar from those derived by in vivo DMD; however, AIA-based marker in concentrate was under-estimated (P < 0.01). These results indicate that ADL and AIA indigestible markers performed similarly to in vivo DMD in mimosa and bahiagrass, although AIA concentration in mimosa seemed to be low compared to others. All markers yielded feed intake estimates that differed from those derived by ADL (P < 0.03), AIA (P < 0.01), and in vitro DMD (P < 0.001) compared to in vivo control, with ADL (P < 0.05) and in vitro DMD (P < 0.01) by period interactions, indicating that estimated intake from ADL and in vitro DMD increased more in mimosa browse diet with time period than in concentrate and bahiagrass diets with that estimated intakes being decreased with corresponding the second period due to lower in vitro DMD (21% to 4%) in second period compared to the first period in both concentrate and bahiagrass diets, respectively. In the present study, mean marker recoveries were higher (P < 0.01) for bahiagrass and mimosa diets than for the concentrate diets for both ADL- and AIA-based markers. It can be concluded that the use of natural markers in ADL and AIA offers advantages over the total fecal collection or direct measurement of in vivo intake methods for digestibility studies. Both ADL and AIA occur in common forages at readily measurable levels and laboratory procedures are not difficult or time consuming. Therefore, both ADL and AIA have possible use in digestibility studies where other methods may not be applicable.