Influence of drying technique on chemical composition and ruminal degradability of subtropical Cajanus cajan L.

Abstract

The experiment investigated the influence of forage drying methods on the dry-matter digestibility of foliage from Cajanus cajan varieties (ICEAP 00557, ICEAP 01514 and CIMMYT100/01). These leaves were harvested at week 20 of growth and either oven- or shade-dried and analysed for chemical components and rumen degradability. Three rumen fistulated lactating Holstein cows (430 ± 18 kg live weight) were used to evaluate ruminal degradation kinetics using in vitro and in sacco procedures. Samples were incubated for 0, 4, 8, 12, 24, 30 and 48 h in vitro (IV DaisyII) procedure. In the in sacco procedure, samples were incubated for 0, 4, 8, 12, 24, 30 and 48 h in the rumen of cows. Dry matter disappearance (DMD) data for both measures were fitted to the equation Y = a + b (1 – e–ct), where b is the slowly degradable fraction and c is the degradation rate constant, to approximate rumen degradability characteristics of varieties. Shade dried leaves contained higher crude protein (CP) (P < 0.05) than oven dried leaves. Oven drying method increased (P < 0.05) neutral detergent insoluble nitrogen (NDIN) and acid detergent insoluble nitrogen (ADIN) content of varieties. However, shade drying method gave the higher concentration of NDIN and ADIN. Drying technique had no effect (P > 0.05) on ash, neutral detergent fiber (NDF), acid detergent fiber (ADF) and acid detergent lignin (ADL) of varieties. Drying method did not affect (P > 0.05) calcium (Ca) and phosphorus (P) concentration in the forage dry matter. Drying method had no effect (P > 0.05) on b and c of all varieties during in vitro procedure. However, shade-drying method increased (P < 0.05) b and c of all varieties during in sacco procedure. It was concluded that shade-drying, in contrast to oven-drying, would be the most suitable method as it improves the nutritive value of the forage for ruminants.