Effect of Maturity and Protein Supplementation on Voluntary Intake and Nutrient Digestibility of Pangola Digitgrass Hays

Abstract

Two experiments were conducted with Pangola digitgrass (Digitaria decumbens Stent) to evaluate the effect of maturity on composition, in vitro digestion and in vivo voluntary intake and nutrient digestibility by sheep. In experiment I, six first-regrowth hays of 2, 4, 6, 8, 10 and 12 weeks were fed without supplemental protein and, in experiment II, four second-regrowth hays of 4, 6, 8.5 and 11 weeks were fed with and without 75 g of soybean meal daily per head. Crude protein declined rapidly with advancing maturity, from 18.3 to 4.3% in experiment I and from 17.8 to 5.8% in experiment II. Cell wall components, with the exception of hemicellulose, increased with advancing maturity in both experiments. Voluntary intake of digestible organic matter (OM) remained high during the first 6 weeks of regrowth (37 to 49 g/d/kg.75), but declined very rapidly thereafter to about 24 g/d/kg.75 after 8 weeks. In experiment I, voluntary intake of OM decreased from 68.5 to 57.1 g/d/kg.75 as maturity increased from 2 to 6 weeks and to 40.6 g/d/kg.75 at 8 weeks, remaining constant thereafter. Digestibility of OM decreased from 69.7 to 62.5% as maturity increased from 2 to 8 weeks and to 54.3 and 54.9% at 10 and 12 weeks, respectively. In experiment II, supplemental protein had little effect on digestibility of OM; however, it increased OM intake of the 8.5- and 11-week hays (43.8 to 55.8, and 47.4 to 54.1 g/d/kg.75, respectively). For all unsupplemented hays, the digestibility of OM was highly correlated with the digestibilities of neutral detergent fiber (r = .99) and cellulose (r = .98). The correlation between intake and digestibility of OM was .83. Digestible OM intake was correlated with OM intake (r = .99) and with digestibility (r = .91)