Optimal stage of maturity for feeding napier grass (Pennisetum purpureum) to dairy cows in Kenya

Two experiments were conducted to determine the maturity at which napier gr ass (Pennisetum purpureum var. Bana) should be fed to dairy cows in Kenya. The grass was grown in two fields and irrigated to simulate precipitation i n the high (1200 mm/yr) and medium (800 mm/yr) rainfall areas in Kenya. The height, chemical composition and yields (Experiment 1) and in vivo digesti bility (Experiment 2) of the grass were determined weekly from week 3 to we ek 15 of growth. Optimal maturity for feeding was determined using crude pr otein concentration, yields of digestible organic matter and crude protein, and crude protein:digestible organic matter ratio methods. Height and yiel d increased and in vivo digestibility and nutrient ratio declined as the gr ass matured (P < 0.001). Although the height and yields of high-watered gra ss were 3 times those of low-watered grass, organic matter digestibility wa s higher on low-watered grass (P < 0.001). The optimal ages for feeding obt ained using these methods were within the 6-10 weeks but the heights were d ifferent from the 60-100 cm ranges that are recommended in Kenya. Further, the recommended maturity was different and more specific for each watering regime. The nutrient-ratio method was preferred since it considered the int errelationship between protein and energy concentrations. This method indic ates that napier grass should be fed to dairy cows at 55-60 cm (7-8 wk) and 130-140 cm (9-10 wk) in the medium and high rainfall areas in Kenya, respe ctively.