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

Abstract

Two experiments were conducted to determine the maturity at which napier grass (Pennisetum purpureum var. Bana) should be fed to dairy cows in Kenya. The grass was grown in two fields and irrigated to simulate precipitation in 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 digestibility (Experiment 2) of the grass were determined weekly from week 3 to week 15 of growth. Optimal maturity for feeding was determined using crude protein concentration, yields of digestible organic matter and crude pro¬tein, and crude protein:digestible organic matter ratio methods. Height and yield increased and in vivo digestibility and nutrient ratio declined as the grass matured (P < 0.001). Although the height and yields of high-watered grass were 3 times those of low-watered grass, organic matter digestibility was higher on low-watered grass (P < 0.001). The optimal ages for feeding obtained using these methods were within the 6-10 weeks but the heights were different from the 60-100 em 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 interrelationship between protein and energy concentrations. This method indicates that napier grass should be fed to dairy cows at 55-60 ern (7-8 wk) and 130-140 em (9-10 wk) in the medium and high rainfall areas in Kenya, respectively.