Rotational Grazing Systems Using Phenological Stage in Kikuyu Grass (Kikuyuocloa clandestina).

Rotational grazing systems must ensure that pastures have high nutritive value to meet the requirements of livestock and reduce supplement use. When pastures mature beyond an ideal phenological stage, young leaves continue to grow but the oldest leaves senesce, reducing the nutritive value of the forage. This study assessed the impact of grazing kikuyu (Kikuyuocloa clandestina) pastures at 4 leaves per shoot in the highlands (1900 masl) of Costa Rica. Dry matter yield (DMY), forage allowance (FA), and nutritive value (crude protein [CP], neutral detergent fiber [αNDF], in-vitro dry matter digestibility [IVDMD], fiber digestibility [NDFD]) were evaluated weekly across seven months. Prior to the study, paddocks were rotated at 30 days of regrowth. In the first two months of the study, existing senescent material was reduced by decreasing the days of regrowth to 25. In the last 5 months, paddocks were grazed at an average of 23 days of regrowth, in an effort to assess the nutritional value at 4 leaves per shoot. DMY (2678 vs. 3139 kg of DM ha^-1) and FA (21.53 vs. 26.82 kg of DM cow^-1) were lower during the 23-d period, whereas phenological stage was higher (3.96 vs. 3.56 leaves). CP content (25.44 vs. 22.76 %), IVDMD (88.09 vs. 85.31 %), and NDFD (77.15 vs. 71.87 %) of kikuyu pastures were higher during the 23-d period, whereas cell wall content was similar (52.31 vs. 52.50 % αNDF). The regrowth capacity of kikuyu pastures was not affected by the fewer days required to achieve 4 leaves per shoot. Although the DMY and FA had lower values during the 23-d period, the supply of biomass to grazing cattle was sufficient to meet DM requirements. Grazing the highly digestible biomass of kikuyu at 4 leaves per shoot could reduce the use of supplements and lower feeding costs on dairy farms.

Keywords: kikuyu, grass phenology, nutritive value, rotational grazing, senescence.