Kikuyu (Pennisetum clandestinum) originates from Kenya and was introduced to South Africa in the early 1900’s. Today kikuyu comprises the greater part of irrigated pastures for summer and autumn grazing for dairy cows in the eastern and southern pasture-based production systems. Pioneering research at Cedara in 1929 illustrated the potential of the grass when milk production on pasture alone averaged about 10 kg per cow per day. Since then, Cedara and Outeniqua became the primary institutions for kikuyu research, with some additions to the knowledge base from other centres such as Bathurst and Elsenburg. In this paper I rely mainly on research results from these institutions.
Kikuyu establishes well, is persistent and tough, provides satisfactory grazing in the higher rainfall areas of the country and responds well to irrigation with respect to dry matter production, thereby supporting stocking rates in excess of 5 cows per hectare (depending on size and breed) and milk yields in excess of 9000 kg per hectare over the grazing period. Forage quality, however, is low compared to temperate pastures such as ryegrass. The primary reason is low available energy, but kikuyu also has other rather peculiar nutritional limitations.
The low available energy is primarily due to a low digestibility compared to temperate grasses, the reason being mainly a high content and low digestibility of the structural carbohydrates cellulose and hemicellulose. This is exacerbated when kikuyu produces stems and therefore the performance of the grazing animal is highly depended on the growth stage when the pasture is grazed. Kikuyu also has other limitations. It contains oxalic acid which binds calcium (Ca), making it largely unavailable to the grazing animal. This results in a wrong ratio with phosphorous (P) which ideally should be 1.5 - 2 Ca to 1 P. Kikuyu, depending on circumstances, may also be deficient in sodium and potassium in relation to Ca and magnesium. If Kikuyu is fertilized moderately with nitrogen (N) to the extent of 50 kg N per hectare per dressing, it should provide sufficient N to uphold dry matter production and meet the soluble protein requirements of the grazing cow. Higher levels will increase nitrate which may reduce rumen microbial activity and disrupt rumen function. These negative factors should be borne in mind when kikuyu pasture is grazed and appropriately corrected for in supplementation.
To improve quality, kikuyu can be over-sown with suitable grasses or legumes, notable ones being annual and perennial ryegrass, and white and red clover. Main limitations with over-sowing are associated with establishment, seasonality and persistence of the species, but if overcome, advantages are an increase in dry matter production of the pasture, higher quality, less fertilizer needs and an increase in milk yield of 25 to 40 %.
Another possibility of improving milk yield from kikuyu pasture is to supplement cows with concentrates. Typically, supplements will contain maize as energy source and comprise 25 to 35 % of cow dry matter intake. Maize however is high in starch which tends to lower rumen pH to the detriment of fibre digestion. The net result is that the benefit is lower than what would be anticipated from the energy value of the diet. In addition, cows may be susceptible to sub-acute ruminal acidosis. To limit these negative effects, two approaches have been adopted with some success: buffers to increase ruminal pH and the partial replacement of maize with readily digestible fibrous energy sources that contain less starch, such as hominy chop, wheaten bran and gluten 20. The viability of this approach however will depend on the availability, quality consistency and price at the farm gate of such products.
Botha, P.R., 2013. Kikuyu over-sown with different ryegrass species or clover: recent research. Research Article Compilation, Outeniqua Research Farm 2008-2013.
Cawood, J.G., Meeske, R & Cruywagen, C.W., 2013. High fibre concentrates for Jersey cows grazing kikuyu pasture, Research Article Compilation, Outeniqua Research Farm 2008-2013.
Dugmore, T.J. & Nsahlai, I.V. (undated). Kikuyu (Pennisetum clandestinum) in South Africa – A Review. KZN Department of Agriculture, Environmental Affairs and Rural Development, Cedara.
Van Dyk, N., Meeske, R. & Cruywagen, C.W., 2013. The use of buffers in the concentrate supplement for Jersey cows grazing ryegrass pasture in spring. Research Article Compilation, Outeniqua Research Farm 2008-2013.