ORIGINAL RESEARCH Effect of supplementation with urea, blood meal, and rumen-protected methionine on growth performance of Holstein heifers grazing kikuyu pasture Armando Gomez & German David Mendoza & Carlos Garcìa-Bojalil & Ricardo Barcena & Jesus A. Ramos & Maria M. Crosby & Juan M. Pinos-Rodríguez & Alejandro Lara Accepted: 12 November 2010 / Published online: 14 December 2010 # Springer Science+Business Media B.V. 2010 Abstract Supplements with corn grain, molasses cane, and different nitrogen sources were evaluated in 16 growing Hosltein heifers [227±33 kg body weight (BW)] grazing kikuyu (Pennisetum clandestinum) pasture in a 10-ha sward (rotational grazing with electric fences) during 90 days in the summer season. The nitrogen sources were urea (U); urea and blood meal (U+BM); and urea, blood meal, and rumen-protected methionine (U+BM+RPM). Heifers were randomly assigned to four experimental supplements defined as follows: control (no supplementation), U, U+ BM, and U+BM+RPM. Two kilograms (as fed) of supplement was offered daily. The final BW of heifers fed U+BM+RPM was higher (P <0.05) than heifers not supplemented. The total and average daily weight gain of heifers supplemented with U+BM+RPM were higher than heifers not supplemented or supplemented with U and U+ BM (P <0.05). The average daily gain of heifers supple- mented with U and U+BM were higher than heifers not supplemented (P <0.05). Grass intake was not affected by supplementation, but total dry matter intake was increased by supplements with U, U+BM, and U+BM+RPM (P < 0.05). Feed conversion was improved by U+BM+RPM (P < 0.05). Total tract digestion was not affected by supplements. Blood urea nitrogen concentrations of heifers supplemented with U, U+BM, and U+BM+RPM were higher than heifers not supplemented (P <0.05). It is concluded that supplements with U+BM+RPM improved growth performance and feed conversion in heifers grazing kikuyu pasture. Keywords Blood meal . Heifers . Methionine . Urea . Grazed kikuyu grass Introduction In México, half of milk production is coming from grazing systems of tropical and subtropical areas. This dairy farming is based on perennial grass pastures in which nutritional quality changes dramatically in a whole year. Kikuyu (Pennisetum clandestinum) is a subtropical grass which has been used for pasturage by dairy cattle in México. Chemical composition of kikuyu grass is also variable with considerable ranges in nitrogen contents [140 to 410 g/kg dry matter (DM)] and neutral detergent fiber (NDF; 581 to 741 g/kg DM), and digestibility (484 to 734 g/kg DM) (Marais 2001). The nutritional variation A. Gomez División Académica de Ciencias Agropecuarias, Universidad Juárez Autónoma de Tabasco, km 25 Villahermosa-Teapa, Villahermosa, Tabasco, Mexico G. D. Mendoza (*) Departamento de Producción Agrícola y Animal, Universidad Autónoma Metropolitana, Xochimilco, Coyoacán, Distrito Federal, Mexico e-mail: gmendoza@correo.xoc.uam.mx C. Garcìa-Bojalil : R. Barcena : J. A. Ramos : M. M. Crosby Programa de Ganadería, Campus Montecillo, Colegio de Postgraduados, Montecillo, Mexico J. M. Pinos-Rodríguez Instituto de Investigación de Zonas Desérticas, Universidad Autónoma de San Luis Potosí, San Luis Potosí, Mexico A. Lara Universidad Autónoma Chapingo, Chapingo, Texcoco, Mexico Trop Anim Health Prod (2011) 43:721–724 DOI 10.1007/s11250-010-9759-z