Feed intake and liveweight of cattle on subtropical native pasture hays. 2. The effect of urea and maize flour, or protected-casein

Abstract

Twenty-five Hereford cattle, of both sexes and a mean liveweight (� s.e.) of 172 �5.6 kg were allocated randomly from stratified groups to five treatments in which urea (UR), urea plus maize (URM), urea plus maize flour and protected casein (URMFC) or protected casein alone (FC) were offered to individually penned cattle on a basal diet of native pasture hay (8.4 g N/kg dry matter (DM)) over 70 days. Rumen ammonia concentrations were low in cattle on the basal hay diet (mean � s.e.d.) of 17 � 10.0 mg N/L but were significantly increased (P<0.01) by a supplement of 280 g/head.day of protected casein (FC) to 70 mg N/L and increased further (1 68 mg N/L) when urea was included with maize (URM) in the treatment. Volatile fatty acid concentrations in rumen fluid were increased (P<0.05) only by URM which also resulted in higher (P< 0..01) molar proportions of propionic acid. All treatments increased (P< 0.01) the hay intake of cattle during the study with the exception of URM, which was based on a high rate of feeding (400 g/day) of maize flour. Liveweight change of cattle was increased (P<0.01) by urea (UR) and maize flour (URM) to 290 and 340 � 56 g/head.day respectively. Higher (P< 0.01) liveweight gains were recorded when protected casein was included in the diet (URMFC, FC), being 550 and 600 g/head.day respectively. The results are discussed in terms of the scope for improving the efficiency of gain in cattle on a low quality grass hay by including low rumen-degradable proteins as a supplement to grass hays.