The aim of this study was to determine the variation of milk urea nitrogen (MUN) concentration according to milk yield and milk protein in Holstein cows in Boyacá, Colombia. Data previously collected (n=4901) over two years were used. Univariate analysis of variance was performed with the variables milk yield (l/day) and milk protein (%) as independent variables and the concentration of MUN as the dependent variable. In addition, a simple linear correlation analysis was performed between each variable. The results showed that MUN values are higher when milk yield is lower, but no statistical differences were found for MUN concentration according to milk protein content. Weak and negative correlation was found between milk yield and MUN concentration, but no significant correlation was found between milk protein and MUN concentration.

The aim of the present study was to evaluate the in vitro efficacy of Cordyceps bassiana for the control of the adult stage of Rhipicephalus microplus. The adult immersion test in a solution containing the BbF2011 strain of C. bassiana at the concentrations of 1x104, 1x106 and 1x108 conidia/ml (30 ticks per treatment) was evaluated. Treated ticks at a concentration of 1x108 conidia/ml reached 100% mortality at 15 days post-treatment (PT), while ticks at concentrations of 1x106 y 1x104 conidia/ml reached it at 18 and 21 days PT, respectively. Tick mortality was directly related to the fungi concentration. Moreover, ticks at the concentration 1x108 conidia/ml showed the lowest oviposition and larva hatching as compared to 1x106 and 1x104 conidia/ml concentrations (p<0.05). The effectiveness shown by C. bassiana on R. microplus opens the option to a new biological control method.

En el presente estudio se evaluó la eficacia in vitro de Cordyceps bassiana en el control biológico de la fase adulta de Rhipicephalus microplus. Se aplicó la técnica de inmersión de garrapatas adultas en una solución con la cepa BbF2011 de C. bassiana en concentraciones de 1x104, 1x106 y 1x108 conidias/ml (30 garrapatas por tratamiento). Las garrapatas tratadas a una concentración de 1x108 conidias/ml alcanzaron el 100% de mortalidad al día 15 postratamiento (PT), mientras que las concentraciones 1x106 y 1x104 conidias/ml lo obtuvieron en los días 18 y 21 PT, respectivamente (p<0.05). La mortalidad fue directamente proporcional a la concentración de C. bassiana. Asimismo, las garrapatas en la concentración de 1x108 conidias/ml presentaron una menor postura de huevos y porcentaje de eclosión de larvas que los tratamientos con 1x106 y 1x104 conidias/ml (p<0.05). La efect...