Eighteen multiparous lactating grazing Holstein cows, 9 ruminally cannulated, average 136.1 +/- 14.6 days in milk, were randomly assigned to three treatments consisting of water containing different levels of total dissolved solids (TDS; mg/l): Treatment 1 = 1,000; Treatment 2 = 5,000 and Treatment 3 = 10,000, at the Experimental Dairy Unit at Rafaela Experimental Station (31 degrees 11'S latitude) during summer 2005. Animals were arranged in a randomized complete block design with three 28-day experimental periods, with 3 weeks for water adaptation and 1 week for measurements. Feed and water intake, milk production and composition, body weight and condition score and rumen parameters were evaluated. No treatment effects were observed in any of the variables evaluated, with the exception of water intake, which was higher for animals receiving 10,000 mg/l TDS in the drinking water (189 l/day vs. 106 and 122 l/day for cows receiving water with 1,000 and 5,000 mg/l TDS, respectively). Water intake was significantly higher for animals in treatment 10,000 (P < 0.05). It was concluded that the rumen presents a surprising buffer capacity and that consideration of TDS alone is insufficient to characterize drinking water quality.

ResumenCon el objeto de mejorar la propiedad de coagular de leche entera tratada bajo condiciones moderadas de temperatura, 10 minutos a 73 °C, se estudió el efecto del pH (6.2-6.6) y la adición de CaCl 2 (200 y 600 mg L -1 ). El proceso de la coagulación enzimática, con la acidificación de Glucono-δ-Lactona, fue medido con el método del alambre caliente. A pH 6.4 y 6.6 los coágulos obtenidos a partir de leche entera tratada, mostraron tiempos de coagulación significativamente inferiores (P<0.05), incremento del máximo voltaje y tiempo en el que se alcanza el máximo voltaje, y una marcada disminución del suero drenado, comparado con aquellos coágulos de leche sin tratamiento. En la elaboración de queso cuartirolo, los niveles de pH 6.4 y CaCl 2 adicionado de 400 mg L -1 , resultaron en la mejor condición seleccionada para no perder la aceptación del consumidor e incrementar el rendimiento quesero en 8.9%, corregido en base seca. AbstractThe effect of pH (6.2-6.6) and CaCl 2 addition (200 -600 mg L -1 ) was studied, with the objective of improving the coagulation properties of whole milk treated under mild condition of temperature, 10 min at 73 °C. The hot wire method to monitor rennet coagulation induced through acidification with Glucono-δ-Lactone was employed. At pH 6.4 and 6.6 the coagulum of heated milk presented lower coagulation time (P<0.05), increased maximum voltage and time where they reach maximum voltage, and a decreased in whey separation, compared to those of coagulum produced by unheated milk. The selected conditions of pH 6.4 and CaCl 2 added 400 mg L -1 , used in the process of cuartirolo cheese proved to be the best condition to increase the yield in 8.9% on a dry basis, without loosing consumer's acceptance.

To evaluate the relationship between the factors affecting coagulation, the hot wire method was used for direct measurements of the renneting milk process as well as a central composite design with 3 factors: rennet concentration (x 1 ), renneting pH (x 2 ), and temperature (x 3 ). Second-order models for maximum voltage (Y 1 ), time at maximum voltage (Y 2 ), and coagulation time (Y 3 ) were employed to generate response surface contours. Optimum conditions for cutting time were found with x 1 = 0.0278 R.U./mL milk, x 2 = 6.60, and x 3 = 35 8C, for which the responses were Y 1 = 2854 6 171 mV, Y 2 = 14.08 6 3.04 min, and Y 3 = 7.16 6 1.12 min. No significant differences (p > 0.01) were found between the 3 responses obtained in the experiment and the ones predicted by the models. The use of the objective and non-destructive monitoring of curd formation and the response surface methodology can be recommended to optimize milk coagulation.

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