**2. Dairy water intake and environment**

No doubt water is the most essential element for the survival of animals. Water requirements for livestock can be met in three ways:


© 2012 Valtorta and Gallardo, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Valtorta and Gallardo, licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### 3. Drinking water

In any event the latter route is the most important in the quantitative sense and in summer is by far the largest source. During this season o0f the year, any factor that limits access to water directly affect the production of milk, which will fall sharply, mainly in highproducing cows. Cows with water restrictions manifest higher body temperature, with a degree of heat stress higher than normal. Furthermore, water restriction causes a greater reduction in the consumption and ingestion of water and dry matter intake are closely related (National Research Council (NRC), 2001). Also, under intense heat, ingestion of large volumes of water affects comfort by reducing the temperature of the rumen reticulum.

Dairy cows normally drink large amounts of water, but with intense heat they could take more than 120 L/day. In a landmark study conducted in climatic chambers, it was recorded water consumption of lactating cows increasing by 29% when the temperature rose from 18 to 30°C. Concomitantly, fecal water loss decreased 33%, but losses via urine, skin and respiratory tract increased by 15, 59 and 50% respectively.

Regarding minerals, heat-stressed cows increase their need for Na+ and K+, due to the electrolyte imbalance generated at the cellular level. The higher needs of Na+ are attributed to increased secretion of urine that reduces the plasma concentration of aldosterone. Instead, the increased demands for K+ are attributable to an increased removal of this element with sweat.

In lactating cows fed a diet based on corn silage, hay and concentrates, typical of many production models, it was found that the main factors that determined water intake were: dry matter consumed; the level of milk production, temperature and Na+ intake. The following equation (NRC, 2001) shows these relationships:

$$\text{MM} = 16 + \left[ \left( \text{158} \pm 0.271 \right)^{\star} \text{(DM)} \right] + \left[ \left( \text{0.9} \pm 0.157 \right)^{\star} \text{(MP)} \right] + \left[ \left( \text{0.05} \pm 0.023^{\star} \text{(Na}^{+}) \right) \right] + \left[ \left( \text{120} \pm 0.106 \right)^{\star} \text{(T}\_{\text{md}} \right) \text{l.}$$

where

WI = Water intake (kg/day) DMI = Dry matter intake (kg/day) MP = Milk production (kg/day) Na+ = sodium (g/day) Tmd = daily minimum temperature (ºC)
