**1. Introduction**

216 Milk Production – An Up-to-Date Overview of Animal Nutrition, Management and Health

Zweifel, C.; Muehlherr, J. E.; Ring, M. & Stephan, R. (2005). Influence of different factors in milk production on standard plate count of raw small ruminants bulk-tank milk in

Switzerland. *Small Ruminant Research*, Vol. 58, No. 1, pp. 63-70, ISSN 0921-4488

Water is essential for animal survival under any environmental condition. Furthermore, it is becoming a limiting factor at a global level. Cattle water needs can be satisfied in three ways: 1. Metabolic water, from tissue and organic substrates oxidation; 2. Feed water; and 3. Drinking water.

Under any circumstances, drinking water is the most important source, mainly during summer months. When animals are in a hot environment, any factor limiting access to good quality water will directly affect milk production, which will dramatically fall, especially in high producing cows. Water restricted animals show higher body temperature, increasing heat stress, and immune system alterations. Besides, water restriction affects feed intake, since water and dry matter intakes are strongly related. This is true even under grazing conditions, regardless of the high water contents many fresh pastures have. Also, under hot conditions, ingestion of high volumes of water contributes to improve animal comfort, since reticulo-rumen temperature decreases.

It should be pointed out that water quality alone is not enough to avoid the effects of heat stress on lactating milking cows during hot weather. Other nutritional, as well as environmental strategies can be implemented to improve grazing dairy cattle performance and mitigate heat stress, and will also be discussed.
