By Marnie I. Shaw, John F. Patience, A. Denise Beaulieu and J. Usry - This article is from Prairie Swine Center and looks at how concerns relating to the use of water resources by the livestock industry, combined with the rising cost of manure management, have resulted in greater interest in defining more precisely the water consumption of pigs.

A study was conducted to determine if the crude protein or mineral content of a diet affected water consumption by growing pigs. Although water utilization was increased when the crude protein or mineral content of the diet was excessive, factors other than the diet appear to have a greater impact on water utilization by the pig.

Introduction

Limited information is available on the impact of diet composition on voluntary water intake in swine. In Canada, water has traditionally been abundant and inexpensive; however, present concerns relating to the use of water by the livestock industry, combined with the rising cost of manure management, have resulted in greater interest in more precisely defining the water requirements of pigs.

Objective

To determine if lowering dietary crude protein (CP) or mineral level reduces drinking water consumption in growing pigs.

Materials and Methods

A total of 48 barrows (70.2 ?2 d, 34.3 ?days) were house in individual metabolism pens. A low CP diet, supplemented with lysine, methionine, threonine and tryptophan was compared to a high and to an excessive CP diet. The excess crude protein diet was formulated to support growth that was 25% above expected. A fourth diet contained excess calcium, phosphorus, and salt (Table 1). Daily water intake (ADWI) and spillage was determined daily using individual water meters connected to bowl drinkers. Faeces and urine were collected on days 11 to 14 of each period to allow us to accurately determine water intake, water output and the water:feed ratio. Water intake included not only drinking water, but also water contained in the feed and water produced by normal metabolic processes. Water output included faeces, urine and water retained as a consequence of growth. Water exhaled from the lungs was not measured.

Results and Discussion

On average, drinking water represented 83% of total water intake; feed and metabolic water represented 3% and 14% of the total, respectively. Of the measured water outputs, growth constituted only 8% of the total, while faeces represented not much more at 9%. Urine output represented 83% of the measured total. If we assume that the unmeasured water balance ?the difference between intake and measured output - was primarily water lost through respiration, this would have constituted 49% of the total. Urine would then have represented only 42% of the total daily water balance.

The ADWI (P=0.06) and water output (P=0.06) tended to increase when pigs received the excess crude protein diet (ExCP; Table 2). Additionally the water:feed ratio increased when pigs consumed this diet (P=0.01; Table 2). Pigs that consumed the excess mineral diet (ExMin) diet had increased output of water in faeces (P=0.02; Table 2).

An attempt was made to develop equations to predict water intake of growing pigs from the diet composition or intake of specific nutrients. A prediction equation containing daily intake of feed, nitrogen calcium, phosphorus, sodium, potassium, and chloride as independent variables resulted in the highest R2. It was, however, only able to explain 33% of the variability in water intake. In all cases, the ability to detect treatment differences was hampered by the large variability among individual pigs for water intake and output. The pigs were housed individually in this experiment; however, it had been shown in previous experiments when the pigs were housed in groups that a lack of social interaction was not the cause of this variability.

Implications

Feeding a diet containing excessive dietary protein will result in increased water utilization by growing pigs. This makes sense as additional water will be required to remove the by-products of protein breakdown from the body. Surprisingly, reducing crude protein by increasing the use of synthetic amino acids will not reduce water intake. Although diet composition may influence water utilization in growing pigs, other factors, such as the environment and the design of the water delivery system appear to have a greater impact. The water:feed ratio was confirmed to be in the range of 2.5:1, provided excess nutrients are not present in the diet.