Vet Column 1-25-10 |

Vet Column 1-25-10

David L. Morris, DVM, Ph.D.
Fort Collins, Colo.

When nutritional assessments and planning of diets are considered, water has been often stated to be the most overlooked nutrient. A recent publication by investigators from Colorado State University and North Carolina State University evaluated this important component in diets fed to yearling steers in a feedlot situation. In this publication, focus was on using two sources of water comparing a high sulfate well water source (sulfate concentration of 1,933 mg/L) with a blended source of reverse osmosis water and well water (sulfur concentration of 608 mg/L).

One of the major dietary elements required by cattle is potassium because it is involved in many metabolic functions, such as acid-based balance and concentrations of various blood constituents. Potassium also plays an important role as a cofactor for enzymes, is involved in carbohydrate and protein metabolism and is a major determinant of dietary cation-anion balance. This cation-anion balance involves the amounts of sodium, potassium, chloride and sulfur in a diet as a function of dry matter.

When potassium is added to diets as a supplement, it is generally as potassium chloride (KCL). Occasionally, potassium bicarbonate (K2CO3) is used. Potassium chloride does not affect the cation-anion balance when added, but potassium bicarbonate does. In areas with elevated sulfur content in the diet, balancing cations and anions involves adding potassium.

Altering the cation-anion balance has been shown to affect milk yield of dairy cows, average daily gain of steers and the feed efficiency of growing steers. In heat stressed cows, increasing the cation-anion balance increases the dry matter intake which, in turn, increase water intake. It is thought that modifying the cation-anion balance affects the blood pH and mineral status. Changing the blood pH can have an affect on calcium metabolism.

For this particular study, the two sources of water were used and three potassium treatments; 0.75 percent potassium with KCL as a supplemental source, 0.75 percent potassium with K2CO3 as a supplemental source, and 1.0 percent potassium with K2CO3 as a supplemental source. This study involved 432 crossbred yearling steers weighing approximately 750 pounds. The feedlot was located in southeastern Colorado.

Results indicated that interactions between water quality and dietary treatments were not significant. Steers consuming the lower sulfate water tended to have greater dry matter intake. Feed efficiency was greater for those steers fed 1.0 percent K- K2CO3. Steers consuming the lower sulfate water had heavier final body weights and greater average daily gain than steers fed the higher sulfate water. Yield grade was not affected by either the water quality or the dietary differences. Carcasses from steers consuming higher sulfate water had greater marbling scores. Steers consuming the 1.0 percent K- K2CO3 supplement had a reduced liver abscess rate.

Improved feedlot performance was achieved with lower sulfate content in the water. This study reinforces with objective data the importance of water quality in yearling feedlot cattle diets. When cattle performance does not meet expectations, and diets are evaluated, water quality should be part of that assessment.

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