---

By Jim Linn and Mary Raeth-Knight

Summer is officially here and with it came heat and humidity last week. As we think about how to help cows through the summer heat stress periods, water comes to the top of the list as an effective heat abatement measure. Cows need water both externally and internally to help alleviate heat stress. Evaporative cooling through the use of sprinklers and fans is an effective way for cows to transfer body heat to the environment. Drinking lots of fresh clean cool water also is important during heat stress to help keep cows cool and feed intake up. However, adding water to diets during summer months is not an effective way of increasing water intake and may actually be detrimental to feed intake.

Adding water to a total mixed ration (TMR) is often suggested as a method to 1) improve diet palatability and 2) reduce preferential feed sorting. Only a few studies have actually measured the impact of adding water to diets on feed intake and sorting behavior of lactating dairy cows.

Canadian researchers (Miller-Cushon and DeVries, 2009) added water to a TMR consisting of haylage, corn silage, high moisture corn and a concentrate pellet. Water was added to the TMR to change the dry matter (DM) 10 percent going from 58 percent with no water to 48 percent after water was added. Sorting was determined by particle sizing of the TMR fed and feed refusal 24 hours after feeding using the Penn State Particle Box. Cows were fed once per day.

Surprisingly, cows in this study sorted both long particles (>19.0 mm) and fines more extensively in the wet diet (47 percent DM) than the drier diet (58 percent DM). The addition of water to the diet also decreased DM intake an average of 7.1 pounds per cow per day compared to no water added. The lower DM intake along with sorting of large particles from forage reduced fiber (NDF) intake and increased the portion of starch intake of cows fed the wet diet. This unbalancing of the diet could lead to increased subacute acidosis and more foot and health problems, especially during heat stress.

Another water addition study was done by Wisconsin researchers (Leonardi et al.) back in 2005. In this study, cows were fed TMR diets of 64 percent (wet) or 81 percent (dry) DM. Diet ingredients were the same for both TMRs consisting of 30 percent chopped hay (106 RFV), 10 percent alfalfa haylage and 60 percent concentrates. Water was added to the wet diet to achieve the 64 percent DM.

In this study, the results were what most people expect when adding water to diets. Sorting of large feed particles was decreased when cows were fed the wet compared to dry diet with cows consuming 75 percent of the large particles predicted to be consumed from the wet diet compared to 61 percent from the dry diet. Sorting of fine particles was also decreased with feeding the wet versus dry diet. However, DM intake was not different between cows fed the dry and wet diets.

Based on the two studies, adding water to a TMR to reduce sorting of long particles may be slightly advantageous when the TMR is very dry and poor quality hay is a high proportion of the forage fed. In contrast, adding water to TMR diets that are more typical of those fed today (fermented forages) may reduce feed intake and increase sorting. Another difference between the two studies, besides the forages fed, was the distribution of particles on the Penn State Box. In the Canadian study, the feed particle distribution for the top, second, third screens and pan averaged 9, 48, 34 and 9 percent, respectively, compared to 6, 9, 40, 45 percent on the same screens and pan for the dry hay TMR fed in the Wisconsin study. The distribution of feed particles in the Canadian study is much closer to what is recommended than the Wisconsin study with 85 percent of the material (third screen + pan) being considered fine to very fine particles.

Thus, the data on adding water to a TMR to decrease sorting is not particularly convincing especially when one considers adding water to diets during summer months generally results in the TMR heating and going out of condition faster. Letting cows drink water appears to be better way of getting water into cows than by adding it to feeds.

[[In-content Ad]]

---