Effect of replacing forage or concentrate with wet or dry distillers' grains on the productivity and chewing activity of dairy cattle

The objectives of this study were to determine effects of including distillers' grain as either a partial forage replacement or as a partial concentrate replacement on the lactation performance and chewing activity of Holstein cows. Eight multiparous and four primiparous lactating Holstein cows were randomly assigned to one of four dietary treatments in three 4x4 Latin squares. The control diet was a standard lactation diet used at the University of Saskatchewan containing 520g/kg of concentrate and 480g/kg of forage consisting of barley silage and alfalfa hay. To determine the effect of using distillers' grain as a partial forage substitute, wet wheat/corn distillers' grain (WDG) were included in the diet at a rate of 100g/kg of dietary dry matter (DM) by replacing barley silage. To determine the effects of using dry distillers' grain as a partial concentrate substitute, dry corn distillers' grain (DCDG) or dry wheat distillers' grain (DWDG), were included at 100g/kg dietary DM by replacing dietary concentrate. Orthogonal contrasts were used to determine the effect of including WDG as a partial forage substitute (control versus WDG), dry distillers' grain as a partial concentrate substitute (control versus DCDG+DWDG) and to compare the two sources of dry distillers' grains used (DCDG versus DWDG). Dry matter intake was not affected by treatment and averaged 25.5kg/d. Feeding WDG increased milk yield by 7% and the yield of milk CP by more than 9% compared to the control. Milk fat yield did not differ between cows fed the control and WDG diets, but milk fat concentration was lower for cows fed WDG than for cows fed the control diet (31.4g/kg versus 34.0g/kg, respectively). The amount of time spent ruminating and for total chewing activity (min/d, min/kg DM, and min/kg aNDF) were lower for the WDG diet compared to the control diet such that cows fed the WDG reduced ruminating time by 1h/d. Partial substitution of dietary concentrate with dry distillers' grains did not affect milk yield, milk composition or chewing activity. Similarly the type of distillers' grain (DCDG versus DWDG) did not affect lactation performance or chewing activity. Results indicate that WDG are a good source of crude protein and digestible energy for lactating dairy cows. However, WDG do not promote chewing activity to the same extent as barley silage, and consequently may lower milk fat concentration and increase the risk for ruminal acidosis when used as a partial forage substitute. Furthermore, dry distillers' grains (DWDG and DCDG) can equally and effectively replace 100g/kg of dietary concentrate without negatively impacting milk yield, milk composition, and chewing activity.