Corn dried distillers grains with solubles (DG) is a common feed ingredient for lactating cows due to its high protein and fiber contents. Because of its lower price compared with soybean meal (SBM), inclusion of DG in a diet can lower feed costs. However, production responses to a DG diet can vary dependent upon its inclusion rate. Typical DG contains high fat (10 to 13% on a dry matter (DM) basis) and polyunsaturated fatty acids. So, if a diet includes high DG (20 - 30% of dietary DM), feed intake and fiber digestibility can be negatively affected and milk fat depression of cows often occurs.
Reduced-fat corn dried distillers grains with solubles (RFDG; 5 to 8% fat on a DM basis) are another type of DG and produced by partial fat removal from DG. Because of low fat content of RFDG, negative effects that were observed with DG (e.g., milk fat depression) are assumed to be alleviated when RFDG are fed compared with DG. However, little information is available about RFDG, such as its safe inclusion rate without affecting production of lactating dairy cows. According to a few previous studies, RFDG was included in dairy rations up to 30% (DM basis) by replacing SBM, corn, and/or some forages and did not have negative effects on production of dairy cows (e.g., feed intake, milk yield, and milk fat yield). However, most experiments were conducted in a short-term Latin square design (2 weeks of diet adaptation followed by 1 week of production observation). Therefore, we conducted an experiment to examine effects of RFDG at about 30% in dietary DM on production of dairy cows. In this experiment, 12 cows per treatment were used and production was monitored for 11 weeks.
In this experiment, the diet containing SBM and soyhulls was used as Control and RFDG replaced the soybean products for the 30% RFDG diet. Although the 30% RFDG diet did not affect milk yield (Table 1), it significantly decreased milk fat and protein yields. Importantly, the decrease in DM intake and milk fat yield became severe as the experiment progressed (11 weeks). In this experiment, although the inclusion of RFDG in a diet replacing SBM lowered feed cost, the income from milk and component yields also decreased due to milk fat and protein depression (Ohio prices of feeds and milk components when the experiment was conducted in 2017 were used). As a result, the income-over-feed-cost was lower for cows fed the 30% RFDG diet compared with the SBM diet. This experiment indicates that inclusion of RFDG in a ration at 30% (DM basis) can negatively affect production of cows, especially milk fat, and may decrease producers’ profits. The full version of the experiment can be found in the Journal of Dairy Science (2018; 101:5971-5983).
If RFDG is available as a feed ingredient in your farm, the following are the tips that you may need to keep in mind and check before and during feeding RFDG to your cows. First, producers need to know what type of corn distillers grain with solubles they have (DG or RFDG). Potential risk of negative production effects (e.g., milk fat depression) is lower for RFDG compared to DG because of lower fat concentration when included at the same level in a ration. However, when purchased, corn distillers grain with solubles may not be labeled as DG or RFDG. Then, check the fat level on the tag and if the fat level is below 8%, then it is RFDG. Second, if what you have is RFDG, we suggest it to be included at a maximum of 15 to 20% in a ration (DM basis). A diet with 25% of RFDG may be okay, but this needs scientific confirmation. Third, when you include RFDG in a diet, monitor production of your cows closely (feed intake, milk yield, and milk fat yield) for at least 5 to 6 weeks. In our study, the decreases in DM intake and milk fat yield of cows fed the 30% RFDG diet become more severe as the experiment progressed, indicating that negative production effects may not be realized in the first 2 to 4 weeks. Fourth, if your ration contains monensin, be careful when RFDG is included in the ration. Inclusion of monensin in the 30% RFDG diet further decreased feed intake, milk yield, and milk fat yield compared to the control diet in our study (Table 1).
Table 1. Dry matter intake and production of lactating Holstein cows fed a diet containing about 30% reduced fat distillers grain (RFDG) with or without monensin.
|Items||Control||30% RFDG||30% RFDG with monensin|
|Dry matter intake, lb/day||58.1||55.9||53.7|
|Milk yield, lb/day||89.8||90.9||86.2|
|3.5% Fat-corrected milk yield, lb/day||94.2||83.8||75.9|
|Milk fat, lb/day||3.41||2.71||2.38|
|Milk protein, lb/day||2.90||2.81||2.64|