In the past decades, an increase in ethanol production increased production and availability of corn dried distillers grains with solubles, DG.
Because DG is high in protein and fiber, it has been used as a feed ingredient in dairy rations. Because of its low price, inclusion of DG in a diet — for example, replacing soybean meal — can lower feed costs.
However, DG contains high fat (10-12 percent on a dry matter basis) and polyunsaturated fatty acids.
If a diet includes high DG (20-30 percent of dietary dry matter), feed intake and fiber digestibility can be negatively affected and milk fat depression of cows is commonly observed.
Recently, reduced-fat corn dried distillers grains (RFDG; 5-8 percent fat on a dry matter basis) have been available in the U.S.
RFDGs are produced by removing part of the fat in DG, reducing the risk of milk fat depression compared to DG.
However, little information is available for producers to answer the question: “how much RFDG can be included in a dairy ration to lower feed costs without negative impacts on production (milk and fat yield)?”
A few studies have suggested that RFDG can be included in a dairy ration up to 30 percent, dry matter basis.
Because most of these experiments were conducted in the short term — 2 weeks of diet adaptation followed by 1 week of production observation — we conducted an experiment with RFDG to monitor production responses to a diet containing about 30 percent RFDG, dry matter basis, for 11 weeks.
In this experiment, the 30 percent RFDG diet contained RFDG by replacing soy products (soybean meal and soyhulls).
Although the 30 percent RFDG diet did not affect milk yield, it significantly decreased milk fat and protein yield. Importantly, the decrease in dry matter intake and milk fat yield gradually became severe as the experiment progressed (11 weeks).
The production results are shown in Table 1.
As a result, although Inclusion of RFDG in a dairy ration lowered feed price from $6.99 to $5.19 per cow per day, income from milk production also decreased from $15.15 to $13.14 (using Ohio prices of feeds and milk components when the experiment was conducted in 2017).
This decreased the estimated income-over-feed-cost from $8.16 to $7.95 per cow a day.
Our results indicate that inclusion of RFDG in a ration at 30 percent (dry matter basis) can negatively affect performance of cows and decrease producers’ profits.
Check the following items before using RFDG on your farm:
1. Make sure that you know what you have, DG or RFDG. Potential risk of negative production effects on cows is lower for RFDG compared to DG when included at the same level in the diet.
2. When you purchase corn distillers grain, it is not labeled as DG or RFDG (actually, labelling is the same between DG and RFDG). Check the fat level and if the fat level is below 8 percent, then it is RFDG.
3. We suggest the maximum inclusion rate of RFDG at 10 to 15 percent in lactating cow diets (dry matter basis). A diet with 20 percent of RFDG might be OK, but, this needs scientific confirmation.
4. When you include RFDG in a diet, monitor production of your cows closely (feed intake, milk yield, and milk fat yield) for at least 5-6 weeks. In our study, the decreases in dry matter intake and milk fat yield of cows fed the 30 percent RFDG diet become more severe as the experiment progressed, indicating that negative production effects may not be realized in the first 2-4 weeks.
5. If you include RFDG in your diet at 10-15 percent (dry matter basis), check dietary phosphorous and sulfur levels. You may need to reduce or may not even need supplemental phosphorus and sulfer in your diet because RFDG is high in P and S.
Without adjustment of supplemental P and S, manure produced will be high in P and S (Table 1).
6. If you usually include monensin in your diet, be careful including monensin with RFDG in your diet. Inclusion of monensin in the 30 percent RFDG diet further decreased feed intake, milk yield and milk fat yield compared to the control diet in our study.
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