A recently published study demonstrated that reducing feed costs by purchasing lower-cost commodities did not translate to more money in the bank. The feeding study, conducted in California, compared two feeding regimens. The first was the control diet, where the added protein source was provided by canola meal. For the test feeding regimen, approximately two-thirds of the canola meal was removed from the ration, and low-fat distillers dried grain (DDG) was substituted (Table 1). This product is produced from DDG that has undergone an additional fat extraction, reducing the likelihood of the meal contributing to milkfat depression, while increasing the protein content of the product.
In this study, this modification in the protein source had very little effect on the nutrient profile of the diet, and the substitution of the regular solvent-extracted canola meal with defatted DDG was sufficient to lower feed costs by 6 cents per cow per day. However, in the final analysis, income over feed cost (IOFC) was found to be 4 cents greater for the control diet containing canola meal.
IOFC is a commonly used metric that is often used to determine if feeding changes or changes in feed management should remain permanent. On the surface it appears to be relatively easy to calculate – simply subtract feed costs from income. The importance of this trial is how IOFC is determined. There are many variables when it comes to evaluating the milking string. This study points out that the results obtained from computations can easily be misleading but also provides some practical solutions to improve the accuracy of the IOFC calculation.
A basic factor that can invalidate the result is not adjusting for changes in cow numbers between the control and test periods. The number of cows fed can easily change from one period to another, resulting in changes in total milk yield and feed consumption, masking the actual value of a test item if not addressed. The authors address this by calculating IOFC on a per-cow basis (IOFC per cow per day).
Another factor that can easily be overlooked, particularly in longer trials, is changes in milk pricing. Income is provided by milk sales. If the price paid for milk changes while an ingredient is being evaluated, this needs to be taken into account. The researchers used an average price per unit of milk sold for both test periods to ensure this factor did not nullify their evaluation.
In this test herd, first-lactation cows were fed separately from the later-lactation cows. The study points out that first-lactation cows produce less milk than mature cows and that this needs to be addressed when evaluating products (Table 1). If there are differences in the relative proportion of first-lactation cows to mature cows during one of the test periods, it can invalidate the results.
Depending on how cows are grouped, it may not be possible to generate values for first-lactation cows separately. However, it is worth determining if the ratio of first-lactation cows to later-lactation cows differed during the testing periods and if an adjustment is needed. For example, in the test herd the first-lactation cows produced 75% as much milk as the later-lactation cows. This value for individual herds should be available from herd record-keeping systems and can be used to adjust for any differences in the proportion of heifers.
This study also accounted for differences in the proportion of cows in early lactation as compared to mid- and late-lactation cows. Early lactation cows produce the most milk but may not be eating as much feed as the mid-lactation cows. A shift in such dynamics can also result in false conclusions. This parameter may need to be taken into consideration to determine the validity of the outcome, as it has a direct impact on feed efficiency and therefore feed costs per unit of milk produced.
The researchers accounted for all the above variables in their evaluation by producing a spreadsheet with IOFC values calculated for a herd of 1,000 cows per treatment and balanced results as if the herd had a constant amount of heifers and mature cows, as well as a constant proportion of fresh cows. They used actual feed costs and milk pricing. In that way, they were able to derive meaningful results.
While IOFC seems like a very simple calculation, it may not be an accurate one. There are many moving parts on a farm, and these can influence the outcome independently of the feed or management change that has been made. Some modifications may be needed to get a true picture of events.
References omitted but are available upon request by sending an email to the editor.
