Dairy Sense: Predicting Dry Matter Intake – Comparing New Versus Old Approaches

December 2022

Production perspective:

The release of the 2021 Nutrient Requirements of Dairy Cattle – Eighth Revised Edition offers two approaches to estimating dry matter intakes (DMI). One focuses on animal factors and the other on ration dynamics. The latter is a more robust approach as it emphasizes gut fill and utilizes many of the common analyses performed on forages and the total mixed ration (TMR). The equation using animal factors requires knowing body weights and body condition scores, which can be difficult and subjective information to obtain on farms. An older approach for estimating intakes is using a percent of bodyweight based on four percent fat corrected milk. The Extension dairy business management team has compiled a lot of ration information in the last few years, so it seemed appropriate to evaluate how the ration focused equation compared to both percent of body weight predictions and to actual intakes.

The ration focused equation utilizes acid and neutral detergent fiber (ADF, NDF) from the TMR analysis, forage NDF from the formulated diet, and forage NDF digestibility from the individual forages and milk yield. The following is the complete equation:  

DMI (kg/d) = 12.0 − 0.107 × FNDF + 8.17 × ADF/NDF + 0.0253 × FNDFD – 0.328 × (ADF/NDF – 0.602) × (FNDFD − 48.3) + 0.225 × MY + 0.00390 × (FNDFD − 48.3) × (MY – 33.1)

Table 1 shows the comparison between using the new equation and using percent of body weight on five herds from the Extension dairy team’s on-farm research projects. Since body weights were not measured on the farms, the average weights from the development and evaluation data set were used (Allen et al, 2019). It was noted that much of the data represented the eastern part of the country and are within line for Pennsylvania dairy operations. There is very close agreement between using both approaches for estimating intakes. The research data typically consists of very high producing cows, and it appears that intakes are more aligned for the two herds milking over 85 pounds.

Note: Farms 1-5 were on extension projects and had the necessary data to incorporate into the new ration focused equation.

¹Penn State fact sheet "Total Mixed Rations for Dairy Cows"
²Body weights from the development and evaluation data set used in establishing equations for dry matter intakes. M. S. Allen, D. O. Sousa, and M. J. VandeHaar. 2019. Equation to predict feed intake response by lactating cows to factors related to the filling effect of rations. J Dairy Sci. 102(9):7961-7969.
³Minor change was using energy corrected milk in place of milk yield so as to better match the 4% fat corrected milk with the percent of body weight recommendations.

The second objective was to compare the new equation to actual intakes of a dairy herd. Table 2 illustrates the ration information for a very well managed operation, especially for feeding management. The forage ration consisted primarily of corn silage with some triticale. Daily intakes were monitored, and adjustments made to account for changes in dry matter percent and cow numbers. There was excellent agreement between the predicted dry matter intake and what was actually consumed. It should be noted that the average for the month was used to compare to the predicted intake. As would be expected, there were daily variations so that if one point in time was used, intakes could be off plus or minus by a few pounds. Because the herd was monitoring intakes daily and adjusted, accordingly, feeding management issues were addressed in a timely manner. Making intake comparisons from one day can be misleading.

The ration focused equation for estimating intakes utilizes common analyses and appears to accurately predict intakes. Since this equation is accounting for gut fill, it would not be appropriate to use for a group of cows less than 60 days in milk. There are other issues occurring during that time, which do not necessarily reflect gut fill. The old standard of using percent of body weight to estimate intakes also appears to be a quick and easy approach to ballpark dry matter intakes. Regardless of the approach, if good feeding management practices are not in place, actual intakes may not be in close alignment with the prediction equation, but that is on management not the equation.

Note: ADF-acid detergent fiber; NDF-neutral detergent fiber; FNDF-forage NDF; FNDFD-FNDF digestibility. The ADF and NDF came from the TMR analysis; FNDF came from the formulated diet; FNDFD came from the forage analyses.

¹Actual dry matter intake is the average for the month of September.

Economic perspective:

Monitoring must include an economic component to determine if a management strategy is working or not. For the lactating cows, income over feed cost is a good way to check that feed costs are in line for the level of milk production. Starting with July 2014's milk price, income over feed cost was calculated using average intake and production for the last six years from the Penn State dairy herd. The ration contained 63% forage consisting of corn silage, haylage and hay. The concentrate portion included corn grain, candy meal, sugar, canola meal, roasted soybeans, Optigen and a mineral vitamin mix. All market prices were used.

Also included are the feed costs for dry cows, springing heifers, pregnant heifers, and growing heifers. The rations reflect what has been fed to these animal groups at the Penn State dairy herd. All market prices were used.

Income over feed cost using standardized rations and production data from the Penn State dairy herd.

Note: November’s Penn State milk price: $26.03/cwt; feed cost/cow: $8.29; average milk production: 83 lbs.

Feed cost/non-lactating animal/day.