MILK2024: Updated MILK index for corn silage

Selecting corn hybrids is an important step in shaping the nutritive value of corn silage, which directly impacts the productivity and profitability of a dairy operation for the next year or more. However, many factors should be considered during hybrid selection, including multiple nutrients and other traits related to yield, plant health and drought resistance. With many choices and a lot to consider, hybrid selection for corn silage can be challenging.

The MILK index combines important nutrients and measurements of digestibility in corn silage into a single value for energy content (milk per ton) and energy yield (milk per acre) to help with hybrid selection.

Since MILK2006 was released in 2006, many advancements have been made in dairy nutrition. This created the need for an updated MILK index, so MILK2024 was developed and released earlier this year. Several changes were made to MILK2024, starting with corn silage inputs. Dry matter concentration is not required in MILK2024 because it was used in MILK2006 to estimate starch digestibility and MILK2024 uses 7h starch degradability (starchD) exclusively. The MILK2024 also requires 240h undigested NDF (uNDF), which is used in fiber digestibility calculations, while MILK2006 did not. Most of the other inputs are similar between MILK2024 and MILK2006. However, MILK2024 can use either traditional fiber measurements (NDF, NDFD and uNDF) or fiber measurements corrected for residual ash (NDFom, NDFDom and uNDFom).

Some changes were also made to energy predictions. The MILK2024 no longer uses TDN to predict energy in corn silage like MILK2006 did. Instead, MILK2024 predicts digestible energy directly from the nutrient composition of corn silage. Digestibility of starch and fiber were also updated in MILK2024. Rather than using in vitro or in situ starchD and NDFD directly like MILK2006, MILK2024 estimates the total tract digestibility of starch and NDF in dairy cows, which is more realistic. Milk composition was also updated in MILK2024. The MILK2024 predicts milk yield with 4.0% fat, 3.1% true protein, and 4.8% lactose, which better represents modern dairies than the 3.5% FCM used in MILK2006.

What to expect with MILK2024

Predicted milk per ton in MILK2024 could be lower (if using starchD in MILK2006) or greater (if using DM in MILK2006). The range in milk per ton is smaller, with less variation, in MILK2024 compared to MILK2006. This could make comparing milk per ton with MILK2024 a little more difficult, so smaller differences should be considered as meaningful compared to MILK2006.

Despite the lower range in milk per ton, MILK2024 can separate samples with different nutrient composition better than MILK2006. This is especially true for samples with different NDF concentrations and 30h NDFD. Lastly, MILK2024 appears to be more sensitive to NDF and starch concentrations, while responding similarly to 30h NDFD and being slightly less sensitive to 7h starchD compared to MILK2006.

Commercial labs will probably introduce milk per ton from MILK2024 to corn silage analysis packages this year. You can also access the MILK2024 spreadsheet and MILK 2024-Background and Guide through UW-Madison extension.

Cole Diepersloot is a graduate student in the department of animal and dairy sciences at the University of Wisconsin-Madison. Luiz Ferraretto is an assistant professor and ruminant nutrition extension specialist in the department of animal and dairy sciences and division of extension at the University of Wisconsin–Madison. Contact him at ferraretto@wisc.edu.