Corn silage (CS) testing programs aid in evaluating hybrids for subsequent use. Ranking metrics such as Rumen Fermentable Carbohydrate–Fill Index (RFCFI; calculated as [(digested NDF at 30h+starch)/undigested NDF (uNDF) at 30h]), and Milk/Ton, as calculated by MILK2006, have been used to assess CS performance. Predicted allowable milk yield (AMY) from the Cornell Net Carbohydrate and Protein System (CNCPS v.6.5.5) was used as a new approach to evaluate the milk producing potential of hybrids. Hybrids (n = 29) were planted in a randomized complete block design, with 4 replications and by 5-d maturity groups in Northern NY (NNY) and Central NY (CNY). A typical NY high CS ration (27.1 kg DMI) was formulated using a CNCPS library CS for an ME and MP AMY of 45.4 kg/d. The library CS was replaced (DM basis, 12.7 kg CS) with each hybrid analysis, creating separate rations (ME AMY range: NNY = 46.4 to 49.1 kg, CNY = 47.9 to 49.4 kg). After substitution, rations were adjusted to supply predicted DMI based at a constant uNDF at 240h (uNDF₂₄₀) intake of 2.661 kg/d (ME AMY range: NNY = 40.2 to 58.1 kg, CNY = 48.0 to 63.2 kg). This approach accounts for DMI differences based on uNDF₂₄₀ supply and rumen fill. The reported ME AMY was more limiting than MP AMY and accounts for nutrient and digestibility characteristics. Comparisons of ME AMY with RFCFI and MILK2006 were made for both locations (Table 1). A stronger correlation existed between ME AMY and RFCFI, than MILK2006, and was greater for the NNY location, which had greater yields and lower digestibility values than the CNY location. Utilizing CNCPS may enhance the information available from CS testing programs. Table 1. Correlation between CNCPS v.6.5.5 predicted ME allowable milk yield on a DMI equivalent or uNDF₂₄₀ intake corrected basis

CNCPS measurement	Ranking metric	R2
		Central NY	Northern NY
Predicted ME AMY,1 DMI equivalent	RFCFI2	0.69	0.93
Predicted ME AMY, DMI equivalent	MILK2006	0.18	0.51
Predicted ME AMY, uNDF2403 adjusted DMI	RFCFI	0.63	0.89
Predicted ME AMY, uNDF240 adjusted DMI	MILK2006	0.49	0.42

¹AMY = allowable milk yield. ²RFCFI = Rumen Fermentable Carbohydrate–Fill Index. ³uNDF₂₄₀ = undigested NDF at 240 h.