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Testing of Corn Hybrids with Lower Heat Unit Requirements for Forage Yield & Quality

Updated: Jun 26, 2023

Research Program Manager: Dr. Akim Omokanye

From: Peace Country Beef & Forage Association 2018 Annual Report

Corn is a high energy feed with protein levels that will normally match the nutritional needs of a dry cow in mid and late pregnancy. Corn has an advantage as a winter grazing crop because it stands above the snow, and it stands up in windy conditions (with minimal leaf loss), as well as providing a windbreak for cattle grazing it. Matching a particular area’s available corn heat units (CHU) to the CHU requirements of corn hybrids or varieties in the market will go a long way in maximizing the potential of using corn to extend the grazing season. Grazing corn should be at 30-50% milk line at first killing frost. Several new corn hybrids that require lower heat units are now available in the market. The objective of this trial was to test some the corn hybrids that require less heat units, for forage quality and suitability for grazing and silage.


The study site was at the Fairview Research Farm (NW5-82-3W6) on RR #35, MD of Fairview. Soil tests from 0-6” depth showed an organic matter of 6.4%, a pH of 6.8, and an electrical conductivity of 0.39 dS/m. The site was lightly harrowed before seeding.

The following 6 DuPont Pioneer corn hybrids were tested:

1. P7202AM™ (2050 heat units)

2. P7005AM™ (2000 heat units)

3. P6909R (1950 heat units)

4. P7213R (2050 heat units)

5. 39F44 (2000 heat units)

6. P7211HR (2050 heat units)

Randomized complete block design was used, with 4 replications.

Seeding rate was 32,000 kernels/acre. Seeding was done on May 28 with a plot drill at 27” row spacing. Fertilizer was applied during seeding, at the rate of 111 lbs N/acre + 37 lbs P/acre + 49 lbs K/acre + 21 lbs S/acre. Roundup at 0.67 L/acre was used for pre-emergent and in-crop weed control.

Harvesting for forage dry matter (DM) yield determination and quality analysis was done on September 24. Two composite forage samples were sent to A & L laboratory in Ontario for quality determination.

The data for forage yield and quality were analyzed with ARM statistical software.


The corn forage DM yield, crude protein (CP), total digestible energy (TDN), and measured minerals were all statistically similar for the corn hybrids tested.

The forage DM yield varied from about 7 - 9 tons/acre (Figure 1).

The forage CP value varied from 9.89-11.1% (Figure 2). Going by the rule of thumb for beef cattle, which says that a dry gestating beef cow requires 7% CP in mid-pregnancy and 9% CP in late-pregnancy, the tested hybrids all had enough CP for a dry gestating beef cow. However, for a lactating beef cow, which requires 11% CP, only P7202AM™ and P6909R met this.

The forage TDN was generally above 70% for the corn hybrids tested (Figure 3). This shows that all corn hybrids surpassed the required %TDN for both young (65-70% TDN) and mature (55-65% TDN) beef cattle.

Table 1 shows both the macro and trace minerals measured here. The forage Ca and P have only been able to meet the requirements of a dry gestating beef cow (0.18 % Ca and 0.16% P), but not a lactating beef cow (0.58 Ca and 0.26% P). None of the hybrids had sufficient Na for beef cattle. Only 3 of the 6 corn hybrids had adequate S for both young and mature beef cattle.

The forage Cu value obtained for all corn hybrids fell far short of the 10 ppm that is needed by both young and mature beef cattle. However, all hybrids had adequate K and Mg for both young and mature beef cattle. Because of the inability of the tested corn hybrids to meet the required amount of some minerals, mineral supplementation would be necessary when grazing any of these corn hybrids.


In terms of forage DM yield, both P7211HR and P6909R seemed to have some advantage over other corn hybrids.All corn hybrids exceeded the %TDN needed by all categories of beef cattle. Mineral analysis demonstrated that supplementation would be necessary during grazing for all corn hybrids to meet animal requirements.

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