Evaluation of 23 Low Heat Unit Corn Hybrids for Forage

Trial Location: Fairview Research Farm, NW-5-82-3-W6 on RR #35, MD of Fairview

Research Coordinator: Dr. Akim Omokanye

From: Peace Country Beef & Forage Association 2015 Annual Report

An important focus by PCBFA has been reducing feed costs by examining different options for extending the grazing season in the Peace. For some years now, corn grazing using low heat unit hybrids has been a big part of PCBFA’s extension service. Producers with experience grazing standing corn to extend the cows' days on pasture have reported that this systems reduces the amount of stored feed required to feed cows in fall and even well into the winter months. Producers have reported that their total cost is well below the alternative cost of feeding stored hay to the animals in a confined area. PCBFA continues to evaluate new corn hybrids as they become available so as to provide producers with a variety of options as to what they can seed for the heat units we have in the Peace.


We carried out small plot field trial at the Fairview Research Farm (NW5-82-3W6) on RR #35, MD of Fairview in collaboration with Mackenzie Applied Research Association (MARA) based out of Fort Vermilion. Prior to seeding, soil test was carried out, we cultivated the land thereafter and we broadcast 104 lbs/ac (urea) + 19 lbs/ac (11-52-0) + 33 lbs/ac (0-0-60) with an ATV mounted spreader.

A randomized complete block design with four replications was used. Twenty three corn hybrids with different heat units varying from 2000-2775 were seeded (see Table 1) for their forage yields and feed quality. Most hybrids used have lower CHU requirements (2000-2300). Only 3 corn hybrids had CHUs>2350. Plot size was 2.25 m x 8.0 m.

A 6-row corn planter with 30" row spacing was used to seed the trial at 28,500 kernels per acre. Seeding was done on May 21. In crop spraying was done once with Roundup @0.8L/acre at the 5 leaf stage.

Harvesting for wet fresh, forage dry matter (DM) & quality was done on September 29. After weighing the harvested corn forage, 5 random plants from each corn hybrid were chopped with a wood chipper for feed tests in a commercial laboratory (Central Testing Laboratory, Winnipeg).


Cob development and stage

Only 8 corn hybrids (39F44, P7213R, 7332R, E47A17R, 2262RR, P7211HR 7332R and P7211HR) had ideal corn development, more kernels and reached or exceeded the half milk line stage. Venza R, Extreme RR and E53B22R in particular had poorly developed kernels. Generally, it appeared that hybrids that require lower heat units performed better in terms of plant growth and development.

Forage Moisture Content

The corn forage moisture content at harvest significantly varied from 63.7% for 39F44 to 74.4% for both 39D97 and 2501RR, giving a difference of 10.7% between the highest and lowest moisture content. For corn silage, moisture content in the range of 65-70% is recommended. Only 5 of the 23 corn hybrids tested fell within this range, with most corn hybrids giving higher moisture content at harvest. For corn silage or grazing, corn hybrids that would reach the half milk line growth stage (about 65% moisture) by the time the killing frost hits are recommended for the Peace region. 39F44 exceeded the half milk line stage and that is why it had lower moisture than others. Generally, the forage moisture content appeared to be related to the corn heat units (CHU) requirements for the corn hybrids seeded. The higher the CHUs, the higher the moisture content at harvest by September 29.

Forage Yield

The wet forage yield was highly influenced by corn hybrids tested. 14 of the 23 corn hybrids had >10.0 tons wet forage yield/acre, while others had between 6.7 to 9.9 tons wet yield/acre (Figure 2). The top 5 corn hybrids in terms of wet forage yield are: E47A17R, P7202-YHR, P7213 R, 7332R & 39F44. Corn hybrids requiring higher CHUs had lower wet forage yield, while those requiring lower CHUs appeared to have higher wet forage yields.

Forage dry matter (DM) yield was generally low because 2015 was dry in Fairview. The DM yield varied from 1.75 tons/acre for Extreme R to 4.90 tons/acre for 39F44 (Figure 3). Only 3 of the 23 corn hybrids tested had >4.0 tons DM/acre. The top corn hybrids in terms of DM yield were: 39F44, P7213 R, E47A17 R, 7332 R &P7202-YHR. Here also, as with wet forage yield, corn hybrids requiring higher CHUs had lower forage DM yield, while those requiring lower CHUs appeared to have higher forage DM yields.

Corn Forage Quality

The forage protein varied from 10.4 to 12.8% CP for all corn hybrids. The CP values are well within the recommended protein values for mature beef cattle. For growing & finishing calves, which require 12-13% CP, only 5 hybrids (Yukon R, P7211HR, 2D093, E50G27R & 13-8084) met the CP requirements of these calves.

The Ca, P, Mg and K requirements of a dry gestating cow (second & third trimester) have all been met by the corn varieties tested here. For a lactating cow, only 3 (39B90, 2D093 and E53B22R) of the 23 corn hybrids tested adequately meet the Ca requirement for this category of cow. Other corn hybrids fell short of meeting the Ca requirement of a lactating cow. None of the hybrids had enough P for a lactating cow. All corn hybrids exceeded the Mg and K requirements of a lactating cow, which requires 0.20% Mg and 0.70% K.

39F44 had the lowest ADF (25.2%) as well as the highest energy (71.7% TDN). 39F44 requires 2000 CHUs, so it exceeded the half milk line stage by about 25% by the time we got the first killing frost. All corn hybrids have been able to meet a beef cow’s energy requirements by the second trimester (55% TDN) and third trimester (60% TDN). But only 3 hybrids fell short of meeting 65% TDN that is needed by a lactating beef cow. Also, most corn hybrids were well within the suggested 65-70% TDN for growing and finishing calves.

For other energy units of measure (ME, NEG, NEL, NEM and DE), 39F44 had higher values than other corn hybrids. The energy available for metabolism by animals is referred to as metabolizable energy (ME) and all corn hybrids met the daily ME requirements of 2.23 to 2.54 mcal/kg for mature beef cattle. A mature beef cow requires 0.97-1.10 Mcal/kg of NEM at the dry gestation stage and 1.19-1.28 Mcal/kg NEM during lactation. All the 23 corn hybrids tested here met the NEM requirement of a mature beef cow. For growing and finishing calves, which require 0.53-1.37 Mcal/kg of NEG, all hybrids were adequate in NEG.

Conclusion – The corn hybrids mostly had similar forage quality, but in terms of forage DM, ADF and TDN, the top performers include 39F44 and P7213R. This shows that it is important to seed low heat units corn hybrids Peace in order to have better cob development and for the kernels to reach the half milk line stage that is required for silage and grazing.

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