Forage DM Yield and Nutritional Value of Oat Varieties Harvested at 3 Stages of Maturity

Trial Site: Fairview Research Farm

Research Coordinator: Dr. Akim Omokanye

From: Peace Country Beef & Forage Association 2016 Annual Report

Producers in Alberta harvest significant acreage of annual crops for greenfeed and silage every year. There are specific requirements for hay for the export market that are different from usual on-farm requirements. These include earlier cutting times, green hay colour, low moisture content, freedom from weeds and thin-strawed varieties. Studies elsewhere have shown that some oat varieties do not meet the exporters’ standard. Export markets demand bright green, dry hay. Selecting appropriate oat cutting time is critical in achieving this standard whilst maintaining oat hay yield and quality. For us in Alberta, the recommended harvest stage for oat is early to late milk stage. Some export processors however may prefer oat hay cut at a different development stage. In 2016, three forage type oat varieties were selected and compared at the various growth stages by PCBFA.


The study site was at the Fairview Research Farm (NW5-82-3W6) on RR #35, MD of Fairview. The site had soybeans in 2015. Soil test at 0-6” soil depth done at Exova laboratory (Edmonton) prior to seeding showed an organic matter content of 7.3%, a pH of 5.4 (acidic) and an electrical conductivity of 0.58 dS/m. The field was cultivated before seeding.

We used randomized complete block design in 4 replications in small plots.

Treatments: 3 forage type oat varieties (CDC Baler, CDC Haymaker, AC Mustang) were seeded and harvested at 3 stages of maturity (boot, heading, milk). AC Mustang is a feed oat but commonly used for silage or greenfeed.

We seeded 300 plants/m2 (27.8 plants/ft2). A 6-row Fabro plot drill at 9” row spacing was used to seed. Seed-ing was done on May 16.

Fertility according to soil tests (actual lbs/acre): 0 N + 33 P + 47 K + 0 S (broadcast). Soil test showed adequate amounts of N & S for the crop, so N & S were not applied.

Spraying: Roundup WeatherMAX® was used as pre-emergent 7 days after seeding. In-crop spraying was done with 2, 4 - D 700 at 0.35 L/acre. Rouging was done a few times.

Measurements taken:

  • Prior to harvest at the boot stage, stand assessment was done for stand uniformity.

  • Field notes were taken on lodging.

  • Forage yield was determined at boot, heading and milk stages.

  • Forage samples were measured for nutritional value.

Results & Interpretation

Forage Moisture Content

The forage moisture content at harvest was significantly affected by oat variety x stage of maturity interaction effects. As expected the forage moisture content at harvest dropped as each oat variety grew older (boot to milk stage, Table 1). For the varieties tested, moisture content was generally below 70% at the milk stage.

Forage Dry Matter (DM) Yield

For oats tested, forage DM yield was similar with delayed harvest stage. This means that forage DM yield was statistically influenced by oats x stages of maturity interactions (Figure 1). The milk stage only produced more DM yield by about 1000 lbs DM/acre over the earliest harvest stage (boot stage), but not over heading stage.

Pooled across stages of maturity at harvest, oat varieties had similar mean forage DM yields, varying from only 3.32 to 3.87 tons DM/acre.

However, stages of maturity did show significant differences on forage DM yield (Figure 2B). Forage DM yield increased from 2.98 tons/acre for boot stage through 3.54 tons/acre for heading stage to 4.13 tons/acre for milk stage. Delaying harvesting till the milk stage had 1.2 tons DM/acre advantage over boot stage.


The forage crude protein content (CP, % DM basis) was similar for the oat variety x stage interactions. The CP was also similar for oat varieties (over stages of maturity) as well as stages of maturity (over oat varieties). But generally, for each oat variety, earliest harvest (boot stage) appeared to have the potential to give higher CP content (Table 1). For each variety, CP seemed to decrease slightly with advanced stage of maturity.

The Beef Cow Rule of Thumb with protein is 7-9-11%, which means an average mature beef cow requires a ration with CP of 7% in mid-pregnancy, 9% in late pregnancy and 11% after calving. Looking at Table 1, with a range of 13-18% CP, regardless of when any of the oat varieties were harvested for greenfeed, the CP requirements by mature beef cattle have generally been met. Similarly, the CP values of all oat varieties at any particular stage of maturity were well within the 12-14% CP needed by growing and finishing calves, and in a few cases the requirements have been exceeded.


The forage minerals (macro and trace) are shown in Table 2. Only forage K content showed a consistent decrease from boot to milk stage. Other minerals did not show any consistencies. Generally, when harvesting at the boot stage, the oats had more minerals than later stages of maturity. For a dry gestating cow, the mineral requirements (except for Cu) have all been met by all oats at any particular harvest stage.

Energy The forage TDN was not significantly affected by oat varieties x stages of maturity interactions. The mean TDN across oat varieties or stages of maturity was also not significantly affected. The forage TDN varied from 61 to 64% TDN (Table 3). As expected, the TDN values show a tendency for oats harvested at milk stage to have higher TDN than those harvested earlier.

Using TDN%, the Rule of Thumb is 55-60-65. This rule says that for a mature beef cow to maintain her body condition score through the winter, the ration must have a TDN reading of 55% in mid pregnancy, 60% in late pregnancy and 65% after calving. Looking at the TDN values in Table 3, only the TDN requirements of a gestating beef cow have been met by all oat varieties at any particular stage of maturity.


When planning for hay cutting it is important to consider rain events. Rain on cut hay may drastically down-grade it compared to hay left standing for an extra week. One of the major factors that affects the nutritional value of a plant to be used as a forage is the stage of maturity at which it is harvested. The forage protein and K decreased slightly with advancing maturity. The RFV appeared to be better at milk stage than other stages.

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