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Stage at Swathing Oats for Swath Grazing

Updated: May 12, 2023

Collaborators: Roland & Faye Cailliau, Valleyview

Research Coordinator: Dr. Akim Omokanye

The cost of feed accounts for a greater portion of the total costs of beef cattle production in Alberta. A major portion of these costs comes from late fall and winter feeding programs. In order to reduce winter feed costs, beef cattle producers have always explored options in extending the fall grazing period. Such options include swath grazing of cereal forages, particularly with oats. Earlier studies at the Lacombe Research Centre have shown that swath grazing could reduce costs of winter feeding programs for beef cows by 40%, due to elimination of harvesting, hauling, and feeding costs as well as reducing manure spreading costs. The objective of this trial is to examine the effects of stage at swathing two oat varieties on forage yield, feed value and animal weight gains.


The trial was located at Roland & Faye Cailliau farm on RGE Road 724, near Valleyview, MD of Greenview. Prior to the trial, the site (40 acres) had been used for feeding for 3-5 years and pasture for the past 10 years. The site was worked in fall and again in the spring. Soil tests showed a pH of 5.5 and 6.2% organic matter. The soil test also showed optimum amount of N, marginal amount of P and optimum amounts of both K and S for oats, so no fertilizer application was made before and after seeding.

Two oat varieties (CDC SO-I and AC Morgan) were seeded on June 29, 2012 with a Flexi-Coil chisel plow at the rate of 3 bushels/acre.

1. AC Morgan – high yielding, later maturing milling oat, commonly used for silage or greenfeed.

2. SO-I (CDC Super Oats, variety number one) is a new forage/feed oat variety. It is an excellent feed oat for backgrounding cattle, very digestible, high fat content, does not need to be rolled.

Each oat variety occupied 20 acres. The oats were swathed at 2 stages of maturity: early milk stage (swathed on Aug 29, 2012) and late milk/early dough stage (swathed on Sept 17, 2012). There were 10 acres for each oat stage of maturity. Forage sampling for determination of forage DM yield was carried out just before swathing using random clippings from eight 1m x 1m quadrat/per oat swathing stage. Dried samples from each stage of maturity at swathing were sent to Central Testing Laboratory in Winnipeg for feed value tests. Swathed oat samples were also sent to Central Testing Lab later on to test for nitrates.

For the grazing part of the trial, selected animals of known weights were being used to monitor weight gains. The grazing aspect of the trial had to be stopped about 3 weeks into swath grazing. Two cows died during grazing and the cause of death was later determined to be fog fever. Also known as Acute Bovine Pulmonary Edema and Emphysema (ABPEE), fog fever is an acute pneumonia of adult cattle which occurs within four to 10 days of moving from an over grazed pasture or dry feed, to lush pasture grasses (high in L-tryptophan). The condition develops rapidly. It typically occurs in Autumn, five to 10 days after the change to lush grass. This occurs when the affected cattle have been on dry feed for an extended period of time and the rumen fermentation pattern has adapted to this situation. With the change to lush green pasture the dietary protein concentration increases dramatically. One of the amino acids in this plant protein, tryptophan, is the culprit. The tryptophan in the feed is converted by rumen bacteria to a substance called 3-methylindole (3-MI) at a very high rate. This 3-MI is absorbed through the rumen wall and circulated around the body. The 3-MI is toxic to the primary cells that line the interior surface of the lungs. Thus, as the high levels of 3-MI move from the rumen to the lungs more and more lung tissue is destroyed. For more information, please visit the following websites:$department/deptdocs.nsf/all/beef11728

Results and Discussion

Forage Dry Matter (DM) Yield

The DM was highest for Morgan oat when harvested at the late milk/early dough stage (7651 lb DM/acre) and lowest for CDC SO-I when swathed at the early milk stage (6250 lb DM/acre) (Figure 1). Over the 2 swathed stages, Morgan oat only slightly out yielded SO-I by 648 lb DM/acre (Table 1). But over the 2 oat varieties, late milk/early dough stage slightly out yielded early milk stage by 753 lb DM/acre (Table 1).

Feed Value

Protein content was highest with Morgan oat but only when it was swathed at the early milk stage (12.01% protein). This was followed by CDC SO-I when swathed also at the early milk stage (9.87% CP). For both oats, delaying swathing till the late milk/early dough stage reduced the protein content

For Morgan oat, the reduction in protein from early to late swathing was 3.48%. Morgan oats swathed at early milk stage had protein content which far exceeded the protein requirements of 7 to 11% for dry gestating and lactating cows. The protein content of CDC SO-I was adequate for cows in the mid and late pregnancy stages.

Both oats, regardless of when swathing was carried out, had sufficient Ca to meet dry pregnant cows requirements of 18% Ca. Morgan oat, when swathed, appeared to favour Ca content. The P requirements of dry gestating cows is 0.16% P, but in this trial both oats when swathed at the early milk had sufficient amount of P that these classes of cows need. Both oats when swathed later fell short to meet this requirements.

None of the oats at any particular swathed stage had a 2:1 Ca:P (Table 1), which is considered as the minimum Ca:P required ratio for beef cows. The short fall in the ratio can be addressed using feed blends or commercial minerals.

The acid detergent fiber (ADF) decreased as swathing was delayed from early milk to late milk/early dough stage for both oat varieties. The decrease in ADF from early milk to late milk/early dough for CDC SO-I and Morgan oats was respectively 5.0 and 3.7%. Overall, CDC SO-I had lower ADF (37.8%) than Morgan oat (42.1%), an indication that the digestibility of CDC SO-I oat would be higher than Morgan oat. The ADF fraction contains cellulose, lignin, and heat-damaged proteins. Cellulose varies in digestibility and is negatively influenced by the lignin content. As lignin content increases, digestibility of the cellulose decreases. ADF is negatively correlated with overall digestibility. Because of this negative relationship between ADF and digestibility, low ADF is desirable.

Nitrates (NO3) content <0.5% is considered generally safe for beef cattle. CDC SO-I swathed either stage had safe level (0.13 –0.30%) of NO3. But looking at Morgan oat when swathed at the early milk stage, the NO3 level was 1.45% and this is considered unsafe and should not be used for pregnant animals. What is responsible for the high NO3 content for Morgan oats is difficult to explain, as both oats were swathed at early milk stage on August 29, and the oats were not are stressed or injured around the time of swathing. Also, no applications of nitrogen fertilizer or manure was made before or after seeding, as the soil tests showed sufficient nutrients. According to the information on the ARD website, immature plants will usually have higher nitrate levels. In cereal forage crops, nitrate levels can start to decline from the milk stage onward. However, never assume that a crop will be safe. Oats can still have relatively high nitrate levels even at the milk stage. Always test to be sure.

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