When growing silage, particularly barley silage, most producers select varieties with proven agronomic traits such as yield, disease and lodging resistance. In contrast, relatively little information is available on the nutritional value of the numerous barley varieties that are available for seeding. Recently a joint research project was run at the University of Saskatchewan and Agriculture and Agri-Food Canada at Lethbridge to specifically evaluate the nutritional quality of common barley varieties grown by beef and dairy producers in Western Canada. The project was funded by the National Beef Cattle Research Council, Saskatchewan Agriculture Development Fund, the Saskatchewan Cattleman’s Association and the National Science and Engineering Research Council and involved two graduate students, Jayakrishnain Nair and Natalie Preston. As many producers will soon be deciding on a barley variety for growing silage, the results of this project may help with the selection process.
First a bit of background on the project. In phase one, barley silage samples, along with detailed agronomic characteristics, were collected from multiple commercial operations by co-operating consulting nutritionists. In total, 80 samples representing seven varieties harvested at the mid-dough stage of maturity (Conlon, CDC Copeland, CDC Cowboy, Falcon, Legacy, AC Metcalfe and Xena) were collected over two years and sent away for detailed chemical analysis. A companion sample was kept at the University of Saskatchewan for evaluation of fibre content and digestibility. Based on the results of phase one, three varieties (CDC Copeland, CDC Cowboy and Xena) were chosen for growing silage for backgrounding and finishing trials involving sheep and cattle at the two research stations.
For the purposes of this article, of the numerous nutritional traits examined, I will focus on crude protein, starch and fibre content, and fibre digestibility.
With respect to protein, there was a two per cent difference between the variety with the highest crude protein content (AC Metcalfe, 12.5 per cent) and that with the lowest (Xena, 10.2 per cent). Crude protein is an important and costly nutrient to supply to all classes of cattle. Selecting varieties with higher crude protein content will reduce supplementation costs, particularly in backgrounding and finishing operations where cattle have higher protein requirements than mature beef cows.
In addition to crude protein, energy content should also be a primary consideration when selecting barley varieties for silage. Energy content is often calculated as total digestible nutrients (TDN) which, in turn, is a summation of digestible protein, fibre, lipid and non-fibre carbohydrate components of a feedstuff. With respect to silage, two important components of this calculation which tend to have opposing effects are the starch and fibre content.
Starch content is a positive indicator of energy content of the silage with values above 20 per cent representing excellent quality silage. In this study, the starch content ranged from a low of 14.5 per cent in CDC Cowboy to a high of 24.7 per cent with Legacy. CDC Copeland, Colon, Falcon and Xena also had starch values of at least 20 per cent. In contrast, high fibre levels, i.e. acid (ADF) and neutral (NDF) detergent fibre content, indicates silage with lower digestibility and energy content. As well, in the case of NDF, high levels can lead to a filling effect in the rumen, limiting dry matter intake. In this study, CDC Cowboy had the highest ADF (30.2 per cent) and NDF (48.6 per cent) content while Colon had the lowest (26.1 and 41.9 per cent, respectively) with other varieties intermediate. As a result CDC Cowboy had the lowest (63.6 per cent) while Colon had the highest (67.4 per cent) TDN content of the seven varieties examined.
One of the key nutritional aspects that we looked at was NDF digestibility. This is not a common feed test and you might wonder why we were interested in this trait. First, the NDF content of a given forage can range from 40 to 70 per cent of the dry matter and thus represents a considerable proportion of the feed. Second, the digestibility of the NDF fraction will influence its contribution to energy content of the forage and will also influence the extent to which an animal can consume the feed. A forage with a high NDF content that is poorly digested will limit dry matter intake. In this study, of the seven varieties examined, CDC Cowboy had the highest NDF digestibility while varieties such as Xena and Legacy had the poorest NDF digestibility.
Phase two of the research was designed to look at the effect of selected varieties (CDC Cowboy, Xena and CDC Copeland) on the performance of growing and finishing calves. In particular, we were interested in determining if the higher NDF digestibility of CDC Cowboy would overcome the low starch and high NDF content of this variety. As in the commercial trial, CDC Cowboy had higher fibre levels than either Xena or CDC Copeland and lower starch levels, while crude protein levels were similar across varieties. When fed as part of backgrounding diets, calves fed CDC Cowboy had lower dry matter intakes and poorer gains that those fed Xena or CDC Copeland. Calves fed Xena were the most efficient at converting feed to gain.
These results show that barley varieties grown for silage do differ in important nutritional traits such as protein, starch and fibre content and that selecting varieties just for agronomic traits may not result in optimum silage quality or animal performance.