Source: Manitoba Agriculture, Food and Rural Initiatives
This article was originally published by Agriculture and Agri-Food Canada written by Hushton Block, Research Scientistâ Beef Production Systems, Agriculture and Agri-Food Canada, Brandon Research Centre, Brandon, Manitoba Email: hushton.block@agr.gc.ca
An ongoing study at AAFCâ Brandon Research Centre is investigating the use of early-seeded swath-grazed annual forages in beef pasture production systems. However, one limitation to the use of swath-grazed annual forages earlier in the year is the potential for loss due to weathering and spoilage in the interval between swathing and grazing. A novel experimental variety of barley with an altered form of wax is currently under development by Dr. Mario Therrien of the Brandon Research Centre. This waxy barley may be able to reduce the risk of weather-related damage and nutrient loss from swathed annual forages. Although the altered wax expression may reduce weathering-related losses, it may also reduce the acceptability and digestibility of the swath-grazed barley.
The Brandon Research Centre initiated a new study in 2007 to evaluate the acceptability of a novel barley variety, relative to other forage barleys and a triticale variety, when used for early-seeded annual swath grazing and subjected to weathering. Researchers also planned to determine the rumen degradability of leaf and stem material from the novel barley variety, relative to a conventional barley variety, when subjected to varying degrees of weathering.
Single strips of AC Ranger, Desperado, AC Ultima and the novel waxy barley were swathed in three paddocks at the end of July/beginning of August and then allowed to weather until the end of September. Samples of swathed forage and regrowth were collected to estimate yield. Each paddock was then grazed by four non-lactating beef cows, with their access to feed restricted by electric fencing. After the grazing period, residue was sampled to determine forage utilization. The plot layout is detailed in Figure 1 (PDF, 60KB).
Samples of leaf and stem material were collected at monthly intervals after swathing from single strips of AC Metcalfe and the novel waxy barley. Both leaf and stem material were ground to pass through a 2-mm screen and then incubated in the rumen of four ruminally cannulated yearling steers for up to 96 hours to allow determination of rumen degradability characteristics (Figure 2, PDF, 60KB).
Initial results from the cow grazing preference trial are presented in Table 1 (PDF, 30 KB). Yield at swathing was highest for AC Ultima, followed by Desperado and the waxy barley variety, and lowest for AC Ranger. Late season rainfall allowed for regrowth. The yield pattern for regrowth was largely the reverse of that observed for yield at swathing, being lowest for AC Ultima, followed by the waxy barley, and highest for AC Ranger and Desperado. Total yield was determined primarily by yield at swathing and was highest for AC Ultima, intermediate for Desperado and the waxy barley variety, and lowest for AC Ranger. After grazing by non-lactating cows, residue was lowest for AC Ranger and the waxy barley, followed by Desperado and then AC Ultima. These results suggest that AC Ranger and the waxy barley are preferentially consumed. When intake is expressed as a percent of available forage, the three barley varieties were similar at about 80% consumption and preferentially consumed relative to the AC Ultima triticale. However, at about 70% consumption, even the AC Ultima triticale was acceptable. Anecdotal observations found all cows to strongly prefer the lush regrowth of all varieties relative to the swathed forage. This finding may suggest an even greater preference for the waxy barley variety as it achieved a level of consumption comparable to the other varieties despite having the lowest regrowth of all the barleys.
Initial results from the degradability trial are presented in Table 2 (PDF, 30KB). There were variety by harvest time interactions noted for the a and b fractions, whereby the immediately available fraction declined with later harvest and more weathering exposure, and the rate of decline was greater for the waxy barley than AC Metcalfe. In contrast, the slowly degradable fraction increased with more weathering exposure for the waxy barley variety and remained constant for AC Metcalfe. The waxy barley had a 1.4% higher unavailable fraction than AC Metcalfe, and both varieties showed substantial increases in the unavailable fraction with later harvesting. There was no effect of variety or harvest date on the extent of the lag period or the rate at which the slowly available portion was degraded.
When all the degradation characteristics are combined to estimate effective rumen degradability, there was a 1.3% reduction in effective degradability (roughly equivalent to Total Digestible Nutrients, or TDN) for the waxy barley relative to AC Metcalfe, and a more substantial 5.2% reduction in degradability with the late versus early harvest date and increased opportunity for weathering.
The researchers have come to a few preliminary conclusions. When the novel waxy barley variety is used as a swath-grazed annual forage and subjected to weathering, it appears to have a level of acceptability at least equal to other forage barley varieties and greater than a spring triticale variety. Over a range of harvest times, the rumen degradability characteristics of the novel waxy barley are poorer than those of AC Metcalfe. Given that the altered wax expression is expected to reduce weathering-related losses, it should also reduce digestibility. However, the difference between the two varieties is not very substantial. What remains to be assessed is the effect the altered wax expression has on reducing loss of nutrients from the swath in the interval between swathing and grazing. Research is ongoing, and the study will be completed later this year.
