The recommendation to cut barley crops at the early-dough stage and oat crops at the late-milk stage for silage has by default been the standing recommendation for stage of maturity to cut these cereals for greenfeed and swath grazing as well.
Findings by a University of Saskatchewan team of researchers with the animal science and crop science departments support changing the recommendation to cutting barley and oat crops at the hard-dough stage for use as greenfeed and swath grazing.
Several related trials to study the question of later cutting from all sides increase confidence that letting these crops advance to the hard-dough stage improves dry-matter (DM) yield without compromising forage intake, digestibility and digestible energy intake.
They calculate that the yield boost from leaving barley the additional three weeks or so in the field to advance from the late-milk stage to the hard-dough stage could provide feed for 23 per cent more cows from the same land base at no extra cost. Likewise, oat crops cut at the hard-dough stage could feed 57 per cent more cows than if cut at the late-milk stage. However, the increase in forage yield is likely to vary from year to year depending on growing conditions.
The original recommendations for silage still stand because certain levels of carbohydrates and high moisture content are needed for proper fermentation and packing silage, but they don’t apply to making dry forage, explains Dr. Greg Penner, a ruminant nutritionist who worked on the project.
For dry forage, letting DM accumulate in the standing crop not only has potential to increase yield, but also improves quality as valuable starch increases in the kernels and can help preserve quality by reducing the dry-down time between cutting and baling.
The big question was whether that additional starch would be in a form available to cattle, and, if so, would it increase the risk of acidosis.
Not just grain on a stick
Work got underway in 2011 with small plots of barley, oat, wheat and millet cut at head elongation, late milk (oat)/early dough (barley), hard dough, and full maturity to confirm the effect of stage of cutting on yield and nutritional characteristics.
Chemical analysis of the whole-crop forage samples revealed more feed-quality advantages than drawbacks as the crops advanced in maturity.
There were significant differences in nutrient composition from the late-milk stage to the hard-dough stage, but very little change from then to maturity. Overall, organic matter and non-fibre carbohydrates (total starch and sugar except those tied up in cell walls) increased as a percentage of DM. Neutral detergent fibre (NDF) decreased as starch accumulated. The decreases in calcium and crude protein (CP) were the notable disadvantages. Although phosphorus decreased, that in itself isn’t viewed as a disadvantage because phosphorus content in cereals is on the high side relative to calcium content and cattle require a balance of around two parts calcium to one part phosphorus.
The forages were put to the true test for feed quality in a feeding trial coupled with a metabolism study involving ruminally cannulated cows to learn how the stage of cereal forage maturity affects forage intake and digestion.
Animals fed rations containing cereal forages cut at the hard-dough and mature stages had lower rumen pH levels than those fed cereals cut at the late-milk stage, indicating that the additional starch in the later-cut forages is digestible. Rumen pH didn’t drop to a level that was of concern health-wise.
Rumen pH normally ranges from 6.5 to 7.0 with temporary dips after eating that are considered normal and a sign of adequate feed quality and feed intake. Acidosis sets in when volatile fatty acids formed during fermentation build up in the rumen faster than they can be absorbed into the bloodstream for energy, causing rumen fluids to become more acidic. Dips in rumen pH below 5.8 for long periods, or bouts of low rumen pH can potentially lead to numerous health issues.
Palatability wasn’t an issue. The cows didn’t eat any more or less regardless of the stage of maturity at cutting.
The next study, recently published in the Journal of Animal Science, involved six ruminally cannulated heifers, fed whole-crop barley or oat cut at either the late-milk, hard-dough or mature stage. The forage portion and supplement (alfalfa pellet, vitamin/mineral pellet, and steam-rolled barley-canola meal combination) to balance the ration were fed in separate feeders.
For barley, DM yield increased by 42 per cent for hard dough and 57 per cent for fully mature relative to late milk.
Intake of forage and supplement didn’t differ among maturity stages. Forage remaining after a feeding was analyzed for starch and fibre components and a sorting index applied to evaluate selective choice or avoidance.
Heifers that received forages cut at hard-dough and mature stages selected slightly more for starch, but didn’t selectively avoid fibre, whereas those fed the forage cut at late milk showed a definite preference for fibre and avoidance of starch.
There were no differences in ruminal DM digestibility, however, total-tract DM digestibility was slightly lower for barley cut at the hard-dough stage than at the late-milk or mature stages.
There were no differences in starch digestibility. The minimum rumen pH was above 6.0, with the daily average near 6.5 and no differences were seen in total ruminal short-chain fatty acid concentration.
Ruminal NDF digestibility was similar (55 per cent digestible) for the later-cut stages, but lower than for barley cut at the late-milk stage (70 per cent digestible). Total-tract NDF digestibility was highest (70 per cent) for the late-milk cut barley, lowest (50 per cent) for the hard-dough cut barley and between for the mature cut barley.
Even though DM digestibility and NDF digestibility were slightly reduced when barley was cut at the hard-dough stage, Penner notes the increase in starch offsets the contribution of NDF towards energy supply.
Overall, there were no differences in digestible energy intake, average daily gain, accumulative weight gain, time spent feeding or chewing, number of feeding bouts, number of chewing bouts, or ruminal dry-matter fill.
It was the same story for the oat crop — no difference in forage intake, ruminal and total-tract DM digestibility, and digestible energy intake.
Dry-matter yield jumped by 122 per cent and 96 per cent when cut at the hard-dough and fully mature stages relative to late milk. The reduction in yield at the fully mature stage likely indicates a pitfall as kernels may shell from the plant, he adds.
At all stages of crop maturity, the heifers selected slightly more for starch with only a slight avoidance of NDF.
Total-tract starch digestibility was greater than ruminal digestibility with both dropping off slightly as the crop advanced in maturity, although it was still available as indicated by the rumen pH drop after feeding. The lowest rumen pH was around 5.8 when fed the hard-dough forage, but the daily average was around 6.3 for all stages and didn’t cause acidosis. Again, there were no differences in total ruminal short-chain fatty acid concentrations.
Unlike barley, total-tract NDF digestibility tended to increase with advancing maturity, from 60 per cent digestible at the late-milk stage up to 80 per cent at the mature stage.
In summary, Penner says harvesting oat and barley at the hard-dough stage has the potential to improve digestible nutrient yield without negatively affecting DMI, sorting, ruminal fermentation, ruminal digestibility or total-tract digestibility.
The cautions — a potential for grain loss due to shelling in the field, the need to provide calcium and protein to balance the diet, and the chance that feeding cereal forages cut at later stages of maturity could cause acidosis.
According to the Beef Cattle Research Council, susceptibility to acidosis varies among animals. Some cattle seem to be very tolerant of highly fermentable diets; others not so much. It is likely that many factors contribute to the varying susceptibility including feeding behaviour (meal patterns, meal size, feed sorting), the types of microbes in the rumen, capability of cattle to regulate pH, saliva production, rumen motility, and prior feed consumption.
A final study evaluated the effect of stage of maturing in combination with feeding behaviour in a controlled setting with cannulated heifers that were fed once a day or once every three days. Measurements were taken for six days following a nine-day adaption to these two feeding regimes.
No differences were noted in total feed intake on hard-dough oat forage or mature oat forage.
Average daily rumen pH was around 6.3 with daily feedings of forage cut at both stages of maturity. It was lower but still above 6.0 in heifers on the three-day regime.
Minimum rumen pH remained above 5.8 when hard-dough forage was fed daily, but dipped below 5.8 for about 75 minutes per day when mature forage was fed daily. Longer periods with rumen pH below 5.8 were observed in heifers on the three-day regime at approximately 275 minutes per day on the hard-dough forage and 500 minutes per day on mature forage.
The authors conclude that the daily fluctuation in rumen pH associated with larger feed allocations coupled with later maturity increases the risk of subacute ruminal acidosis. How often the forage will be fed should be taken into account when deciding on the stage of maturity to target for at harvest.
For more information, contact Saskatchewan Ministry of Agriculture beef and forage specialists at 306-694-3727.