Corn silage and corn grain inclusion rates in the daily ration of cows are on the rise. No other crop has such a high availability of supply, energy density and consistency. Corn silage has a high palatability and delivers a considerable amount of starch that by-passes the rumen. By-pass starch is digested in the intestine and is more efficient as a glucose source for early lactating dairy cows, than broken down to volatile fatty acids in the rumen.
Wheat and barley are both poor sources of by-pass starch because they are very rapidly degraded in the rumen – only 5-10% leave the rumen unfermented. Corn starch, on the other hand, is a slowly degradable energy source and is more likely to by-pass the rumen. In fact, up to 30% of the corn starch can leave the rumen undigested. A cow in early lactation yielding 40 kg of milk per day has a glucose requirement of about 3 kg for milk production (Table 1). Therefore, corn starch that by-passes the rumen can easily match about 60% of the daily glucose requirement for milk production (Table 2).
Dairy producers are therefore not only investing in cow genetics but also in corn hybrid genetics. Modern corn hybrids that are grown for silage and/or corn grain should deliver the most from every hectare in terms of energy from starch but also from the forage part. In order to achieve high energy concentration in the feed, special attention has to be paid to the starch content and its rumen degradability, as well as on the fiber content and its digestibility.
Ruminal corn starch degradability is strongly influenced by which corn hybrid is used in the feed, and its maturity. Varieties with almost all hard or vitreous endosperm are called flint, while those with a softer or flourier endosperm are called dent hybrids. The proportion of starch from corn that is fermented in the rumen can therefore vary considerably - between 50 to 95% depending on corn varieties and maturity (Figure 1).
Undegraded starch from the rumen will flow into the small intestine, where it will be digested by endogenous enzymes produced by the cow. Although the increased intestinal starch flow can increase the direct absorption of glucose, being an important precursor of lactose for high producing dairy cows, the capacity of the small intestine to digest large quantities of starch is limited. Therefore, some undigested starch can move through the duodenum towards the hindgut and is then lost via feces, having a negative impact on feed utilization and incurring costs for the dairy producer (see figure 1).
Another undesirable effect that can result from feeding high amounts of very slowly degradable starch is a limited availability of oligosaccharides or rapidly available energy in the rumen directly after a meal. This leads to a lack of energy for the fiber colonizing and digesting bacteria and will therefore limit the capacity and the speed of the microbes to degrade the dietary fiber (NDF) of the ration. Moreover, microbial biomass and thus microbial protein yield might be compromised, due to the lack of more readily available energy. Synchronizing energy and protein metabolism in the rumen is, however, the key for maximizing microbial protein output, for optimum feed utilization and thus performance.
The rate and site of starch digestion in the gastro-intestinal tract can be modified by various grain processing methods, by harvesting corn at the right maturity and dry matter content. Recently it was proven that feed enzymes can also have an impact on starch degradability in the rumen. In vitro experiments using buffered rumen fluid showed that the addition of an alpha amylase enzyme to different grain varieties increased gas production as an indicator of fermentation intensity. The strongest effect was on corn grain where the alpha amylase showed a higher fermentation intensity of almost 80% (Figure 2). In addition, different corn varieties reacted differently to the alpha amylase. For example, fermentation intensity is higher in flint corn than in dent corn hybrids.
Feed enzymes are a radical innovation in dairy cow nutrition and one in particular can be used as a new approach to maximize corn starch utilization and fiber digestion in early lactation. RONOZYME® RumiStar™ is registered as a feed additive and is currently the only enzyme for dairy cows on the market that works in the rumen. RONOZYME® RumiStar™ catalyzes the hydrolysis of corn starch to oligosaccharides in the rumen without compromising on pH (Figure 3).
Oligosaccharides can be used as an energy source by the fiber degrading microbes – also known as “cross-feeding”. The time it takes for fiber to be digested can be reduced when there is more energy available to the fibrolytic microbes. It has been demonstrated that RONOZYME® RumiStar™ almost doubled the ruminal degradation rate of starch and fiber (NDF) in situ (Figure 4). The degradation of the organic matter in the rumen therefore increased, leading to an overall improvement of the total tract digestibility of the ration. A higher total tract organic matter digestibility exploits the energy potential of the ration and leads to better animal performance.
The increased digestibility of the diet results in more energy that is available to the cow for milk production. This was shown in a trial conducted at the University of Delaware in the US. RONOZYME® RumiStar™ improved the digestibility of dry matter, of organic matter and fiber (NDF) in a corn-based diet and this also resulted in a 9% increase in fat corrected milk yield or +3.6 kg per cow per day (Figure 5).
Adding RONOZYME® RumiStar™ to a typical diet in the north of Italy increased not only milk yield but also milk fat content, leading to 15% more fat corrected milk (FCM) of 4.4 kg per cow per day in early lactating cows (<150 days in milk) (Table 3).
Commercial field trials, as well as University trials, were conducted over several years in North America, Latin America and Europe. They show that RONOZYME® RumiStarTM increased the milk yield of cows in diets that contained 20 – 30% of corn starch on average by about 2 kg per cow per day, ranging from 0.5 to 4.4 kg per cow per day (Figure 6). Moreover, the additive could also alleviate the typical energy gap in the first 150 days of lactation, allowing the cow to recover more rapidly from energy deficiency during this critical period.
A trial conducted in Spain (IRTA, Barcelona) showed that RONOZYME® RumiStar™ also has an effect on the intermediary metabolism of the cow. Cows fed the enzyme gained increased blood glucose levels and the insulin/glucose ratio became higher. This is a very interesting observation because it indicates that the enzyme is also active in the small intestine helping the cow’s endogenous pancreas amylase to digest the by-pass starch (Table 4).
Cows have a limited capacity to digest starch that is entering the duodenum and this can lead to considerable amounts of starch excreted via the feces. A simple calculation shows the financial dimension of this loss: in a dairy herd of 500 cows with a daily intake of 5.6 kg of corn starch at a digestibility of 95% the cows excrete the equivalent of 21 Mton of corn grain in the first 100 days of lactation. This is an extra need for growing 2.5 ha more corn. At the current price level this is a financial loss of € 3,000. If such a herd was to increase milk production by 2 kg when supplemented with RONOZYME® RumiStar™ per cow per day, in the first 100 days of lactation, this would account to 100,000 kg more milk, and at a current milk price of 0.28 €/kg the total gain would be €31,000.
Currently, dairy farmers are struggling because milk prices are very low and will continue to stay low throughout 2016. There is therefore little desire to further increase milk production. However, attitudes towards increased milk production would perhaps shift with the knowledge that the same amount of milk could be produced with less cows. Dairy producers can achieve this by turning to innovative new approaches for feed, such as the use of specific feed enzymes. This would result in a significant rise in herd efficiency, as well as better rumen health and would also allow for maximum profit to be achieved from every hectare of corn grown.
07 September 2018
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