The Centre for Animal Nutrition in the Netherlands, in partnership with Lallemand Animal Nutrition organized an international symposium devoted to the importance of plant cell walls characteristics in nutrition management of Dairy Cattle, on March 2010 in Wageningen, NL.
The high attendance of the event, which gathered over 240 delegates from no less than 22 countries from all over Europe, as well as North and South America and India, is a good indicator of the industry's interest to improve fiber utilization for better feed efficiency, at a time when, as moderator Dr Van Vuuren reminded the audience, the worldwide protein demand is bound to double within the next four decades and a key issue is to answer the associated need for growing feed without aggravating environmental pressure.
A large proportion of the solar energy reaching our planet is fixed in plant cell walls which, due to their chemical properties, are indigestible for humans and animals and therefore not suitable as an energy-yielding food source. By symbiosis with specific micro-organisms, ruminants are capable of utilizing the energy and molecules embodied in plant cell walls.
Plant cell walls are an important feed component of the ruminant diet, not only as an energy and nutrient source, but also as a regulatory factor controlling feed intake and leading to healthy rumen function. In Wageningen, world-leading experts in animal nutrition explored not only the factors that influence plant cell walls characteristics and their digestibility, (both intrinsic and extrinsic); their impact on feed intake and animal performance but also their effect on methane emissions, and how this can influence feed formulation.
Intrinsic factors affecting fiber characteristics
Dr John Cone, from Wageningen Animal Nutrition group, reminded the participants that plant cell walls represent a great part of forage dry matter (DM): NDF (see NDF boxed text) accounts for 35-45% of maize silage DM to 40-60% for grass silage. If fiber content is important, fiber quality (or digestibility) is also a key factor, and may be a very variable one.
It is influenced by:
- the plant genotype (degradability is a selection criteria for crop breeders) e.g. NDF digestibility of various maize crops range from 40-60%
- the fiber's physico-chemical properties: lignin content correlates with degradability (see boxed text), but Cone emphasizes that this correlation varies between forages, suggesting the role of lignin molecular structure (type and number of bonds) may also play an important role.
- plant tissue composition
- Growing conditions (weather, water, fertilizers)
- Harvest date and maturity stage. Dr Cone presented a systematic study looking at the evolution of plant cell wall structure and degradability during maize plant development, for two different genotypes (high and low expected degradability). This study showed that degradability decreases along with plant maturity. The investigators concluded that, "during the growing season, the content of hemicellulose in the cell walls decreases while cellulose increases as well as lignnification, correlating with a decrease in the degree of degradation".
Not only fiber digestibility has to be taken into account, but also other feed characteristics can influence the degradation rate as shown by Prof. Charles Sniffen (Fencrest LLC, USA), who presented the latest model theories integrating NDF digestibility criteria. Especially important are the size and fragility of feed particles. Both will influence passage rate and digestibility and consequently feed value.
Extrinsic factors: microbes rule!
NDF digestibility values are assessed in vitro, using standard methodologies, and can be described as "theoretical digestibility", thereby describing the fiber intrinsic quality. But things are certainly different in vivo. In a study by Oba and Allen (1999), conducted on 28 dairy cows fed a common diet, total tract NDF digestibility appeared to range from 21.6 to 42.2%! In the same experiment, DMI ranged from 21.3 to 32.1 Kg/day.
Beside the diet and fiber characteristics, other factors could explain cow-to-cow variability. Feeding behavior and total intake could be implicated, and may be partly linked to the cow's body weight.
Another key factor is the rumen environment. It is in this large fermenter that fiber degradation occurs, by the action of various fibrolytic bacteria and fungi. The rumen environment, pH and microflora populations affect degradation and passage rates (see ‘Rumen turnover' box).
As demonstrated by Dr. Ana Lourenço, from University Tras-os-Montes e Alto Douro, in Portugal, the use of a ruminant specific live yeast (S. cerevisiae CNCM I-1077), which is known to positively interact with the rumen flora, in particular to stabilize the ruminal pH and stimulate endogenous fibre-degrading microbial populations (see Levucell SC boxed text), can play a part in improving NDF degradation in situ.
Dr. Lourenzo presented two in vivo studies looking at the effect of live yeast supplementation on fiber degradation for a range of forage samples of variable quality: first maize silages (40 different samples), then grass silages (66 samples). For the maize silages, she reported an average +23.9 % increase of digestibility in the case of "low degradability" silages, and an average +4.3% for the higher degradable silages. The same trend was observed with grass silage: NDF degradation for low degradability silages was increased by 18.6% on average, vs. 9.8 % for the higher degradable samples.
John Cone also reckons that treatment of forage with lignin degrading enzymes or fungi could help improve degradability and hence feeding value of low quality forages.
SC I-1077 effect on Maize silage NDF digestibility according to initial degradability (Guedes et al. 2009). LFD: low fiber degradability samples, HFD: high fiber degradability samples.
As explained by moderator Dr. Van Vuuren, the rumen turn-over is a major controller of DMI and hence animal production
Effects of fiber characteristics on feed intake and performance
One of the roles of fiber in the rumen is to regulate rumen digesta turn-over: fiber forms the ‘rumen mat', effectively entrapping feed particles. This in turn will increase digestibility and thus feed efficiency, and slow down feeding rate. Increased digesta volume will also decrease risks of displaced abomasums and increase the rumen buffering capacity.
Feed intake can also decrease with a high fiber diet. The effect of gut fill upon feed intake is increased as milk yield increases. Both fiber content and characteristics (degradability) will influence DMI (Dry Matter Intake).
Dr. Mike Allen, from Michigan State University, demonstrated that fiber quality effects on feed intake depend on the cows lactating phase or productivity. In lower producing cows, poor NDF digestibility increased feed intake, while in higher producing cows, feed intake decreased. Poor digestibility decreases milk yield peak. This could be linked to the effect of the diet on energy partitioning (energy repartition between milk production and body condition). Increasing diet fiber content in late lactation can help maintain milk production vs. body weight gain.
Allen concludes that "the benefits of reducing forage NDF concentration and improving NDF digestibility are greater for high producing cows."
Oba and Allen (1999) proposed an equation to quantify the effect of forage NDF digestibility on DMI and milk yield. They showed that an increase of 1 point of NDF digestibility permits to improve intake by 0.17kg DM and increases milk production by 0.25kg/day, without any problems of weight loss André Bannink, from Wageningen UR Livestock Research added an environmental and economic perspective by looking at the impact of NDF quality on enteric methane production, claiming that the potential for methane emission and feed value are two sides of the same coin.
Again, NDF quality alone is not sufficient, feed intake, feed chemical composition and digestibility should also be part of the equation. According to Bannink, NDF quality is linked to grassland management practices. High NDF quality is associated with practices leading to higher feeding value, lower NDF content and higher crude protein content, leading to lower methane emission.
Various factors influence fiber characteristics. As we start to get a grip of the impact that fiber quality can have on animal digestion, feed intake and performance, we are starting to redefine the importance of these characteristics.
But these relationships are complex, depending not only on the fiber's characteristics, but also on the feed form (particle size...), interactions with other feed ingredients, the rumen flora and rumen environment, or even the cow's physiological state. Among the tools and additives that can influence forage fiber utilization, an important body of evidence shows the potential of ruminant specific yeast Levucell SC to enhance fiber degradability. An effect all the more important if the initial quality of the fiber is poor, as shown by Dr Lourenzo and coll. If until now, Levucell SC had been well recognized for its benefits associated with high starch diets (anti-acidotic effect, improved feed value), more recent research clearly demonstrates its potential to improve forage and fibre utilization. As Lallemand Animal Nutrition General Manager P. Raoul commented after the seminar: "Experts around the world tell us that new feeding models will emerge, with higher utilization of forages in the diets, produced locally by the farms. In that sense, micro-organisms will play a key role in the quest for a more sustainable farming model around the globe." No doubt that the Wageningen meeting will inspire new ideas in dairy feed management and new areas of research concentrating on getting the most out of plant cell walls.
If you want to see the video interviews from the NDF 2010 Symposium, click here
For a detailed report of the symposium, please click here. For more technical information, please contact: Laurent Dussert, Ruminant Product Manager at email@example.com, or Aurelien Piron, Ruminant Technical Service at firstname.lastname@example.org .