Rethinking The Role of Fibre

Rethinking the role of fibre to improve profitability of dairy farms

With ever increasing pressure on farm margins, coupled with increased bought in feed costs, maybe now more than ever is a time to look again at the role of effective fibre and NDF in rations to improve on farm profitability.

Effective fibre is defined as any particle that has a physical structure. Seen broadly as forage particles, that lend themselves to the formation of the rumen matt and stimulating rumination. Under current rationing mind-sets, it is a fine balance between having sufficient effective fibre and providing too much fibre, being detrimental to energy intake and therefore milk yield.

Neutral Detergent Fibre (NDF) is a measurement of structural elements of a feed, the Lignin, Cellulose and Hemicellulose. This is our best attempt at chemically assessing the fibre provision of a ration but in practice it has many limitations. Within the measurements of NDF, there are huge variables in digestibility, passage rate and palatability, all affecting the energy output and rumination output of a feed.

A rumen’s predominant role is to break down fibres that would otherwise be indigestible to yield metabolites for the cow. Through the use of rumen microflora, the process of ruminating to break down the structural elements of feeds is fundamental to the health, function and profitability of ruminant agriculture.

The ability to maximise the efficiency of this process provides huge opportunities in increase profitability of production systems. To do this, we need to fully understand the role of fibre provision in diets.

Processfibre-1

Rumination centres on the formation of a rumen matt. The basic principle is that the fibre element of the ration forms a raft that floats on top of a rumen liquor, with gases excreted collecting on top for expulsion. Rumination and cudding breaks down the fibres, so rumen microflora can break down fibres further, releasing carbohydrates and proteins inside. Particles which exit the rumen through the reticulo-omasal orifice, into the omasum, can be up to 5cm, but are typically 1cm in diameter (Welch et al 1986). Maximising the throughput of this process provides huge opportunity for improved efficiency.

 

The rate of passage of feedstuffs through the rumen is a limiting factor to milk production. The faster the process can happen, the more energy can be extracted from feed. Work by Reynolds (2010) found 40% of a heifer’s maintenance energy goes to digestion through the gastro intestinal tract, so there is reason to believe that a lot of energy is used to digest feed in lactating cows. Any digestion of low calorific value feed will be detrimental to the energy demand of the cow.

If ration digestibility can be increased, rumination effectively has less to do to extract the energy from feeds, making it possible to increase dry matter intake (DMI). There is very little correlation between DMI and rumination (K. Schirmann et al 2012). Krause et al 2002, found a correlation between long fibre intake and rumination time, supporting the theory that it takes more rumination to break down long forage fibres. Schirmanns work concluded that cows which spent more time ruminating, spent less time eating

Work by Welch et at (1986) demostrated that fibre particle size had no effect on the function of fibre, but specific gravity did. The specific gravity is thought to affect the ability of that fibre to form part of the rumen mat, or to sink to the bottom. It may well be that it is the specific gravity of lignified particles which show signs of improved rumen function, and not the NDF level.

Rumination

Rumination – muscular contractions by the rumen is the key function needed for rumens to intake, process and excrete – maximising this function is often seen as one of the main reasons for fibre provision in rations. Neural control of this process is done predominantly by stimulation of low and high tension receptors. The low threshold stretch receptors are stimulated at 4mm Hg to increase rumination, and the high threshold stretch receptors are stimulated at 20mm Hg to reduce rumination.

There is secondary tactile stimulation only by the cardiac sphincter (entrance to rumen) to generate an uplift in digesta towards the cardiac sphincter. With this in mind, it would seem it is rumen tension, not ‘scratch factor’ that has the most significance in stimulating rumination, therefore the provision of low digestibility forages to aid rumination simply maintains tension by staying in the rumen matt for longer.

This effectively reduces the capacity of the rumen, limiting forage intakes and jeopardising maximum profitability.

Rumen Degradability

If the above theories are accepted, then adding low digestibility feedstuffs to aid rumination is a false economy. Digestibility of NDF is an important parameter of forage quality because forage NDF varies widely in its degradability in the rumen (Allen et at 1996). NDF digestibility influences animal performance as excess dietary NDF can limit voluntary feed intake because of physical fill in the rumen. Basically, the cow gets full so stops eating.
The rumen matt will be formed out of particles based on specific gravity, effectively a matter of buoyancy. To maximise throughput and gross energy output, digestibility of feeds and rate of passage both need to be maximised. The easier rumination can hydrolyse NDF particles, the faster and more complete fibre degradation may be, leading to higher intakes of forage. So more digestible, shorter chopped forage will provide a higher gross NDF over a time period and yield more energy.

We should not look at NDF levels alone, in the ration or particle length, or indeed digestibility, but all in combination. Theoretically, the suggestion is to reduce particle size and make the most digestible forages as possible, but if that was done without full consideration, poor rumen health and depressed milk fats may occur.

If a holistic approach to this concept was taken however, it could certainly be successful. Work by Remond et al (2004) suggested starch degradation in the rumen could be as low as 54% if coarsely ground, compared to 70% if finely ground and recent thoughts towards lactic acid supply from forages all need to be factored in. If balanced correctly, full consideration of the degradability of NDF could lead to lower energy density rations which achieve higher intakes providing greater returns for the farmer.

Compact feeding

outdoor feedingThis theory is already well practised in parts of Europe that have a similar climate and forage base to the UK.

In Demark, they have called it ‘Compact Feeding’; a system where concentrates are pre hydrated, forages heavily processed and a mix fed to the cows that more resembles a moist feed than a TMR. The advantages are there to be had, with zero sorting, healthy rumination and forage intakes which no other system can get close to.

No sorting leads to more consistent intakes, less time pushing feed up, and the opportunity to get refusals to below 2%. The rations are typically 35% dry matter, are smooth to the touch and ball up when squeezed. Cows just eat it up, without nosing through it, spending less time at the feed fence and have higher intakes. After 2 years on this system, dairies have reported higher milk yields and herd health improvements. Full implementation of this system has its drawbacks, but we can use theories that this system proves to enhance our nutrition in the UK.

Conclusion

In conclusion, more research is needed into the role of fibre in rations, the true cost of sorting and the best chop length for UK rations. That said, there is evidence that many common practices in the UK are leading to inefficiency, ration sorting and holding dairy profitability back. A holistic approach to fibre provision in rations is recommended. Rumination is stimulated by rumen tension predominantly and there is a need to look beyond the total NDF in the ration, with digestibility of NDF being far more important. By increasing ration digestibility and reducing particle size, gross NDF targets can be raised, leading to higher forage intakes, less sorting and more profitable milk production at no detriment to cow health.

Mark Price
Dairy Specialist

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