Rumen health seminar: Improving the productivity and nutrient use efficiency of pasture-fed cows

Key points

Cutting-edge nutritional research, being undertaken in Ireland, is unlocking new understandings of dry matter intake (DMI) regulation, rumen function and N metabolism in grazing dairy cows.

Dr Michael Dineen says well managed pasture-based systems can sustain high levels of animal performance through a keen focus on plant maturity and pasture management.

“Pasture-based dairy systems robustly convert human inedible feed into highly nutritious food, while supporting a resilient business model for the producer” he says.

“The challenge now is how to further increase productivity, to meet rising consumer demand, in an environmentally benign manner.’’

“There are a number of potential solutions available such as alternative pasture species, genetically improved plants and/or optimised supplementation strategies. However, to understand which solution may be optimal we first need to understand what is limiting animal performance.’’

“Limiting factors could potentially include rumen physical fill, metabolisable energy supply and metabolisable protein or amino acid supply.’’

The research team utilised the latest version of the CNCPS (version 7.0) and new in-depth feed chemistry to gain a greater understanding of these potentially limiting factors.

“We applied the new developments in fibre digestibility analysis, from the Van Amburgh lab at Cornell University, to our immature pastures and discovered the huge capacity of these pastures to digest rapidly.’’

By slightly adapting the analysis (i.e. adding an additional fermentation time point) the researchers were able to quantify the rapid digestion behaviour by fractioning the pasture fibre into 3 distinct digestion pools of fast, slow and indigestible fibre.

“Immature pasture fibre is primarily comprised of a large fast pool, which can digest at 20%/h, and small pools of slow and indigestible fibre.’’

These fibre pools have been demonstrated to impact animal variables such as DMI, rumen pool size, rumination and milk production.

“A large fast pool appears to result in faster ruminal disappearance, higher intakes, faster eating and more ruminal buoyancy leading to greater chewing and rumination’’.

As the fibre digestibility analysis was performed in the laboratory, the researcher wanted to confirm the digestion characteristics that they were observing in vivo.

“We performed an omasal sampling experiment which allowed us to quantify ruminal fibre digestion in the cow. When we offered the cows immature pasture, their rumens had a massive capacity to digest the fibre, over 70% of fibre consumed and over 80% on a total-tract basis.”

The researchers then compared the in vivo observations with CNCPS predictions.

“When the model was provided with comprehensive inputs from the new fibre digestibility analysis the model could predict within 200 g of the observed in vivo fibre digestion, which also improved the model’s ability to predict actual milk production” Michael says.

The researchers are now applying these tools within their research programs to describe the effect of factors such as season, weather conditions and plant genetics on animal productivity.

“The tools are unlocking the mechanisms behind rumen fill and turnover, which is helping to describe how plant species, such as white clover, can increase dry matter intake and milk solids production within our systems.’’

“We also wanted to utilise the CNCPS and the omasal sampling technique to gain a greater understanding of the N metabolism in pasture-fed cows. We discovered that although pasture can be high in protein, the protein is extremely digestible and there may be opportunity to refine amino acid supplies.’’

The researchers are now utilising these new insights to refine nutritional strategies for improving the productivity and nutrient use efficiency of pasture-fed cows.