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Improving animal performance from grazed pasture


A pre-requisite to exploiting improvements in the nutritive value of pasture is the optimisation of pasture management practices. Researchers Michael Dineen and Micheal O’Leary discuss the methods of improving animal performance from grazed pasture.

PastureBase Ireland (PBI)

The farm-level adoption of grazing technologies, such as PastureBase Ireland (PBI), has been critical for consistently achieving optimal herbage mass. For example, PBI users have reduced herbage mass from 1,601 kg of DM/ha in 2017 to 1,558 kg of DM/ha in 2020, on average across the whole year. Furthermore, this technology helps to increase the duration of the grazing season through the use of autumn and spring rotation planners. Increasing the duration of the grazing season can improve animal performance and reduce methane emissions. Over the last four years, the average grazing season lenght for PBI users was 40 days longer (278 days) compared with the national farm survey (238 days).

Improving nutritive value of pasture

The inclusion of white clover in perennial ryegrass (PRG) swards increased the milk production efficiency of lactating dairy cows (+48 kg of milk solids/cow) while simultaneously reducing the amount of chemical nitrogen fertilizer required (-100 kg of nitrogen/ha). Increased dry matter intake (DMI) and pasture digestibility have been suggested to contribute to this increased milk production efficiency; however, amino acid (AA) supply might also play a role. In an experiment incorporating a novel experimental procedure (omasal sampling), it was observed that extensive rumen degradation of perennial ryegrass AA occurs, which indicates that cows consuming pasture-based diets are highly dependent on microbial AA to support metabolisable AA supply. In a follow-up experiment, strategically supplementing cows fed a grass-only diet with a small quantity of a rumen-protected protein resulted in a large milk response, highlighting that specific nutrients are limiting milk production on grass-only diets.

Perennial ryegrass typically contributes 50-90% of the diet when cows consume perennial ryegrass-white clover swards, emphasising the importance of continued development of enhanced perennial ryegrass cultivars. The recent introduction of perennial ryegrass nutritive value evaluation into testing systems, as well as the inclusion of a ‘quality’ sub-index into the Teagasc Pasture Profit Index, will likely enhance  the rate of genetic gain for nutritional value of grass.

A pre-requisite to exploiting improvements in the nutritive value of pasture is the optimisation of pasture management practices, which can help avoid grazing swards with a high herbage mass. High herbage mass swards contain increased amounts of fibre. This fibre has a slower rate of digestion and an increased concentration of indigestible material when compared with optimal herbage mass swards. Results from a new laboratory-based fibre digestibility analysis demonstrated that the fibre in swards with optimal herbage mass is comprised of a large potentially digestible pool that degrades rapidly in the rumen. Grazing these swards increases DMI, digestibility and milk production efficiency and reduces methane production.

More information on PastureBase is available here.

If you liked this article you might also be interested in Managing the final grazing rotation with PastureBase Ireland - Webinar or PastureBase Ireland adds new functionality to benefit all grassland farms.