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NWF Weekly Grass Watch

GrassWatch 2020 ran for 30 weeks from 20th March until the 9th October. The season saw a total of 6,207 fresh grass samples being submitted and 549 milk yield from grazing (MYFG) samples.

Grass Growth
The total grass growth across GB from the week ending 29th March to the week ending 11th October was 1,381kg DM/ha, down 132kg DM/ha on last year’s figures. Across the regions, the greatest total grass growth was seen in the North West with a total of 1,550kg DM/ha, with a maximum growth rate of 78kg DM/ha/day during the week ending 12th July. In comparison, the lowest total grass growth this year was recorded in the South East at 1,163kg DM/ha.

Due to rainfall being 143% of the average from 1981-2019, the South East experienced drops in growth rate around mid-June and again in August because of exceedingly high temperatures and droughts. The highest growth rate this season, of 108kg DM/ha/day, was experienced in Yorkshire during the week ending 13th September.

Average weekly grass growth first peaked at 47kg DM/ha/day during week ending 19th April, at 7kg DM/ha greater than figures seen during the same period in 2019. Grass growth then peaked again during week ending 5th May, with the highest average peak of 73kg DM/ha/da, 4kg DM/ha/day less than the peak seen in 2019. From here grass growth steadily declined to 33kg DM/ha/day during the week ending 16th August, before rising in a late-season peak of 57kg DM/ha/day in the week ending 13th September, 18kg DM/ha/day greater than for the same period in 2019.

Milk Yield from Grazing (MYFG)

Potential MYFG is calculated based upon the number of handfuls of grass submitted, a prediction of potential dry and fresh matter intake, as well as spoilage and average metabolisable energy (ME).
The highest potential MYFG and dry matter intake (DMI) for the 2020 grazing season was reported during the week ending 24th May at M+16.34 litres/day and 13.36 kg/day respectively. A steady decline followed this because of reduced rainfall, and thus reduced grass growth and potential DMI. The lowest potential MYFG was recording during the week ending 20th September at M-0.66 litres/day, alongside a low potential DMI of 6.62 kg/day. A negative MYFG indicates there is insufficient intakes from grazing grass to support maintenance requirements or any additional litres of milk. The low figure was as a result of high temperatures and reduced rainfall, resulting in poor grass growth rates.

Rumen Protein Energy Balance
If NutriOpt Fermentable Energy Protein Balance (NFEPB) is negative, the diet is high in fermentable carbohydrate. If the NFEPB is positive, the diet is high in protein. The optimal value in the total diet for a balanced rumen and effective nitrogen utilisation is between 0 and 200g/day, with higher figures resulting in significant waste of rumen fermentable protein.
The highest risk period for milk and liveweight loss occurred around the weeks ending 28th June to 19th July, where the NFEPB from grass remained consistently above 825g/day, giving a potential milk loss of 0.60-0.66 litres/head/day and a potential liveweight loss of 0.11-12 kg/head/day.

Butterfat Factors from Grass

There appeared to be a trend towards a higher risk of decreased butterfat from grass through the end of April to mid-June according to the rapidly fermentable carbohydrates (RFC), acid load, fibre index and rumen unsaturated fatty acid load (RUFAL) levels reported. The highest risk of reduced butterfat occurred during week commencing 4th May. In comparison, this overall risk appeared to be lower towards the end of the season where acid load was low and fibre index much higher.

Temperature Humidity Index

The risk of heat stress this grazing season has fluctuated. A mild risk was reported up until late July, after which higher summer temperatures and mixed humidity levels resulted in variable risk of heat stress through to mid-August. The record breaking temperatures experienced from the 3rd to 16th August resulted in a high/severe risk of heat stress across all regions, with temperatures reaching a max of 36.4 ˚C and remaining at or above 34˚C for six consecutive days in the South East. In comparison, August 2019 was unsettled and showery, with the risk of heat stress highest during July.

Growing Cattle

For growing cattle, an estimate of the potential daily live weight gain (DLWG) was calculated throughout the season using weekly average fresh grass ME and the assumption that ad-lib grazing is sufficient to satisfy daily DMI requirements. The average ME for the 2020 season was 11.86 MJ/kg DM, compared to 11.89 MJ/kg DM last year. The highest estimated ME for the season was reported during week ending 12th April at 13.11MJ/kg DM, meaning a potential growth rate for 200kg and 400kg animals of 0.8 and 1.2kg/day, respectively. In comparison, the highest ME reported in 2019 was 12.66 MJ/kg DM. The lowest estimated ME was reported during week ending 23rd August at 11.23MJ/kg DM thanks to increased rainfall, resulting in a potential growth rate for 200kg and 400kg animals of 0.6 and 1kg/day, respectively. The lowest ME average for 2019 was 10.87 MJ/kg DM.

For more information on NWF Grass Seeds, call our traded products team on 0800 756 2787 or download the 2020 NWF Grass Seed Brochure HERE.

Source: Trouw Nutrition.

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