GrassWatch Demonstrates Increasing Grass NFEPB

20 August 2018

Over the past few weeks, the GrassWatch monitor farms have seen some improvement in grass growth rate, thanks to the recent rainfall. However, the weekly grass growth rate is still well below average for this time of year (AFBI, 2018).

Average pre-grazing covers on the GrassWatch farms have increased, but most farms have adopted a longer grazing rotation to help paddocks to reach target covers again.

The farms in the project which continued normal or slightly reduced rate of fertiliser application during the driest weeks, have noticed a more rapid increase in grass growth rate than those that stopped applying fertiliser altogether. Some of the paddocks that had no fertiliser applied now appear to have yellow tips on the grass leaves – a typical sign of nitrogen deficiency. 

Oversupply of protein is traditionally associated with spring grazing, however results from GrassWatch this year and in 2016 showed a consistent oversupply of protein throughout the grazing season. This is reflected by the sharp increase in average grass crude protein from 17.7% to 24.6% on the monitor farms from mid-July to August this year.

In addition, as a result of grass crude protein increasing along with a downward trend in grass metabolisable energy and rapidly fermentable carbohydrates, the average grass NFEPB (NutriOpt fermentable energy and protein balance) increased last week to 1,306g/day, with potential milk loss of 1.1 litres.

Rumen microbes require a constant supply of fermentable energy and protein for optimal microbial protein synthesis. An ideally balanced diet will have an NFEBP of 0g/day. If NFEPB is greater than 200g/day, there is an oversupply of protein relative to energy in the rumen. This results in a reduced efficiency of protein digestion and protein losses. Excess ammonia is absorbed into the blood, converted to urea and then excreted in the urine and milk (milk urea nitrogen).

However, this process requires energy, which could have been used otherwise for milk production or liveweight gain. There may also be negative effects on fertility and the environment, therefore, it is important that fermentable energy and protein are balanced. The use of lower protein and higher energy concentrates may aid this. 

There has been continued gradual increase in grass NDF (fibre), perhaps due to approaching the later stages of the grazing season. Higher grass fibre coupled with falling milk yield has meant that milk butterfat has continued to increase.

Following the grazing shortages, there is need for efficient management of autumn grazing. Optimal regrowth can be promoted through longer grazing rotations to allow recovery of grazing covers along with careful monitoring of the weather forecast to establish ideal timing of fertiliser application.

As some of this winter’s forage supplies were used for supplementation during the drought period, it is important to maximise the potential of third and fourth cut silages to rebuild stocks. Fodder budgets should be calculated to establish the forage supply and demand with regards to minimum rumen requirements. Alternative forages and concentrates may then be viable options to make up any shortfall in production.

There are a number of forage calculators available to assist these types of calculations. However, Trouw Nutrition’s Forage Budget Calculator, available in conjunction with your compounder’s nutritional advisor, goes further and states minimum requirements for forage.