Ryegrass seed head time

By Charlotte Westwood, Veterinary Nutritionist, PGG Wrightson Seeds

Depending on where you are in NZ, the types of ryegrasses on you farm and your grazing management strategies, you might be 4-6 weeks into having to deal with ryegrass seed head. For some of you, you’ll be well through seed head production and coming back onto leafy regrowth.

For most of us we know the hassles of managing ryegrass seed head - stock don’t like to eat seed head when given a choice, and lambs with lactating ewes are least enthusiastic. With sheep able to select and browse their way through the pasture, given a chance, they’ll browse clovers, herbs and the green leaf part of pasture and leave seed head behind. So, if we don’t push ewes and lambs to eat down hard, on average what they eat is of much better quality than pasture is standing in the paddock. Cattle can pick and choose around seed head to a much lesser extent, since they use their tongue to wrap around and tear pasture off. That said, often at this time of year you might notice quite a variation in dung consistency among dairy cows grazing 100% of their diet as pasture – seems some cows might be more clever at selecting amongst ryegrass seed head than others!

The only real positive about ryegrasses flowering then going to seed is that you might get viable seed drop that helps fill up gaps amongst tillers with new seedlings. And, of course, seed companies can harvest seed from the latest cultivars so you can keep planting the very best ryegrass genetics.

What are some of the challenges?

Aside from those couple of positives, you’ll all have your own views on what the worst things about ryegrass seed head on farm might be. Some challenges include:

• The ryegrass tiller dies

Once a tiller flowers and sets seed, that tiller dies. If a paddock is just a mass of seed head, there’s a chance persistence might be reduced unless there’s a heap of new daughter tillers coming through to replace the flowering tillers. The majority of annual ryegrass tillers flower (part of the reason annual ryegrass struggles to persist from one year to the next). Only some of the tillers of perennial ryegrasses flower/throw seed head each year, so the pasture persists much better than an annual ryegrass (though of course there’s many other things that help ryegrass persist). Grazing management affects this too – if pastures are laxly grazed pre-flowering, a higher percentage of tillers will flower and therefore die after seed set.

• Seed head doesn’t taste good

Lots of seed head can be a put-off for grazing animals, potentially reducing overall dry matter intake (DMI).

• 'Stemmy' seed head gets left behind in the paddock

Often when cattle wrap their tongues around hard reproductive stem and try to tear the stem off, the stem rips off higher than the level of the cows’ tongue and dental pad (that’s the hard part of the upper jaw where there’s no teeth). The post-grazing residual looks all tatty – lots of those higher patches in the paddock where cattle simply haven’t been able to easily tear the plants off. In this situation, out comes the topper.

• Seed head might contain endophyte alkaloids

For endophyte-containing ryegrasses, alkaloids are concentrated in the seed head, as well as at the base of the pseudostem. For newer ‘novel’ endophtyes, this isn’t typically a problem. For older ryegrasses that contain the standard or ‘wild’ endophyte, seed head might contain enough alkaloids to cause ryegrass staggers or heat stress (from ergovaline) if we push stock to eat seedhead. Remember though, almost all ryegrasses sold in NZ contain novel endophytes, not many contain the standard endophyte with the 'hot' alkaloids anymore. Older paddocks that haven't be re-grassed for a long time likely contain ryegrasses that contain the old standard endophytes.

• Seed head can also encourage other stuff we don’t like

Specifically, ergot and associated toxicity risks.

Overall feed quality of ryegrass is low when seed head is present. With the ryegrass plant pushing much of its effort into producing lower quality seed head, the overall quality of the ryegrass plant drops through flowering and seed head production.

What proportion of a ryegrass plant is reproductive stem and seed head? 

Some researchers in Canterbury published last year the proportions of different parts of the ryegrass present when seed head emerges - and the quality of those different plants parts (Chen et al, 2019 “Morphology and nutritive value of perennial ryegrass cultivars at different phenological stages”, Grass and Forage Science 74: 576-581)

Averaged across eight different perennial ryegrass cultivars, during flowering the plant was made up of 40% lamina (leaf), 30.1% reproductive stem, 12.5% pseudostem and 17.4%. So, that’s not really ideal having almost one third of your ryegrass made up of stem/seed head.

Ryegrass quality

The quality of different parts of the reproductive ryegrass plant is very different. This is one of the reasons why your ryegrass-based pasture quality crashes at this time of year.

• Crude protein (CP):

Most of the protein is found in the leaf of a reproductive ryegrass – average 21.4% CP. Reproductive stem and pseudostem 'tie' for second place with levels of around 10% CP. Dead material, that rubbish at the base of the sward, contains just under 12%. Overall, no surprises that the CP levels of late spring/early summer ryegrasses crash out.

• DOMD (Digestibility of organic matter in DM):

This is another way of saying “energy”. The best energy was in the pseudostem (76.3% DOMD). The worst DOMD was the dead material at only 46.5%. Leaf was 74.4 % DOMD and reproductive stem wasn’t flash at just 65.7%.

• Water soluble carbohydrates (WSC or ‘sugars’): 

Best levels were in the pseudostem (32.8%), dead material contained hardly any (5%), leaf contained almost 17% WSC while stem/seedhead contained 27% WSC.

• Neutral Detergent Fibre (NDF): 

All parts of the ryegrass part contained quite high levels of NDF, reproductive stem was the highest at 59% NDF, pseudostem was 50% NDF. Leaf was lowest at 48% NDF – quite high for leaf, but standard for late spring when even the nice green parts of the leaf contain more fibre due to warmer weather and longer daylength.

What ryegrass breeding advances can help us manage better?

Overall, ryegrass reproductive stems and seed heads do have a big effect on feed quality. Luckily for us there’s been some really good advances made in ryegrass breeding to help us all better manage – for example:

• Later maturing ryegrasses

These have been bred to produce seed head later in the season. By planting different ryegrass types with different heading dates, the whole farm doesn’t all go to seed at the same time. Some are very late, for example there’s a very exciting new tetraploid perennial ryegrass “Vast” that PGG Wrightson Seeds is bringing to the market next year that is +35 days later heading than a mid-season ryegrass (e.g. Nui). Current later heading ryegrasses are not close to being as late as Vast, for example Base is +22 days. This new Vast ryegrass is going to be quite a game changer.

• More compressed heading periods

Newer ryegrasses have been bred to get their seed head production over and done with faster. You might remember older varieties that seemed to not stop setting seed head all summer.

• Reduce aftermath heading (AMH)

AMH means that ongoing seed head formed after you’ve managed to get on top of and smash the first round of seed head formed in late spring. Thankfully ryegrass breeders have worked for the last 20 or so years to select against this ongoing seed head production through the summer.

• Clovers and herbs

And last but certainly not least, it’s a given that it’s much easier to manage pastures that contain not only ryegrasses but also white and red clovers, and potentially plantain and/or chicory. “Dilution is the solution” as the expression goes – getting these species coming through into the sward when ryegrasses are doing their reproductive thing.

If you have any questions on ryegrass seed head manage don’t hesitate to get in touch, or ask a question in the comments box below.