Green does not mean good all the time
A paddock that still looks green in late spring can be worth only half as much to a cow or ewe as it was six weeks earlier. As pasture runs to head, digestibility falls, fibre climbs and protein drops, well before the colour changes. The cheapest fix is usually protein for the rumen, not more energy.
What happens as pasture matures
As plants shift from leaf to stem and seed, cell walls thicken and lignify. Lignin is indigestible to rumen microbes and shields the fibre bound to it, while protein moves out of the leaf and into the seed head. Typical, approximate values for temperate improved pastures in south-eastern Australia:
| Growth stage | Dry matter digestibility (%) | Metabolisable energy (MJ/kg DM) | Crude protein (% DM) | NDF (% DM) |
| Leafy, vegetative (winter–early spring) | 75–80 | 11–12 | 20–28 | 40–48 |
| Stem elongation / early head (mid–late spring) | 65–70 | 9.5–10.5 | 12–18 | 50–58 |
| Flowering to seed set (late spring–early summer) | 55–62 | 8–9 | 8–12 | 58–65 |
| Dry, hayed-off standing feed (summer) | 45–55 | 6–7.5 | 4–7 | 65–75 |
Once grasses run to head, digestibility commonly falls 0.3–0.5 units a day, or 12–20 units over six weeks. Stems and seed heads can stay green while digestibility is already in the low 60s, so the eye overrates the feed.
Dry matter intake is king
Ruminant nutritionists say “dry matter intake is king” because how much an animal eats drives its performance more than any quality figure. Daily energy intake is simply intake multiplied by energy density, so when both fall, the losses multiply.
On pasture, stock stop eating when the rumen is full, not when energy needs are met. The build-up of low-digestible feed in the rumen is why it is common to see cattle in late-spring and summer with large bellies, but in a declining condition. In feed tests, neutral detergent fibre (NDF) is the best predictor of this fill effect and essentially how much dry matter an animal can consume in a day. The table below is a widely used guide (Mertens) matching NDF with DMI of a 500kg dry cow.
| Pasture NDF (% DM) | Approximate maximum DMI (% of liveweight) | DMI for a 500 kg cow (kg DM/day) |
| 45 | 2.7 | 13.3 |
| 55 | 2.2 | 10.9 |
| 65 | 1.8 | 9.2 |
| 72 | 1.7 | 8.3 |
For a 500 kg cow, leafy pasture gives about 13 kg DM × 11 MJ/kg = 143 MJ ME/day. Maturing pasture gives about 9 kg × 8.5 MJ/kg = 77 MJ ME/day. Energy density fell 23%, but energy intake fell 46%, against roughly 60–65 MJ a dry cow needs just to maintain.
Impacts on cattle and sheep heading into summer
Cattle. Steers gaining 1.0–1.2 kg/day on leafy spring pasture commonly slow to 0.3–0.5 kg/day on maturing feed, and can lose 0.2–0.5 kg/day on dry feed below 7% crude protein. Spring-calving cows face falling feed while lactating and rejoining; one condition score is roughly 80–100 kg, and cows below score 2.5 conceive later and less often.
Sheep. Selective grazing buffers sheep for a while, but intake falls fast once green leaf is gone. Lambs growing 200–250 g/day in spring often drop below 100 g/day. Each extra condition score at joining adds roughly 20 lambs per 100 ewes, and feed restriction weakens staple strength.
The cheapest condition to keep is the condition an animal already has. MAINTENANCE.
Feeding the rumen: how Rumen Degradable Protein (RDP) lifts digestibility and intake
On maturing pasture, protein for the rumen microbes, not energy, is often the first limiting nutrient. RDP is the protein and non-protein nitrogen (urea) broken down in the rumen, which microbes need to grow and digest fibre.
Below about 7–8% crude protein, the microbes run short of nitrogen and a cycle sets in:
- Fibre-digesting microbes slow down.
- Fibre stays in the rumen longer.
- The rumen stays full, so intake falls.
- Less energy and protein are eaten, and condition is lost.
RDP supplementation reverses this cycle. On forage below about 6–7% crude protein, typical responses are:
- Intake: up 20–40%.
- Digestibility: up a few percentage units.
- Liveweight: cattle losing 0.3–0.5 kg/day often hold weight or lose only 0.1 kg/day, saving 20–40 kg over a 100-day dry period.
Because RDP unlocks energy from feed already in the paddock, it is usually far cheaper than feeding energy.
What to do about it?
The trigger is falling protein, not falling colour. Start when a feed test shows crude protein nearing 8% and NDF above 60%, or when most of the paddock has gone to seed, dung firms up and stock begin losing cover over the ribs.
We can test your feed for free
Talk to your local ANP sales support officer to get your feed tested, so you know when to act. Supplementing early with RDP is much more affordable than trying to play catch up in the middle of a dry summer or autumn.
The bottom line
Rising NDF cuts intake, and because dry matter intake is king, energy supply falls further than feed tests suggest. Targeted RDP feeds the rumen microbes so stock digest and eat more of the feed on hand, making it one of the most cost-effective ways to carry cattle and sheep through a dry summer.
Figures are typical, approximate ranges and vary with pasture, location and season. Seek feed testing and advice from a livestock nutritionist before supplementing; urea in particular must be introduced gradually.
