Why Kiwi farmers feed livestock grass
We mainly feed our cows grass. But farmers in other countries have chosen not to be pasture-based. There are many reasons for this but one is that their grass grows differently to New Zealand grass.
The sole purpose of most plants is to reproduce.
A ryegrass plant first grows a new leaf or tiller. It then grows a second leaf, then a third and eventually a fourth leaf emerges and the first leaf starts to die off.
With three live leaves photosynthesising, the plant builds up its energy reserves.
With plenty of energy stored, the plant then starts growing its seed head. It grows a stalk in its centre and eventually the seed head emerges.
Feed is measured in a few ways. Kilograms of dry matter (kgdm) is what is left when the water has been removed. The higher the dry matter the more feed there is. Another measure is megajoules of metabolisable energy known as ME. We want feed to have a high ME content.
The other important measure is the crude protein content.
When a ryegrass plant is in the three-leaf stage, it contains everything a cow could want. It is soft and leafy. It is easy to eat and digest. A cow could eat 20 kgdm per day of leafy ryegrass. The crude protein content is 25 per cent and the pasture will have 11.5 ME/kgdm.
We don’t really need to know what those numbers mean but it is helpful to compare them with other feeds. When a ryegrass plant is going to seed and becoming stalky, it will have
15 per cent crude protein content and ME/kgdm of 10. Because the grass is stalky, the cows probably won’t be able to eat
20 kgdm per day. So their intake will be lower too. The reduction in milk yield between the two pastures will be significant.
When pasture is at the threeleaf stage, it is a quality, complete feed. When it is not at the three-leaf stage, it becomes an average feed. New Zealand farmers are very good at ensuring their animals are eating grass at the three-leaf stage. But it is a balancing act.
If the cows start in paddock number 1, they have to return to paddock number 1 when the grass is at the three-leaf stage.
If the grass is growing fast it may take 12 days but it could take 25 days too. If the cows get there too early, they will graze the grass too low; too late and they will be eating poor quality stalky feed. New Zealand farmers have tried to use this three-leaf grazing system in other countries like the United States. But it just doesn’t seem to work that well. From what they have told me, there are too many variables that make it hard to manage the pasture quality like they do in New Zealand. The result is poor quality feed.
Pasture-based dairy is common in the US but most US farmers choose to grow and harvest crops to feed their cows.
When they grow a crop they know exactly what the components of that feed are.
For instance, the US dairy farmer will still feed 20 kgdm per cow per day but 49 per cent of the diet may be maize/corn that has been chopped up. The maize has quite a low crude protein content of 8 per cent and ME of 10 (the same as stalky pasture).
The other 49 per cent may be lucerne (alfalfa). This has a crude protein of 21 per cent and ME of 10. To increase the ME of the cows’ diet, the farmers may supplement 2 per cent of the diet with a highly concentrated product like soybean meal. This has a crude protein of 50 per cent and ME of 12.5.
When you add all of these US feeds together they match roughly the nutritional value of a pasture at the three-leaf stage.
The difference is the cost of growing a kg of dry matter of grass in New Zealand is about 10 cents. Grass is cheap feed to grow, as it needs little fertiliser or labour. We also let the cow harvest the grass herself.
The US ration of corn, lucerne and soybean meal is closer to 60c-80c per kgdm. That is because there are costs to plant the crops, fertilise, harvest and transport them to the farm.
The only certain thing about farming systems and feeding cows is that farmers all have different opinions and will come to varying conclusions.
Even among grass-based farmers there is debate. Organic or regenerative farmers might say the three-leaf grazing system is flawed too.