Protein in Summer.

By Intelact Consultant Helwi Tacoma.

Why do cows not produce more milk than they do in summer? Look at the main fractions in grass for an answer. These are Energy, Protein and Fibre. (there are more of course).

Energy is lower in summer than in spring (10-25% less energy in summer), Protein is lower and Fibre is often higher.

All three of these could be limiting production, and it will be the weak link that makes the chain break.

Assuming pasture management is reasonable, the Energy fraction should be somewhere around the 10.5-11 MJ ME in summer. A 500 kg Friesian cow, eating 15 kg of this grass, will consume enough energy to produce about 23 litres of milk. And yet most herds would struggle to do this. Why?
If fibre content is high, (long, over mature grass), intakes will be less than 15 kg, therefore energy may be the limiting factor. Besides, this long grass will often contain less than 10.5 MJ ME, making the problem worse.

But even if grass looks good and leafy, cows may still not reach their 23 litres. Usually, the problem is low protein intake. Cows need approx. 18% of their diet to be protein to fulfill all of their needs for first, staying alive, second pregnancy, third milk production. If there is any protein left over after all that, it will be burnt for energy (bodyweight). Summer grass often contains in the order of 15% Protein.

So if protein is the weakest link in the chain, it makes sense to feed some, and make the cows reach their potential, provided it is economical to do so.

My starting point would be pasture quality. The right stocking rate for the farm should ensure that cows go into no more than 2800-2900, and leave no more than 1500-1600. A long round (and a low stocking rate) will usually result in pre grazing covers to be higher, and residuals to be lower than this. Result: lots of DM on the farm, but low Energy, and low Protein, and low milk yields

Application of Nitrogen helps both quantity, and perhaps more importantly, quality. This was really brought home to me last year. One of my clients had spread Nitrogen at the start of a dry spell. He didn’t realize the spreader wasn’t working properly and it only threw the Urea to one side. Four weeks later, there were bands of green, lush, high quality pasture (and lots of it) next to dry, brown low quality stuff, mixed with lots of summer grasses. It taught me that Urea still works even in a drought, and that you get not only quantity but also quality.

Good quality pasture silage will have a high protein content, so makes a very good summer supplement. But there isn’t a lot of good pasture silage around. Many farmers still go for quantity, cutting grass well over 4000 kg DM. This is mainly fibre, with protein content only 10-15 %, well short of the required 18%.

Maize Silage contains good levels of energy, but little protein, so for a summer situation is less than ideal. Turnips on the other hand provide good energy (12-12.5 MJ), and good protein levels (18-20%). Providing good yields (12ton or better), they make perfect sense. Lucerne is another good one, palatable, high energy, high protein. Sometimes high protein byproducts are available at economic prices. The key is to find products that fit your individual farming system and that work economically. It is perhaps fair to say that the climate is changing to milder winters and hotter summers, and this will make farming through summer even more of a challenge than before.

Helwi Tacoma D.V.M
Intelact Nutrition Consultant