May 22, 2013
At Alltech's annual meeting in Kentucky this week I've been in several sessions where dairy topics were more prevalent than beef topics. Nonetheless, I found some interesting science about the negative effects of high-protein diets.
Seems they're a problem for dairy operations because they've actually been formulating too much protein into the rations. This doesn't surprise me considering our long-standing paradigm that the protein level in feedstuffs is the primary measurement of quality.
It is not. I've written about this before. Energy is nearly always more limiting to production in the diets of grazing beef cattle and, as it turns out, in the rich diets of high-producing dairy cows.
With beef cattle on pasture the situation of overly high protein usually sets up in three or four scenarios. They all involve grazing young grass, which is nearly always high in protein and low in energy.
By young grass I don't mean it can't be a mature stand of forage. It is physiological age to which I refer. This is controlled by weather and grazing or mowing pressure. Fresh regrowth in a recently mowed hay field would be "young" grass.
Here are three situations in which it appears protein would be high and energy low.
1. Too-rapid return to grazing paddocks which are not fully recovered in a rotation grazing system.
2. Early spring growth of any forage with no old grass or hay to supplement it.
3. Wheat pasture or other high-quality and lush forage that is young and immature.
I also suspect protein is relatively high in short-grazed stands of forage, perhaps even during mild drought. Typically such grass is very short and trying to regrow and being bitten off by the cattle at a very young and tender stage.
The dairy experts I've been listening to this week have been saying excess protein is pretty costly to the bovine body. Like humans, cattle can convert protein to energy, but it's apparently an inefficient process and it leaves a lot of excess nitrogen which must be disposed of.
Mike Hutjens, a retired University of Illinois dairy science professor, talked about high measurements of Milk Urea Nitrogen and says dairy producers should keep that measurement lower even than current recommendations. In other words, protein content of the diet should be limited.
Hutjens said when all this excess protein is converted to blood urea and ammonia it can cause several problems. He said it affects the pituitary-ovarian axis by suppressing luteinizing hormone and progesterone. It has a toxic effect in the uterine environment and can damage the gametes and the embryo. It also suppresses the immune system and generally damages reproductive efficiency.
We also know that blood urea nitrogen testing of heifers on wheat pasture in Oklahoma showed breeding problems were correlated with high nitrogen, therefore with high protein consumption, a staple of the wheat pasture diet.
Jack Corless, a global dairy consultant from Ireland, was very blunt about all this. "We over-feed crude protein in the dairy industry."
Corless said when you reduce the amount of excess protein in the diet and decrease the amount that must be passed out of the body you reduce energy demands by that act alone. Further, you make room in the rumen for feeds of higher energy value. Ultimately, Corless said, you get more milk for less protein.
Usually lactation and gain are relatively similar in dietary response to nutrients, so it stands to reason a bovine diet better balanced in protein and energy would improve gain as well as it would improve milk production.
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