For those of us with a little silver and gray atop our noggins, or in my case when my hair turned gray and turned loose at about the same time, we’re very familiar with the old paradigms that heifers need to be at 65% of their mature weight and in a BCS of at least 6 and 7 is better at the beginning of breeding season.
However, research over the last decade or so has challenged those thoughts. Earlier this spring, I had the pleasant opportunity to spend part of a day at the Fort Keogh Livestock and Range Research Laboratory at Miles City, Mont. And I learned a thing or two in a discussion with researchers Andy Roberts and Mark Petersen.
Roberts told me that it’s not that those familiar paradigms aren’t valid, but it’s helpful to look at them through a different set of lenses. For starters, the research many decades ago that led to those paradigms and the NRC nutritional requirements to make them happen were conducted with university research herds. Those cattle may have been managed differently than commercial herds—particularly commercial herds in more challenging environments like eastern Montana.
Looking at the old paradigms, Roberts said if we fed 100% of the NRC requirements, we might get 90% pregnant. “Well, if we fed 85% of that amount, we would lose 5-10% of those animals because of reproductive failure.”
So then, the question is, what is the biological description of the animals we lose? Are they efficient animals or inefficient animals? “And my thought would be they are the least efficient animals in the herd because we had to feed them more than the other 80% to get the same response. So we’ve overfed 80% to get this 5-10% to work. And that’s a huge inefficiency when you think of that on a nationwide basis.
“And another thing it does, it removes any selection pressure for efficiency because we don’t know which animals those are when we feed them to succeed and we keep replacement heifers on them. So we basically propagate the problem into our future cowherd.”
Fort Keogh has several herds, one of which is a composite herd that’s managed very much like a commercial cow-calf herd in a challenging environment. “We decided we’ll just ask this question. If we feed less in half of that herd, what will happen after a lifetime of productivity of these animals? So we started in 2001 and are still following these cattle today,” Roberts said.
The research is fascinating and I plan to do a more extensive article in the future. However, for this blog, I’ll cut straight to the meat. They separated the herd into two halves, with one getting less nutritional input than the other. But even the “restricted” cows weren’t just left to scratch out a living on their own. Both groups, and the subsequent groups in following years, were supplemented during the winter, just at different levels.
“So after seven years of that, we basically had no significant difference in reproductive performance, pregnancy rate, on the cowherd. The thing you might conclude from that is either our estimations of what we were working with were wrong and we were feeding adequate amounts to everything, or the cows don’t operate under what we think they do, the NRC requirements,” Roberts said.
“Basically, between our work and some work that was done by Mark [Petersen] at New Mexico, what it appears is that cows managed very extensively probably have lower requirements than what we predict they should have in the NRC recommendations. They can operate at a lower level of nutritional input or nutritional availability, than what NRC says they will,” Roberts concludes.
“So the requirements are exaggerated because that 20% that need more are in there [the early research that led to the present-day NRC recommendations]. If you get rid of those, then you’ve got that other 80% that don’t need more and the requirements come down,” Petersen adds.
According to Roberts, “The other aspect of that is these are groups of cattle, both at New Mexico and here, that have been managed pretty extensively, what you would consider a traditional or maybe the commercial cattle operations in this area. They’re managed at a lower level of input. So either you’ve selected out or they’ve adapted to working at that level. It could be either way.”
And that’s basically the take-home lesson. By keeping an animal smaller, you reduce its nutritional requirements. And you can do that through genetics or management.
But there’s more. As they followed the heifer calves into adulthood, becoming part of the cowherd, they found another take-home: “So the short of the story is cows managed with less produce offspring that are probably what you might call more drought resistant or function more favorably with less,” Roberts says. “So cows managed with more inputs, their daughters had a greater negative response when they were put in a lower feed environment post-weaning and every year of their life.”
And heifer weight at breeding? The Fort Keogh research is finding that heifers from the non-restricted group can enter the breeding season at 57% of mature weight, or around 700 pounds. The heifers from restricted dams enter breeding season at 54% of mature eight, or around 650 pounds.
“Sometimes I present these results to producers and they say my heifers are 650 pounds at weaning. These animals are 450 pounds at weaning,” Roberts said.
“When we manage an animal to be smaller, you can program that animal to be more efficient,” he concludes. “Same genetics, just changed it with management.”