For decades, cattle producers have been told that providing enough feed to their cows and their developing heifers is critical for ensuring high pregnancy rates. But researchers at the Agricultural Research Services Fort Keogh Livestock and Range Research Laboratory have found that’s not necessarily so. The results of their long-term study show that heifers fed 27% less over the winter months gain weight more efficiently on pasture, are more resilient when forage is marginal or scarce, have pregnancy rates similar to cows fed a typical diet, and wean calves just as big as their well-fed counterparts. Just as importantly, these skinnier heifers pass on these traits of resilience and efficient weight gain to their offspring.
Don’t Feed Them
to Breed Them
“For the last 3 to 4 decades, the mantra has been ‘feed them to breed them,’ which means providing enough feed during the first year to ensure that young heifers reach puberty to start reproducing,” says ARS animal scientist Andrew Roberts. “But our studies indicate this doesn’t seem to be optimal in the long run. Our research shows that by feeding to get all the animals bred, you are also propping up the inefficient animals—those that won’t consistently produce calves when put in nutrient-limited environments later in life.”
Not only does feeding to maximize reproductive rate help inefficient cows stay in the herd, it also creates heavier cows that need more calories to maintain themselves. The Fort Koegh study has shown that when forage quality and or quantity is limited, the cattle that were fed the normal, recommended diet over winter can lose weight on pasture, while their skinnier counterparts actually gain weight.
But does feeding us our cows and heifers get us the improved reproductive rates we hoped for? No. When compared over a ten-year period heifers fed a standard diet had an 89% pregnancy rate compared to the 88% pregnancy rate of heifers fed 27% less.
Figure 2 charts the growth rate for the control and restricted animals in the study over a 10-year period. The two vertical lines mark the 140-day period of restricted feeding and show daily gains for restricted heifers, at 1.1 pounds of gain per day, compared to control heifers at 1.4 pounds per day. As expected, the restricted heifers grew more slowly, but you can see they did better at gaining weight on pasture, so that by 20 months of age they were similar in weight to heifers that had been supplemented. The chart also shows that the cost of developing a pregnant heifer is conservatively estimated at $30 less for the restricted group.
Setting Up For Resilient Offspring
One of the things unusual things about this study by the Livestock and Range Research Laboratory’ is that it has been going since 2001 and it continues today. “There can be tremendous variation from year to year. We don’t care if we find something that would work one year but not nine others,” says Roberts, so a lifetime production study was the only way to go. It means that researchers can monitor how the treatment of the mother impacts its offspring, not just immediately after birth, but throughout its life.
And what have they learned? “When we feed less than the science textbook says we should, we come up with drought resistant offspring,” Roberts concludes.
His statement is based on following just over 1300 cows who were part of the project between 2002 and 2011. As daughters were born to the first heifers in the study, they became part of the project too, and were fed either restricted or adequate diets. By including them, researchers could look at the long-term productivity of four different groups of animals:
• Control heifers on adequate diets from dams on adequate diets
• Control heifers on adequate diets from dams on restricted diets
• Heifers on restricted diets from dams fed adequate diets
• Heifers on restricted diets from dams on restricted diets
What they discovered is that growth beyond 2 years of age was influenced by both how dams had been fed as well as how the cow herself was fed. Animals whose dams had been fed adequate diets were not able to maintain their weight as well as animals whose dams had been fed restricted diets.
“The small differences in winter supplementation influenced the fetuses inside the cows, resulting in differences in the body weight and condition several years after the fetus was born, explains Roberts. “This phenomenon is referred to as fetal programming.”
Longevity in the herd was also impacted by the treatment of the dam. Any cow that did not become pregnant was removed from the herd. Cows on restricted diets whose dams had also been restricted remained in the herd longer than cows fed restricted diets whose dams had been fed adequate diets.
Why Didn’t We Know This Before?
The National Research Council (NRC) feed recommendations are based on data from research done on well cared for University herds. These data were reinforced any time these heavier cows went to pasture and lost weight. It turns out that if you manage cattle with higher levels of input, they don’t do as well when they encounter harsher natural environments, as animals that have practice dealing with shortages and marginal feed.
Andy Roberts came at this problem from a different perspective. His family has a ranch between Tucson, AZ and Las Cruces, NM. In that arid environment their cattle were mostly a 3 in Body Condition Score. Yet they were very productive, and much more productive than NRC feed recommendations would have predicted. This study has given him the opportunity to find out why past research didn’t match his observations of his family’s cattle, and in the process, he and his colleagues have come up with new information that could be very helpful to producers working on large landscapes in the West.
“NRC requirements overestimate the feed necessary for animals raised on large landscapes,” says Roberts.
What Can You Do With This?
If you want to create your own herd of smaller, more resilient cows, and you already feed plenty, Roberts says you could gradually begin to reduce inputs and then get rid of the first 5% that fall out because they can’t maintain themselves on reduced feed. Since you know that some animals won’t make the shift well, be sure to have a plan for how getting rid of these cows will affect your bottom line. Do it in a way that minimizes your risk.
You might also keep this information in mind if you buy replacements. Do you know the history of their mothers and how they may have been fed?
If you have other questions that aren’t answered here, let me know in the comments below.