By Mark Werner
Livestock Production Specialist
As we approach the upcoming grazing season, we must keep in mind that breeding season for our cow herds is just over the horizon.
What we need to remember is that our virgin replacement heifers may need a bit of extra thought put into their management plan to maximize their reproductive success. Those heifers have a lot of time, labor and money tied up in them, and we still will not see a calf out of them for another 12 months. Further, we will not see a saleable feeder-calf for another 18 months.
As many of us do, with grass starting to peek a shade of green out of it, we hope to get our cattle out to grass as soon as possible. What most do not consider, however, is the level of nutrition, specifically the energy difference between the balanced, concentrated ration that the heifers are receiving in the dry lot versus the grass. We forget that the low dry matter content of the lush spring grass on the pasture can have a negative effect on those heifers at the most important time in their life. By allowing for this access to grass, we also expose them to a new environment, stress from moving and handling, and a new level of activity traversing their summer range versus what they expended in their winter confines.
Even though that nice, lush grass is great to look at, and is very appealing to those cattle, we may be putting those heifers into a negative energy balance which can have a rather undesirable effect on estrus. We could not choose a worse time to have this happen—her whole future hinges on when and if she comes into estrus, whether or not she can maintain a pregnancy, or worse, even express estrus.
A trial was described in the 2001 OSU Animal Science Research Report on this very issue. The study, which was conducted by Glenn Selk and Oklahoma State University Extension, looked at the effects of acutely restricting nutrition on ovulation and metabolic hormones in Angus and Hereford crossbred heifers. Within the study, all of the heifers were housed in individual pens in a barn and fed a diet supplying 120 percent of their maintenance requirements for protein and energy (1.2 M) for 10 days to allow time to adjust to the environment and diet. All of the heifers were determined to be cycling at the conclusion of this adjustment period. The next step was to split the heifers into two groups. Half of the heifers in the study were then fed a diet supplying 40 percent of their maintenance requirements (0.4 M). The other half of the heifers were persistent on the original diet that supplied 120 percent (1.2 M) of their maintenance requirements. As a way to keep constant, all of the participating heifers were injected with prostaglandin so they should ovulate 14 days in to the trial. 70 percent of the heifers receiving only 40 percent of their maintenance requirements did not ovulate as a response to the injection, whereas, 100 percent of the heifers receiving 120 percent of their maintenance requirements had normal ovulation.
With the results that were uncovered, it is my opinion that it pays to put an efficient and detailed plan together to give each heifer every chance possible to earn a place in your herd. By going the extra mile, you can help manage a few small factors that can have a big effect on her future in your herd. I would encourage you to help reduce her stress with calm handling and comfortable hauling conditions going to pasture—and while synchronizing and artificially breeding. Likewise, I would encourage the use of a high-quality breeder mineral like the Wind and Rain 7.5 Availa 4 XPC. This mineral will help boost the reproductive efficiency and overall health of the animal. To address the negative energy balance issue, offer the animal a Purina Accuration Hi-Fat block for a free choice source of energy and protein. This product is intake-dependent on forage quality and will help give your heifers the nutritional boost they need, all while minimizing your labor and delivering a supplement to the pasture.
We hope these small changes have a positive impact on the next generation of cows in your herd.