Measuring the effect of nutrition on reproduction can be difficult, says University of Nebraska beef reproductive specialist Rick Funston, PhD. “An animal’s nutritional status is usually assessed on changes in its live weight and body condition. However, these are long-term changes, while many of the events of reproduction, such as ovulation, fertilization and placentation, take only a short time,” he says.
However, research has shown an increase in pregnancy rates with a “flushing effect,” when cattle bred on an increasing plane of nutrition have shown higher pregnancy rates than cattle bred on a declining plane of nutrition. Depending on your location, the timing of breeding plays a role. For example, a March-calving herd in the Nebraska Sandhills has access to high-quality forage at breeding time in June. But a May-calving herd would be grazing lower-quality grass at breeding time in August.
“During a normal year, I would recommend supplementing the ‘high risk’ animals, but this year the entire herd may need supplementation,” says Funston, about the later-calving herd. The effects of drought could impact nutrition for early-calving herds this year, Funston adds. If pastures remain dry, the forage availability and quality could be poor, even in June. If abundant rains do come, the forage may be high in protein but lacking energy, causing lower pregnancy rates. “Just as we take precautions while grazing irrigated grass while breeding cows, a lush pasture with no old grass may cause a similar effect,” Funston says. Research at Nebraska’s Gudmundsen Sandhills Laboratory indicates a lower pregnancy rate in the May-calving herd, especially among fi rst- and second-calf females.
Last year, they tried “flushing” the younger females in the May herd. The heifer calves and first-calf heifers received a protein supplement 10 days prior to the breeding season and during the breeding season. Both groups were synchronized and bred for 45 Pre-breeding nutrition affects fertility NUTRITION days, and received supplement for 55 days total. In the first year of the study, heifer calves receiving 1 pound of 30 percent protein cake bred 82 percent versus a 59 percent pregnancy rate among non-supplemented heifers.
Pregnancy rate was 87 percent among first-calf heifers receiving 2 pounds of a 30 percent protein cake compared with 53 percent in non-supplemented heifers.