Breeding season for replacement beef heifers destined for a spring-calving herd will be here soon, emphasizing the need for producers to ensure proper nutritional management of the animals.
Replacement heifers will be turned in with bulls or put on a synchronization program to be bred in April. In some cases, this means the heifers must be moved from one location to another that is closer to working facilities.
“A major consideration is to not let the heifers go on a steep downslide in energy intake as we approach the breeding season,” said Glenn Selk, Oklahoma State University Cooperative Extension emeritus animal scientist and editor of the university's "Cow-Calf Corner" newsletter.
As parts of the Southwest have recovered from the recent historic levels of drought, many cattle producers in the region have been able to take greater advantage of improved pasture resources in managing herd nutrition requirements.
Much of southeastern Oklahoma, where there is some wheat pasture but many more acres of ryegrass and fescue, hit the proverbial “bump in the road” last fall.
“We had good moisture and then hit about a month-long dry spell starting in September,” said Brian Freking, Oklahoma State Cooperative Extension area livestock specialist. “The growth of our cool-season forages was affected, of course, but hay supplies generally seem to be holding up well, in part thanks to mild winter weather. Livestock physically haven’t needed to eat as much as past years, when they were exposed to harsher environmental conditions.”
Research has shown that if heifers near the time of reaching puberty undergo a severe reduction in dietary intake of protein — especially energy — breeding success may be disappointing.
Previously, researchers with Oklahoma State’s Division of Agricultural Sciences & Natural Resources studied the impact of short-term energy restriction on ovulation rates of cycling replacement heifers, as reported in the "2001 Oklahoma State University Animal Science Research Report."
“The effects of acutely restricting nutrition on ovulation and metabolic hormones were evaluated in Angus x Hereford heifers,” Selk said. “All the heifers were housed in individual pens in a barn and fed a diet supplying 120% of their maintenance requirements for protein and energy 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 heifers were then split into two groups. Half of the heifers were fed a diet supplying 40% of their maintenance requirements. The other half continued on the original diet that supplied 120% of the maintenance requirements. All heifers were injected with prostaglandin so they would ovulate on about day 14 of the trial.
“Seventy percent of heifers receiving only 40% of their dietary requirements did not ovulate as a response to the injection, whereas all heifers in the other group experienced normal ovulation,” Selk said. “Furthermore, restricting nutrient intake for 14 days prevented ovulation in a large percentage of beef heifers without altering visible body condition.”
The take-away is that heifers should be managed to avoid short-term nutrient restriction and maintain normal estrous cycles.
“Research-based best management practices help cattle producers maximize the likelihood of their heifers and cows getting pregnant, staying healthy and carrying their pregnancy to term to give birth to healthy calves, which is the whole point,” Freking said.