Rick Funston of the University of Nebraska spoke on this at the Applied Reproductive Strategies in Beef Cattle Symposium in Manhattan, Kansas, this past August. “One of the things going on in the beef industry is a lot of discussion on efficiency … it’s a numbers deal,” he said. “I would say the most important part of reproduction is when animals conceive.”
Funston stressed the significance of obtaining earlier conception rates. Heifers that conceive earlier have increased longevity and average two more weaned calves in their lifetimes. These animals will also have a longer period to rebreed after their first calves.
Success in achieving this type of reproductive performance is a balance of synchronization protocol selection, mating decisions and herd management.
Protocol selection
According to Funston, long-term progesterone protocols, such as feeding MGA, work better in heifers. Cows tend to respond better to other protocols, such as the 14-day Cosynch and CIDR program. He pointed out breeders are consistently seeing advancement by two to three estrous cycles just by using CIDRs and giving prostaglandin, then putting animals in with bulls.
“We can get anestrous animals pregnant just as well as those that are cycling.” Typical fixed-time A.I. protocols work just as well as protocols with estrous detection, Funston added.
An important question to consider before implementing a specific protocol is whether animals are cycling as they should. “Just observe those cattle on any given day and see how many are potentially cycling before implementation,” said Funston. “It might give you some information on what protocols to implement.”
If they are not, the problem may or may not be overcome with synchronization. Disease, for example, is an underlying issue an additional protocol will not fix. Factors in picking good candidates for synchronization protocols include age, calving success and distribution, fertility and body condition score.
Preventing embryonic loss
Funston noted, on average, 30 percent or more of the embryos resulting from A.I. or natural breeding are lost before day 40. Factors influencing this include genetics, post-breeding stressors and nutrition.
Nutritional changes, he said, from the time of A.I. until days 40 to 50 are especially critical. He referenced one study which compared the fertility of heifers raised on corn residue and those on a drylot with supplemented grain.
When both groups were turned out on grass, the corn residue-fed heifers outperformed the grain-fed heifers in rate of gain per day and better conception rates. Funston attributes this to the corn residue-fed heifers being able to better respond to their environment due to their previous development.
This points to the importance of learned behavior as being a component to animal performance. “I think there’s a lot to be learned yet going on about what we can do to optimize our response to A.I. based on both behavior and compensatory gain,” said Funston.
As with nutrition, supplemental minerals can also impact overall pregnancy rate. Funston noted it is important not to rely on mineral availability to be a cure-all to underlying issues that may be affecting the breeding herd. “Considering what’s in the environment but also what are the antagonists in the environment potentially can have an impact on pregnancy rates in cattle as well,” he said.
Additional factors
Other feed additives can be of benefit to improving pregnancy rate in both A.I. protocol and natural-service animals, according to Funston.
“If I’m going to feed a supplement, I always recommend including an ionophore,” he said, “for the benefits of the ionophore, which improves feed efficiency but, independent of other benefits, there are some positive effects on reproduction by increasing propionate and glucose in the system, which potentially increases our pregnancy rates in these cattle as well.”
Water is another critical checkpoint in a herd’s reproductive influence. Water sources in certain locations, such as those near oil industries, can be suspect for containing trace minerals that will bind and inhibit other important minerals for reproduction, said Funston. Consequences of nutrient restriction can impact not only the well-being of an individual animal but also any calves being carried.
Another point of consideration is where semen used is coming from. Funston referenced research in which semen samples from each of the four major A.I. companies showed a 61 percent conception rate, whereas custom-collected semen showed a full 10 percent lower.
Sire selection can have a major impact on the future of a herd’s reproductive success – a subject that, Funston noted, is little discussed. “This is where the genetic change happens,” he said. “It is in the sire.” A single female will make a very small genetic contribution compared to a single sire’s overall effect, he said. Understanding expected progeny differences and indexes, and what their selection pressure can do, is crucial in making mating decisions.
Funston stressed the importance of replacement decisions, how it impacts breeding herds and the industry. “Probably two-thirds of this beef industry should be a terminal system,” he said. “How much wasted resources do we have in our industry by breeding for keeping a 15 percent replacement rate? Sadly, a lot of the genetic decisions being made are terminal, but the cows are not being treated as such.”
“There are a lot of things that influence estrous response and success rate,” Funston said, which include knowing how to select good and poor candidates for treatment with progestins, nutrition and sire selection. “What we do with those cattle post-breeding is, I think, one of the most important things that influence a successful A.I. program.” 
PHOTO: Females line up at the PX Ranch in Antelope Valley, Nevada, for a project that eventually bred 1,700 heifers. Photo by Paul Marchant.
Jaclyn Krymowski is a freelance writer based in Ohio.
