Embryonic loss can negatively affect pregnancy rates. Management helps increase the odds of success.
If you look at the averages, where would you guess the most room for improvement lies in increasing the cash flow and, therefore, the potential profitability of a beef cattle operation?
Feed costs? Pasture rent? Cow longevity? All those matter and all work in concert to affect the bottom line. But if a cow or heifer doesn’t get pregnant, nothing else matters because a calf that’s never born is never weaned and never sold. And “never” will never generate a single dollar.
In fact, according to Lannett Edwards, University of Tennessee beef reproduction specialist, only 76-80% of cows in the Volunteer State will wean a calf. Standardized Performance Analysis (SPA) data for Texas, Oklahoma and New Mexico show the average weaning rate in that region is around 85%.
Certainly, averages are just that, an average, which means half of the cattlemen included in the data base are weaning a higher percentage calf crop. While a 95%+ weaning rate may not be feasible or profitable in many climates, those numbers indicate there’s plenty of room for improvement. “A producer’s ultimate goal should be to have a 90%+ calf crop every 365 days,” Edwards asserts.
However, when you consider the rather amazing process that occurs to create a pregnancy, it’s a miracle any cows get settled at all. Without getting into the details (which you can do by clicking here), suffice it to say it’s not a simple process. And, as with any complex system, the opportunities for things to go wrong are legion.
Some of those factors are beyond your control. But there are some important management points you can emphasize to help the process along and ultimately wean a calf.
“Because of the complexity of changes occurring during this time (those critical days just before and just after breeding), the maturing oocyte is very susceptible to environmental stressors. In particular, those stressors resulting in elevated body temperatures include heat stress, ingestion of toxic plants, illness and others.” Throw in nutrition and other stress, such as working cows or moving them to a new pasture, and early embryonic loss can begin to really affect pregnancy rates.
In fact, research indicates embryonic losses account for 75-80% of all reproductive losses occurring between fertilization and calving, she says. And those losses occur early – most by day 8 of the pregnancy, with losses also occurring between then and day 14. Around 42-45 days of gestation, the embryo is fully developed and the fetus begins to more fully develop. “From there forward, little loss is expected to occur if disease and other issues are minimized,” Edwards says.
Of the factors that impact early embryonic loss, two are easily manageable – stress and nutrition.
“Most heifers are developed in a feedlot and moved to pasture after insemination,” says George Perry, South Dakota State University beef reproduction specialist. “However, when animals are loaded on a trailer and hauled to a new location, they become stressed and release hormones related to stress,” he says. That creates changes in the uterus that are detrimental to the developing embryo.
“The most critical time points are between days 5 and 42 after insemination,” he says. “Before day 5, the embryo is in the oviduct and is not subject to changes in the uterine environment. Consequently, if heifers or cows need to be transported to pasture following fixed-time artificial insemination, this should occur before day 5 or after day 42.”
Then there’s the cows’ and heifers’ nutritional plane. A preponderance of research indicates weight gain in heifers following insemination is critically important. Research indicates heifers developed on grass tend to have higher conception rates. Regardless of whether heifers were developed in a feedlot or on pasture, however, supplementation after breeding was critical in achieving sufficient weight gain after heifers were moved to grass.
And prebreeding nutrition is critical as well, for a variety of reasons. While the old rule of thumb that a heifer should be at 65% of her mature weight at breeding is still the best advice, Perry says, some research indicates that breeding heifers at 50-55% of mature weight is also feasible. However, he says research shows that fewer heifers are cycling and get bred early in the breeding season when targeted at 50-55% of mature weight.
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Video: Solving Reproduction Inefficiencies