Effects of Peri-AI Nutritional Management on Embryo Development and Pregnancy
By Troy Smith, field editor
DES MOINES, Iowa (Sept. 7, 2016) — Contrary to what most cattlemen may think, fertilization rates among artificially inseminated (AI’ed) beef cows and heifers are quite high. According to South Dakota State University reproductive physiologist George Perry, fertilization is successful about 90% of the time, when animals are detected in estrus and semen is present at the time ovulation occurs. So why is it that most well-managed AI programs result in just 70 percent AI-sired calves, or even fewer?
In a presentation to the Applied Reproductive Strategies in Beef Cattle conference, Sept. 7-8 in Des Moines, Iowa, Perry said the reason is early embryonic mortality. He explained that much of the loss is due to natural causes – things like poor oocyte quality, disease or genetic abnormalities — but management practices that place nutritional stress on cows and heifers also decrease embryo survival. To understand why requires some understanding of how an embryo develops.
“What a lot of people don’t realize is that it takes two weeks (following fertilization) to achieve maternal recognition of pregnancy. Until then, the female (her body) doesn’t even know she’s pregnant,” explained Perry. “And definitive attachment of the embryo to the uterus doesn’t occur until Day 42.”
During this time, an embryo is vulnerable to the dam’s biological responses to stress created by environmental factors, shipping or a negative shift in nutritional status. Focusing on the latter, Perry said nutrition limitations can trigger nutrient partitioning, whereby the dam’s body takes care of its own needs first, and only leftovers, of which there may be none, go toward maintaining pregnancy.
Perry said maintaining adequate energy intake is particularly important. When energy intake is limited at or immediately after insemination, this lack of energy may perturb fertility through direct or indirect regulation of the uterine environment. This may include changes to components of uterine secretions or by influencing the circulating concentrations of progesterone that regulate uterine environment.
Perry said abrupt changes in diet around the time of AI, such as moving heifers with little or no grazing experience to pasture, can result in inadequate energy intake.
“Even when ample forage for grazing is available, naïve animals may not eat enough to meet energy requirements,” warned Perry.
Citing studies involving drylot-developed heifers that were turned out to graze forage without supplementation, Perry said they exhibited increased activity (steps per day), lost weight, and had decreased conception rates compared to heifers that had prior grazing experience. He explained that nutritional stress from decreased intake does not have to last long to prompt a negative response. Research suggests that restriction of intake for only six days immediately after AI can result in decreased embryo quality and delayed embryo development.
“Any big changes in diet, around the time of AI, can have negative impacts,” emphasized Perry. “Consistency of diet is important, especially during the first month following AI.”
Perry also talked about shipping stress as related to early embryo mortality. For producers needing to haul animals from the site where AI is performed to pasture, he advised transporting them as soon after AI as possible and certainly within four days. He explained that until Day 5, the embryo remains in the oviduct and should not be subjected to uterine hormonal changes brought on by shipping stress. Alternatively, animals may be shipped after the time of embryo attachment to the uterus (Day 42).
The period between Day 5 and Day 42 is the time of greatest risk of embryonic loss due to shipping. However, Perry said animals typically can be trailed a reasonable distance during this time without negative effects. Driving animals does not appear to prompt the stress response that occurs as a result of loading and hauling them to a different location.
Perry spoke during Wednesday’s ARSBC session focused on the nutritional effects on reproduction. Visit the Newsroom at www.appliedreprostrategies.com, which features comprehensive coverage of the symposium, to view his PowerPoint, read the proceedings or listen to the presentation. Compiled by the Angus Media editorial team, the site is made possible through sponsorship by the Beef Reproduction Task Force.
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