The Angus Journal® is a monthly magazine known for in-depth coverage of American Angus Association® programs and services; the Angus business; herd management; and advertising reflecting genetics and herd philosophies.
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232 n ANGUSJournal n February 2017 C ontrary to what most cattlemen may think, fertilization rates among beef cows and heifers bred by artificial insemination (AI) 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%, or even fewer, AI-sired calves? According to Perry, the reason is early embryonic mortality. In a presentation to the Applied Reproductive Strategies in Beef Cattle (ARSBC) Symposium last fall, 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. "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 nutritional limitations can trigger nutrient partitioning, whereby the dam's body takes care of its own needs first. Only the 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 Applied Reproductive Strategies in Beef Cattle PHOTO BY SHAUNA ROSE HERMEL Guard Against Embryo Loss Nutritional management affects embryo development, pregnancy. by Troy Smith, field editor @ "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 George Perry. "De- finitive attachment of the embryo to the uterus doesn't occur until Day 42." PHOTOS BY TROY SMITH