Understanding Postpartum Anestrus
by Barb Baylor Anderson for Angus Productions Inc.
NASHVILLE, TENN. (Aug. 5, 2010) — Anestrus may be the most challenging factor reducing reproductive efficiency in beef cow-calf operations, but Les Anderson does offer some explanations and solutions for its management. The University of Kentucky animal scientist addressed participants at the Applied Reproductive Strategies in Beef Cattle Conference in Nashville, Tenn., Aug. 5.
"At today's current market price, a rancher loses $3.17 per calf for every day later in the season it is born," Les Anderson, UK animal scientist, says.
“Unfortunately, anestrus occurs annually in productive females. Heifers are anestrus prior to puberty, and cows undergo a period of anestrus after each calving,” he says. “The length of the anestrous period in both is governed by many factors, including the presence of a calf, nutritional status of the cow, the cow’s age and degree of calving difficulty.
Anestrus ranges from 14 to 180 days in postpartum cows. Anderson says the normal range for mature cows is 30 to 90 days. For young cows, the normal range is 60 to 120 days.
“Producers need to get cows cycling at the beginning of the breeding season,” he says, adding that can help with conception rates at the right time of the year. “The presence of a calf, for example, can affect that. Having the calf establishes estrogen negative feedback and a low LH pulse frequency, but short-term calf removal of about 48 hours has been shown to be effective in inducing estrus.”
Body condition score (BCS), parity, and days postpartum are also associated with the incidence of anestrous and pregnancy failure. Anderson compares the cow to a water tank. As nutrients pour in, the energy level rises so the cow’s length of the anestrous period is reduced. Cows that calve with a body condition score less than 5 generally have longer postpartum intervals than cows calving with a higher BCS. To minimize the length of the anestrous period, cows must calve at BCS 5 or greater.
With parity, Anderson has found that 2-year-old cows need 20-30 days longer to resume estrous cycles than older cows. He recommends first-parity cows then calve 20-30 days before the mature cow herd. Additionally, the longer the time that has passed since calving occurred, the more likely a cow is to cycle. The percentage of cows cycling peaks at 70% at 81-90 days postpartum.
“Early calving appears critical and has a tremendous impact on profitability,” Anderson says. “At today’s current market price (500- to 550-lb. feeder steers at $1.27 per lb.), a rancher loses $3.17 per calf for every day later in the season it is born (assuming 2.5 lb. of gain per day growth).”
So, in order to successfully induce estrus in anestrous cows, he says producers must use protocols that increase progesterone before ovulation and enhance pulsatile LH secretion and follicle growth.
“Administration of a progestin to anestrous cows for a short time period (five to nine days) can successfully induce estrus in many anestrous cows and is the core treatment used to induce resumption of estrous cycles in most protocols to synchronize estrus,” he says. “The most effective method to induce puberty in heifers involves administration of a progestin.”
Anderson continues, “Effectiveness of progestin treatment appears to be dependent upon the progestin used. Treatment of cows with progesterone from CIDR appears to be more effective than the orally active synthetic progestin melengestrol acetate (MGA). Use of gonadotropin releasing hormone (GnRH) has been shown to increase estrus and ovulation rate in anestrous cows. The induction rate appears to be highest when cows receive a combination of progestin and GnRH.”
Several different protocols and combinations of strategies have been shown to effectively synchronize a fertile estrus in anestrous cows. Anderson outlined a number of the possibilities, along with the accompanying research, which can all be found in the conference proceedings.
“Whether prepubertal or postpartum, protocols are available to effectively induce a fertile estrus in anestrous females and help producers maximize reproductive potential,” Anderson reiterates. “Induction is essential for producers to maintain a high reproduction rate in their herds.”
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