GnRH is secreted from the hypothalamus and affects the anterior pituitary. Several economical prostaglandin products are available by prescription from a veterinarian.įigure 1 Gonadotropin Releasing Hormone (GnRH) Prostaglandins will synchronize heat only if cows are cycling however, they are not effective on all days of the estrous cycle. This allows the cow to return to heat, ovulate and start a new cycle. Prostaglandin is naturally produced by the uterus and terminates the normal cycle when a cow is not pregnant. Prostaglandin is a naturally occurring hormone approved for use in beef cattle in 1979. The CIDR(TM) is approved for use in suckled beef cows and replacement beef heifers. When inserted in the vaginal tract, it releases progesterone at a constant rate. CIDR(TM)s are T-shaped flexible silicone and nylon devices containing progesterone. Understanding that progesterone concentrations are elevated for most of the estrous cycle and knowing how they are reduced is useful when selecting an estrous synchronization protocol.Īn example of a progesterone product used in estrous synchronization protocols is a CIDR(TM) (controlled internal drug releasing device). If she is not pregnant within 15 to 18 days of a normal cycle, prostaglandin is synthesized and released to regress the CL. As the CL matures, progesterone concentrations increase and remain elevated throughout pregnancy or the estrous cycle (see Figure 1) until the female either calves or is not pregnant.
The CL is the primary progesterone source in the bloodstream. When the female ovulates, the site of ovulation develops a structure known as a corpus hemorrhagicum, which quickly (within four to seven days) develops into a corpus luteum (CL). Both can be used to synchronize estrous in cattle. Progesterone can be given in the natural (progesterone) or synthetic (progestin) form. Progesterone is a hormone used to maintain pregnancy. Depending on the protocol, these hormones can be used independently or in combination with one another. Progesterone, prostaglandin, gonadotropin releasing hormone (GnRH), follicle stimulating hormone (FSH) and luteinizing hormone (LH) are a few of the hormones involved in the estrous cycle (see Figure 1). Since different reproductive hormones are used in estrous synchronization, developing a basic understanding of several reproductive hormones is helpful for determining which protocol will work best for your herd. Numerous estrous synchronization protocols have been developed that use a combination of different drugs and products to alter hormonal changes in the female's estrous cycle. There are several advantages to consider when following an estrous synchronization protocol, including: 1) shortening the calving interval, which allows females (especially heifers) to conceive earlier in the breeding season 2) more effectively using AI and embryo transfer to reduce time and labor in detecting estrus (heat) and 3) producing a more uniform calf crop with similar ages.Įstrous synchronization will not substitute for lack of nutrition, herd health or poor herd management therefore, it is not effective in non-cycling females. The normal 21-day estrous cycle in beef cattle can be altered by following an effective estrous synchronization protocol.
Estrous (heat) synchronization in beef cattle involves manipulating the females' estrous cycle so they can be bred at about the same time.
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