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Protocols for Synchronization of Estrus and Ovulation
Beef Reproduction Task Force
Introduction The potential for genetic improvement in beef herds in the US through advances in biotechnology has never been greater. Recent improvements in our understanding of methods of inducing and synchronizing estrus and ovulation in postpartum beef cows and replacement beef heifers creates theopportunity to significantly expand the use of artificial insemination in both purebred and commercial herds. Technology now exists to successfully inseminate beef cows at predetermined fixed times with pregnancy rates comparable to those achieved with heat detection. While many options exist for synchronization of estrus and ovulation, this short list of protocols was developed based on availableresearch data and field use by the Beef Cattle Reproduction Leadership Team. This group is composed of representatives from the AI and pharmaceutical industries, veterinarians, and reproductive physiologists from the Beef Reproduction Task Force with active research programs in this area. Selecting a synchronization protocol Each producer should evaluate available resources and assess the cows orheifers intended for synchronization before selecting a protocol. Key considerations should include time and skill available for heat detection, body condition of the cows or heifers, days postpartum in cows, facilities, experience, and cost. Amount of Heat Detection The first step in selecting a synchronization protocol is to determine how much, if any, heat detection is feasible or desired. Somemanagement systems make heat detection and the sorting of animals very simple and effective. In other cases, heat detection can be very difficult. Poor detection efficiency can result in a low AI pregnancy rate. The recommended protocols are divided into three groups based on amount of heat detection required; 1) heat detection for 7 to 8 days, 2) heat detection for 3 days followed byfixed-time AI of all remaining animals not previously detected in heat (clean-up timed AI) or 3) strict fixed-time AI. Cow factors Any of the synchronization protocols are recommended for mature cows with a body condition score of 5 or greater that are 50 days or

more since calving at the time of AI. Young, thin, and late calving cows are all less likely to have resumed their estrous cycles at thebeginning of the breeding season. If a high percentage of cattle are in these categories, consideration should be given to protocols that include a progestin such as a CIDR®. The progestin will induce some non-cycling cows to cycle and improve their chance of conceiving to AI. If cows are too thin or have calved too recently, the investment in synchronization of estrus may not be cost effective.Heifer factors Age and weight are key factors that influence time of puberty in heifers. Heifers should attain 60% of their mature weight prior to breeding. Because selection pressure on growth has increased mature cow size, producers may tend to underestimate future mature size. Producers that score heifer reproductive tracts at 50 to 60 days prior to breeding have a true measure ofphysiological maturity and time to adjust rations prior to breeding. If 50% of heifers have a tract score of 3 or greater 50 to 60 days prior to breeding, estrous synchronization programs tend to be more successful. Protocols including a progestin such as MGA® or CIDR® will induce some prepubertal heifers to cycle. Other Length of the protocol, number of times handled, and the ability to successfullydeliver treatments such as MGA® are other factors that must be considered when choosing a synchronization protocol. Management system, feed resource flexibility, and facilities will play a role in which protocol works best in each particular environment. Success of any protocol is dependent on the proper administration and timing of treatments. For help see the Estrus Synchronization Planner at...