Lowering Sperm Dose Rates in Frozen Semen for Bovine Artificial Breeding

Abstract

The New Zealand Dairy industry relies on artificial breeding to produce high genetic merit replacement stock. Proven bull semen is extended and preserved as either ambient temperature product or as frozen doses. High fertility is essential to maintain synchronicity of lactation with the spring surge of grass growth. To improve efficiency in the utilization of the very best bulls producers try to lower sperm dose rates without compromising fertility. Livestock Improvement Corporation's (LIC) Long Last Liquid ™ (LLL) is most commonly used during the peak season and is their most important product. However, shortfalls and specifically targeted matings are met with frozen semen. Lowering sperm dose rates in both liquid and frozen semen maximises the usage of elite sires increasing genetic gain, lowering overheads and garnering premium prices for the semen producer. A product for improving frozen semen technology was developed whereby a discrete quantity of pretreated semen was placed alongside a beneficial post-thawing redilution medium in a standard semen straw. This emulated a larger-scale process developed to freeze semen in times of low demand and redilution into the LLL form for use as an ambient temperature product. This rediluted product has been proved to enhance semen survival and to allow fertility to be maintained at sperm dose rates lower than the widely accepted standard for frozen semen. The physical packaging of the semen into the industry standard single dose straw in a configuration that separated incompatible components was novel. This configuration was essential to prevent damage to the sperm during the freezing process from low solubility components in the post-thaw redilution medium. Separation between the semen and diluent within the straw was achieved by the introduction of a gas partition or air bubble between the two liquids. A large-scale field trial showed that the new product could produce savings of up to 25% of the sperm needed for a semen dose to achieve equivalent fertility. Furthermore, the production cost per dose was lowered in comparison to the standard semen processing system used at LIC.