Characterising responses to GnRH before AI in dairy cows

Artificial Insemination (AI) conception rates are declining and delayed ovulation is occurring more often in high producing dairy cows.  Fertility is highest in the window of 0-16 hours before ovulation and a recent study revealed that less than half of all artificial inseminations occurred within that period.

In an attempt to improve conception rates, dairy farmers are increasingly treating all cows at AI with GnRH, to trigger ovulation in the cow. This treatment is applied to synchronise ovulation across the herd, making ova present in more cows when AI is performed.

While previous work has shown that GnRH substantially improves conception rates, the response has been variable, suggesting that individual cows can respond differently to the treatment.

Sixteen spring-calving herds from the Macalister Irrigation District were recruited. All farms used AI, performed early pregnancy testing and herd recorded.  Approximately 3,000 inseminations from 2,350 cows were available for analysis and this allowed detailed examination of the interplay between treatment and cow characteristics.

• • • Blanket treatment of all cows with GnRH at AI is unlikely to be profitable but selective use can be beneficial.
    • An increase of 12% in conception rate was obtained in approximately 10% of cows.
    • These cows can be clearly identified:

1. 1. milk protein (MP) greater than 3.75%
   2. MP between 3.00% and 3.50% and less than 40 days since calving.

• • • It is not effective to treat cows with milk protein concentrations of 2.75% or less and this is strongly discouraged.
    • Increased conception rates in recently calved cows suggests that the effect may be due to enhanced oocyte maturation and/or improved luteal function, rather than by driving earlier ovulation.

There is an opportunity for farmers using GnRH treatment to markedly reduce the cost, effort and negative effects of treating the wrong cows, while making a worthwhile gain in conception rate in the 10% of cows which respond positively to it.

This opportunity only applies to farmers who herd test, since this data is required to identify cows that may benefit from treatment with GnRH. This finding illustrates how herd testing has benefits beyond that of simple production analysis.

Project date: August 2012 to July 2013
Key external stakeholders: Dairy farmers, veterinarians, AI technologists
Partner organisations: HiCo, Herd Health Pty Ltd, Jemora Pty Ltd
Project identifier: INN-12-010
GDF Contribution: $85,000