Insemination volume
An interaction between the total number of sperm inseminated, volume inseminated and sperm concentration has been suggested (Pickett & Shiner, 1994) and sperm concentration may be more important than volume (Katila, 2005). When insemination of mares with a constant total number of sperm, larger volumes reduce pregnancy rates (Jasko, Martin, et al., 1992; Pickett & Shiner, 1994; Rowley et al., 1990), however when the concentration of sperm was consistent (50 x 106sperm/ml) there was no difference in pregnancy rate between 30-ml and 120-ml (Bedford & Hinrichs, 1994) of semen. Large insemination volumes (> 50-mL) are not thought to be beneficial as most of the semen will be lost through the mares dilated cervix post insemination (Brinsko et al., 2011; Jones, 1995; Rowley et al., 1990). When considering the inflammation in the mare’s uterus post-breeding, the data is confounding. Two studies have found an increase in uterine inflammation with increased sperm concentration(Fiala et al., 2007; Kotilainen et al., 1994). Another study found no effect of sperm concentration on uterine inflammation (Sinnemaa et al., 2005) while a second study found mares infused with 40-mL of extended semen with a concentration of 500 x 106 sperm/mL and significantly less uterine inflammation than those infused with 40-mL at a concentration of 50 x 106(Nikolakopoulos & Watson, 2000). Thus, it is this author’s recommendation to minimize the insemination volume while having enough sperm to produce acceptable pregnancy rates.