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.