EFFECT OF SEMINAL EXTENDERS CONTAINING EGG-YOLK AND GLYCEROL ON MOTION CHARACTERISTICS AND FERTILITY OF STALLION SPERMATOZOA

Three experiments were conducted to evaluate the effects of egg yolk and(or) glycerol added to a nonfat dried skim milk-glucose (NDSMG) extender on motion characteristics and fertility of stallion spermatozoa. In Experiment II ejaculates from each of 8 stallions were exposed to each of 4 extender treatments: 1) NDSMG, 2) NDSMG + 4% egg yolk (EY), 3) NDSMG + 4% glycerol (GL), and 4) NDSMG + 4% egg yolk + 4% glycerol (EY+GL). Samples were cooled at -0.7 degrees C/min from 37 to 20 degrees C; subsamples were then cooled at -0.05 or -0.5 degrees C/min from 20 to 5 degrees C. Percentages of motile spermatozoa (MOT) and progressively motile spermatozoa (PMOT) were determined at 6, 24 and 48 h after initiation of cooling. There was no overall effect (p>0.05) of cooling rate. PMOT was highest (P<0.05) for spermatozoa extended in NDSMG+GL at 48 h. At 24 and 48 h, MOT and PMOT were lowest (P<0.05) for spermatozoa extended in NDSMG+EY. In Experiment 2, ejaculates from 8 stallions were exposed to each of 4 treatments: 1) NDSMG, 2) NDSMG+EY, 3) semen centrifuged in NDSMG and resuspended in NDSMG, and 4) semen centrifuged in NDSMG and resuspended in NDSMG+EY. Samples were cooled from 20 to 5 degrees C at each of 2 rates (-0.05, -0.5 degrees C/min). A detrimental interaction between seminal plasma and egg yolk was noted for PMOT at 6 h and for both MOT and PMOT at greater than or equal to 24 h postcooling. Experiment 3 determined if egg yolk or glycerol affected fertility. The seminal treatments were 1) NDSMG, 2) NDSMG+EY with previous removal of seminal plasma, and 3) NDSMG+GL. All samples were cooled to 5 degrees C and stored 24 h before insemination. Embryo recovery rates 7 d after ovulation were lower for mares inseminated with spermatozoa cooled in NDSMG+EY (17%, 4/24) or NDSMG+GL (13%, 3/24) extenders, than semen cooled in NDSMG (50%, 12/24). We concluded that egg yolk (with seminal plasma removal) or glycerol added to NDSMG extender did not depress MOT or PMOT of cooled stallion spermatozoa but adversely affected fertility.