Sperm concentration at freezing affects post-thaw quality and fertility of ram semen

ITRA-ULE, INDEGSAL, University of León, León, Spain.
Theriogenology (Impact Factor: 1.8). 12/2011; 77(6):1111-8. DOI: 10.1016/j.theriogenology.2011.10.013
Source: PubMed


We have investigated the effect of sperm concentration in the freezing doses 200, 400, 800, and 1600 × 10(6) mL(-1) on the post-thaw quality and fertility of ram semen. Semen was collected from seven adult Churra rams by artificial vagina during the breeding season. The semen was diluted in an extender (TES-Tris-fructose, 20% egg yolk, and 4% glycerol), to a final concentration of 200, 400, 800, or 1600 × 10(6) mL(-1) and frozen. Doses were analyzed post-thawing for motility (computer-assisted sperm analysis system [CASA]), viability, and acrosomal status (fluorescence probes propidium iodide [PI]/peanut agglutinin conjugated with fluorescein thiocyanate (PNA-FITC), SYBR-14/PI [Invitrogen; Barcelona, Spain] and YO-PRO-1/PI [Invitrogen; Barcelona, Spain]). Total motility and velocity were lower for 1600 × 10(6) mL(-1) doses, while progressive motility and viability were lower both for 800 and 1600 × 10(6) mL(-1). The proportion of viable spermatozoa showing increased membrane permeability (YO-PRO-1+) rose in 800 and 1200 × 10(6) mL(-1). Intrauterine inseminations were performed with the 200, 400, and 800 × 10(6) mL(-1) doses at a fixed sperm number (25 × 10(6) per uterine horn) in synchronized ewes. Fertility (lambing rate) was similar for semen frozen at 200 (57.5%) or 400 × 10(6) mL(-1) (54.4%), whereas it was significantly lower for 800 × 10(6) mL(-1) (45.5%). In conclusion, increasing sperm concentration in cryopreserved semen, at least at 800 × 10(6) mL(-1) and more, adversely affects the postthawing quality and fertility of ram semen.

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    • "spermatozoa concentrations < 0.8 × 10 9 spermatozoa/ml) are beneficial for liquid storage is interesting given its similarity with the results of experiments investigating the concentration at which ram spermatozoa should be frozen for optimal results. These studies have shown that a greater pre-freeze dilution is advantageous to the post-thaw quality (D'Alessandro et al., 2001; Leahy et al., 2010b) and fertility (Alvarez et al., 2011) of frozen-thawed ram spermatozoa. Unlike the numerous empirical studies of semen freezing (Salamon and Maxwell, 1995), relatively few studies have directly compared the effect of dilution rate and/or spermatozoa concentration on the function of liquid stored ram spermatozoa (Maxwell and Salamon, 1993). "
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