Microscopically evaluated sperm parameters, as well as computer-aided sperm
motility analysis (CASMA), were used to assess sperm quality and the effect of
cryopreservation on ram semen obtained from two genetically diverse Merino
lines. These lines were divergently selected on maternal ranking values for
multiple rearing ability from the same base population since 1986.
Replacements in the high (+) line were preferentially the progeny of ewes
rearing >1 lamb per joining. Progeny of ewes rearing <1 lamb per joining
was preferred as replacements in the low (–) line. Sperm quality, as
assessed by percentages of live, abnormal and acrosome-intact spermatozoa as
well as by motility, was independent (P≤0.20) of
line, time of sampling and their interaction in ejaculated samples obtained
from the eight rams used as sires in 1995. Sperm quality of
frozen–thawed samples was adversely affected
(P≤0.01) by cryopreservation and thawing at 35˚C
for 30 s relative to fresh ejaculated samples. No consistent differences
between lines were found in epididymal sperm samples obtained from 12
slaughtered rams (6 from each line). The adverse effect
(P≤0.05) of cryopreservation and thawing at 35˚C
for 30 s on sperm viability and motility was also demonstrated for these
samples.
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