The NRR high or low was depended upon that it can
be attributed in part to visual oestrus signs examination
and follicle sizes evaluation, which led to optimal timing
of insemination. In addition, cows with undetected
oestrus and variety of other reproductive abnormalities
during the research period must be excluded from
consideration. The results of the present study indicate
that NRR was noticeably high in cows that were
inseminated at visual oestrus signs which overall mean
values of the rectal and vaginal temperature, vulva
edema, vaginal hyperemia and pH, ferning of cervical
mucus and ovulatory follicle size were founded about
38.36-38.49ºC and 38.76-38.81ºC, 2.73, 2.45-2.65, 7.19-
7.33, 2.42-2.73 and 16.36-17.01mm respectively. This
same trend was noted previously for cows as increase in
body temperatures, vulva edema, vaginal hyperemia and
ferning of cervical mucus but also decrease in vaginal pH
8,17,23,25,26.
Follicular activity in cattle is known to be greater in
the right than the left ovary2,27. This is consistent with the present results as well as those of Townson et al.18, in that ovulations occurred more frequently in the
right ovary. Indeed, it was observed that approximately
64 % of dominant follicles developed in the right ovary. In
contrast, other studies28,29 found no such differences
in location of the dominant follicles. The results cannot
be attributed solely to reproductive status, as the study
used cows, whereas the others used heifers. Of further
interest is that in cows of the present study, there was a
tendency for NRR to increase when ovulation occurred
from the right ovary. The reasons for this observation are
unclear at this time although it s not due to a higher
incidence of fertile oocytes from the right ovary. In fact,
the analysis showed that there was no interaction
between location of the ovulatory follicle and NRR (Table 2).
Contributing factors for decreased inseminated
pregnancy rates in cows that are subjected to premature
estrus and/or ovulation, ovulation from smaller sized
follicles resulting in low lifespan and reduced function of CL. Short lifespan of the male and female gametes in the
female tract necessitate accurate timing of artificial
insemination. In cows, delayed ovulation following estrus
minimizes the chances of successful fertilization due to
the short fertile lifespan of bovine gametes30-33. The
lifespan of the oocyte is determining factor for successful
fertilization, which means the oocyte is waiting for the
arrival of eligible sperm. If the oocyte is aged before the
arrival of the capable sperm cells than failure of
fertilization and/or embryonic development may results.
Inadequate oocyte development is another possible
explanation when small follicles are induced to ovulate19,34. Little is known about variation that exists in
oocyte quality among bovine preovulatory follicles.
Similar trends were observed in the present study and
spontaneously oestrus and ovulation occurred,
differences in minimum (0 %) and maximum (100 %)
NRR rates were detected among different (P<0.05)
follicle sizes (Table 1). The mean values of OFS was
founded as 17.01±0.27 mm when return was no.
However, the highest NRR was achieved in cows which
were inseminated the OFS range were about 15-18 mm.
Consequently, when a follicle has matured and is
capable of initiating the cascade of events leading to
ovulation, a viable embryo can develop according to
follicular size.
In this study evaluated the relationship between the
non-return rates and the visual examination findings of
oestrus signs at insemination times in cows. Especially,
NRR was positively correlated with ovulatory follicle size (P<0.05), vulva edema, vaginal hyperemia and ferning of
cervical mucus (P<0.01). It was showed that these
findings support the hypothesis that visual estrous signs
are indication of the ovulatory follicle size in cows
undergoing spontaneous oestrous cycles and the
findings were in accordance with the references findings
that pregnancy rates were correlated with some oestrus
signs1,5,11,22,33. According to the result, mucus
crystalization test may be offered to breeders and
veterinarians a natural and affordable way to increase its
chances of pregnancy. Another finding from the present
study was that visual estrous signs of cows were
correlated with ovulatory follicle sizes of its and were
interrelated.
NRR was greater in cows undergoing spontaneous
oestrus period inseminated that vulva edema, vaginal
hyperemia and ferning of cervical mucus were very clear
and high with moderate ovulatory follicle sized.
Therefore, the exhibiting behavioral oestrus can be
evaluated with ovulatory follicle size and ferning of
cervical mucus, and management practices that optimize
ovulatory follicle size may improve fertility. If it is
developed new practicable methods for favouring
ovulatory follicle size and ferning of cervical mucus
estimation particularly, it is developed and/or created a
practical, minor and mobile device insist of microscope
equipment to use in veterinary practice for determination
of the cervical mucus ferning, it may be guide to arrange
of the optimal insemination time and thus NRR may be
boosted with using the tool.
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