Epsilon Archive for Student Projects

Abstract

The repeat breeding problem in cattle is widespread among all the heavy dairy breeds in cattle and is being considered as a major problem throughout the world.
The aetiology of the repeat breeding is of various origins. It is notorious for causing disturbance in the overall cattle health leading to lowered fertility and economic loss in dairy herds. Repeat breeding is caused by fertilization failure or early embryonic death, and the reasons for the reproductive failure may be due to
various disturbances occurring at different sites along the genital tract, including the delicate hormonal regulation system. There are many diseases and disturbances
held responsible for repeat breeding. Even intrinsic factors, such as oocyte quality, have been found to cause repeat breeding. Body condition and body weight also
have an impact on fertility in cattle. Body condition scoring helps to isolate external scores and relate it to the internal condition of the animal and hence forms
a good indication for grading the cattle. It has been observed previously that repeat breeder heifers (RBH) often are over weight and fat. For the present study, three
RBH and two virgin heifers (VH, controls) of the Swedish Red breed were selected. The immature oocytes were collected by ovum pick-up twice weekly during five weeks. The oocytes were classified quality-wise and further examined under transmission electron microscope, TEM. Similar numbers of follicles were available for puncture in the ovaries of RBH and VH, but significantly more (P<0.05) of the follicles were aspirated for retrieval of oocytes in RBH (76.4 %) than in VH (64 %). There was a numerically higher occurrence (NS) of low quality oocytes collected from RBH (60 %) than from VH (52 %). The occurrence
of cytoplasmic vacuoles and lipid droplets was similar in oocytes from RBH and VH with a tendency (P = 0.07) for more lipid droplets in RBH. The VH oocytes as a group were more uniform compared to RBH that displayed a great variation
especially in numbers of lipid droplets. The most prominent difference between RBH and VH oocytes was the significantly higher total lipid amount present in the cytoplasmic lipid droplets in RBH oocytes (P<0.001), which was clearly visible as heterogeneous cytoplasm already under the stereomicroscope and confirmed by TEM. The results indicate that there are morphological differences in the appearance of RBH and VH oocytes, particularly due to higher lipid content in the cytoplasm, which can indirectly explain the low oocyte quality and the sub fertility in RBH.