A large proportion of the beef industry in northern Australia is composed of tropically adapted cattle, due to their propensity for tick and drought resistance. It has been suggested that a large conical cervix is responsible for decreased fertility in these cattle where a conical cervix is defined as having a caudal to cranial cervical diameter difference of greater than 15 mm. Studies were conducted in order to ascertain the incidence of conical cervix and the heritability of cervical diameter in tropically adapted beef cattle in Queensland. An initial study was conducted on 246 Santa Gertrudis females from four properties. Caudal and cranial cervical measurements were taken with transrectal B-mode ultrasound using the Aloka SSD_500 scanner and a 5 MHz linear probe. Analysis of data was by AS REML, including the effects of sire, parity and property. Sire was included as a random effect, whereas parity and property were included in the analysis as fixed effects. Sire effects were significant. A sire model was used to calculate a heritability estimate of 0.60 ± 0.27 for uterine cervical diameter. An analysis of variance showed that parity had a significant effect on cervical diameter, with cervical diameter increasing as parity level increased. Property had no effect on cervical diameter A more detailed study was conducted on 850 cattle from five properties. Breeds represented were Santa Gertrudis, Brahman, Brahman Cross, Belmont Red and Belmond Red Cross. Caudal and cranial cervical diameter, sire, parity and breed were recorded for each animal. Once again, sire effects were significant resulting in a heritability estimate of 0.46 ± 0.15. An analysis of variance showed parity effects to be significant (α=0.05) while property and breed effects did not influence cervical diameter. However property and breed were heavily confounded due to the practice of many stud breeders of running one breed per property. Breed and parity were also heavily confounded as Santa Gertrudis breed cattle were the only cattle available that had already produced one or more calves. In order to examine the relationship between cervical diameter and liveweight, a subset of 568 cows from the above group also had their weight in kilograms recorded. Animals were chosen for this study based on the availability of scales at each property. A Pearson correlation test resulted in a correlation coefficient of 0.043 between uterine cervical diameter and animal liveweight. This demonstrates that there is a negligible linear relationship between cervical diameter and liveweight. The relationship between cervix diameter and calving outcome was not investigated in this study. Although calving records were obtained for a number of animals in this study, many variables affecting calving outcome could not be accounted for such as disease outbreaks, artificial insemination technique and other management factors. Previous studies have suggested a relationship between cervical diameter and infertility but the present study was unable to draw conclusions regarding this. Although this study has shown that uterine cervical diameter is a moderately to highly heritable trait, it is not recommended that producers cull animals based on their uterine cervical dimensions at this stage, as the relationship between uterine cervical diameter and fertility is still poorly understood.
| Identifer | oai:union.ndltd.org:ADTP/289601 |
| Creators | Finch, Tricia Maree |
| Source Sets | Australiasian Digital Theses Program |
| Detected Language | English |
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