CHAPTER 3 THE RELATIONSHIP OF RECTAL AND VAGINAL
3.2 Materials and methods
Six cyclic, non-lactating, multiparous Holstein cows weighing an average of 564.4 (± 29.9) kg were used in this experiment. Oestrus was synchronised initially using a double injection of 2 ml of a synthetic prostaglandin (Estrurnatef')" ten days apart. Vaginal and rectal temperatures were measured at approximately two-hourly intervals beginning at the second injection, until after ovulation had occurred.Visual observations of oestrous behaviour were also made at these times. Microllfe'" digital pen-type electronic thermometers (MT 1681)4with an accuracy of O.1°C were used to measure VagT and RecT,
3Schering-Plough (PTY) LTD, 54 Electron Avenue, Islando, 1600 RSA
4 '
Advanced Health Care, 20 Boland Street,p.a.Box 3852, Honeydew, 2040,RSA
one used solely for vaginal temperatures and the other for rectal temperatures. The thermometer used for vaginal temperature measurement was rinsed in a 2 percent chlorhexidine (disinfectant) solution and dried between readings on successive cows to lessen the chances of spreading infection. Environmental temperature was recorded using an Oregon Scientific digital thermo-hygrometer (model ETHG913R)5. A Pie Medical ultrasound machine (Scanner 200}6 with a 5 MHz rectal probe was used to observe the follicle status of the ovaries at four-hourly intervals, starting 10 hours after the observation of standing heat. The follicle diameters were measured, and ovulation was determined by the disappearance of the largest (dominant) follicle (Rajamahendran et al., 1989). This procedure was performed after the temperature measurements were recorded, and dishwashing liquid was used as a lubricant when entering the rectum.These measurements were repeated over four consecutive oestrous cycles in each cow. It was hoped that the cows would remain synchronised after the initial treatment with Estrurnate", but the second oestrous cycles were too spread out to maintain the intensive recordings, so oestrus was again synchronised with a single injection of Estrurnate" for the third and fourth cycles.
The cows had an adverse reaction to the dishwashing liqUid that was used as a lubricant during trans-rectal ultrasound examination during data collection in the first measured cycle, which made it very uncomfortable for the cow each time an examination of the ovaries was made. Due to the cows' reaction it was not possible to determine the time of ovulation with accuracy. The reaction to the dishwashing liquid could have affected temperature; therefore, the data obtained from cycle one was not included in the analysis.As oestrus was not synchronised for the second cycle, there were two cows whose oestrus and SUbsequent ovulation were missed, and they were thought to have cycles shorter than 21 days. One of these cows did not show signs of heat, nor ovulate in the fourth cycle either, and therefore only contributed data for one cycle, hence, all data from this cow were excluded from the analysis.
Another cow in the fourth cycle did not show signs of oestrous behaviour nor
5Oregon Scientific,Inc.Portland,Oregon,USA
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ovulate, and another ovulated, but no standing heat was observed, although there was a bullstring present,which was recorded as oestrus. Either this cow showed no signs of standing heat, or standing heat was less than two hours long, and therefore not observed at the two-hourly interval observation times.
The duration of standing heat in this cow was recorded as 0 hours. Therefore, data from five cows were included in the analysis, and each cow was treated as an experimental unit (replicate).
Statistical procedures were performed with Genstat" 6th edition (2002).
Analyses of variance (ANOVA, no blocking) were performed for both RecT and VagT in relation to the time of oestrus as well as in relation to the time of ovulation, with time, cow and cycle as factors.The ANOVA's were performed to identify if there were significant differences in RecT and VagT both between and within cows, different cycles and at different time increments before either oestrus or ovulation.
When associating RecT and VagT with oestrus, the 2-hourly time increments starting 24 hours before oestrus until the time of oestrus were used.Because there was no significant effect of either cow or cycle, the data were pooled and the means used in the subsequent analysis.There were also no cycle x time interactions, but the main effect of time was significant. Therefore, linear regression analyses were used to determine the relationship between time and both RecT and VagT leading up to oestrus.
Similar analyses were conducted for both RecT and VagT in relation to the time of ovulation. Again, there were no significant effects of cow or cycle from the ANOVA, so data were pooled, and the means used in the subsequent . analyses. Linear regression was performed using the 2-hourly time increments from 24hours before ovulation until the time of ovulation. A limit of 24 hours before ovulation was set, as it was assumed that cows would have ovulated 24 hours after oestrus. A multiple regression was also performed with both RecT and VagT considered in the model.
Temperatures before and after these time periods were not considered,as the aim was to determine if the time of ovulation could be predicted from temperature and not to investigate the use of temperature as a heat detection aid.