Farm environmental factors in the KwaZulu-Natal Midlands were investigated to see if any of them affected calf sex ratios in dairy herds in the area. Where the work of others has been used, this has been duly acknowledged in the text. And finally, to my Heavenly Father, my early morning companion, for his unfailing love.
LITERATURE REVIEW
Introduction
This will allow greater profit as crossbred dairy/beef calves have a better growth rate compared to dairy calves (McElhenney et al., 1986).
The 50:50 gender ratio
- Explanation ofthe 50:50 ratio
- Causes of differential gender ratios
- Skewed ratios of X- or V-bearing sperm
- Age of oocytes
- Multiple births
- pH of the female reproductive tract
- Maternal-biased gender selection
There do appear to be circumstances in which the sex ratio of offspring may not be 50 percent. The sex ratio of 2-cell bovine embryos after in vitro fertilization depends on the timing of insemination. Karam (1957) and Napier and Mullaney (1974) found no significant difference in the sex ratio of single or twin births in sheep.
Predetermining gender in cattle
- Differential development rates of male and female embryos
- Early foetal gender determination in cattle
- Ultrasonography
- Amniocentesis
The different results with the sex ratio manipulation in the above experiments may be due to the inaccuracy of the expected time of ovulation after the onset of estrus. The discrepancy between the time of the temperature peak and the time of the LH surge between Clapper et al. 1990) have been attributed to different experimental methods. Skewness of the sex ratio in early embryos has been attributed to different developmental stages of males and females, with males predominating in the earliest developing embryos (Longergan et al., 1999).
In addition to its use in pregnancy diagnostics, ultrasound can be useful in determining the sex of the fetus. For example, the urachus (non-echoic structure) is located in the region of the pubic bone in male fetuses (Curran et al., 1989), and fetal landmarks such as the beating heart, pulsating umbilical cord, hind legs and tail can e.g. used for orientation (Curran and Ginther, 1991).
Conclusions
Ultrasound and amniocentesis are suitable tools in the early determination of the sex of the fetus, which can be useful for both dairy farmers and beef farmers. THE POTENTIAL USE OF PRODUCTION AND MANAGEMENT VARIABLES TO MANIPULATE THE CALF RATIO IN DAIRY CALVES.
Introduction
Materials and methods
Minimum and maximum temperatures on the day of insemination (Tmin and Tmax) were obtained for all geographical areas. If any variable was missing for a given calf, the entire calf record was excluded from analysis so that each calf analyzed was represented by the full set of variables. This is an appropriate statistical procedure for testing the hypothesis that the group means of a set of independent variables for two or more groups are equal.
This results in a discriminant Z-score for each individual in the analysis which, when averaged, results in the group mean (Hair et al., 1998). Two groups (males and females) showed discrimination and therefore logistic regression is preferred over discriminant analysis (Hair et al., 1998). Consequently, a stepwise multiple logistic regression was performed (using GenStat®). Terms with a variance ratio greater than 3 were included in the model, to identify which variables significantly influence KGR.
The variable with the largest contribution is added first and variables are then selected for inclusion based on their incremental contribution over the variable(s) already in the equation (Hair et al., 1998). Predictions for a female calf were then determined based on the variables that were significant in the model, using the prediction guideline in GenStat®, which forms predictions based on a generalized linear model. Because the outcome of logistic regression is binary, it directly predicts the probability of an event occurring (Hair et al.,1998).
However, the available data set did not represent all combinations of each variable, so some predictions were based on estimates.
Results and discussion
- Bull presence ;
- Area
- Timing of artificial insemination
- Number of inseminators
The positive relationship between CGR and HDS suggests that as heat detection improves on a farm (this is believed to be the case as more heat detection tools are used), the CGR becomes closer to one (i.e. female). Regardless of the specific probability scores, the general trend is that the probability of a female calf increases as heat detection improves. If heat detection is poor, a cow is more likely to be served later, after heat behavior is first detected and therefore closer to ovulation.
81 no bulls on the farm, one inseminator, direct/am-pm AI and heat detection score 3. 83@\] no bulls on the farm, one inseminator, direct/am-pm AI and heat detection score 3;. Another explanation for the low probability of a female calf being inseminated immediately could also be due to the heat detection methods and the way the farmer estimated how long the cow was in heat.
Therefore, inseminators would benefit from improved heat perception to achieve this, and insemination could be expected to occur earlier when there were more inseminators on the farm, increasing the probability of a female. The highest male probability was obtained in site group 1, with no bulls on the farm, two inseminators and an am-pm AI schedule, with probability. Natural service is commonly used in the beef business, so it is the presence of bull(s) that also negates the need for heat detection.
S1 Area group 2, no bulls on farm, both immediate/am-pm AI and heat detection score 3;.
Conclusions
THE RELATIONSHIP OF RECTAL AND VAGINAL
Introduction
The purpose of this experiment was to investigate whether the time of ovulation can be predicted using an alternative, cheaper method, so that sex ratios can be manipulated through the correct timing of insemination. Vaginal temperature has been found to increase at the time of estrus (Wrenn et al., 1958, Lewis and Newman, 1984). An increase in physical activity is observed in estrus (Lewis and Newman, 1984; Schofield et al., 1991; Walton and King, 1986), which may cause the temperature to rise at this time.
The time interval from body temperature rise to ovulation appears to be consistent, with ovulation occurring between hours (multiparous cows) and 27 (binary cows) (± 3.5) hours after the vaginal temperature peak (Rajamahendran et al., 1989). However, the measurement of vaginal temperature leads to the risk of introducing infections into the reproductive tract. Therefore, this study aimed to investigate the relationship between body (rectal) temperature (RecT) and vaginal temperature (VagT) to oestrus and ovulation.
Materials and methods
The cows had an adverse reaction to the dishwashing detergent used during transrectal ultrasound examination during data collection in the first cycle measured, making it very uncomfortable for the cow each time an examination of the ovaries was performed. Due to the cows' reaction, it was not possible to accurately determine the time of ovulation. The reaction to the dishwashing detergent could have affected temperature; therefore, the data obtained from cycle one were not included in the analysis. As estrus was not synchronized for the second cycle, there were two cows whose estrus and subsequent ovulation were missed and were thought to have cycles shorter than 21 days.
Therefore, data from five cows were included in the analysis, and each cow was treated as an experimental unit (replicate). Analyzes 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 ANOVAs 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 estrus or ovulation. When RecT and VagT were associated with estrus, the 2-hour time increments starting 24 h before estrus until the time of estrus 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.
Similar analyzes were performed for RecT and VagT according to ovulation time. There were also no significant effects of cow or cycle in the ANOVA, so the data were pooled and the means used below. Linear regression was performed using 2-hour time steps from 24 hours before ovulation to the time of ovulation.
Temperatures before and after these periods were not considered, as the aim was to determine whether the time of ovulation could be predicted from temperature and not to investigate the use of temperature as a heat detection aid.
Results and discussion
- Standing heat
- Environmental temperature
- Relationship of rectal and vaginal temperature with oestrus
- Relationship of rectal and vaginal temperature with ovulation. 57
Since this answer was obtained with temperature data 24 h before the onset of estrus, it limits the application of the equation to this period of the cycle. This can therefore mean that a knowledge of the approximate time for the start of heat, e.g. Thus, misleading predictions of the time of estrus could be made using this equation without knowing the approximate time of estrus onset.
For example, a RecT of 38.4cC in the middle of the estrus cycle would result in an incorrect prediction of 15 hours to estrus using the above equation. The temperature then increased for the next six days and no drop was reported until ovulation. 1990) measured the vaginal temperature every hour and considered prolonged (;~~3 hours) elevated temperature rises (;?:0.3°C) compared to the average at that time the previous day as a "temperature rise". 1997) base this assumption on the altered conditions of the female reproductive tract near the time of ovulation, which have a differential effect on the capacitation abilities of X- and V-bearing sperm.
The manipulation of heat detection, timing of insemination and the number of inseminators can be explained from the theory proposed by Wehner et al. However, it is more likely that the explanation is attributed to another unknown factor, such as the size of the farm. Determining the sex of the bovine fetus by ultrasound assessment of the relative location of the genital tubercle.Anim.
Association of the type and timing of insemination in the menstrual cycle with the human sex ratio at birth. 1997. Effectiveness of the OVATEC device for oestrus detection and calf sex control in beef cows. A technique for sexing mouse embryos by a visual colorimetric assay of the X-linked enzyme, glucose-6-phosphate dehydrogenase. Theriogenology 25:733-739.
