Assessment of the accuracy of estimation of gestational age in cattle from placentome size using inverse regression.

AIMS: To assess, in dairy cows between 60-160 days of gestation, whether the agreement between actual gestational age and that predicted by placentome size could be improved by using individual placentome measurements rather than a single average, and to identify how increasing the number of placentomes measured improved the prediction. METHODS: Data were obtained from 58 cows examined using transrectal ultrasonography every 10 days between 60-130 days, and every 15 days between 130-160 days of gestation. For each cow, four to six placentomes in each of the pregnant and non-pregnant horns were examined from the region of the uterus near to the cervix. A mixed-effects model, which included cow as a random effect, and a simple linear regression which ignored within-cow correlation, were fitted to the data. Inverse regression was used to compare the 95% prediction bands obtained for estimating gestational age using the means of three, five or eight placentome measurements. RESULTS: The fit of the mixed effects model was better than a simple linear regression (p<0.001) but the fitted lines from the two models were very similar. Using the simple regression model, for a mean placentome length of 15 mm estimated gestational age was 100 days, with 95% CI of 68-131 days for measurement of three placentomes, and 80-120 days for eight placentomes. CONCLUSIONS: The agreement between placentome size and gestational age was improved by increasing the number of placentomes measured. Direct comparison of these CI with those for other published fetal measures was not possible as similar prediction bands have not previously been calculated for fetal measures; however one study reported a residual SD which had been calculated using size measurements as the predictor variable and age as the response variable. Using these data 95% CI were calculated to be ±9 days for crown-rump length and ±25 days for uterine diameter. These are likely to be an underestimate of the true CI and do not take account of the increase in variance of the difference between predicted and actual gestational age as gestational age increases. CLINICAL RELEVANCE: Placentome measurement may be useful for estimating fetal age in late gestation. Further research is required to better establish the agreement between gestational age and the fetal measurements which are currently used to estimate fetal age.

Association between placentome size, measured using transrectal ultrasonography, and gestational age in cattle.

AIM: The aim of this study was to estimate whether fetal age could be accurately estimated using placentome size. METHODS: Fifty-eight cows with confirmed conception dates in two herds were used for the study. The length of the long axis and cross-sectional area of placentomes close to the cervix were measured once every 10 days between approximately 60-130 days of gestation and once every 15 days between 130-160 days of gestation. Four to six placentomes were measured using transrectal ultrasonography in each uterine horn. A linear mixed model was used to establish the factors that were significantly associated with log mean placentome length and to create an equation to predict gestational age from mean placentome length. Limits of agreement analysis was then used to evaluate whether the predictions were sufficiently accurate for mean placentome length to be used, in practice, as a method of determining gestational age. RESULTS: Only age of gestation (p<0.001) and uterine horn (p=0.048) were found to have a significant effect on log mean placentome length. From the three models used to predict gestational age the one that used log mean placentome length of all placentomes, adjusting for the effect of horn, had the smallest 95% limits of agreement; ±33 days. That is, predicted gestational age had a 95% chance of being between 33 days greater and 33.7 days less than actual age. This is approximately twice that reported in studies using measurement of fetal size. CONCLUSIONS: Measurement of placentomes near to the cervix using transrectal ultrasonography was easily achieved. There was a significant association between placentome size and gestational age, but between-cow variation in placentome size and growth resulted in poor agreement between placentome size and gestational age. CLINICAL RELEVANCE: Although placentomes can be easily visualised during diagnosis of pregnancy using transrectal ultrasonography, mean placentome size should not be used to estimate gestational age.

Effect of progesterone secretion on egg production in the grey helmet guinea fowl (Numida meleagris galleata).

The effect of progesterone (P4) on egg production was investigated using twenty female guinea fowls raised on deep litter. The birds were given feed and water ad-libitum. They were routinely bled by wing jab between the hours of 9.00 and 10.00 am twice a month for P4 determination. Sera harvested from the samples were stored at -20 degrees C until assayed for P4 by Radio-Immuno-Assay method (RIA). Egg production had a very high (p<0.001) and positive correlation with progesterone level. A high value of coefficient of determination (R2 value) was observed, which implies that there is a high accuracy of prediction of egg production from progesterone level.