Study of Appearance and Course of Estrus in Prepubertal Heifers

Veterinarni Medicina 36, 1991, 525-531

In 1990 three experiments were performed in heifers 184 to 505 day-old with the weight 190 to 390 kg to test some biotechnical methods while studying the level of reproduction functions. Heifers were examined in 4 to 24-hour intervals by direct observations of animal behaviour, by clinical and gynaecological examinations of larger animals. The progesterone concentration in the peripheral blood was determined by the RIA method and simultaneously with the blood samplings, the values of impedance of vaginal mucosa were measured by means of several types of the Estral device (CSFR) for cattle. To detect the functional responses to prostaglandins administered, the following forms of substances were used: racemic mixture of optically active forms D (+) and L (-) in the Czechoslovak preparation Oestrophan inj. Spofa (0.25 mg of cloprostenol in 1 ml of solution) and the dextrorotatory D isomer - cloprostenol (0.075 mg in 1 ml of solution) in the Czechoslovak preparation Remophan inj. Spofa. Evaluating the results of the group 1 based on clinical and ethological examinations, the values of impedance of vaginal mucosa and progesterone levels (Tab. I), the functional maturity of sexual organs in heifers were determined. No significant differences were found while compared the luteolytic effects between D-cloprostenol in the Remophan preparation and the conventional mixture of optically active forms of Oestrophan. All methods used confirm the functional maturity of sexual organs (including a response to prostaglandin analogues administered) in heifers 11-12 month old. The values of impedance of vaginal mucosa varied during oestrus in some heifers and this fact is to be taken into account in practice. A correlation between daily time and the time of prostaglandin application may be predicted on the basis of the results when the appearance of oestrus is formed in heifers. To focus the manifestations of induced (synchronized) oestrus in the morning hours of the third day following the application of prostaglandin, a treatment with these preparations seems to be more efficient in afternoon hours. No high correspondence was confirmed between quality of the first induced oestrus in prepubertal heifers and subsequent pregnancy after the first insemination. When prostaglandin is applied in large scale to young heifers, the synchronization of oestrus cycles appear, but this synchronization does not persist for another two cycles. The study of prepubertal heifers (group 2) at the age of 6-9 months indicated the ovarial activity even on the basis of the level of progesterone investigated (Tab. II). This activity was also confirmed either by ethological examination of experimental heifers in individual boxes or the results of measurements of impedance of vaginal mucosa by the modifies Estral device. It has been showed that the measurements of impedance of vaginal mucosa provide the applicable and comparable results in heifers of this age (Fig. 1). Thus, heifers at the age 6-9 months may be detected as being at the stage of an ovarial cycle stabilization. Clinical and ethological examination of prepubertal heifers (experiments 1 and 2) indicated that the individuals with the dominant position among animals in the box have more apparent sexual response and thus, there seems to be a certain advance in this way. All these animals exhibited a higher weight. Weight gain as a very influential biological factor probably affects significantly the appearance of the date of the first ovulation and maybe also affects indirectly the time of the first mating. It follows from the results of gynaecological examination and of the finding of small ovaries with temporary acyclic period in heifers at the age of 13-15 months, the number of inseminations required for good conception increases. In two experiments in heifers 6-9 month old, it was found out that the ovarial activity at this age is at the stage of gradual maturity. The levels of progesterone and impedance of vaginal mucosa in heifers 6-9 month old are given in Tabs. II, III and Figs. 1 and 2. These experiments confirmed repeatedly the higher importance of live weight prevailing the importance of age at the appearance of the first ovulation. Further, it was found that the decrease in the service weight by 10-20 kg has no adverse effects on the subsequent fertility, provided that an average weight gain was about 0.65 -0.67 kg per head and day. This method of rearing, the most suitable is run rearing, promotes the development of all organs, including sexual organs. A positive effect of technological and zoohygienic and climatic conditions is combined in the rearing of heifers. The effect of exogenous factors is such that no ambiguous criterion can be derived from present observations for heifers to discover the future, potential reproduction performances in heifers. Detailed studies are to be done along with studies of the potentials how to shorten an interval between the first ovulation and the first insemination (A. I.) aimed at increasing the economy of rearing, including the increase in its reproduction performance

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