عنوان مقاله [English]
Background and objectives: Thyroid hormones are effective on reproductive performance of animals, especially in response to photoperiod. In different animal species, changes in serum concentrations of these hormones have been observed throughout the year. According to available data, by determining the serum level changes of these hormones, the sensitivity of the livestock species and breeds to photoperiod was predicted. The aim of this study was to compare the sensitivity of imported breeds (Saanen and Alpine) and indigenous goats (Mahabadi and native Semnan) to photoperiod change in the year, using thyroid hormones.
Materials and methods: This experiment conductedin the south of Damghan (Semnan province: 36 ° North and 54 ° East), at a height of 950 m above sea level, that has a warm summer and cold and dry winter. Sixteen male goats of 3 to 4 years old were selected from four Saanen, Alpine, Mahabadi and native goats of Semnan province. From the beginning of March, every 15 days, sampling was done from jugular vein. Serum T3, T4 was measured by ELISA method. The effect of breed and photoperiod on hormonal concentrations was analyzed by repeated measures method in a completely randomized design.
Results: T3 and T4 levels had changes during each year (p≤0.01). In all four breeds, T3 was high in autumn and winter and peaked in March. The T3 variation pattern was the same in four breeds, but the Saanen breed showed the most variation in T3. Differences in inter-species variation in some months were significant (p≤0.01), but in general, there was no significant difference in the maximum and minimum points of T3 between Saanen, Alpine and Mahabadi breeds. This difference was only significant for Semnan goats with other breeds (p≤0.01). Hormone level was significantly lower in Semnan native goats than in other breeds in March, April, November and December (p≤0.01). The level of T4 has also been influenced by variations in the photoperiod. Concentration of this hormone was highest in winter and autumn and in summer it was the lowest (p≤0.01). There was a significant difference between breeds in terms of sensitivity of changes in T4 concentration to changes in photoperiod (p≤0.01). In the months of the heat season (July, August and September); the concentration of T4 in Semnani goats was significantly higher From Saanen and Alpine goats (p≤0.01). Semnani goats were less influenced in the amount of thyroxin during photoperiodic changes.
Conclusion: The results of this test showed that male Saanen goats more than Alpines were affected by changes in photoperiodic changes and climatic conditions in the southern foothills of Alborz mountain. There was no significant difference between two indigenous genetic populations in response to climatic conditions and photoperiodic changes. According to these results, it seems that the Alpine breed is a more appropriate option for use in these climatic conditions in our country.