Dalagh: An Iranian half-tailed sheep breed with continuous annual ovarian activity at a mid-latitude temperate region

作者：Hassani S R; Ahangari Y Jafari; Moslemipour F; Akhlaghi A^*

来源：Livestock Science, 2014, 160: 219-222.

DOI：10.1016/j.livsci.2013.12.018

• Dalagh
• Ovarian activity
• Progesterone
• Seasonal breeding
• Thyroid

At mid and high latitudes, seasonal breeding is prevalent in sheep production which makes ewes to reproduce for a restricted window of time. Unconfirmed local reports have declared a continuous reproductive activity in a half-tailed sheep breed, Dalagh, at a mid-latitude region (37 degrees N) in Golestan province, northern Iran. The present study aimed to evaluate the ovarian and thyroidal activity in Dalagh ewes during a one-year-long trial. Fifty-five fertile healthy ewes were isolated from rams and bled weekly to quantify the serum levels of progesterone (P-4), tri-iodothyronine (T-3), and tetra-iodothyronine (T-4), using radioimmunoassay. The day-length and ambient temperature were recorded daily. The lowest overall mean of P-4 level was recorded in winter; whereas, no differences were found among those of other seasons. The overall mean values of serum T-3 level were comparable in spring, autumn, and winter, being higher than that recorded in summer. The highest mean value of T-4 level was found in winter and the lowest ones were observed in spring and summer with that of autumn lying between these extremes. The weekly variation of P-4 level showed a decreasing trend towards the end of the trial, where the highest P-4 levels were found in late May and September and the lowest one was noted in mid March. Interestingly, individual weekly records of P-4 for each ewe revealed that none of the animals studied showed an 8-week or longer period wherein P-4 level fell below 1 ng/mL, the threshold reported for anestrous status. Although T-3 levels had a steady trend, serum T-4 showed an increasing trend as the trial proceeded, with the highest and lowest records found in January and July, respectively. Correlation coefficients between serum P-4. T-3, and T-4 levels with day-length were +0.21, -0.25, and -0.42, respectively. The corresponding values with ambient temperature were +0.30, -0.57, and -0.84 for P-4, T-3, and T-4, respectively. Data suggested that despite reproducing in a mid-latitude temperate region, Dalagh ewes showed a continuous cyclicity in ovarian activity throughout the year that would be beneficial to exploit it in breeding schemes to decrease seasonality at mid or possibly high latitudes. Future studies may be interested in searching for the underlying mechanism(s) involved.

• 出版日期2014-2