Clinical and endocrine study on the causes for failure of heat synchronization in dairy cattle in Thailand
1998
Suneerat Aiumlamai | Chockchai Chaimongkol | Kindahl, Hans (Khon Kaen Univ., Khon Kaen (Thailand). Faculty of Veterinary Medicine. Dept. of Veterinary Surgery and Theriogenology)
Sixty-two European-breed heifers with normal clinical findings at rectal palpation and ultrasound scanning, aged 18-24 months and weighed more than 270 kg were used. A protocol of two intramuscular injections of 25 mg PGF 2 alpha was used 11 days apart to induce oestrus. The animals that did not respond were injected with a third dose of PGF 2 alpha on day 7-12 of the successive oestrous cycle. Clinical examinations and blood samples were taken before and at 24 h and 48 h after each injection and then every 2-3 days throughout the study period and carried out daily in non-responding animals. After the first injection of PGF 2 alpha, 53 percent (33/62) of the animals showed signs of oestrus and were inseminated; 58 percent (19/33) of them became pregnant. Sixty-eight percent (15/22) of the animals responded to the second dose of PGF 2 alpha 11 days later and 60 percent (9/15) became pregnant. A third injection of PGF 2 alpha was given to the seven non-responding animals. Four animals were injected on day 11-12 of the oestrous cycle and responded with signs of oestrus. Three animals were given the injection on day 7-8 of the oestrous cycle and only one animal responded. From the clinical and endocrine outcome of the 7 non-responding animals, 3 reasons of the causes were found. Rebound of progesterone levels was one, administration of the PGF 2 alpha during too early or too late stages of the oestrous cycle was the second and silent heat was the third. The causes for failure of heat synchronization found from this study were in accordance with previous reports.
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