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Effect of Thyrotropin-Releasing Hormone on Serum Thyroxine of Lactating Sows and the Growth of their Suckling Young¹

Pig Research Institute, Taiwan, Chunan and and Academia Sinica, Taipei

Abstract

The ability of exogenous thyrotropin releasing hormone (TRH) to stimulate release of pituitary hormones which act directly or indirectly to increase milk production was studied. Thirty-six lactating sows were utilized in an experiment of 3 x 3 factorial design consisting of three levels of litter size (five to six, seven to eight or nine to 10 piglets) and three doses of TRH (0, 50 or 100 µg). Sows were given a daily intramuscular injection of TRH from day 1 to 26 postpartum. Serum thyroxine (T₄) concentration of sows and weaning weight of piglets were determined. Injection of TRH, regardless of dose level, failed to increase serum thyroxine concentrations. The relationship between growth rate of suckling piglets and dose of TRH injected was best described by a quadratic curve with a predictive maximum growth at 60 µg TRH per day. Administration of TRH may have caused the release of prolactin or growth hormone resulting in increased milk production. Failure to detect increases in serum T₄ after TRH injection may have been due to increased demands of the mammary glands for this thyroid hormone.

¹ Supported in part by a grant from Chinese National Science Council to Walter Chia-Mo Wan [Grant No. NSC-63B-0409-03(04)], Institute of Zoology, Academia Sinica, Taipei, Republic of China, part from Pig Research Institute, Taiwan, Chunan, Republic of China. Send reprint request to Dr. W. Chia-Mo Wan.

² Pig Research Institute, Taiwan, Chunan, Republic of China.

³ Biometry Laboratory, Institute of Botany, Academia Sinica, Taipei, Republic of China

⁴ The authors wish to express their thanks for the assistance given by the Animal Industry Research Institute, Taiwan Sugar Corporation. Special thanks are due to Dr. Kai-Chyr Chen, Director and the members of Nuclear Medical Center, Tri-Service General Hospital, Taipei, for making tha Gamma Counting system available for our use in this study.