Clinical Use of Hormones in the Control of Reproduction in Bitches and QueensProf. Stefano Romagnoli, DVM, MS, PhD, Dipl ECAR
Dipartimento di Scienze Cliniche Veterinarie, Facoltà di Medicina Veterinaria, Università di Padova Legnaro (PD), Italia stefano.romagnoli@unipd.it P: 39-049-827.2948 F: 827.2954 |
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Introduction Synthetic analogues of progesterone, also termed progestins or progestogens (PG), are pharmaceutical compounds commonly used to control the reproductive cycle of domestic animals The following PGs are commonly used in dogs and cats for temporary (starting the treatment shortly before proestrus onset) or prolonged (starting in anestrus) postponement of estrus, or for suppression of estrus (starting the treatment after proestrus onset): medroxyprogesterone acetate (MPA), megestrol acetate (MA), proligestone (PR), chlormadinone acetate (CMA), delmadinone acetate (DMA), norethisterone acetate (NTA) and melengestrol acetate (MGA). From the clinical point of view all these product act in the same way through a block of the production and/or release of GnRH from the hypothalamus. These compounds show a variety of action on the reproductive and endocrine system (such as hyperplasia of the endometrium, hyperplasia of the mammary parenchyma, decreased production of adrenocorticosteroids, increased secretion of prolactin and growth hormone, insulin resistance) as well as some local skin reactions at the injection site and behavioral modification (increased appetite and weight, polydipsia, slight depression, decreased libido in males). In pregnant bitches and queens use of PGs may cause masculinization of female fetuses if administered early in pregnancy (during organogenesis) or delayed parturition if administered in the last decade of pregnancy. Clinical considerations for a safe use of progestogens All the above cited effects are reversible and do not generally cause problems in healthy young to adult animals treated for not too long and using the recommended dosage. In general, a treatment period of 6 months is considered adequate in most individuals, although longer treatments can also be safe provided that the female is given a rest of 1-2 months every 4-6 months. While most bitches and queens may tolerate well treatment periods of more than 6 months, animals with a pre-existing disease such as subclinical diabetes, microscopic mammary lesion/tumor or cystic endometrial hyperplasia may see their condition worsen rapidly as a result of the PG treatment. The following is a series of considerations on patient selection and type of presenting complaint for which a PG treatment should or should not be used.
Choosing the right candidate The ideal candidate is an adult postpuberal female in anestrus. Prepuberal females should not be treated long acting compounds because of the risk of precipitating a subclinical uterine, endocrine or mammary condition (such as diabetes, cystic endometrial hyperplasia-pyometra in the bitch or mammary hyperplasia in the queen) which are rare but have been reported in young animals. If one of the above conditions is present the administration of a long acting progestogen prior to diagnosis may pose a serious health threat on the female. A minimum database of clinical information to be gathered prior to administering a long-acting compound should include:
Table 1. Shows the suggested dosages of the most commonly used progestogen-based compounds in the bitch and queen.
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