Does oral administration of the amino acid tyrosine affect oestradiol-17ß concentration and sexual behaviour in the bitch?

The oral administration of the amino acid, tyrosine, has been for years recommended in order to improve fertility, especially to improve copulation behaviour in female dogs. However, evidence is comparatively poor. The objective of our study was to determine whether oral administration of tyrosine has an effect on oestradiol-17ß concentrations and the oestrous behaviour in the bitch. Fifty bitches were randomly allocated to one of two treatment groups in which each dog received 100mg/kg/day of either tyrosine or milk sugar orally between Day 3 and Day 9 of heat. Every two to three days, a gynaecological examination was performed and blood samples were taken to determine oestradiol-17ß and progesterone concentrations. The day of ovulation was estimated by clinical findings, and according to the specifications of the laboratory, once progesterone values exceeded 12.7nmol/l. The observed copulation behaviour was not different between the groups. No differences in volume and visual nature of vaginal discharge were observed. At the day of ovulation, mean oestradiol-17ß concentration in the treated group was 163.4pmol/l and 162.2pmol/l in the placebo group, respectively. In conclusion, feeding tyrosine to female dogs between Day 3 and Day 9 of heat did not alter visual signs of heat or copulation behaviour, and did not alter oestradiol-17ß concentration.

[Validity of the use of L-Tyrosine to enhance fertility of female domestic animals. A study on the evidence from the literature]. / Validität des Einsatzes von L-Tyrosin zur Steigerung der Fruchtbarkeit weiblicher Haussäugetiere. Eine Studie zur Evidenz der Literatur.

OBJECTIVE: In order to improve fertility in female domestic animals, especially in bitches, several authors recommend the feeding of the amino acid L-Tyrosine during the follicular phase of the oestrous cycle. The aim of this article was a systematic and statistical analysis of current literature in terms of evidence-based medicine. MATERIALS AND METHODS: Literature research, statistical analysis and classification in levels of evidence. RESULTS: Fifteen German and two English studies on the effect of L-Tyrosine on the fertility in domestic animals were found. The statistical analysis and evaluation of evidence showed that most studies feature methodical deficits and often findings were inconsistent with one another. CONCLUSION AND CLINICAL RELEVANCE: Heterogeneous results indicate a considerable need for further research on the effectiveness and dose of L-Tyrosine to legitimate its appliance in practice.

Follicular cysts and prolonged oestrus in a female dog after administration of a deslorelin implant.

CASE HISTORY: A 7-year-old female Bernese Mountain dog was presented for treatment to prevent oestrus. One 4.7-mg deslorelin implant was injected S/C between the shoulder blades. Three months later, the dog was re-examined because of prolonged oestrus. CLINICAL FINDINGS: Ultrasound showed multiple thin-walled cysts on both ovaries. Blood samples were taken at various intervals during the following weeks. Concentrations of oestradiol and vaginal smears indicated pro-oestrus. Follicle stimulating hormone (FSH) and luteinising hormone (LH) remained at basal concentrations. DIAGNOSIS: Follicular cysts and prolonged oestrus. TREATMENT: Two treatments of 360 IU human chorionic gonadotrophin (hCG) were administered 42 days apart, that induced a partial or complete degeneration of the cysts. However, concentrations of oestradiol rose again within a few weeks. After the second treatment with hCG the bitch developed pyometra. After successful conservative treatment with antibiotics and aglepristone the dog underwent ovariohysterectomy. CLINICAL RELEVANCE: Slow-release biocompatible implants containing deslorelin provide an opportunity for effective contraception for male dogs. Some authors describe deslorelin also as safe and efficacious for the use in female dogs but those recommendations are derived from few studies, with a small number of animals. Based on the outcome of this case and the experience of other authors we suggest a complete gynaecological examination be performed before implanting deslorelin, and weighing the risks against the advantages in controlling fertility. It is well known that the risk of induction of oestrus can be reduced when implants are administered at concentrations of progesterone in plasma of ≥16.0 pmol/L. The implant should be administered S/C, cranial and close to the umbilicus, to have the option of relocation and excision if necessary.