Postponement of canine puberty by neonatal administration of a long term release GnRH superagonist.

The objective of this study was to assess the efficiency and clinical safety of postnatal administration of a GnRH agonist on canine puberty postponement. Sexual steroids and histological gonadal changes were also described. Twenty-four littermate puppies were randomly assigned to: Deslorelin acetate 18.8 mg sc (DESLO; n = 12) or Placebo: sc (PLACE; n = 12) postnatally. The dogs were clinically and endocrinologically followed up until puberty when they were gonadectomized and their gonads histomorphometrically studied. Deslorelin postponed the age of puberty (72.7 ±â€¯4.8 vs. 35.8 ±â€¯1.9 weeks; P < 0.01) in these dogs. At the time of this submission, 3 DESLO dogs (108 weeks old) remain non-pubertal. All dogs concluded growing at a similar age (29.75 ±â€¯2.44 vs. 29.25 ±â€¯0.90 weeks; P > 0.1) independently of their group and pubertal status. None of the females had side effects while the 2 non pubertal DESLO males presented bilateral cryptorchydism. All the bitches ovulated at puberty (P > 0.1) and the 2 DESLO that were mated became pregnant. Deslorelin postponed basal serum sexual steroids up to puberty in both genders (P < 0.01). The histomorphometrical study of the testes revealed that the tubular diameter (P < 0.05), germinal epithelium height and composition (P < 0.01) were decreased in DESLO group. Ovarian structures did not differ between treatments (P > 0.05). It was concluded that postnatal deslorelin decreased sexual steroids reversibly postponing puberty in both genders without side effects in bitches and causing 2/6 of cryptorchydism and impairment of testicular histomorphometry in male dogs.

Domestic queens under natural temperate photoperiod do not manifest seasonal anestrus.

Domestic cat seasonality between the tropics and the arctic zones is scarcely described and results are inconsistent. The aim of this study was to describe domestic feline seasonal patterns under a natural temperate photoperiod. A total of 372 estrous cycles were studied in 34 post pubertal cats during 900 days. The queens were housed in a cat colony (31°25' South Latitude, 64°11' West Longitude), acclimated under natural photoperiod and daily observed for reproductive behavior. Vaginal cytology was conducted three times a week. For each cat the number of estrous cycles and days in estrus per month for each year were recorded. The months of the year were grouped in four periods of 3 months each according to day length and photoperiod. Comparisons of estrous days among periods were performed by ANOVA for repeated measures. All the cats had estrous cycles throughout the year without intervals of anestrus. Mean number of estrous days differed among the periods (P<0.01), those of long day length and ascending photoperiod being greater (12.5±0.6) to those of descending photoperiod either with long (8.9±0.7) or short (9.3±0.7) days. When the two periods with ascending day lengths were merged and compared to the two periods with descending day lengths merged, the number of estrous days were greater when day length ascended (P<0.01). Nearly 60% of the estrous cycles occurred during the periods of ascending day length. It is concluded, that domestic cats under natural temperate photoperiod have estrous cycles throughout the year showing peak activity the months with increasing photoperiod.

Long-term melatonin treatment prolongs interestrus, but does not delay puberty, in domestic cats.

The objective was to assess the efficacy and safety of long-term administration of melatonin (either as an implant or given orally) on interestrus intervals in domestic cats. Additionally, the effect of melatonin implants on puberty postponement was studied. For these purposes, two randomized controlled trials were conducted. In the first, 68 interestrus intervals (in 28 postpubertal queens) were studied, and in the second, 32 prepubertal female cats were used. During anovulatory interestrus intervals (27 ovulatory interestrus intervals were excluded), postpubertal cats were assigned to the following three treatments: melatonin implant 18 mg/cat SC (n = 17; MEI); melatonin tablets, 4 mg/cat/d orally until the onset of estrus (n = 12; MEO); or control (n = 12; CTL). Prepubertal females were randomly assigned to the following three treatments: melatonin 18 mg/cat sc implants at either 1.9 ± 0.3 kg (MEI-A; n = 12) or 1.5 ± 0.3 kg (MEI-B; n = 10) body weight; or control (CTL; n = 10). Interestrus intervals in postpubertal MEI, MEO, and CTL groups were 63.8 ± 5.4, 63.0 ± 5.3 and 19.2 ± 1.4 d (P < 0.05), respectively. In these groups, intervals between onset of treatment and the first estrus cycle were 51.0 ± 4.7, 50.0 ± 6.1, and 12.6 ± 1.1 d (P < 0.05). In the second experiment, neither age (MEI-A: 232.4 ± 10.5, MEI-B: 208.6 ± 13.0 and CTL: 192.4 ± 20.1 d; P > 0.1) nor body weight (P > 0.1) at puberty differed among groups. None of the cats in either study had clinically apparent side effects. We concluded that long-term melatonin treatment of domestic cats slightly prolonged interestrus intervals, but did not postpone puberty.