Estrus in dogs refers to the periodic physiological and behavioral changes exhibited by dogs after reaching sexual maturity under the hormonal control of the hypothalamus-pituitary-gonadal axis. Dogs are seasonal mono-estrus or diestrus animals, typically showing estrus in the spring and autumn of each year. However, due to the unique reproductive physiology of dogs, the ovulation time of different breeds varies greatly. In addition, the ova excreted after ovulation in dogs are immature and need to develop in the body for a period of time before they are fertile. This specificity of the reproductive cycle in dogs poses significant challenges for dog breeding work.
1.1 Materials
A total of 222 female dogs in estrus who underwent progesterone monitoring at the Teaching Animal Hospital of China Agricultural University from October 2014 to May 2015 were selected. VIDASProgesterone progesterone detection kit (enzyme-linked fluorescence method) was purchased from BioMérieux Diagnostic Products (Shanghai) Co., Ltd.; Eppendorf pipettor; miniVIDAS.
1.2 Estrus Status
All dogs in the study were considered to be in the early stages of estrus based on the observation of the owners, marked by the appearance of swollen vulva and bloody secretions.
1.3 Determination of Serum Progesterone
1.5 ml of blood was collected from the hind limb saphenous vein, centrifuged at 3500 rpm for 5 minutes to separate the serum for use.
- Results
2.1 Age Distribution
As shown in Table 1, 34.5% of the dogs who underwent progesterone testing during the survey were under 1 year old, typically experiencing their first estrus. Among them, German Shepherd dogs accounted for more than half (52.9%) of this breed. The majority of dogs tested for progesterone were between 1 and 5 years old, accounting for 55.9% of the total. A small proportion (9.5%) of dogs were over 5 years old.
2.2 Breed Distribution
The survey results indicate that the majority of dogs undergoing progesterone testing during the study period were large breeds, with Tibetan Mastiffs accounting for 70.5%. Approximately 23.2% were German Shepherd dogs. Other breeds included Pit Bulls, Doberman Pinschers, Golden Retrievers, Greyhounds, Labrador Retrievers, Poodles/Teddy Bears, Pekingese, and other small to medium-sized breeds.
2.3 Serum Progesterone Levels
During the study period, a total of 220 dogs from the animal hospital were effectively included in the analysis. It was found that Tibetan Mastiffs in breeding farms generally undergo artificial insemination for reproduction. When the progesterone levels of Tibetan Mastiffs (N=155) were between 10-30 ng/ml, the breeding success rate was greater than 70%, showing a significant difference compared to other range groups. Notably, when the serum progesterone levels of Tibetan Mastiffs reached the range of 20-30 ng/ml, the breeding success rate exceeded 80%.
On the other hand, German Shepherd breeding farms adopt a combination of artificial insemination and natural mating. The statistical results indicate that when the progesterone levels of German Shepherd dogs (N=51) were within the range of 10-20 ng/ml, the overall breeding success rate was the highest compared to other groups, showing significant differences among the groups.
2.4 Optimal Breeding Time
Breeders typically consider the first day of bloody secretions from the vulva as the start of estrus. Based on the relationship between the number of estrus days and progesterone levels in Tibetan Mastiffs, it was observed that the serum progesterone levels of Tibetan Mastiffs typically reached the optimal breeding range around 10-15 days into estrus. The statistical data is presented in Figure 3, with the data points between the two dashed lines indicating the optimal range of serum progesterone levels for conception in Tibetan Mastiffs.
Statistical data also indicates that German Shepherd dogs typically have their serum progesterone levels rise above 10 ng/ml, reaching the optimal breeding range, around 9-14 days after the appearance of bloody secretions.