Geese are the oldest domesticated poultry species whose domestication dates back 7,000 years [1] and they are seasonal breeding animals regulated by natural light [2]. Taiwan is located in a subtropical region with high temperatures and humidity. In the Changhua county, for instance, the egg-laying period of female geese in the natural environment is approximately from the beginning of October to the end of May of the following year, and the sunshine time (between sunrise and sunset) is 11 hours and 56 minutes and 13 hours and 31 minutes, respectively. However, during the egg-laying period of female geese, the sunshine time is at its shortest, at 10 hours and 39 minutes on December 22 [3]. Under natural conditions, the egg-laying rate of female geese shows a curve reaction. Influenced by sunlight and temperature in the natural environment, the egg-laying period of Taiwanese female geese is from the beginning of October to the end of May of the following year. In addition, the productive period is from January to March, while the rest period is from June to September [4].

The proportion of goose weight loss may influence the uniformity of laying geese in the next laying period [4]. Bogenfürst et al [5] suggested that feeding geese should be restricted to reduce their body weight to less than 4.75 kg, which can increase the number of eggs laid per goose and the fertilization rate of eggs in the next laying period. Therefore, breeding geese are given restricted rations during and before the laying period, mainly to avoid over-fat geese and delay their production. Breeding geese weigh approximately 3.5 kg during the off-production period and can reach 4.9 kg when fed with egg-laying material from the start of production to the peak of egg-laying. In a study, the body weight of primiparous female geese was 3.27 to 3.83 kg during the rest period, 4.78 to 5.01 kg at the peak egg production, and 4.61 to 5.11 kg at the end of the experiment [6]. The above data demonstrated that breeding geese should be fed at an appropriate time during the laying off period to control their weight, considering that excess and lack of weight may influence their egg-laying performance during the laying period.

In high-yielding geese the serum estradiol, glucose, and triglyceride concentrations are high and they have significant pubic spacing and abdominal circumference [7]. The body scoring method is applied to waterfowl and swans, which allows one to avoid grasping animals to repeatedly check the weight of individual animals and other data. In addition, it roughly examines the animal’s current weight and internal tissue changes to predict when the breeding geese start to lay eggs [8,9].

The body weight, muscle mass, and tibial parameters of geese after 28 d vary according to sex [10]. Lipid and protein stores are determined as an index of body condition in arctic geese. Protein stores are more stable than lipids, which change with migration. The geese could increase endogenous lipid stores when they intake enough food resources [11]. Further, Pacific greater fronted geese have a nonlinear change in body conditions. They adapt to their migration area and adjust their body conditions accordingly [12]. A study found that gandersin the breeding stages had heavier testicular weights than those of the non-breeding stages [13]. According to Madsen and Klaassen’s abdominal profile index (API) scoring method, it is possible to distinguish the body changes of breeding geese during the laying process. Notably, the API range of pink-footed geese can range from 0 to 7 points. Further, animal physiology and nutritional status are related to body and organ weights. Landers et al [14] suggested that the heart and liver weights of geese treated with restricted feeding are significantly lighter than those in the free-feeding group. With adequate nutrition, geese gradually gain weight and accumulate body fat for reproduction and growth. Hence, body part percentages and organ weights change accordingly. Before the breeding season, geese need to gradually accumulate their energy prior to breeding. During the breeding season, its reproductive system develops with the season and physiology. Once laying commences the weight of the chicken and its oviduct and ovary are heavier [15,16]. On the other hand, tissue development in turkeys prior to laying has demonstrated that oviducts develop faster than ovaries by 3 days [17]. On the male side, the penis size of various poultry species varies greatly—the ostrich’s penis length is 30.1 cm, and its weight is 870 g [6]; the male duck’s penis length is 22.3 cm, and its penis weight is 10.8 g [18]. Some waterfowl species are seasonal animals, and there is little information on the development status before and after the breeding season. In this study, the goose body posture method was utilized to evaluate the reproductive system development during egg-laying to uncover the correlation between the observation index and the reproductive system and predict the reproductive system changes of the goose during the egg-laying period.

Hocking and Duff [20] suggested that the excess body weight of males could influence the fertilization rate of their eggs. The results of this study differ from the above studies that infer that the body weight of breeding geese should be controlled during the laying off period. Hence, the feeding method of the male goose during the laying off period needs to be adjusted, and the weight of the breeding male goose should be controlled below 4.75 kg. Although the weight control of the breeding male goose during the laying off period can influence the reproductive performance of the laying goose, this aspect still requires further research. The weight of the male geese in this survey reached 5.25 kg before the breeding season, demonstrating that the feeding restriction rhythm during the lay-off period has not reached the expected target.

The increase in light stimulation during the growing period of broiler males could significantly increase the testicular weight, follicle-stimulating hormone, and testosterone content. However, there is no regression relationship between testicular weight and body weight, mainly because the testicular weight of cocks has a significant variation (i.e., 4 to 5 kg–rooster’s testicles weigh 0.9 to 44 g) [21]. The long and short diameters of the left testis of Argentine lake duck are 37 to 45 mm and 15 to 20 mm, respectively, and the long and short diameters of the right testis are 37 to 43 mm and 14 to 22 mm, respectively. The testicular weight is 10.8 g, accounting for about 1.7% of the body weight. McCracken [18] suggested that the penis length of a male duck is 22.3 cm. However, the current literature has not yet compared the changes in the developmental process of the reproductive system throughout the breeding season. Gumułka et al [13] indicated that the right testis weight at the onset of laying weighs heavier than in the non-breeding stage (6.8 g vs 1.7 g, p<0.05). The left testis weight at the onset of laying and breeding (April) weighed heavier than in the non-breeding stage (9.8 g and 8.2 g vs 1.7 g). The serum sex hormone levels of the ganders at various reproductive stages are presented. This study demonstrated that the testicular weight, the short diameter of the testis, and the testicular weight in the breeding season accounted for the percentage of the carcass weight, illustrating a curvilinear response. The egg-laying period of geese is from the beginning of October to the end of May of the following year, and its most productive period is from January to March in Taiwan [4]. This finding indicates that the growth rate of testicles of male geese is similar to the egg-laying curve of female geese. This phenomenon may have a significant impact on the fertilization rate of breeding geese.

Tome [22] suggested that the body weight of ruddy ducks before laying eggs could increase by 21% of the original body weight, which mainly accumulates fat for the energy source required for laying eggs.

Bogenfürst et al [5] implied that feeding geese should be restricted to make their body weight less than 4.75 kg, which could increase the number of eggs laid per goose and the fertilization rate of eggs in the next laying period. Free-feeding birds can result in lower egg production, poor feed efficiency, heavier body weight, and heavier egg weight [23]. Renema et al [15] indicated that ovarian weight was positively correlated with body weight and abdominal fat mass. The number of 2 to 3 cm follicles in female geese in the first month after laying is significantly higher than that in the second and first months before laying and in the fourth and fifth months after laying (1.4 vs 0, 0.40; 0.60, 0 and 0.20 egg/bird; p = 0.0074), implying a quadratic equation (p<0.001). The percentage of ovarian weight to carcass weight of female geese in the second and third months after laying was significantly higher than that in the second month before laying and the third and fourth months after laying (2.2 and 3.21 vs 0.08, 0.21, and 0.11%; p = 0.0139), implying a quadratic equation (p<0.01). The ovary weights of hens during the laying period were 200% heavier than that of unlighted hens before laying, whose fallopian tube weights were also significantly increased [17]. Guangdong geese have 10 small and large yellow follicles before laying eggs, and about 8 of them will ovulate and be laid [24]. The ovary weight of hens before laying was significantly lighter when laying the first egg, and the number of large follicles in hens when laying the first egg was significantly higher than that before laying [25]. The number of small and large yellow follicles at the beginning of egg-laying of geese was significantly higher than that at the end of hatching, and the number of small and large yellow follicles at the beginning and peak of egg-laying of geese was also significantly higher than that at the end of egg-laying [24]. The above research shows that the weight and length of the reproductive tract of poultry increase as they enter the laying stage. The data of this experiment are similar to the above data. The reproductive system of the female goose has apparent changes in preparation for laying eggs in the laying stage before the end of egg-laying. The reproductive system also has apparent shrinkage; in the number of follicles, it can be seen that the number of follicles at the peak of egg-laying is higher than that at the end of egg-laying.

The growth equation involved the body weight, weight gain, feed consumption, and feed conversion efficiency of white and grey geese from China [26]. The API range of the pink-footed goose used by Madsen and Klaassen [8] can be broadly classified as 0 to 7, which is less difficult in distinguishing the abdominal classification of the Roman. Observing the relationship between the male goose and the reproductive system using API and ASI is not easy. However, these methods can be applied to the reproductive system observation of female geese. The correlation between ASI and the reproductive system of female geese during the laying period is high, and the net correlation coefficient between it and the laying rate is 0.790, indicating that the ASI observation in female geese during the laying period can be used to predict the reproductive system of female geese during the laying period. The system changes and their correlation with egg production are the findings of this study. In the future, this method can be used to predict the commencement of female goose egg production.

The goose observations can take advantage of ASI during egg-laying. It can predict the reproductive system development during laying and determine when breeding geese begin to lay eggs. In particular, female ASI was positively correlated with the reproductive tract length and egg production per female. Based on the above findings, the ASI classification method was more objective and easy to distinguish. This scoring method has a high correlation with the number of eggs laid by each goose and the length of the reproductive tract.