Collect breast milk samples in various administrative regions of China to measure the nutrients in breast milk; analyze the composition of nutrients; and establish the database of breast milk in China.

The study cities are Guangzhou, Weihai, Chengdu, Beijing, Harbin, Wuhan, Jinhua, Zhengzhou and Lanzhou.

Breast milk will be collected at 9:00-11:00 in the morning from 15 to180 days after giving birth. The nutrients (protein, triglyceride, phospholipid, oligosaccharides and probiotics) in the collected breast milk samples will be measured. These data will be used to establish the breast milk database in China. This databased will provide references for infant nutrient intake and for the formulation and revision of infant formula standards. It will also provide references for the development of new infant formula products in China.

Inclusion Criteria:

• Lactating mother 25 ~ 35 years old;
• Breast-feeding infants (15 ~180 days old );
• Physically healthy by self-evaluation;
• Does not smoke;
• Does not drink alcohol;
• Have given birth to physically healthy infants;
• Signed the informed consent forms.

Exclusion Criteria:

• Being treated for gastrointestinal symptoms;
• Suffering from mastitis;
• Suffering from infectious diseases (tuberculosis, viral hepatitis and HIV infection);
• Suffering from cardiovascular disease;
• Suffering from metabolic diseases (such as diabetes);
• Suffering from mental system diseases;
• Suffering from cancer and other malignant diseases;
• Having history of taking antibiotics;
• Not able to answer the study questions;
• Participating in any nutritional or pharmaceutical intervention study recently.

Healthy lactating mother of 25 ~ 35 years old who are currently breast-feeding infants of 15 ~180 days old. Subjects are equally distributed in the postpartum time period of 15~35 days, 36~65 days, 66~95 days, 96~125 days, 126~55 days and 156~185 days