**Background:** Cashmere production is economically important, and photoperiod manipulation is known to influence cashmere growth in goats. However, the impact of light-controlled housing on indoor air quality, specifically concentrations of harmful gases like CO₂ and NH₃, has been largely overlooked. This study aimed to evaluate both the cashmere growth benefits and the environmental gas parameter changes in a light-controlled goat house.
**Methods:** The experiment was conducted at a breeding farm in Hengshan District, Shaanxi Province, China (latitude 37°38′ N, longitude 109°12′ E, altitude 1487 m). One hundred and thirty female non-pregnant Shanbei white cashmere goats, aged 4–5 years with similar body weights (control mean 47.36 kg, treatment mean 46.08 kg; p = 0.87), were randomly allocated into a control group (n=65) and a treatment group (n=65). Both groups received the same diet (concentrate to roughage ratio 4:6). The control group was exposed to natural light and free movement all day. The treatment group received light for only 7 hours daily (9:30–16:30) and was kept in darkness (<0.1 Lx) from 16:30 to 9:30 the next day, from 15 May to 15 October 2015. A 7-day adaptation period preceded the formal experiment. Harmful gas parameters (CO₂ and NH₃) were recorded dynamically from 16 May to 22 September 2015 using a multi-channel gas analyzer, with three monitoring points per goat house and one outdoor point. Cashmere samples were collected from five goats per group in October 2015 and again in April 2016. Cashmere weight, wool weight, and straightened fiber length were measured. Statistical analysis used t-tests in SPSS 20.0, with p < 0.05 considered significant.
**Key Results:** Short photoperiod treatment significantly increased cashmere production. In October samples, the treatment group showed a 23.1% increase in mixed cashmere and wool weight (723.0 g vs. 587.5 g, p = 0.030), a 57.3% increase in cashmere weight (302.7 g vs. 192.4 g, p = 0.049), and a 23.8% increase in cashmere fiber length (6.20 cm vs. 5.01 cm, p = 0.023) compared to controls. In April samples, increases were 13.2% for mixed weight (1252.4 g vs. 1106.9 g, p = 0.021), 18.8% for cashmere weight (589.7 g vs. 496.4 g, p = 0.024), and 7.7% for fiber length (9.80 cm vs. 9.10 cm, p = 0.044). The annual cashmere yield was significantly higher in the treatment group (755.1 g vs. 561.5 g, p = 0.007), representing a 34.5% increase. The cashmere-to-wool ratio improved but did not reach statistical significance (p > 0.05). Regarding harmful gases, the treatment group had markedly higher CO₂ and NH₃ concentrations than the control and outdoor points. All-day CO₂ ranged from 0.07–0.16% in the treatment group vs. 0.02–0.04% in controls. During the dark period, CO₂ in the treatment group reached 0.09–0.29%, corresponding to an average of 3734 mg/m³, far exceeding the Chinese livestock standard of 1500 mg/m³. NH₃ concentrations in the treatment group ranged from 7.1–15.9 ppm all-day and 8.1–20.3 ppm during dark periods, compared to 2.5–8.7 ppm (all-day) and 3.6–10.2 ppm (dark) in controls. The NH₃ concentration did not exceed the cowshed standard of 20 mg/m³. CO₂ concentration changes after opening the door at 9:30 followed a logarithmic function (Y = −0.033 ln(X) − 0.0651), and after closing at 16:30 followed a power function (Y = 0.4368X^0.3834). NH₃ showed seasonal variation, decreasing from June to September during dark periods.
**Clinical Implications:** Short photoperiod treatment is an effective, low-cost method to significantly increase cashmere yield and fiber length in Shanbei white cashmere goats. However, the resulting accumulation of harmful gases, particularly CO₂, in light-controlled goat houses poses a health risk to animals, potentially causing hypoxia, respiratory disease, and reduced productivity. The study recommends increasing ventilation, especially during dark periods and high-temperature seasons, and possibly reducing feeding density to maintain air quality. The mathematical models of gas concentration changes can inform ventilation scheduling. Further research is needed to establish species-specific air quality standards for goats and to develop more precise gas change models for light-controlled housing systems.