The limited availability of peat-based substrates, a nonrenewable resource, and the negative environmental impacts associated with their extraction require the conservation of this resource. We assessed the use of cattle dung compost as a stand-alone nursery substrate, replacing peat substrate for the production of lettuce (Lactuca sativa L.) seedlings. A completely randomized design was employed, using cattle dung compost (C) and commercial peat (P, control treatment) in various combinations (100% P; 25% C/75% P; 50% C/50% P; 75% C/25% P; 100% C) to assess their effects on different growth parameters of lettuce. Twenty-eight parameters (e.g., seed germination, seedling survival, diameter, height, biomass growth) were assessed, corresponding to the time when the seedlings are transplanted. All treatments achieved 100% seed germination and seedling survival; indicating the successful establishment of lettuce seedlings across all tested substrates. However, seedling growth was found to be significantly influenced by substrate type. Seedling diameter was significantly increased by 10.8% in the 50% C/50% P substrate, while seedling height was significantly increased by 7.7, 6.8, and nearly 10%, respectively, within the 25% C/75% P, 50% C/50% P and 100% C substrates, relative to the control. Other substrate treatments were not significant. Similar or significantly higher values than the control were also observed for biomass growth under the tested substrates, indicating the beneficial effect of cattle dung on the initial growth of plants during the nursery phase. Cattle dung compost, used as a growing substrate, demonstrated similar or superior results to commercial peat, suggesting its potential as a viable alternative potting medium for sustainable horticulture.