Effect of Slow-Release Urea Administration on Production Performance, Health Status, Diet Digestibility, and Environmental Sustainability in Lactating Dairy Cows

SIMPLE SUMMARY: The dairy system is facing many environmental issues, such as greenhouse gas emissions, land use, and consumption of human-edible raw materials, as well as increased demand for milk by the growing world population. Dairy cow farming must evolve toward more efficient and sustainable methods of production. Strategies to reduce the carbon footprint of the animal feed used and enhance overall productivity should be considered. Feed production, especially soybean meal, represents the second source of total dairy greenhouse gas emissions. Moreover, there is a positive correlation between production efficiency and environmental footprint. Using slow-releasing urea sources as an alternative to soybean meal can enhance rumen efficiency, functionality and reduce emissions related to the feed used due to a lower carbon footprint. ABSTRACT: The effects of partially replacing soybean meal (SBM) with a slow-release urea source (SRU) on production performance, feed efficiency, digestibility, and environmental sustainability of dairy cows were evaluated. A total of 140 lactating Holstein Frisian cows were allocated into two study groups: (i) control (diet entirely based on SBM), and (ii) treatment (diet of 0.22% on dry matter basis (d.m.)) of SRU. Milk yield, dry matter intake (DMI), feed conversion rate (FCR), body condition score (BCS), reproductive parameters, and milk quality were evaluated. The chemical composition of the feeds and feces were analyzed to calculate the in vivo digestibility of the two diets. The carbon footprint (CFP) and predicted methane (CH(4)) emissions were evaluated. The inclusion of SRU significantly increases milk yield, DMI, and FCR (p < 0.0001), whereas milk quality, BCS, and reproductive indicators were not affected (p > 0.05). In the treatment group, the digestibility of crude protein (CP) (p = 0.012), NDF (p = 0.039), and cellulose (p = 0.033) was significantly higher, while the other nutritional parameters weren’t affected. All the environmental parameters were significantly improved in the treatment group (p < 0.0001). Replacing SBM with SRU can be a strategy to enhance dairy cows’ sustainability due to improved production efficiency, reduced feed CFP, and predicted CH(4) production.