CASE STUDY: Farm-level evaluation of implementing nitrogen and phosphorus feeding best management practices on Pennsylvania dairy farms

Feeding best management practices (BMP) can have a significant effect on the environmental footprint of dairy farms. This case study was conducted to evaluate the environmental and productive effects of implementing several feeding BMP on commercial dairy farms in Pennsylvania. Fifteen farms (124.8 ± 20.5 ha, 169 ± 39 cows, and 31.4 ± 0.2 kg/d milk yield) participated in the study. Four baseline TMR, forage, milk, feces, and urine samples, as well as feed intake and production data, were collected from each farm every 2 wk between January and March of 2013 (PreBMP period). Feeding BMP were offered, and participating producers chose a set of BMP to implement on their farms, including reduction of dietary CP (n = 7) and P (n = 3) concentrations, adjusting rations for changes in forage DM (n = 10), group feeding of the lactating herd (n = 2), and no use of BMP (n = 3). Following BMP implementation, another 4 sampling and data-collection events took place between June and August of 2013 (PostBMP period). Seven farms reduced dietary CP (from 17.2 to 15.8%; P < 0.001), which resulted in decreased concentrations of total urinary N (0.75 vs. 0.57%; P < 0.001), urinary urea-N (544 vs. 461 mg/dL; P = 0.007), and milk urea-N (16.8 vs. 13.7 mg/dL; P < 0.001) from PreBMP to PostBMP, respectively. Three farms lowered dietary P (from 0.42 to 0.40%; P = 0.06), which resulted in decreased fecal P (0.83 vs. 0.69%; P = 0.001). Dry matter intake (23.3 vs. 22.7 ± 0.46 kg/d; P = 0.05), milk yield (32.7 vs. 31.9 ± 0.76 kg/d; P < 0.001), bulk-tank milk fat (3.91 vs. 3.56%; P < 0.001), and milk protein (3.13 vs. 2.98%; P < 0.001) decreased on all farms from PreBMP to PostBMP period, due to seasonal effects. In conclusion, reduced dietary CP decreased N concentrations in urine, feces, and milk, and reduced dietary P decreased fecal P concentration on commercial dairy farms.