Farm-level Evaluation of Implementing Feeding Best Management Practices on Pennsylvania Dairy Farms
Open Access
- Author:
- Weeks, Holley Lynn
- Graduate Program:
- Animal Science
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- November 17, 2014
- Committee Members:
- Alexander Nikolov Hristov, Thesis Advisor/Co-Advisor
Lisa Holden, Thesis Advisor/Co-Advisor
Clarence Alan Rotz, Thesis Advisor/Co-Advisor - Keywords:
- dairy cattle
best management practices
crude protein
phosphorus
environment
milk urea nitrogen - Abstract:
- Feeding best management practices (BMP) can have a significant impact on the environmental footprint of dairy farms. The objective of this thesis was to evaluate the environmental and productive effects of implementing 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 of milk yield) in central and southeast Pennsylvania participated in this study. A set of four background total mixed ration (TMR), forage, milk, feces, and urine samples, as well as feed intake and production data, were collected from each cooperator farm biweekly between January and March of 2013 (PreBMP period). Feeding BMP were chosen by the producer, including reduction of dietary crude protein (CP; n = 7) and phosphorus (P; n = 3) concentrations, adjusting rations for changes in forage dry matter (DM; n = 10), and group feeding of the lactating herd (n = 2). Following the implementation of applicable feeding BMP, another set of four sampling and data collection events took place between June and August of 2013 (PostBMP period). Data were analyzed using the MIXED procedure of SAS with farm as a random effect. Seven farms reduced dietary CP (from 17.2 to 15.8%; P < 0.001), which resulted in decreased 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 (MUN; 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 concentration (0.83 vs. 0.69%; P = 0.001). Group feeding was implemented on 2 farms and average CP of the lactating rations decreased (from 15.7 to 14.7% (high) or 14.3% (low); P = 0.03 and P = 0.02), which resulted in decreased total urinary N (0.81 to 0.51% (high) or 0.51% (low); P < 0.001 and P < 0.001), urinary urea-N (594 to 398 mg/dL (high) or 384 (low) mg/dL; P < 0.001, respectively), and MUN (17.4 to 13.7 mg/dL; P = 0.03). Dry matter intake (DMI; 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. Environmental effects of implementing feeding BMP were evaluated using the Integrated Farm System Model (IFSM). On farms that reduced dietary CP, nitrogen (N) imported onto the farm (313 vs. 293 kg/ha; P = 0.02), N lost by leaching (53 vs. 49 kg/ha; P = 0.01), N lost by denitrification (15.3 vs. 14.7 kg/ha; P = 0.008), N lost in runoff (1.69 vs. 1.61 kg/ha; P = 0.008), and N concentrate in leachate (22.5 vs. 20.4 ppm; P = 0.01) decreased from PreBMP to PostBMP period. Greenhouse gasses (GHG) emitted by manure (196,083 vs. 191,960 kg/yr; P = 0.003) and feed production (201,207 vs. 195,256 kg/yr; P = 0.02) decreased for farms that reduced dietary CP. On farms that reduced dietary P, P imported onto the farm (24.6 vs. 22.1 kg/ha; P = 0.19), P lost in runoff leachate (1.67 vs. 1.53 kg/ha; P = 0.42), and P buildup in soil (4.43 vs. 2.47 kg/ha; P = 0.22) numerically decreased when evaluated using IFSM from PreBMP to PostBMP period. Environmental effects of implementing group feeding or monitoring forage DM when evaluated using IFSM were minimal from PreBMP to PostBMP period. Milk urea-N is a useful measurement to monitor dietary CP intake and N utilization in lactating dairy cattle. Two experiments were conducted to explore discrepancies in MUN results between three laboratories, one experiment to compare the effect of two preservatives (bronopol and Broad Spectrum Microtabs II; BSM) on MUN, and one experiment to evaluate MUN with increasing levels of bronopol. In experiment 1, 10 milk samples, collected over five consecutive days, were sent to three milk processing laboratories. Average MUN differed (P < 0.001 to P = 0.05) between Laboratory A (14.9 ± 0.40 mg/dL), Laboratory B (6.5 ± 0.17 mg/dL), and Laboratory C (7.4 ± 0.36 mg/dL). In experiment 2, milk samples were spiked with urea at 0, 17.2, 34.2, and 51.5 mg urea/dL of milk. Two 35-mL samples from each urea level were sent to three laboratories. Average analyzed MUN was higher than expected for Laboratory A (23.2 vs. 21.0 mg/dL; P = 0.001), Laboratory B (18.0 vs. 13.3 mg/dL; P < 0.001), and Laboratory C (20.6 vs.15.2 mg/dL; P < 0.001). In experiment 3, three samples of control (without preservative), milk preserved with bronopol, and milk preserved with BSM were sent to Laboratory A and two samples of both bronopol and BSM were sent to Laboratory B. Milk urea-N results from Laboratory A differed (P < 0.01) between control (9.2 mg/dL), BSM (9.7 mg/dL), and bronopol (11.2 mg/dL), however, no difference (P = 0.60) in MUN was observed between bronopol and BSM at Laboratory B. In experiment 4, milk samples contained 0 to 0.30 g of bronopol and ranged in MUN concentration from 7.7 to 11.9 ± 0.27 mg/dL on Foss 4000 and from 9.0 to 9.3 ± 0.05 mg/dL on CL10, respectively. In summary, implementing one or more feeding BMP did not affect average DMI or milk yield of the cows, but reduced N and P excretions on commercial dairy farms in Pennsylvania, and consequently had a positive impact on the environment. Milk urea-N concentrations may vary depending on type and amount of preservative, analytical procedures, laboratory, and equipment used to measure MUN concentrations.