|ERICKSON, MARYGRACE - University Of Wisconsin|
|WATTIAUX, MICHEL - University Of Wisconsin|
Submitted to: American Dairy Science Association (ADSA) - American Society of Animal Science (ASAS) Joint Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 3/8/2022
Publication Date: N/A
Technical Abstract: Limited research has assessed nitrogen (N) partitioning in relation to dietary crude protein (CP) level and feeding pattern. To test a hypothesized interaction, we examined eight mid- to late-lactation Holsteins (Mean = 142, SD = 23 DIM) in a Latin Rectangle with 2x2 factorial treatments CP level (Low Protein:LP, 13.9%; High Protein:HP, 15.4%) and feeding pattern (O = oscillating, S = static). O alternated two diets (O-LP 12.2-15.5%, O-HP 13.9-16.9% CP) every 48 hr so mean diet composition equaled that of corresponding S treatments (S-LP, S-HP). Diets exchanged soy hulls and ground corn with solvent soybean meal to maintain constant ratios of neutral detergent fiber (NDF) to starch (1.18), rumen-degradable protein:CP (0.61), and forage:concentrate (60:40). Each 28-d period on d 25-28, we weighed and sampled total collections (three times daily) of feces and urine and collected samples of milk (two times daily) and orts (once daily). We analyzed feed and feces composites and individual urine samples. We fit linear mixed models with fixed CP level, feeding pattern, and period effects, and a random intercept for cow; computing model-implied means and standard errors (SEM). Neither CP level, feeding pattern, nor the interaction affected production of milk (38.9 ± 1.9 kg/d) or fat-protein-corrected milk (37.1 ± 1.4 kg/d). Neither CP level, feeding pattern nor the interaction affected dry matter intake (24.9 ± 0.9 kg/d) or apparent total tract digestibility of neutral detergent fiber (aNDFom; 56.4 ± 1.4%) or organic matter (72.9 ± 0.8%). Relative to LP, HP increased N intake (543 vs. 625 g/d, SEM = 23) and urine N (153 vs. 207 g/d, SEM = 7), and tended to increase fecal N (185 vs. 202 g/d, SEM = 8). Neither CP level, feeding pattern, nor the interaction affected milk N (178.0 ± 6.6 g/d), N digestibility (69.6 ± 0.6%), or apparent N balance (38.6 ± 11.3 g/d). Compared to LP, HP reduced N use efficiency (32.6 vs. 29.1%; SEM = 1.2) and increased N intake allocated to urine (28.4 vs. 33.5%; SEM = 0.8) both of which were unaffected by feeding pattern or the interaction. Results showed CP level affected N partitioning regardless of feeding pattern, which had minimal effects.