|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 examined the interaction between dietary crude protein (CP) level and feeding pattern. We examined 16 mid- to late-lactation Holstein cows (Mean = 133, SD = 21 days in milk) in a 2x2 factorial experiment of CP level (LP, 13.9%; HP, 15.4%) and feeding pattern (O = oscillating, S = static). Cows were housed in tie-stalls and fed a total mixed ration once daily. Formulated diets had constant ratios of neutral detergent fiber to starch (1.18), rumen-degradable protein (RDP):CP (0.61), and forage-to-concentrate ratio (60:40), exchanging soy hulls and ground corn with solvent soybean meal. O alternated two diets (O-HP 13.9-16.9%; O-LP 12.2-15.5% CP) every 48 hours so mean diet composition equaled that of the corresponding S treatment (S-HP; S-LP). In four, 28-d periods, eight cannulated and eight non-cannulated cows formed two Latin Rectangles. On d 25-28 of each period, we recorded individual cow feed intake and milk production, took samples of orts (once daily) and milk (twice daily). 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 dry matter intake (25.9 ± 0.6 kg/d), feed efficiency (1.46 ± 0.03) or production (kg/d) of milk (38.5 ± 1.2), fat-protein-corrected milk (37.6 ± 0.9), fat (1.57 ± 0.04), true protein (1.12 ± 0.03), or lactose (1.80 ± 0.06). Milk urea nitrogen (MUN) yield was lesser for LP, with no feeding pattern or interaction effects (O-HP = 4.54, S-HP = 4.68, O-LP = 3.31, S-LP = 3.53 g/d; SEM = 0.16). LP and O decreased MUN concentration with no interaction (O-HP = 11.93, S-HP = 12.46, O-LP = 8.70, S-LP = 9.19 mg/dL; SEM = 0.32). CP level tended to interact with feeding pattern so that milk true protein (%) was greatest for O-HP, with neither main effect observed (O-HP = 2.93, S-HP = 2.89, O-LP = 2.88, S-LP = 2.90%; SEM = 0.04). Neither CP level, feeding pattern, nor the interaction affected concentrations of fat (4.11 ± 0.09%) or lactose (4.66 ± 0.03%). O and LP increased the ratio of daily true protein to MUN production with no interaction (O-HP = 258, S-HP = 239, O-LP = 338, S-LP = 321 g/g; SEM = 10). Results suggested that LP- and O-fed cows allocated more nitrogen to milk true protein and less to MUN without penalizing performance relative to HP and S.