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Varying forage type, metabolizable protein concentration, and carbohydrate source affects manure excretion, manure ammonia, and nitrogen metabolism of dairy cows

W. P. Weiss^*,1, L. B. Willett^*, N. R. St-Pierre, D. C. Borger^*, T. R. McKelvey^* and D. J. Wyatt^*

^* Department of Animal Sciences, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster 44691
Department of Animal Sciences, Ohio Agricultural Research and Development Center, The Ohio State University, Columbus 43210

¹ Corresponding author: weiss.6{at}osu.edu

Effects of forage source, concentration of metabolizable protein (MP), and type of carbohydrate on manure excretion by dairy cows and production of ammonia from that manure were evaluated using a central composite experimental design. All diets (dry basis) contained 50% forage that ranged from 25:75 to 75:25 alfalfa silage:corn silage. Diets contained 10.7% rumen-degradable protein with variable concentrations of undegradable protein so that dietary MP ranged from 8.8 to 12%. Starch concentration ranged from 22 to 30% with a concomitant decrease in neutral detergent fiber. A total of 15 diets were fed to 36 Holstein cows grouped in 6 blocks. Each block was a replicated 3 x 3 Latin square resulting in 108 observations. Manure output (urine and feces) was measured using total collection, and fresh feces and urine were combined into slurries and incubated for 48 h to measure NH₃-N production. Feces, urine, and manure output averaged 50.5, 29.5, and 80.1 kg/d, respectively. Manure output increased with increasing dry matter intake (~3.5 kg of manure/kg of dry matter intake), increased concentrations of alfalfa (mostly via changes in urine output), and decreased concentrations of starch (mostly via changes in fecal output). The amount of NH₃-N produced per gram of manure decreased with increasing alfalfa because excreted N shifted from urine to feces. Increasing MP increased NH₃-N produced per gram of manure mainly because of increased urinary N, but increased fecal N also contributed to the manure NH₃. Manure NH₃-N production per cow (accounts for effects on manure production and NH₃-N produced per unit of manure) was least and milk protein yields were maximal for diets with high alfalfa (75% of the forage), moderate MP (11% of diet dry matter), and high starch (30% of diet dry matter).

Key Words: dairy cow • manure ammonia • forage • protein

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Varying type of forage, concentration of metabolizable protein, and source of carbohydrate affects nutrient digestibility and production by dairy cows

W. P. Weiss, N. R. St-Pierre, and L. B. Willett
JDS 2009 92: 5595-5606. [Abstract] [Full Text]