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ARS Home » Plains Area » Bushland, Texas » Conservation and Production Research Laboratory » Livestock Nutrient Management Research » Research » Publications at this Location » Publication #243602
Title: Nitrogen and phosphorus balance of beef cattle feedyards

Author
item Cole, Noel
item Todd, Richard

Submitted to: Manure Management Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 8/30/2009
Publication Date: 9/28/2009
Citation: Cole, N.A., Todd, R.W. 2009. Nitrogen and phosphorus balance of beef cattle feedyards. In: Proceedings of the Texas Animal Manure Management Issues Conference, September 29-30, 2009, Round Rock, Texas. p. 17-24.

Interpretive Summary: Large quantities of nutrients enter beef cattle feedyards in feed ingredients. These nutrients subsequently 'leave' the yard in finished cattle, manure, or through the atmosphere. A better understanding of the movement of these nutrients would be helpful in developing nutrient management plans and technologies to capture more of these nutrients in a usable form (i.e. the animal carcass and manure fertilizer). To that end, we obtained samples of diets, fresh feces, and air dried manure at two commercial feedyards in the Texas Panhandle over a year. The samples were analyzed for nitrogen and phosphorus. The feedyards provided us with information on cattle head counts, body weights, and feed consumption. We then calculated a nitrogen and a phosphorus balance for the feedyards using a combination of chemical analyses and mathematical equations in the National Research Council – Nutrient Requirements of Beef Cattle (2000) publication. Daily nitrogen consumption averaged 164.7 kg /1000 head and daily nitrogen retention by the animals averaged 23.3 kg/1000 head. Approximately 141.4 kg of nitrogen was excreted daily per 1000 head of which 36% was in feces and 64% was in urine. Approximately 41% of nitrogen fed was subsequently captured in manure. Twenty five (winter) to 58% (summer)(mean 44.3%) of fed nitrogen was apparently lost via volatilization, most likely as ammonia. When dietary protein intake exceeded the animal requirements losses of nitrogen via volatilization increased as nitrogen intake increased. Daily P intake averaged 28.9 kg /1,000 head. Approximately 23.1 kg of P was excreted daily per 1,000 head; 63% in feces and 37% in urine. The quantities of nutrients lost via volatilization and captured in the manure were affected by the diet and season of the year.

Technical Abstract: Large quantities of nutrients enter beef cattle feedyards in feed ingredients. These nutrients subsequently 'leave' the yard in finished cattle, manure, or through the atmosphere. A better understanding of the movement of these nutrients would be helpful in developing nutrient management plans and technologies to capture more of these nutrients in usable form. To that end, diet, fresh feces, and air dried manure samples were collected monthly at two commercial feedyards in the Texas Panhandle over a year. The feedyards provided data on cattle head counts, body weights, and feed consumption. Nitrogen (N) and phosphorus (P) retention were calculated using National Research Council (NRC, 1996) equations. Diet digestibility was calculated using acid insoluble ash as an indigestible marker. Urinary N and P excretion were determined by difference and N volatilization losses were estimated via the change in the N:P ratio between the diet and air-dried manure, and as N unaccounted for in the total N balance. Daily N intake averaged 164.7 kg /1000 head and daily N retention averaged 23.3 kg/1000 head. Approximately 141.4 kg of N was excreted daily per 1000 head of which 51.0 kg (36% of excreted) was in feces and 90.4 kg (64%) was in urine. Approximately 66.9 kg (41% of N intake) was subsequently captured in manure. Of the N intake, 25% (winter) to 58% (summer)(mean 44.3%) was apparently lost via volatilization. When metabolizable protein (MP) intake exceeded animal requirements N volatilization losses increased linearly (r**2 = 0.53: P < 0.001). Daily P intake averaged 28.9 kg /1,000 head and daily P retention averaged 5.7 kg/1,000 head. Approximately 23.1 kg of P was excreted daily per 1,000 head; 14.5 kg (63 % of excreted) in feces and 8.6 kg (37% of excreted) in urine. Excretion and volatilization losses were affected by feedyard diet and season.