Location: Livestock Nutrient Management Research
Project Number: 3090-31630-006-044-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Aug 1, 2019
End Date: Jul 31, 2022
Objective:
Determine rations of beef cattle in feedyards, beef cattle on pasture, and dairy cows on the Southern High Plains that maximize nutrient retention and decrease nutrient losses in feces, urine and emissions.
Approach:
A 2 × 2 factorial arrangement of treatments was used in a Latin squares design, varying two feed ingredients at two levels from a diet that would be representative of what Texas High Plains feedlots would use. An indirect calorimetry system used throughout the study consisted of 4 chambers under negative pressure. The external dimensions of each chamber were approximately 210 cm high by 244 cm long by 115 cm wide (internal volume of 6,500 L). Each chamber was constructed with 5-cm pipe panel. The panel exterior was covered with clear Lexan (0.6 cm thick). The flooring inside each chamber was made of plastic boards, with a high density polyethylene pan for urine collection. Feces was collected using fecal bags. Each chamber ceiling was made of a sheet of polyvinylchloride approximately 1.3 cm thick. Outside air was pulled into each chamber through 7.6-cm i.d. polyvinylchloride pipe and air outgoing from each chamber was pulled through 5.1-cm i.d. polyvinylchloride pipe to the gas sampling system. An air-conditioning system was located inside each chamber to facilitate air circulation, remove humidity, and maintain the temperature within a thermoneutral range.
Before gas measurements, the system was calibrated for oxygen consumed and carbon dioxide produced by burning absolute ethanol with alcohol lamps. Recoveries averaged 98.99% for O2 and 101.56% for CO2. Before each gas exchange collection period, each gas analyzer (CO2, CH4, O2) was calibrated with commercially prepared gas standards. The chambers were sealed approximately 23 h per day. A minimum of two 23-h runs were used to determine gaseous exchanges for each animal, and in turn used to calculate heat production.
Outdoor air was pulled into the chamber using a mass flow system at a rate of 300 L/min. A sample of outside air was collected as a baseline every 30 minutes, whereas each chamber was sampled for 10 min every hour through the use of an intelligent multiplexer. Relative humidity, air temperature, and barometric pressure were also measured. Air was dried then analyzed for gas concentrations in an open-circuit indirect respiration calorimetry system using paramagnetic and infrared gas analyses. Air flow was measured using the mass flow system. Before gas measurements were taken, each steer was adapted to a respiration chamber by being housed in the chamber for 1-, 2-, 4-, and 6-d blocks of time.
