This study provides a quantitative evaluation of dietary and other factors that influence the production outputs critical to the profitability and environmental sustainability of cattle production in feedlots. There is a particular focus on the effects of dietary protein and nitrogen intake, evaluated using different methods, on the production performance and on the retention and loss of these dietary components. Initial searches identified more than 20,000 studies. After screening for suitability, studies were extracted into a large database of 77 studies using NDS software (RUM&N Sas, Italy) containing Cornell Net Protein and Carbohydrate Systems (CNCPS 6.55) protein estimation methods, crude protein (CP), estimates of rumen degradable and undegradable protein (RDP and RUP), and metabolisable protein (MP) derived from NRC (2000) level 1. Papers containing detail of nitrogen retention and loss provided a set of 20 studies.
There were three data sets established that addressed: production responses using classical meta-analytical methods; lean muscle yield (LMY) using mixed models regression and; nitrogen retention and loss using classical meta-analytical methods. The data sets contained mutual studies, but the study content differed markedly between the production responses and the nitrogen balance studies and the latter included Latin square studies, whereas the other two data sets did not.