Recent advances to improve nitrogen efficiency of grain-finishing cattle in North American and Australian feedlots

Abstract

Formulating diets conservatively for minimum crude-protein (CP) requirements and overfeeding nitrogen (N) is commonplace in grain finishing rations in USA, Canada and Australia. Overfeeding N is considered to be a low-cost and low-risk (to cattle production and health) strategy and is becoming more commonplace in the US with the use of high-N ethanol by-products in finishing diets. However, loss of N from feedlot manure in the form of volatilised ammonia and nitrous oxide, and nitrate contamination of water are of significant environmental concern. Thus, there is a need to improve N-use efficiency of beef cattle production and reduce losses of N to the environment. The most effective approach is to lower N intake of animals through precision feeding, and the application of the metabolisable protein system, including its recent updates to estimation of N supply and recycling. Precision feeding of protein needs to account for variations in the production system, e.g. grain type, liveweight, maturity, use of hormonal growth promotants and β agonists. Opportunities to reduce total N fed to finishing cattle include oscillating supply of dietary CP and reducing supply of CP to better meet cattle requirements (phase feeding).

Genetics and nutrition impacts on herd productivity in the Northern Australian beef cattle production cycle

“… Cowley et al. (2019) proposed that by including minimum crude protein (CP) content and consequently overfeeding nitrogen, a low-cost and low-risk finishing diet would be produced.…”

“…The low rumen degradable protein (RDP) content of corn was subsidised by non-protein nitrogen (NPN) supplementation generating a major surplus of protein. Reports show that Australian finishing diets involve wheat or barley base with protein supplied by cottonseed, or less commonly by canola meal and lupins ( Cowley et al., 2019 ). Dry Distillers Grains (DDG) are high in NDF and low in lignin content, thus providing readily digestible fibre, however, vary in other nutritional composition.…”

“…Dry Distillers Grains (DDG) are high in NDF and low in lignin content, thus providing readily digestible fibre, however, vary in other nutritional composition. Although good sources of protein, calcium, phosphorus and sulphur, DGGs require supplementation due to containing some undesirable components and a minimal soluble carbohydrate fraction ( Cowley et al., 2019 ). A summary of the different nutritional properties of different grain types is presented in Table 1 .…”

“…Growth promoters increase deposition of lean muscle mass, protein accretion and hormone mediated cellular proliferation alongside reducing protein degradation. Cumulatively, this increases dietary requirements for MP during compensatory growth in the early finishing period ( Cowley et al., 2019 ). Beta agonists are thought to increase the requirements of CP by modifying protein metabolism on a cellular level as well as NPN requirements by upregulating protein synthesis ( Cowley et al., 2019 ).…”

Intake, Growth and Carcass Traits of Steers Offered Grass Silage and Concentrates Based on Contrasting Cereal Grain Types Supplemented with Field Beans, Peas or Maize By-Products

“…A key strategy to reduce urinary nitrogen losses is to decrease the concentration of dietary CP [ 34 , 35 ]. In the context of increasing environmental regulations and the relatively high cost of protein feed sources, there is a need to improve nitrogen efficiency in beef production [ 14 , 36 ]. Although there is evidence to suggest that, overall, growth response to protein supplementation in finishing cattle offered grass silage-based diets is small [ 37 ], effects are inconsistent across feeding experiments.…”