Beef cow–calf production system integrated with sugarcane production: Simulation model development and application in Japan

The objective of this study was to develop a simulation model for the integration of a beef cow–calf production system and sugarcane production system on Tanegashima Island. A survey was carried out to characterize and identify the role of sugarcane as an alternative feed resource and determine the different interactions within the system. The model was divided into two sub-systems; beef cow–calf and sugarcane and manure production sub-systems. The model is able to simulate the total requirement for energy and protein, and subsequent losses of nitrogen via faeces and urine, throughout the reproductive cycle of a mature cow and the growing stages of her calf. It also estimates the area under sugarcane cultivation for feed and the area on which manure can be applied to complement inorganic fertilizer. A linear programming (LP) approach was used to formulate the least-cost diet and a system simulation method was used to calculate the nitrogen (N) excretion for a cow and her post-weaning calf in the different physiological stages. The model was used to evaluate two scenarios (integrated and specialized scenarios) using production conditions on Tanegashima Island. In the integrated scenario, sugarcane tops were the principal roughage source and organic (manure) was used to complement inorganic fertilizer. In the specialized scenario, Italian ryegrass was the principal feed source and manure was not used. These two scenarios were compared based on the respective feed and fertilizer costs, and the difference between the two scenarios was evaluated as the merit of integration. Sensitivity analyses were also performed to determine the effects of changes in nutritional and management conditions, animal genotype parameters and manure variables on economic variables. The results showed that feed and fertilizer costs were lower in the integrated than in the specialized scenario. Economic variables were sensitive to changes in feeding strategies, especially the metabolizability of feed, days of availability of sugarcane tops, mature liveweight, and manure variables. Utilization of sugarcane tops and manure is economically feasible under the conditions on Tanegashima Island. It is proposed that the developed model is capable of evaluating the biological and economic interaction of beef cow–calf production and sugarcane production systems.