Predicting nutritional requirements and lactation performance of dual-purpose cows using a dynamic model

Abstract A dynamic application of the Cornell Net Carbohydrate and Protein System (CNCPS) model was developed to predict annual cycles in animal nutrient requirements and performance of dual-purpose (milk and beef) cows. Interactions from mobilisation and repletion of body tissue reserves and feed biological values are accounted with a time step of one day, which considers physiological status of the animal, variation in dietary composition, and other environmental factors. This outcome was achieved by modifying the input and output structure of the CNCPS version 4.0 to compute body weight and changes in body reserves based on predicted milk production, intake of feed dry matter, and energy balance. The supply of metabolisable energy from dietary intake is supplemented by tissue mobilised to support milk synthesis in early lactation; body tissue is repleted when energy balance is positive. Predicted animal nutrient requirements, milk production, dry matter intake, and changes in body weight and body condition score over the reproductive cycle were consistent with patterns and values in published reports and field observations in the Gulf Coast of Mexico case study region. Our simulations showed that a dynamic application of the CNCPS facilitates more accurate monitoring and management of cyclic changes in energy and protein balances over the calving interval of dual-purpose cows, which can help producers to achieve productivity and profitability goals.