A Composite Model of Growth, Pregnancy and Lactation

摘要

Mathematical models of pre- and postnatal growth, pregnancy and lactation were combined and implemented using object-orientated computer code to form an energy-based model of a dairy cow. Each simulated cow 'grows', can have a computer pregnancy withmultiple offspring, growing its fetuses to term, and 'lactates' at parturition. Each fetus is implemented as a separate entity and thus, after birth, is also capable of growth, pregnancy and lactation. Every cow (and fetus) can have different genetics, allowing the evolution of a herd over time to be modelled. The model uses dynamic energy partitioning between growth, pregnancy and lactation in a manner sensitive to intake. Additionally, milk production is sensitive to milking frequency (MF), and fetalgrowth is sensitive to number of siblings.The model was fitted to milk yield (MY) and live weight (LW) data from 82 Hoi-stein x Friesian cows on an individual cow basis, with up to 3 consecutive years of data for each cow. The model had R2 values of 0.57 for LW and 0.88 for MY. The parameterizedmodel proved useful for simulating the effects of management decisions either on a single animal or at a herd level. Results are presented from previous studies, which used the model to investigate the outcomes of different MFs under different nutritional scenarios, and as part of a decision-making tool for manipulating MF and feed to optimize profit in a pasture-based system. Additionally, simulations of singleton and twin fetal growth, and the response of the mammary gland to varying demand during suckling, are presented.