Development and evaluation of the herd dynamic milk model with focus on the individual cow component

Abstract

The herd dynamic milk (HDM) model is a dynamic model capable of simulating the performance of individual dairy animals (from birth to death), with a daily time step. Within this study, the HDM model is described and evaluated in relation to milk production, body condition score (BCS) and BCS change throughout lactation by comparing model simulations against data from published experimental studies. The model's response to variation in genetic potential, herbage allowance and concentrate supplementation was tested in a sensitivity analysis. Data from experiments in Ireland and France over a 3-year period (2009-11) were used to complete the evaluation. The aim of the Irish experiment was to determine the impact of different stocking rates (SRs) (SR1: 3.28 cow/ha, SR2: 2.51 cow/ha) on key physical, biological and economic performance. The aim of the French experiment was to evaluate over a prolonged time period, the ability of two breeds of dairy cows (Holstein and Normande) to produce and to reproduce under two feeding strategies (high level and low level) in the context of compact calving. The model evaluation was conducted at the herd level with separate evaluations for the primiparous and multiparous cows. The evaluation included the two extreme SRs for the Irish experiment, and an evaluation at the overall herd and individual animal level for the different breeds and feeding levels for the French data. The comparison of simulation and experimental data for all scenarios resulted in a relative prediction error, which was consistently <15% across experiments for weekly milk production and BCS. In relation to BCS, the highest root mean square error was 0.27 points of BCS, which arose for Holstein cows in the low feeding group in late lactation. The model responded in a realistic fashion to variation in genetic potential for milk production, herbage allowance and concentrate supplementation.

Linkage between predictive transmitting ability of a genetic index, potential milk production, and a dynamic model

“…The PBHDM model (Ruelle et al, 2015) is a dynamic, stochastic agent-based model developed in C++. The PBHDM model comprises the "herd dynamic milk" model (Ruelle et al, 2016) adapted for grazing and management conditions and the "Moorepark St Gilles grass growth" model (MoSt GG; Ruelle et al, 2018). The model simulates all the main aspects of the life of an animal from birth to culling and death through several different submodels.…”

“…Step 2.1. The inputs to the model in terms of milk production correspond to the potential peak milk yield of a mature animal without any gain or loss of BCS (Ruelle et al, 2016). Consequently, the milk yield predicted by the regression has to be a potential milk yield only linked to the PTA MYkg , which is why the SR, concentrate, year, and parity values in the equation had to be replaced by fixed values.…”

“…When predicting milk production, simulation models generally have 2 options: either predict milk production based on previous milk records or predict milk production based on the genetic potential of the animal, which is independent of actual historical milk production (Baudracco et al, 2011;Ruelle et al, 2016). The first method is the easiest in terms of on-farm parameterization and is used in several models (Shalloo et al, 2004).…”

Using models to establish the financially optimum strategy for Irish dairy farms

“…The pasture-based herd dynamic milk (PBHDM) model is a dynamic, stochastic agent-based model developed in C++ (Ruelle et al, 2015). The PBHDM model comprises the herd dynamic milk model (Ruelle et al, 2016a) adapted for grazing conditions and management. Each animal and paddock are described and simulated individually on a daily basis.…”

“…The models included a grass growth model, the Moorepark and St Gilles grass growth model (MoSt GG; Ruelle and Delaby, 2016;Ruelle et al, 2016b), which has been merged with an animal intake and performance model (Ruelle et al, 2015(Ruelle et al, , 2016a. The outputs from those models have been combined into the Moorepark dairy systems model (MDSM; Shalloo et al, 2004b) to evaluate the overall effect of 20 options on the economic performance of the farm.…”