A Gaussian Process Model of 3D Udder Point Clouds for Teat Length Phenotyping in Dairy Cows

Abstract

Phenotyping conformation traits is important for dairy cattle breeding and management. Although large-scale phenotyping is possible with 3D imaging technologies, manual annotation of anatomical landmarks and long run times prevent full pipeline automation. In particular, the morphological heterogeneity of cow udders makes automated detection of teat landmarks challenging. To address this limitation, we propose and evaluate a method for teat length estimation from udder point clouds with a Gaussian process. We model the vertical coordinates as the sum of a Gaussian process representing the udder floor and an unknown function representing the teat. Since the udder floor process is smooth and has a significantly wider dependence lengthscale than the teat function, this model allows separating the two terms needed for teat landmark definition. To ensure computational feasibility, we implement a low-rank approximation of the covariance matrix, reducing the computational complexity of the method from $\mathcal{O}(n^3)$ to $\mathcal{O}(n)$. This approach is both faster and more accurate than existing methods, reducing RMSE by a factor of two. It is also more robust to uncommon udder morphologies, making it better suited for automated phenotyping of large numbers of individuals.