Genetic evaluation of Holstein-Friesian and Jersey sires using records from pure- and cross-bred progeny in New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in animal science at Massey University

Milk Yield, Milk Fat Yield, Milk Protein Yield and Days in Milk of 72,480 dairy cows of Holstein-Friesian, Jersey and their reciprocal crossbred were analysed. The main objective of this study was to investigate possible use of crossbred progeny records to genetically evaluate sires. Bulls of each breed were evaluated separately using their purebred, crossbred or both purebred and crossbred progeny. First, crossbred progeny were used without including genetic groups. Secondly, crossbred progeny were used with genetic groups included. Rank correlations for different types of evaluations were calculated. In total, 10 different comparisons, 5 for each breed, were performed. The expected correlation of ranks of sires obtained using different data sets were estimated where applicable. Reliability and Prediction Error Variance of sire proofs were estimated both by an approximate method and direct calculation. Over-estimation of reliability and under-estimation of Prediction Error Variance by the approximate method was given. High correlations between ranks of Holstein-Friesian sires evaluated using different data sets were observed, while, the correlation between ranks of Jersey sires evaluated using purebred progeny with ranks of the same sires evaluated using only crossbred progeny was less than expected. Correlations of ranks of Jersey sires evaluated using all progeny with ranks of the same sires evaluated using only crossbred progeny were also low. After plotting EBVs of sires of each breed obtained using only purebred against EBVs of the same sires obtained using both purebred and crossbred progeny, two lines with slightly different slopes were observed. The reasons for the formation of these two lines were investigated. It was found that the number of effective crossbred progeny of sires was affecting the regression of EBVs of sires obtained using all progeny on EBVs of same sires obtained using only purebred progeny. It was concluded that crossbred progeny of Holstein-Friesian sires may be used to assist in their evaluation under New Zealand conditions, but, further research is recommended before using crossbred progeny of Jersey sires in sire evaluation

A Big World in Small Grain: A Review of Natural Milk Kefir Starters

Milk kefir is a traditional fermented milk product whose consumption is becoming increasingly popular. The natural starter for kefir production is kefir grain, which consists of various bacterial and yeast species. At the industrial scale, however, kefir grains are rarely used due to their slow growth, complex application, bad reproducibility and high costs. Instead, mixtures of defined lactic acid bacteria and sometimes yeasts are applied, which alter sensory and functional properties compared to natural grain-based milk kefir. In order to be able to mimic natural starter cultures for authentic kefir production, it is a prerequisite to gain deep knowledge about the nature of kefir grains, its microbial composition, morphologic structure, composition of strains on grains and the impact of environmental parameters on kefir grain characteristics. In addition, it is very important to deeply investigate the numerous multi-dimensional interactions among different species, which play important roles on the formation and the functionality of grains

A disk-shaped domain integral method for the computation of stress intensity factors using tetrahedral meshes

A novel domain integral approach is introduced for the accurate computation of pointwise J-integral and stress intensity factors (SIFs) of 3D planar cracks using tetrahedral elements. This method is efficient and easy to implement, and does not require a structured mesh around the crack front. The method relies on the construction of virtual disk-shaped integral domains at points along the crack front, and the computation of domain integrals using a series of virtual triangular and line elements. The accuracy of the numerical results computed for through-the-thickness, penny-shaped, and elliptical crack configurations has been validated by using the available analytical formulations. The average error of computed SIFs remains below 1% for fine meshes, and 2–3% for coarse ones. The results of an extensive parametric study suggest that there exists an optimum mesh-dependent domain radius at which the computed SIFs are the most accurate. Furthermore, the results provide evidence that tetrahedral elements are efficient, reliable and robust instruments for accurate linear elastic fracture mechanics calculations

A finite element framework for modeling internal frictional contact in three-dimensional fractured media using unstructured tetrahedral meshes

AbstractThis paper introduces a three-dimensional finite element (FE) formulation to accurately model the linear elastic deformation of fractured media under compressive loading. The presented method applies the classic Augmented Lagrangian(AL)-Uzawa method, to evaluate the growth of multiple interacting and intersecting discrete fractures. The volume and surfaces are discretized by unstructured quadratic triangle-tetrahedral meshes; quarter-point triangles and tetrahedra are placed around fracture tips. Frictional contact between crack faces for high contact precisions is modeled using isoparametric integration point-to-integration point contact discretization, and a gap-based augmentation procedure. Contact forces are updated by interpolating tractions over elements that are adjacent to fracture tips, and have boundaries that are excluded from the contact region. Stress intensity factors are computed numerically using the methods of displacement correlation and disk-shaped domain integral. A novel square-root singular variation of the penalty parameter near the crack front is proposed to accurately model the contact tractions near the crack front. Tractions and compressive stress intensity factors are validated against analytical solutions. Numerical examples of cubes containing one, two, twenty four and seventy interacting and intersecting fractures are presented

On the use of quarter-point tetrahedral finite elements in linear elastic fracture mechanics

This paper discusses the reproduction of the square root singularity in quarter-point tetrahedral (QPT) finite elements. Numerical results confirm that the stress singularity is modeled accurately in a fully unstructured mesh by using QPTs. A displacement correlation (DC) scheme is proposed in combination with QPTs to compute stress intensity factors (SIF) from arbitrary meshes, yielding an average error of 2–3%. This straightforward method is computationally cheap and easy to implement. The results of an extensive parametric study also suggest the existence of an optimum mesh-dependent distance from the crack front at which the DC method computes the most accurate SIFs