Short communication: Selection for persistency by changing the shape of lactation curves with geometric morphometrics

The objective was to simulate the response to selection by modifying the shape of the lactation curve to improve persistency in Israeli first-parity Holstein cattle using geometric morphometrics and multivariate quantitative genetics. The 2-dimensional Cartesian coordinates representing the shape of the lactation curve were characterized using geometric morphometrics. Genetic parameters of daily milk yield were estimated for the individual animal model using REML. Results of selection were simulated using the multivariate breeders' equation. We defined 6 selection regimens: (1) decrease in the third month in milk (MIM), (2) increase in the ninth MIM, (3) decrease in the third MIM and increase in the ninth MIM, (4) decrease in the first MIM, (5) decrease in the second MIM, and (6) decrease in the fourth MIM. The first 3 selection criteria targeted changes in the MIM of previous measurements of persistency in the Israeli Holstein population, and the last 3 targeted the months with the highest variability. All selection regimens attempted to modify the shape of the lactation curve while keeping total milk yield constant. The first 3 selection regimens showed greater total responses, with the highest response for decrease in the third MIM and increase in the ninth MIM. Magnitudes of correlated responses consistently surpassed direct responses in all selection criteria, suggesting that selection on specific parts of the lactation curve would produce correlated responses in other parts. Predicted responses to selections were depicted as shape changes from the mean shape in the data set. Most predicted responses demonstrated a fairly similar shape compared with the lactation curve. The predicted responses of lactation shapes of the last 3 selection regimens were overall lower in the first 3 MIM and decreased less in the last MIM, demonstrating a much flatter shape and thus improved persistency.

Using geometric morphometrics for the genetics analysis of shape and size of lactation curves in Israeli first-parity Holstein cattle

Our objective was to combine the methods of geometric morphometrics and multivariate quantitative genetics to genetic evaluation of the size and shape of lactation curves of milk of 3,492 Israeli first-parity Holstein cattle. Lactation records were treated as morphological data, for which 2 different lactation shape functions were evaluated, one depicted by a line graph and the other by an orbital graph. The lactation curves from both shape functions were represented by 2-dimensional Cartesian landmark coordinates. The 2 sets of landmarks were then analyzed individually for each shape function with geometric morphometrics to separate variation into components of size and shape. The analysis yielded 2 size measures and 2 sets of shape variables, and they were the inputs to estimate variance components using the MTC REML individual animal model program. Variance components were also estimated for the 305-d lactation production as a reference. Shape variables showed negligible correlation with 305-d production, providing evidence of size and shape of lactation curve as separate characters. The size measure derived from the orbital-depicted lactation curve had equal heritability (0.39 ± 0.01; ± standard error) and complete genetic and environmental correlations with 305-d production, whereas the size measure derived from the line-depicted lactation curve showed low heritability (0.09 ± 0.01) and environmental correlation (0.02 ± 0.004) and relative high genetic correlation with 305-d production (0.48 ± 0.04). This may validate both the orbital graph to depict lactation records and the use of geometric morphometrics to split variation of lactation curve into size and shape components. The maximal heritability for shape of lactation curve was 0.55 for orbital- and 0.56 for line-depicted lactation curves. The respective patterns of variations were visualized as shape changes from the mean shape in the data set. Geometric morphometrics are well grounded within the theory of shape analysis and can be paired with conventional methods in the field to characterize the patterns of phenotypic and genetic variation of shape and size of lactation curve in dairy cattle.

Relationship between the lactation curve and udder disease incidence in different lactation stages in first-lactation Holstein cows

We examined the relationships between the shape of the first parity lactation curve and udder disease incidence at different stages of lactation in 538 Holstein cows. Data used were first-parity daily milk yields and treatment records. Each cow was classified according to whether or not it had had udder disease at least once over the whole lactation period or in one of three stages within the lactation period. We then examined the differences in the shapes of the lactation curves between the disease incidence and non-incidence group in each stage. Cows that had high rates of increase in milk yield and high milk yields in early lactation were predisposed to udder disease afterwards. Cows with high milk production over a long period but with low lactation persistency were predisposed to udder disease after the peak of lactation. There was no difference in total milk yield between incidence and non-incidence groups in all stages, suggesting that, for a comparable level of lactation, cows without udder diseases have flatter lactation curves.

Prediction of genetic growth curves in pigs

Genetic growth curves of boars in a test station were predicted on daily weight records collected by automated weighing scales. The data contained 121 865 observations from 1477 Norwegian Landrace boars and 108 589 observations from 1300 Norwegian Duroc boars. Random regression models using Legendre polynomials up to second order for weight at different ages were compared for best predicting ability and Bayesian information criterion (BIC) for both breeds. The model with second-order polynomials had best predictive ability and BIC. The heritability for weight, based on this model, was found to vary along the growth trajectory between 0.32-0.35 for Duroc and 0.17-0.25 for Landrace. By varying test length possibility to use shorter test time and pre-selection was tested. Test length was varied and compared with average termination at 100 kg, termination of the test at 90 kg gives, e.g. 2% reduction in accuracy of estimated breeding values (EBV) for both breeds and termination at 80 kg gives 5% reduction in accuracy of EBVs for Landrace and 3% for Duroc. A shorter test period can decrease test costs per boar, but also gives possibilities to increase selection intensity as there will be room for testing more boars.