Sperm DNA integrity in Landrace and Duroc boar semen and its relationship to litter size

The sperm chromatin structure assay is a method for assessment of sperm DNA fragmentation, a parameter reported to be negatively related to field fertility in several mammal species. This method calculates a DNA fragmentation index (DFI) whose high values indicate abnormal chromatin structure. In this study, running from March 2010 until June 2017, the aim was to assess sperm DFI in stored liquid extended semen from two different pig breeds, Norwegian Landrace (NL; n = 693) and Norwegian Duroc (ND; n = 655), and to evaluate the influence on total number of piglets born (TNB). There was a significantly higher median DFI (p < 0.0001) in ejaculates from the 478 ND boars compared to the 452 NL boars. Data from 19,496 NL litters and 3,877 ND litters of the same boars were retrieved. For either breed, sow herd (p < 0.0001), parity (p < 0.05) and DFI (p < 0.05) showed significant effects on TNB. The DFI was negatively correlated to TNB in both breeds. The boars with the 5% lowest TNB had a least square means DFI of 3.05% and 2.24% in NL and ND, respectively, compared to 1.67% and 1.23% for the boars with the 5% highest TNB (p < 0.01). The DFI and the motility of the same semen samples were negatively correlated (p < 0.0001), and the high and low TNB groups showed significant differences in motility. However, this difference could not be used for practical prediction of TNB group (92.1% vs. 89.7%; p = 0.0038 and 92.3% vs. 89.5%; p = 0.018; NL and ND, respectively). In conclusion, our results indicate that sperm DNA integrity in semen with good motility and morphology may be an additional prediction parameter for fertility in pigs.     

Analyzing nonlinear population dynamics data

We consider the problem of analyzing long-term experiments with panels of nonlinear time-series data in the framework of generalized additive models. Our approach is developed for testing and estimating the (partial) common dynamic structure across treatment groups. We illustrate our approach with a detailed analysis of an ecotoxicological experiment on the effect of sublethal doses of a toxic substance (cadmium) on the long-run dynamic structure of the greenbottle blowfly (Lucilia sericata). The general model for the blowfly experiment is a generalized additive model which is derived from a stage-structured ecological model. We discuss the relationship between the components of the generalized additive model and those of the underlying stage-structured model. In particular, our proposed approach casts new insights on the effect of toxic diet on the population dynamic structure of the blowfly.     

Forecasting of Rodent Outbreaks: Models and the Real World1

Theoretical and practical purposes of mathematical modelling are discussed. Of these, special attention is given to large scale simulation models and regression models. It is pointed out that, for proper use of simulation models for predictive purposes, it is necessary to realize the uncertainties associated with such model predictions. These uncertainties are mainly due to insufficient knowledge of parameter values included in the simulation model. As these model predictions are made iteratively (i.e. by short time steps), biases in parameter estimates have, with increasing length of simulated time, an accumulating effect on the biases in the output variables. Regression models are described and methods for finding the best mathematical model are discussed. Assumptions regarding statistical properties of the data from which the regression model is constructed are discussed. It is pointe out that valid predictions are made only within the domain defined by the data Examples of regression models for forecasting rodent outbreaks are discussed. Some further developments are proposed. Results from a model emphasizing spatio-temporal heterogeneity in a heterogeneous region are discussed. Based on this model conclusions regarding what type of landscapes are likely to cause rodent outbreaks are deduced. Furthermore, proposed control treatments are suggested by analyzing the model. It is concluded that larger regions should be composed of suitable and non-suitable rodent habitats interminded with each other. It is suggested that treatments for increasing the local extinction rate be applied uniformly over the whole region, but varyjng in time as much as possible and not correlated with the density in local habitats nor in the entire region. Within these limits, treatments should be applied during periods of low mobility and low reproduction.