University of Minnesota researchers are collaborating to find new applications for groundbreaking cold plasma research.
The two measures studied would allow to reduce liveweight variability at slaughter by 10-15%.
What statistics were used to test if the varation amongst the pigs was different between treatments ?
Regarding the performance in terms of BW, pigs were the experimental unit in all calculations except when mentioning the variability (expressed as coefficient of variation (%) and referred to the pen as experimental unit).
In Trial 1, the combination of feeder type (HD or LD), sex (male or female) yielded a 2 x 2 factorial arrangement that was analyzed using the GLM procedure defining the model:
Yijk = µ + treati + sexj + sex*treatij+ Ɛij
where Yijk relates to each observation of the outcome variable, µ is the global mean, treati is the main effect of treatment, sexj is the main effect of sex, and sex*treatij corresponds to the interaction between sex and treatment and, finally, Ɛij is the experimental error term. Regarding the interaction term, it was found to not be significant, so it was removed from the model. The BW at day 64 (end of nursery period) was used as a covariate because the distribution was defined at weaning. Regarding the variability, measured as CV, the model used in Trial 1 (feeder type) was almost the same but simplified, using a One Way ANOVA with treatment as the main source of variation as we were interested in the general effect of the treatment. We also check for the ‘period effect’ on CV and we observed a significant effect for both treatments meaning that as pigs approached to slaughter were less variable (not included in the paper). In Trial 2 (feeding program management), the effect of treatment (Sp or Std diets) on BW and ADG of piglets was analyzed with a repeated measures ANOVA by using the Proc MIXED. Sex was also added as a factor in the model, but as it was not significant. It was declared the pig as the repeated unit, with the option AR(1) of SAS (Autoregressive method) to define the structure of the error (co)variance matrix. Data was grouped by treatment. The same model was used to compare the effect of treatment considering only the light piglets (LSp or LStd) or as group basis (G1, Sp. or G2, Std.).Finally, and regarding the variability, the model used was the same as previously used in Trial 1. In this case, differences among treatments were significant between treatments.
Were pigs weighed and sorted for market or visually evaluated ?
The accuracy in which pigs are sorted for market has subnstantial impact on the variance in BW and carcass wieght. In all cases, the selection for slaughter was performed by picking up the animals that had reached their slaughter weight (105 kg, checked by weighting them individually) the day before slaughtering and fasting them overnight. The same procedure was conducted two or three more times until the finishing barn was emptied.
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