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A new view on the growth of pigs in relation to frequent body weight monitoring
Frequent body weight (BW) monitoring of growing pigs can be useful for identifying production (e.g. feeding), health and welfare problems. However, in order to construct a tool which will properly recognize abnormalities in pigs’ growth a precise description of the growth process should be used. In this study we proposed a new model of pig growth accounting for daily fluctuations in BW.
Data on BW measurements of 1,710 pigs (865 gilts and 843 barrows) originating from 5 consecutive batches from one Danish commercial farm was collected. Pigs were inserted into a large pen (maximum capacity = 400) between November 2014 and September 2015. On average, each pig was observed for 42 d and weighed 3.6 times a day when passing from resting to feeding area. Altogether, 243,160 BW measurements were recorded. In order to properly account for the diurnal pattern, the time of BW measurements was corrected for Daylight Saving Time.
A multilevel model of pig growth was constructed and fitted to available data. The BW of pigs was modeled as a quadratic function of time. A diurnal pattern was incorporated into the model by a cosine wave with known length (24 h). The model included pig effect which was defined as a random autoregressive process with exponential correlation. Variance of within-pigs error was assumed to increase with time. The intercept, time, square value for time and cosine wave were significant fixed effects (P<.0001). Additionally, the interaction between these fixed effect elements and each batch was determined to be significant (P<.0001). The gender effect was not significant and was removed from the final model (P=0.52).
According to results, pigs were lighter in the morning and heavier in the evening (the minimum BW was obtained around 1000 h while the maximum around 2200 h). However, the exact time of obtaining maximum and minimum BW during the day differed between batches. Pigs had access to natural light and, therefore, existing differences could be explained by varying daylight level during observations periods. Because the diurnal amplitude for pig growth ranged between batches from 0.9 kg to 1.4 kg, BW monitoring tools based on frequent measurements should account for diurnal variation in BW of pigs. This proposed description of growth was built into a monitoring tool (a dynamic linear model) consisting of an updating, forecasting and filtering procedure. The constructed monitoring tool will be applied to farm data in future studies.
Keywords: bodyweight, pigs, diurnal pattern