Studies in Human and animals have shown that aligning feed intake with the day/night cycles is necessary for optimum energetic metabolism, sleep and well-being. This results from the molecular components of the circadian clock, which are endogenous and autonomous oscillators of physiological activities that developed with evolution. Then, organisms can anticipate and adapt to variations of day/night cycles (temperatures, access of feed, etc.). Ad libitum access to feed shows individual variability in feeding rhythms, that generates variability in individual metabolism. Recording all feeding events in pigs raised in groups with free access to feed is possible: animals are equipped with electronic transponders on one ear, to record their ID when they visit the feeding station that weights and records every feed intake. Therefore, the complete feeding pattern can be described daily, quantitatively and temporarily, for groups and individuals. Such individual data have been recorded since 1999 in two lines of pigs divergently selected for feed efficiency, representing about 4000 pigs (Gilbert et al., 2017). This selection generated a difference of daily feed intake between the lines of 400g/d (1.9kg/d versus 2.3kg/d, difference equal to 1.7 standard deviation). These lines thus have different motivations for spontaneous feed intake as a result of selection. In a previous study, we showed that selection affected some of the feeding patterns, with pigs eating less having larger and faster meals (Meunier-Salaün et al., 2014). The objective of this internship will be to evaluate the changes of the temporal distribution of feeding patterns during the selection process and test 1. If there is a relationship between feed efficiency and feeding rhythm, 2. If this relationship has been affected by selection.
Work to do
To fulfill this objective, the work will be divided in three main steps. First, the elementary data recorded by the feeding stations will be cleaned using criteria already developed in the lab (outliers can be generated by technical issues, leading to abnormal visit durations and intervals between visits to the feeders). Next, the daily feeding patterns will be described for each pig using indicators proposed in the literature (for each hourly slot: duration and size of the meals, time between visits, number of visits per meal, and daily total for these indicators, plus indicators of variability of the meal frequency). The effect of the line selection on these indicators will be tested using linear mixed models. Finally, genetic parameters (heritabilities, genetic correlations between indicators of feeding rhythm and feed intake) will be estimated jointly for the two lines, and then separately. If large differences of feeding rhythm are evidenced between lines, the effect of genomic variants segregating in genes regulating the circadian clock will be tested. All data and softwares to be used in this project are already available in the group.
The project requires skills to manage large datasets and use elementary statistics. Skills in animal production and genetics will be appreciated.
6 month internship (Master 2 or AgSchool 2021-2022)
Location: INRAE centre de Toulouse-Occitanie, UMR GenPhySE https://genphyse.toulouse.inra.fr