Between-goat variability in feeding behaviour and feed efficiency under diets differing in acidogenic potential
Résumé
Feeding behaviour is a key factor to explain between animals variability in feed efficiency. This study aimed to link the variability in feeding behaviour and feed efficiency on a basal TMR diet, and to evaluate changes when modifying the diet. Twenty dairy goats were housed in individual pens during the whole trial. Cumulative dry matter intake (DMI) was measured every 2 min to compute daily DMI and characterize the first bout after afternoon distribution (intake, duration, intake rate). All goats received a basal diet (40% hay, 40% concentrate, 20% beetpulp). Then, they were assigned to three groups according to their milk yield, body weight and first bout characterization. Percentage of concentrate was decreased to 30 % (C30) for 6 goats or increased to 50% (C50A or acidogenic diets) for 2 groups of 7 goats, with one supplemented with sunflower grains (C50AS). A variation in feed efficiency, i.e., Fat corrected milk (FCM)/DMI, was noted between goats fed the basal diet (1.36 ± 0.109, n = 20), mainly related to the FCM/Body weight ratio (r = 0.49, n = 20, RSD = 0.10). The residual of this equation is positively linked (r = 0.50) to the intake rate during the first bout. In other words, faster eating goats had a better feed efficiency when fed the basal diet. According to a paired samples Wilcoxon test performed within each group, rate of intake during the first bout never changed with the modification of the percentage of concentrate. Both total DMI and intake during the 1 st bout decreased with the C30 diet without any modification of its duration. This is possibly related to the increase in dietary fibrosity. With the C50A and C50AS diets, duration and intake during the 1 st bout decreased. This could be explained by a modification of feeding behaviour when animals were fed an acidogenic diet as previously observed. Total DMI decreased with the C50AS diet, but remained constant with the C50A one. In the context of Prediction Livestock Farming, feeding behaviour could be an interesting tool to better understand variability in feed efficiency and detect health problems such as sub-acidosis.