Feeding style alters the growth and behavior of artificially-reared pigs

Early-life pig growth is influenced by protein synthesis facilitated by sow milk intake. However, factors such as teat disorders, timing of milk letdown, and seasonal fluctuations can limit milk intake, leading to slower growth and higher mortality rates. Artificial rearing systems allow precise regulation of milk intake, providing a valuable platform for researchers to investigate various feeding strategies, such as ad libitum or weight-based feeding and their impacts on behavior, growth, and health. In our study on feeding style in an artificial rearing system, pigs (85 boars) were removed from the sow on postnatal day (PND) 2 and allotted to treatment based on litter of origin and body weight (BW). Pigs were reared in 4 cohorts across 2 trials over a 15-d feeding period. Experimental treatments included: AD, nutritionally adequate milk replacer provided ad libitum or PRE, nutritionally adequate milk replacer delivered at a prescribed basis according to individual pig BW, which was provided once per hour throughout a 20 h daily feeding cycle. Home-cage tracking and growth performance were measured throughout the study. On PND 6 and 14 an ethogram-based video analysis was performed, spanning the 20-h feeding cycle, to assess home-cage behavioral outcomes. Insulin responsivity was measured near the study conclusion utilizing a feeding-stimulated method and static blood collection time-points. In the study conclusion, pigs were euthanized and underwent body composition analysis. Data were analyzed via a repeated measures or 1-way analysis of variance (ANOVA), with significance accepted at an alpha level of 0.05. Pigs in the AD group exhibited increased (P < 0.05) intake and BW gain but decreased feed efficiency when compared with the PRE group. Additionally, feeding style increased (P < 0.05) serum insulin concentrations 0.5 h after the first feeding in AD pigs when compared with PRE pigs. Feeding style altered (P < 0.05) spatial preference in trial 1 with PRE pigs spending relatively more time in the home-cage quadrant that housed the milk bowl compared with AD pigs. Moreover, PRE pigs spent more (P < 0.05) time visiting the feeding bowl and performing milk consumption behaviors at the bowl than AD pigs. Lastly, the relative proportion of water within soft tissue was increased (P < 0.05) in PRE pigs compared with AD pigs. In conclusion, feeding style impacted growth performance, insulin concentrations, spatial preference, and behavior of artificially-reared pigs.