Few differences found between early- and late-weaned pigs raised in the same environment

Segregation and medicated early weaning are technologies used to optimize t he productivity and health of pigs, but these practices may also cause aber rant behaviors indicative of stress. Thus, differences in early- (approxima te to 10 d of age) and late- (approximate to 30 d of age) weaned pigs were investigated. At weaning, pigs were housed in groups of four in 16 pens (ei ght pens per treatment) in the same facility, and, thus, they were not segr egated. Body weights were recorded at birth, weaning, and at approximately 42, 65, 102, 137, and 165 d of age (at slaughter). One-minute, instantaneou s scan samples during a 10-min period (at 0600, 1000, 1400, and 1800) were used to record the frequency of lying, standing, and sitting, total number of drinks, feeder investigations, and time spent playing/fighting on 2, 3, and 4 d after weaning. Five-minute, direct observations of each pig were co nducted at approximately 40, 60, 80, and 150 d of age. Direct observations were also made of the entire pen for 10 min at approximately 50, 95, 123, a nd 160 d of age to record aberrant behaviors. At 62 d of age, a handling an d blood collection stress was imposed. At 165 d of age, a second stress tes t was conducted in response to rough handling and transport. Early-weaned p igs spent more time playing/fighting (P < .006) than late-weaned pigs durin g the 4 d after weaning, manipulated conspecifics more often at 40 d of age (P < .002), had greater percentage of hemoglobin (P < .03) during Stress T est 1, had greater ADG at 42 d of age (P < .03), and had greater hypothalam ic growth hormone-releasing hormone receptor mRNA at slaughter (P < .06). L ate-weaned pigs had greater ADG between 137 and 165 d of age (P < .03) and greater pro-opiomelanocortin at slaughter (P < .04). Overall, most differen ces found between early-weaned and late-weaned pigs were evident soon after weaning, but they disappeared before slaughter.