Frequent social regroupings affect corporal and reproductive development, metabolic status, and behavioral time budget in dairy heifers.

We aimed to evaluate the corporal and reproductive development, metabolic status, and behavioral patterns of resident dairy heifers subjected to social regroupings (SR). Holstein replacement heifers (153.3 ± 16.1 kg, 11 months old) were homogeneously allocated to: 1) Control (CON; n = 14 resident + 5 "permanent") and 2) Regrouped (RG; n = 14 resident + 5 "changing"). "Changing" heifers were exchanged for 5 novel heifers every 21 d over 205 days (total = 10 SR). At each SR, body weight, wither height, body condition score (BCS), eating, ruminating, lying and standing behaviors were recorded, and blood hormones and metabolites were determined. Behavior was registered through scan sampling every 10 min., and estrus was detected using patches. Wither height and BCS were greater in CON than RG at SR9 and 10, and at SR4 and 5, respectively (P < 0.01). Control heifers showed first heat earlier (93 ± 9 d vs 126 ± 14 d; P = 0.03) and presented greater insulin growth factor- 1 (171.3 vs 120.0 ng/ml ± 10.1; P < 0.01) and glucose (4.3 vs 4.2 mmol/L ± 0.07; P = 0.04) concentrations than RG, while non-esterified fatty acids concentration was greater in RG (0.35 vs 0.30 mmol/L ± 0.04 P = 0.04). Regrouped heifers were observed more times eating (0.45 vs 0.33 ± 0.01), but fewer times ruminating (0.21 vs 0.24 ± 0.01) than CON (P < 0.01). Frequent SRs negatively affected corporal and reproductive development and energy metabolism, and altered behavioral patterns in dairy heifers.