Factors influencing social organization in postpartum Angus cows under confinement. Effect on cow-Calf weight change

The objective was to determine factors influencing social organization in postpartum Angus cows and its effect on variation of cow–calf weight after 90 d. Postpartum Angus cows (N=90) with no history of puerperal problems, a calf suckling, and body condition score (BCS) no less than 3 were allocated into 3 groups of 30 (A, B, and C) according to parity (P) and cow body frame (CF). Using the agonistic interactions recorded during the study, a raw dominance value with subsequent Arc-sin conversion (Arc-sin DV) was calculated to generate a linear social dominance order (DO) with 3 social categories (dominant—D-, intermediate—I-, and subordinate—S-cows). The effects of postpartum body weight (PPBW), BCS, CF, and P on Arc-sin DV were statistically analyzed using ANOVA. Similar procedure was applied to analyze the effects of group, P, CF, and DO on cow body weight at 90 d (CW90), and the effects of DO of dams, P, group, calf gender (CG), and sire within breed (SWB) on calf body weight at 90 d (CFW90). Cows with larger CF and heavier PPBW obtained greatest (P<0.0005) Arc-sin DV. The youngest and the oldest cows tended (P<0.10) to obtain the lowest Arc-sin DV. After 90 d of trial, D cows were heavier than I (P<0.002) and S cows (P<0.0001). Calf birth weight was influenced by SWB (P<0.03) and P (P<0.05), and D cows had heavier (P<0.05) calf at birth than S cows. At 90 d, calf body weight was influenced by P (P<0.03) and DO of dam (P<0.008). Thus, calf weight at 90 d increased with DO of dams. In conclusion, CF, PPBW, and to a less extent P, influenced DO. Parity and CF influenced PPBW. Variation of CW90 was influenced by DO. Calf birth weight was influenced by SWB, P, DO of cow, and CG. Meanwhile, CFW90 was influenced by P and DO of cow. Interactions among social organization, management strategies, calf growth, and reproductive aspects need more attention