Effect of sex and birth weight on the performance, microbiome, immune response and colostrum intake of piglets

The objective of this study was to evaluate the effect of sex and birth weight classes (BWC) on the colostrum intake, performance, permanence in the production system, immune response and microbiome of piglets in the farrowing and nursery phases. A factorial design was used with two sex categories (female and male) and three BWC (low - 0.8 to 1.1 kg; medium - 1.101 to 1.4 kg; and high - 1.401 to 1.7 kg). A total of 757 piglets in the farrowing phase and 228 piglets in nursery phase were used. Serum glucose concentration at birth and 24 hours, colostrum intake, performance parameters, removal rates, mortality, medication, and serum concentrations of immunoglobulin G (IgG), interleukin 10 (IL-10) and tumor necrosis factor alpha (TNF-α) on the 4^th day after weaning, and fecal microbiome on the 6^th day of nursery were evaluated. The serum glucose levels were not changed (P > 0.05). Piglets with high birth weight ingested more colostrum (P < 0.001). Low birth weight piglets (P = 0.077) and males (P = 0.027) had a higher removal rate and mortality. A higher percentage of females with high birth weight required medication (P < 0.001). The body weights of piglets at all weighings were higher for those with high birth weight (P < 0.001). The daily weight gain and feed intake during the nursery phase were affected by the BWC (P < 0.001). Low birth weight piglets had a lower concentration of TNF-α (P = 0.009), and there was no difference in IL-10 concentration (P > 0.05). Males tended to have higher serum IgG concentrations (P = 0.067). Medium- and high-weight piglets, as well as males, showed a higher abundance of pathogenic bacterial species (Fusobacterium mortiferum, Campylobacter jejuni, Clostridium neonatale and Ruminococcus torques). In conclusion, females had a higher rate of permanence in the production system and a fecal microbiome with a lower abundance of pathogenic bacteria, and low birth weight piglets had lower colostrum intake with reduced zootechnical indices.