Influence of genotype and environment on piglet vitality and metabolic state during the suckling period of divergent birth weight classes.

The high mortality rate of suckling piglets in commercial farms is a cause for concern and requires the adoption of innovative breeding and management approaches for effective mitigation. Piglets are particularly vulnerable during the first days of life, which concerns especially neonates with a low birth weight. In this study, neonatal adaptation was analysed regarding genotype and housing conditions following hormonally induced farrowing. A total of 96 piglets from 27 farrowings of German Landrace (GL; birth induction at day 115 of gestation) and German Saddleback sows (GS; birth induction at day 112 of gestation), kept either in crates (1.0 square metre) or pens (6.5 square metre) were studied. The piglets were assigned to birth weight categories (hypotrophic: 800-1 100 g; eutrophic: > 1 100-1 500 g; hypertrophic: > 1 500 g) and examined via repeated blood analyses on the following time period: 0-6 h, day 1, day 4, day 20 postnatum, and one-day postweaning. Analysed plasma metabolites included albumin, ammonia, chloride, cortisol, creatinine, fructose, glucose, haptoglobin, inositol, insulin, lactate, non-esterified fatty acids, sodium, total protein, triglycerides, triiodothyronine, urea, and uric acid. Eutrophic and hypertrophic piglets were grouped as controls due to metabolic similarities (P = 0.272), whereas hypotrophic piglets could be discriminated from heavier littermates (P = 0.025). The GS piglets appeared to have higher tissue maturity compared to GL piglets, as indicated by improved clearance of plasma ammonia and creatinine levels. This suggests that inducing birth in GS sows at gestation day 112 corresponds to the physiological gestation length of this breed. The housing environment during farrowing influenced plasma glucose and inositol levels during the neonatal adaptation period, which might be attributed to differences in physical activity in farrowing pens compared to crates. Results suggest a higher risk for hypotrophic neonates to exhibit a hypoglycaemia-hypothermia complex at birth, which can have significant implications for neonatal health and development but might be mitigated by the observed increased release of cortisol. These findings highlight that piglet vitality and plasma metabolite dynamics during the suckling period are shaped by genetic background, housing conditions, and birth weight, reflecting differences in tissue maturity, physical activity, and energy reserves.