Maternal chromium supplementation increases lamb weaning weight and modulates rumen microbiota.

Maternal nutrition during gestation can program offspring development and may influence the establishment of the rumen microbiome, with implications for growth and rumen health. However, the effects of maternal chromium (Cr) supplementation on offspring rumen microbial communities and performance in sheep remain poorly characterised. This study investigated the effects of maternal Cr supplementation during late gestation and early lactation on the offspring microbiome and performance in lambs. Fifteen pregnant ewes were assigned to two treatments in a randomised design: no Cr supplementation and 1.5 mg chromium propionate per ewe/day. Male Dorper × Santa Inês lambs (n = 19) were weaned at 80 d. They were provided creep feeding from 20 d to weaning, and finished in individual feedlot pens until slaughter at 132 d. The rumen microbiota of the offspring at slaughter was characterised. Feed intake, BW, daily gain, feed efficiency, and carcass yield were measured. Maternal Cr supplementation increased the weaning weight of lambs (P = 0.048), although no differences were observed in the feed intake, daily gain, or carcass weight. While the overall microbial diversity was unchanged, Cr increased Flexilinea (P = 0.042), SP3-e08 (P = 0.040) and U29-B03 (P = 0.037), genera linked to fibre degradation and volatile fatty acid modulation. Conversely, Cr reduced Streptococcus (P = 0.029), potentially lowering lactic acid accumulation and ruminal acidosis risk, and Oribacterium (P = 0.025) and Pseudobutyrivibrio (P = 0.008), genera involved in glycolysis and cell wall biosynthesis. In conclusion, supplementation with 1.5 mg chromium propionate during late gestation and early lactation increased lamb weaning weight and modulated rumen microbial taxa, suggesting potential improvements in nutrient utilisation and rumen stability.