Increased growth rate post-weaning affects mammary gene expression of two-year-old ewes during their second pregnancy and lactation

Lay Summary This study examined how faster growth between three and seven months of age affects mammary glands in non-dairy ewes during their second lactation. Nineteen twin-bearing ewes, that either had a faster growth rate between three and seven months of age (9 Heavy ewes) or did not have a faster growth rate (10 Control ewes) were selected. Mammary gland samples were collected during pregnancy and early lactation to examine the expression of 37 genes involved in mammary development and lipid metabolism. Ewes in the Heavy group tended to show lower expression of acyl-CoA synthetase short-chain family member 1 (ACSS1), a gene for energy production and milk fat synthesis, and a trend toward lower expression of signal transducer and activator of transcription 5A (STAT5A), a regulator of mammary cell development. These results suggest potential carry-over effects of faster growth rate. However, no differences were observed in lamb growth, live weight or in the expression of gene regulated by ACSS1 or STAT5A, indicating limited impact on mammary development and lamb performance. Additional research on milk production and detailed gene analysis, is needed to better understand how faster growth after weaning might influence mammary development and subsequent milk quality in non-dairy ewes.