Effects of Dietary Sulphur Amino Acid Levels on Growth Performance, Meat Quality, Nutrient Digestibility, Serum Biochemistry and Feather Follicle Transcriptomics in Jiangnan White Goslings

This study evaluated the effects of dietary sulphur-containing amino acid (SAA) levels provided during the early (1–28 d) and late (29–63 d) growth stages on production traits and feather follicle gene expression in 63-day-old Jiangnan white goslings. A total of 288 one-day-old male goslings were assigned to a 2 × 2 factorial design with two early SAA levels (0.64% and 0.87%) and two late SAA levels (0.62% and 0.74%), which created four treatments: Dd (low–low), Dg (low–high), Gd (high–low), and Gg (high–high). All measurements were performed on 63-day-old birds. Final body weight was significantly affected only by early SAA levels (p = 0.03), with the high early groups (Gd and Gg) showing a 3% higher weight (3.99 vs. 3.88 kg) than the low early groups. Late SAA levels had no effect on growth but markedly reduced breast muscle cooking loss (p < 0.01) from 26.64% (low late) to 22.70% (high late), which represents a 15% relative improvement in water-holding capacity. A significant early × late interaction (p = 0.03) indicated that late high SAA levels partially compensated for early deficiency. High late SAA levels also slightly reduced dry matter digestibility (73.45% → 73.16%, p = 0.03), while high early SAA levels increased crude ash digestibility (33.59% → 35.66%, p = 0.04). The Dg treatment (low early + high late) caused significantly elevated serum low-density lipoprotein (2.06 vs. 1.42–1.58 mmol/L) and uric acid (348.15 vs. 243.60–294.97 μmol/L), which indicates metabolic stress (p < 0.01 and p = 0.02 for interaction). Transcriptomic analysis of feather follicles from the Gg and Gd groups (both receiving identical high early SAA supplementation) identified 121 differentially expressed genes, including the downregulation of MAT1 (cysteine/methionine metabolism) and upregulation of GHRHR (neuroactive ligand–receptor interaction) in Gg, providing a molecular basis for improved feather growth. q-PCR validated five selected genes. In conclusion, final body weight is determined by early SAA supply, while late SAA supplementation improves meat juiciness, but abrupt increases from low to high SAA levels cause metabolic disturbances. Under this test conditions, The optimal feeding strategy is 0.87% SAAs (1–28 d) followed by 0.74% SAAs (29–63 d).