Whole steamed corn enhances growth performance and alters rumen microbiota in fattening lambs

To evaluate the effects of four processing methods: intact corn (IT), ground corn (GD; ground to 2 mm), steam-flaked corn (SF; steamed at 85°C-100°C for 90 min and flaked to 2.5 mm thickness), and whole steamed corn (WS; steamed at 85°C-100°C for 90 min without flaking), on growth performance, digestibility, blood biochemistry, rumen microbiota, carcass traits, and meat quality in fattening lambs.

Eighty-four male crossbred lambs (Small tailed Han×Northeastern Fine wool; 4.5 months; 34.2±3.5 kg) were blocked by stratifying body weight and then randomly assigned to four treatments (n = 21), each with 50% (as-fed) corn in the diet. In GD and WS treatments, corn was pelleted with other ingredients; in IT and SF treatments, corn was fed separately alongside non-corn pellets at a 1:1 (as-fed) ratio. After a 14 d adaptation period, lambs were fed for 60 d. Body weights were recorded on d 0, 30, and 60; blood samples were collected on d 31 and 60; and rumen fluid was sampled on d 35. Apparent total tract digestibility was determined by total fecal collection in a subset of lambs, and six lambs per treatment were slaughtered for carcass evaluation.

Lambs fed the WS diet showed the greatest average daily gain (ADG) at 319 g/d, improving 22%, 24%, and 7% over GD (261 g/d), SF (257 g/d), and IT (298 g/d) diets, respectively (p = 0.013). Dry matter intake did not differ significantly among treatments (p = 0.307), though WS, GD, and IT numerically exceeded SF by 6.7%-10.8%. Apparent total tract dry matter digestibility was greatest in SF (74.1%) and WS (72.1%), exceeding GD (69.3%) and IT (66.3%; p = 0.001) for the overall diet. Corn processing also altered rumen microbiota: WS tended to increase Erysipelotrichaceae_UCG 002 abundance sixfold over IT, SF enriched Actinobacteria, and IT uniquely harbored minor phyla such as Acidobacteriota. Hot carcass weight tended to be higher in WS (18.4% over GD; p = 0.078), while heart and kidney indices were greater in IT and SF (p<0.05). Meat quality parameters were not significantly affected by corn processing.

Whole steamed corn enhanced growth performance, likely associated with improved starch utilization and modulation of the rumen microbiota, without compromising meat quality. Compared with grinding or flaking, steaming corn kernels provided a practical and energy-efficient approach, yielding 22%-24% higher ADG. Further research should refine steaming conditions and evaluate the economic viability of this method.