Abstract: [Objective] This experiment aimed to investigate the effects of replacing Tiankang 7818 (corn crushed with a 2.0φ screen) with Tiankang 682AT-3 (corn crushed with a 1.0φ screen) in the diet on milk yield,dry matter intake,and feed conversion efficiency of lactating dairy cows. [Method] A total of 270 healthy Holstein cows with similar parity and an average milk yield of 35 kg were selected for a self-control experiment. The cows were fed with the diet containing corn crushed by 2.0φ screen before the experiment. The experimental period was 21 days,including a 7-day pre-feeding period and a 14-day formal feeding period. Milk yield and dry matter intake were recorded throughout the experiment,and feed conversion efficiency was calculated. [Result] The results showed that compared with the control group,the average daily milk yield of lactating cows fed with Tiankang 682AT-3 increased significantly by 0.99 kg (P< 0.05),the dry matter intake decreased slightly by 0.24 kg (-0.89%),and the feed conversion efficiency increased from 1.306 to 1.355 (+3.75%). Moreover,when the corn particle size in the concentrate feed decreased from 2.0φ to 1.0φ,the cost per kilogram of milk was reduced by 0.07 yuan/kg. [Conclusion] Reducing the corn particle size in dairy cow diet from 2.0φ to 1.0φ could significantly increase milk yield,improve feed conversion efficiency and reduce breeding costs,but it would cause a slight decrease in milk quality. Ranches could comprehensively evaluate the economic benefits combined with the milk price system (such as milk component pricing method) to select the appropriate corn particle size rationally. This study provided theoretical basis and data support for the selection of suitable corn particle size in dairy cow diet.

Key words: lactating dairy cow, production performance, milk yield, corn particle size, milk indicator