[目的]本试验旨在研究在日粮中使用天康682AT-3（1.0φ筛片粉碎玉米）试验料替代天康7818（2.0φ筛片粉碎玉米）试验料,对泌乳奶牛产奶量、干物质采食量和饲料转化率的影响。[方法]试验选用270 头健康、胎次相近且平均产奶量为35 kg的荷斯坦牛,采用自身对照试验设计,试验前饲喂2.0φ筛片粉碎玉米的基础日粮,试验周期21 d,其中包含7 d预饲期和14 d正饲期,试验全程记录产奶量及干物质采食量并计算饲料转化率。[结果]与对照组相比,泌乳牛饲喂682AT-3试验料后日均产奶量显著提升0.99 kg（P<0.05）,干物质采食量小幅下降0.24 kg（-0.89%）,饲料转化率从1.306提升至1.355（+3.75%）;当精补料中玉米粉碎粒度从2.0φ降至1.0φ时,公斤奶成本降低0.07 元/kg。[结论]将奶牛日粮中玉米粉碎粒度从2.0φ降至1.0φ可显著提升产奶量、提高饲料转化率并降低养殖成本,但会造成乳品质小幅下降,牧场可结合乳价体系（如乳成分计价方式）综合评估经济效益后合理选择玉米粉碎粒度。本研究为奶牛日粮玉米适宜粉碎粒度的选择提供了理论依据与数据支撑。
[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.
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