Effect of ensiling time on apparent total tract starch digestibility in Southern Brazilian dairy herds

ABSTRACT: Ensiling corn for longer periods is a strategy used to increase rumen bacteria access to starch. In fact, when corn is ensiled for insufficient periods, starch digestibility decreases, as evidenced by excreted starch. This study investigates the effects of corn silage ensiling time on starch digestibility of dairy cows through fecal starch analysis. The trial was conducted during the spring of 2013 and the fall of 2014 on twenty dairy herds located in the state of Paraná, southern Brazil. Total mixed ration (TMR), whole-plant corn silage (WPCS) and fecal samples were collected for determination of dry matter (DM), neutral detergent fiber (NDF), acid detergent fiber (ADF), lignin and starch. Apparent total tract starch digestibility (ATTSD) was calculated using equations developed by Fredin et al. (2014) and Bal et al. (1997). Data were analyzed using the CORR, REG and GLM procedures of SAS. Spring and fall WPCS were ensiled for 260 and 132 days, respectively (p 0.05) in ATTSD-Fredin from season to season though there was a trend (p = 0.11) towards greater ATTSD-Bal for spring samples. ATTSD-Bal was positively correlated with ensiling days (r = 0.31). Starch digestibility was not negatively affected by WPCS harvesting maturity. Differences in post-ruminal starch digestion, variation between farms in DM intake and diets, limitations of the equations, influence of uncontrolled factors, and the small number of experimental units might have contributed to the absence of significant results. Overall, Bal et al. (1997) equation was more efficient in distinguishing ATTSD from different ensiling periods.

摘要：长期青贮玉米是提升瘤胃细菌对淀粉利用效率的常用策略。事实上，若青贮周期不足，淀粉消化率会下降，这一点可通过粪便中排出的淀粉得到证实。本研究旨在通过粪便淀粉分析，探究玉米青贮发酵时长对奶牛淀粉消化率的影响。本试验于2013年春季及2014年秋季在巴西南部巴拉那州的20个奶牛牧场开展。采集全混合日粮（total mixed ration, TMR）、整株玉米青贮（whole-plant corn silage, WPCS）及粪便样本，用以测定干物质（dry matter, DM）、中性洗涤纤维（neutral detergent fiber, NDF）、酸性洗涤纤维（acid detergent fiber, ADF）、木质素与淀粉含量。采用Fredin等（2014）与Bal等（1997）提出的计算公式，计算总肠道表观淀粉消化率（apparent total tract starch digestibility, ATTSD）。数据通过SAS软件的CORR、REG及GLM过程进行统计分析。春季与秋季采集的整株玉米青贮发酵时长分别为260天与132天。不同季节间，基于Fredin公式的总肠道表观淀粉消化率（ATTSD-Fredin）未呈现显著差异（p>0.05），但春季样本的ATTSD-Bal存在升高趋势（p=0.11）。ATTSD-Bal与青贮发酵天数呈正相关（r=0.31）。整株玉米青贮的收获成熟度未对淀粉消化率产生负面影响。瘤胃后淀粉消化的差异、各牧场间干物质采食量与日粮的差异、计算公式的局限性、未控制因素的影响，以及实验单元数量较少，可能均为未获得显著统计结果的原因。总体而言，Bal等（1997）提出的公式在区分不同青贮周期下的总肠道表观淀粉消化率方面表现更优。