is shredlage a good idea ?揉丝青贮是个好主意吗？正文+译文 十年跟踪观察

In the past few years, there has been renewed interest in a corn silage chopping system using differentially sized and rotating rollers in a corn harvester to create a longer particle size corn silage known as shredlage. Quite a bit of research into a similar chopping method was done about 20 years ago, but it was never pursued due to a few problems and the increased cost of production. The system has been altered some, and shredlage has gained new attention. The harvesters that produce shredlage have processing-type rollers where one is larger than the other and each moves at a different speed. The result is a kernel-processed corn silage that is both ripped apart and cut. Most often the cutting is done at a longer theoretical length, making a softer, less coarse silage material. The thought 20 years ago was that it might make the forage more digestible by rumen bacteria and therefore improve the value of the crop to the cow, but that has not ever been shown to be true. To date, studies have demonstrated that shredlage has the same overall dry matter and fiber digestibility as conventional silage. Shredlage Changes Particle Size Distribution This harvesting system does change the particle size distribution of corn silage, which is easily viewed using the Penn State Particle Separator (PSPS). In shredlage forge particles generally shift from the second sieve of the PSPS (7 to 19 mm) and instead land in the top sieve with a length of more than 19 mm. This change in the particle size distribution can create three problems. First, by making longer corn silage you increase the risk of not getting it well packed in the bunker silo; especially if it gets a bit too dry. Sooner or later this is going to happen in most harvest seasons, likely near the end of the silo filling time. We know well that the drier the silage at ensiling, the more important it is to chop finely for packing. Coarse, dry silage will be prone to increased dry matter losses, poor fermentation, and mold growth. It is important to understand that coarse, wet silage (shredlage) will pack with little problem. In the event that the silage gets too dry, we are increasing the risk of packing problems by making shredlage. Second, it is well proven by research that increasing particle size of corn silage prolongs eating time by high producing cows and lowers dry matter intakes. Sometimes these are small decreases, but often in research the drop in dry matter intake is statistically significant and in the range of 1 to 2 pounds of dry matter per day on high corn silage diets. Obviously, this is not desirable for high producing dairy cows. Finally, research has shown that the physically effective fiber in a forage is related to the top 2 or even 3 sieves of the PSPS--everything > 4 mm has been shown to be physically effective in the cow. Shredlage does not increase physically effective fiber levels, it just changes the proportion found on the top two sieves. Furthermore, these top two sieves often add up to the same number for conventional silage or shredlage. In the end, shredlage does not give the cow any more physically effective fiber (peNDF) or provide any advantage over conventionally chopped silage in this aspect of the diet. Another factor to consider is that shredlage costs more to produce, due to the equipment needed and its power requirement. This can be quite substantial and increases the cost of the final product by $1 to $3 per ton of silage. Shredlage Research The research 20 years ago primarily considered the engineering aspects of the system and energy requirements to produce the material. Recently there have been two studies conducted comparing shredlage to conventionally processed corn silage. To my knowledge, these are the only two milking cow studies conducted; the first used a conventional silage variety and the second used a BMR corn variety. Both studies showed longer silage was produced as shredlage as compared to a kernel-processed silage, as is usually observed; however, the calculated physically effective fiber levels in the resulting silages were equal. The second study measured rumination of the cows and found it to be the same for both groups as would be expected. There were no differences in nutrient analysis of the two silages from each study, and no differences in fermentation patterns of the silage or digestibility of the feed. In all cases it appeared that the silages were well fermented. In the first trial, 2 groups of Holstein and Holstein-Jersey cross cows were fed for a 12-week period. Cows were not given the opportunity to be on each treatment and were housed and fed in pens of 8. In the second trial, only Holsteins were used for 16 weeks in a similar design also with pens of 8 cows. They found no significant differences in intake in either study, however all cows did some sorting in the second study. They also found no difference in milk and milk component production when comparing kernel-processed and shredlage silages in either study (in the second study, they had a treatment with coarse hay added), yet in the second study both groups had low milk fat (3.3%). The difference that they did have however, was a large difference in kernel processing score between the two crops in both studies. In the first study, the shredlage had a kernel processing score of 75 on average, which is in the range that we typically consider excellent, while the kernel-processed silage was on average 60%; below the recommended range. From methods described in the paper, the shredlage was processed with rollers spaced 2.5 mm apart and the kernel-processed silage at 3 mm. Clearly, the kernel-processed silage was not processed well enough. In the second study both rollers were set using a similar gap (2 mm), but the shredlage resulted in a processing score of 72 and the kernel processing a score of 68. Data in the paper show that the kernel-processed silage had some samples with processing scores of 55 to 60 up to 80, while the shredlage had kernel processing scores of 66 to 70 up to 80. Obviously, the processing was more variable for the kernel-processed silage and some loads of silage did not meet the goal of 70 or higher. Lower processing scores are likely to yield undigested corn in the manure of high producing cows that consume it. I draw two conclusions from this re-visit of shredlage. First, there are no advantages to going to shredlage; increased risk of a poor fermentation, no change in rumination time or peNDF, possible reduction in dry matter intake by high producing cows, and an increased cost. The research so far does have a very important take-home message--when you or your custom harvestor are making silage this fall pay close attention to the dry matter and particle size of the whole plant material in addition to the processing of the grain kernels. We know kernel processors can do a great job, and we see from the above studies that shredlage also does a good job of kernel processing. Check the first load and every few loads as the harvest progresses. Dry matter, particle size, and kernel processing score are items that will have huge impacts on the fermentation, digestion, and utilization of your silage and can easily and accurately be checked on the farm in minutes. References Ferraretto, L. F., and R. D. Shaver. 2012. Effect of corn shredlage on lactation performance and total tract digestibility by dairy cows. Prof. Anim. Sci. 26-639-647. Vanderwerff, L. M., L. F. Ferraretto, and L. D. Shaver. 2015. Brown midrib corn shredlage in diets for high-producing dairy cows. J. Dairy. Sci. 98:5642-5652.

《揉丝青贮是个好主意吗？》

过去几年里，一种在玉米收割机上使用大小不同且转速不同的对辊，来生产更长颗粒玉米青贮的切碎系统重新引起了人们的兴趣，这种青贮被称为揉丝青贮（shredlage）。大约20年前，针对类似的切碎方式曾有过不少研究，但由于存在一些问题以及生产成本增加，当时并未推广开来。如今这套系统经过了一定改良，揉丝青贮再次获得了关注。

生产揉丝青贮的收割机配有类似破碎辊的对辊装置，其中一只辊子比另一只大，且两只辊子以不同速度运转。这样生产出的是既被撕裂又被切碎的籽粒破碎玉米青贮。通常，这种切碎的理论切断长度更长，制作出的青贮料更柔软、不那么粗糙。20年前的想法是，这或许能让饲草更容易被瘤胃细菌消化，从而提升其对奶牛的价值，但这一点从未得到证实。迄今为止的研究表明，揉丝青贮在整体干物质和纤维消化率方面与传统青贮完全相同。

揉丝青贮改变颗粒度分布
这种收割系统确实改变了玉米青贮的颗粒度分布，这一点用宾州颗粒度分级筛（PSPS）很容易观察到。在揉丝青贮中，饲草颗粒通常会从分级筛的第二层筛（7至19毫米）转移到顶层筛（长度大于19毫米）。这种颗粒度分布的变化会带来三个问题。首先，更长的玉米青贮增加了在青贮窖中压实的难度，尤其是在青贮料偏干时；在大多数收贮季节，这种事情迟早会发生，很可能出现在青贮窖装填接近尾声的时候。我们清楚知道，入窖时的青贮料越干，就越需要切得细碎以便压实。粗而干的青贮料更容易造成干物质损失增加、发酵不良和发霉。需要明确的是，粗而湿的青贮料（揉丝青贮）压实起来问题不大。然而，一旦青贮料变得过干，制作揉丝青贮就会增加压实出现问题的风险。

第二，研究充分证明，增加玉米青贮的颗粒长度会延长高产奶牛的采食时间，并降低干物质采食量。有时这种下降幅度较小，但在研究中，下降通常具有统计学显著性，在高玉米青贮日粮中，每天干物质采食量会减少1到2磅（约0.45-0.9公斤）。显然，这对高产奶牛来说不是好事。

最后，研究表明，饲草的物理有效纤维与分级筛的上两层乃至上三层筛上的物料有关——所有大于4毫米的颗粒都已被证明对奶牛具有物理有效性。揉丝青贮并没有增加物理有效纤维的总量，它只是改变了分布在上两层筛上的比例。而且，传统青贮和揉丝青贮上这两层筛上的物料总和往往是相等的。归根结底，揉丝青贮并未给奶牛提供更多的物理有效纤维（peNDF），在日粮的这个方面，它相对于传统切碎青贮没有任何优势。

另一个需要考虑的因素是，揉丝青贮的生产成本更高，因为需要专门的设备和更大的动力。这可能是相当大的一笔开销，使得每吨青贮的最终成本增加1至3美元。

揉丝青贮相关研究
20年前的研究主要关注这套系统的工程学方面及其生产所需的能耗。近期有两项研究将揉丝青贮与常规籽粒破碎玉米青贮进行了对比。据我所知，这是仅有的两项使用泌乳牛进行的试验；第一项使用了常规玉米品种，第二项使用了褐色中脉（BMR）玉米品种。两项研究都显示，与籽粒破碎青贮相比，揉丝青贮生产出的青贮料更长，这与通常观察到的情况一致；然而，计算出的两种青贮料中物理有效纤维水平却是相等的。第二项研究测量了奶牛的反刍情况，发现两组奶牛反刍时间相同，这也在意料之中。两项研究中，两种青贮料的营养分析没有差异，青贮发酵模式和饲料消化率也没有差异。从各方面看，青贮料的发酵状况都良好。在第一项试验中，两组荷斯坦牛及荷斯坦-娟姗牛杂交牛被饲喂了12周，奶牛没有机会同时接受两种处理，按每栏8头饲养和饲喂。第二项试验仅使用荷斯坦牛，持续16周，采用类似设计，也以8头牛为一栏。两项研究中均未发现采食量有显著差异，但在第二项研究中所有奶牛都出现了一定程度的挑食。在比较籽粒破碎青贮和揉丝青贮时，两项研究均未发现产奶量和乳成分存在差异（第二项研究中设有一个添加粗切干草的处理），但在第二项研究中两组奶牛的乳脂率都偏低（3.3%）。

然而，它们之间确实存在一个差异，那就是两项研究中两种青贮的籽粒破碎评分差距很大。在第一项研究中，揉丝青贮的平均籽粒破碎评分为75，这在我们通常认为的优秀范围内，而籽粒破碎青贮的平均分仅为60%，低于推荐范围。根据论文中描述的方法，揉丝青贮的破碎辊间隙设为2.5毫米，而籽粒破碎青贮的间隙为3毫米。显然，籽粒破碎青贮的破碎程度不够好。在第二项研究中，两种青贮的辊子都采用了相近的间隙（2毫米），但揉丝青贮的破碎评分为72，籽粒破碎青贮为68。论文数据显示，籽粒破碎青贮部分样品的破碎评分在55-60到80分之间，而揉丝青贮的评分在66-70到80分之间。很明显，籽粒破碎青贮的加工质量波动更大，部分青贮车次未能达到70分或更高的目标。较低的破碎评分很可能导致高产奶牛采食后粪便中出现未消化的玉米粒。

我对这次揉丝青贮的再探讨得出两个结论。第一，转向揉丝青贮没有任何好处：发酵不良的风险增加，反刍时间和物理有效纤维没有变化，高产奶牛干物质采食量可能降低，并且成本增加。目前的研究确实传递了一个非常重要的信息——今年秋天，当您或您的定制收割商制作青贮时，除了关注玉米粒的破碎情况，还要密切关注全株物料的干物质和颗粒度。我们知道籽粒破碎机能出色地完成工作，从上文研究也可看出揉丝青贮系统同样能很好地破碎玉米粒。从第一车开始检查，并在收割过程中每隔几车检查一次。干物质、颗粒度和籽粒破碎评分这些指标，对青贮的发酵、消化和利用有着巨大影响，而且都可以在牧场内迅速、方便且准确地完成检测。

参考文献
Ferraretto, L. F., and R. D. Shaver. 2012. 揉丝玉米青贮对奶牛泌乳性能和全消化道消化率的影响. Prof. Anim. Sci. 26:639-647.
Vanderwerff, L. M., L. F. Ferraretto, and L. D. Shaver. 2015. 高产奶牛日粮中的褐色中脉揉丝玉米青贮. J. Dairy. Sci. 98:5642-5652.