Corn Silage Feeding to Dairy Cows


By Don Haycock, Technical Specialist - Dairy Nutrition, Wallenstein Feed & Supply Ltd.

Every year around this time many questions arise about corn silage, such as:  Why is feeding fresh corn silage not recommended?  What if we have no choice and have to feed fresh silage?  How can we make feeding fresh CS have a less of a negative impact?  Why is that some years my cows drop in milk more than other years when feeding fresh CS?  And there are also questions such as what makes a really good corn silage for dairy cows? And then, Which corn silage variety should I grow next year?  I will attempt to answer some of these questions here.

First of all the level of corn silage in the ration has a major impact on how cows will adjust when new corn silage is introduced. If you are feeding a high amount of CS (>9 kgs DM eg 24 kgs As Fed at 62% moisture) then this represents a significant change in the overall diet and therefore in how much the cow’s rumen needs to adjust. The rumen microbes which are digesting forages that are well fermented are different than the ones required to digest unfermented CS. Basically a repopulation of rumen bacteria needs to occur which means old bacteria dies off and new bacteria grows back again inside the rumen. This process takes some time and again the higher the level of CS in the diet, the longer this may take. Milk production is quite often reduced as less of the forage is being digested. Nutritionists can add yeast products in the diet to help this rumen bacteria adjustment. Also since fresh CS is high in sugars rumen acidosis can occur because the sugar is rapidly available to the cow. We may need to add more rumen buffers such as sodium bicarbonate to help prevent acidosis. In 2 weeks post-harvest a considerable amount of sugar has been used up in fermentation and lactic and acetic acids have increased significantly; by 6 weeks the new corn silage has very much stabilized but it isn’t until about 4 months that corn silage is fully fermented. Having said that, corn silage continues to go through changes after fermentation is complete especially in terms of protein solubility and starch digestibility which is why we have CS analyzed a few times after harvest and then again in the spring to measure these changes. Regarding moisture levels at harvest, many producers are harvesting closer to 60% moisture than 65% in recent years. The drier corn silage is at harvest the longer it takes to ferment. Dry corn silage does not pack as well to remove oxygen so that anaerobic fermentation can occur. Corn silage which is harvested too dry is not as palatable to dairy cows since it does not have the well-fermented smell and flavour which is important to maintain high dry matter intakes.  Avoid harvesting CS under 60% moisture to ensure a better, more complete fermentation for a more palatable silage which will in turn help to maintain high intakes.

Next we need to compare the nutrient quality of the old vs new CS aside from being fermented vs fresh. If your CS last year was low starch and poor digestibility because of the late spring etc. and this year the growing conditions were much better, then your new CS may be higher in starch and better fibre digestibility and therefore your cows may actually go up in milk when the switch occurs. Also, you may have grown a superior CS variety this year which was better suited for your farm and for your cows. Corn silage hybrid selection is one of the most important decisions dairy farmers make each year.

Now, In terms of what makes a good corn silage remember this forage is generally the major source of energy in the diet (which is the most limiting nutrient in lactating dairy cows) so overall energy level is the most important factor. Energy comes from various sources; overall starch level and as well starch digestibility and then overall NDF level and then NDF digestibility. Dual purpose corn varieties (silage + grain corn) can have higher starch levels (37-44%) while silage specific varieties will have higher NDF digestibility. BMR corn silage has a lower lignin content and therefore has very high NDF digestibility. There are also high floury starch corn silage varieties that have higher starch digestibility. If you are feeding a low to average level of CS then a conventional dual purpose CS variety may be for you and if you would like feed a high CS level to lower or possibly remove grain corn in the lactating diet then BMR or a floury starch CS variety may be best suited for your farm. Silage specific corn silage varieties can help achieve higher levels of milk production.

Feel free to contact me for more information regarding your corn silage. Lastly, safe harvesting everyone, avoid cutting corners and remember to watch for silo gases when entering silos.

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