Q: Silage is the main component of a dairy ration. On some farms, it accounts for as much as 60-70% of the ration, whereas on other farms in the same region, the diet contains less than 50% silage. If milk production levels are the same, why is there such a big difference in intake?
ZC: There are some farms where the problem of low feed intake is practically non-existent whereas on others, there is a constant struggle. One reason lies in the preparation and quality of the forage. As it is such a large component of the dairy ration, it has a big influence on feed intake. Forage quality varies according to plant species, variety, fertility, environmental conditions and most importantly, stage of maturity. Figure 1 illustrates how feed intake decreases as the plant gets more mature. In addition, the management practices used for the preservation and storage of the forage are of great importance.
Figure 1. Effect of alfalfa-brome greenchop stage of maturity on dry matter intake
Q: What determines forage quality?
ZC: Protein and energy content play the largest roles in determining forage quality. Good quality forage is high in protein content. This is easily predicted by measuring the plant nitrogen content and multiplying it by 6.25 (the average nitrogen content of protein). Plant maturity at harvest has a large impact on crude protein content. Mature forages have fewer leaves and more stems. Leaves contain soluble proteins like chlorophyll whereas stems are high in fiber and low in protein. Energy content depends on the digestibility of the various chemical fractions of the forage. One common way of predicting forage energy content is by measuring the amount of fiber. Plants that contain large amounts of fiber are generally less digestible.
Q: If forage is grown under controlled conditions on farm, why do we struggle with quality?
ZC: In practice, a lot depends on the priority of the individual farm. Farms focused exclusively on milk production will produce a very different quality forage to those focused primarily on plant production. If the quality of forage is compromised, high costs will be incurred to purchase supplements to correct the forage quality to ensure high milk production. Due to the high demands on machinery, labor and equipment at specific times of the year, especially around the time of first and second cuts of grass and grain harvesting time, the harvest can be delayed, resulting in a lower feed value of the collected and stored material. Forage that is delayed in its collection is difficult to ensile; increased fiber levels result in resistance to compaction and all the associated problems related to aerobic stability. Crops that are harvested late are often contaminated with molds, toxic alkaloids (like those found in most tall fescues) and mycotoxins that enter the bunker silo and pits, and consequently hinder animal performance. Mycotoxins are secondary metabolites of molds belonging to several genera but in particular, Aspergillus, Fusarium, and Penicillium spp. which all cause mycotoxicosis. When livestock ingest one or more mycotoxins, the effect on health can be severe, producing evident signs of disease and in some cases, leading to death.
Q: Is harvest delay a common problem?
ZC: Unfortunately, it is very common. There are farms that manage to harvest on time and milk more than 40 liters per cow per day based on rations with up to 80% forage. To produce such high milk output, the quality of the harvested material must be very high. Feed accounts for approximately 60% of all costs in a dairy operation. If efforts are concentrated on collecting good quality, palatable material with a high nutrient content, the cost of purchased feed can be reduced. Associated veterinary bills will also go down due to fewer problems related to low feed intakes.
Table 1. NDF intake targets throughout lactation and the dry period
Q: What does producing high quality forage mean in practice for farm managers?
ZC: We used to say that every year is different, but every year after winter comes spring. Winter is the time where all the necessary work should be done. Here are my top three winter tasks:
- Carry out a forage inventory – a calculation of all current forage that is stored, including proper identification of the nutrient value and day of harvest. A forage inventory should be carried out every three months. This will help to avoid unforeseen situations of ration changes caused by poor allocation of forage (e.g. running out of corn silage or having to switch from grass to corn silage in a ration). Cows do not adjust well to ration changes.
- Analyses – the nutritional value of all stored material with separate analyses for mycotoxin contamination should be carried out.
- Planning ahead - to anticipate change is the best way to deal with it.
The use of silage inoculants is common to control fermentation and reduce dry matter losses. Biostabil® Plus for grass encourages proper fermentation and supports the aerobic stability of the forage. Mycotoxin prevention costs are much lower than the cost of fighting disease. Mycofix® Plus is the only registered product in EU that is recommended for the deactivation of mycotoxins.
Q: How much forage is needed on the dairy farm?
ZC: The amount of forage needed by a lactating dairy cow is based on dry matter (DM) intake and the concentration of forage in the diet (Table 1). The same is true for non-lactating animals and young stock. Optimum forage intake (the amount of neutral detergent fiber (NDF) needed to support maximum milk production), has been calculated by Mertens (2009) as 1.2% of the body weight of the cow. This applies to cows in mid and late lactation.
Q: What is NDF?
ZC: Neutral detergent fiber, or NDF, is the most common measure of fiber used for animal feed analysis. It includes most of the structural components of plant cells. Fiber is inversely correlated to energy content. Too much fiber in the ration reduces passage rate, limits intake and supplies only a moderate amount of energy for milk production. Cows fed with high levels of fiber in the ration remain healthy, but do not produce milk to their full genetic potential. If the forage harvest is delayed, NDF content increases which consequently means that less forage should be used in the ration. On the other hand, a deficiency of fiber in the dairy ration leads to rumen acidosis and other metabolic disorders so a balance must be found.
Q: What can be done if forage harvest is delayed?
ZC: Every effort should be made to avoid delays to the forage harvest. However, when a delay does occur, silage inoculants should be applied to speed up the fermentation process and increase the digestibility of the ensiled material. One good solution is to use BioStabil® Plus, as it will also reduce shrink losses during storage and feeding. Material that is ensiled without inoculants can lose as much as 20% of the nutritional value due to shrinkage. When harvest is delayed, the cutting length should be reduced, and proper attention should be paid to the compaction and covering of the forage.
Q: Are there any other suggestions for when the forage harvest is delayed?
ZC: The amount of silage that has a high NDF content should be reduced in high lactating cows, and replaced with purchased feed. For dry cows, those in late lactation and growing heifers, it should be sufficient to include a mycotoxin deactivation product such as Mycofix® Plus with the forage, and include it in the ration as normal. An alternative solution is to replace the low-digestible silage with by-products that are high in NDF, but that also have a high neutral detergent fiber digestibility (NDFD) such as soy hulls, beet pulp and in some situations citrus pulp. These products offer a more rapid source of NDF that is highly digested. The mycotoxin content of by-products is generally high so there is a need to use Mycofix® Plus to provide full protection against all mycotoxins.
Q: Can NDFD in forages be too high?
ZC: In practical conditions, it is unusual for forage to be too digestible. It could occur when, for example un-matured, very early cut grass containing a high sugar content and high NDFD content is ensiled. This could be counteracted by reducing the amount of grain in the ration.