Post-Harvest Mycotoxin Risk Management

Dr. David Davies - Silage Solutions Ltd

Post-Harvest Mycotoxin Risk Management

Dr. David Davies - Silage Solutions Ltd

This article aims to describe how to reduce mycotoxin risk from the point of harvest in the field to the point of presentation to livestock on the feeding table.

However, I will also take the liberty to include immediate preharvest decision-making on correct harvesting time, which can have a massive effect on initial, field-formed mycotoxin load.

Scroll to read more...

When to Harvest

All forages for ensiling should be harvested when the nutritional quality is optimum for the livestock for which the crop is intended. Thus, for productive and growing animals, high energy and/or protein, depending on the forage.

For dry cows, low protein and high fiber. In terms of mycotoxin potential, the productive and growing stock criteria will, under normal growing conditions, result in relatively low mold and mycotoxin challenge in the field. The dry cow forages do, however, offer a greater potential challenge. Therefore, these types of crops need excellent post-harvest management to reduce the risks of mycotoxin challenges becoming a major problem during feed-out.

However, there is one golden rule that many miss and some climate challenges that would alter the rules.

All forages that are to be ensiled in a clamp, bunker or drive-over pile should be ensiled at between 32–36% dry matter (DM), without exception, if they are for feeding to any class of stock except the dry cow. This is because field-formed mycotoxins increase as the crop matures, which is closely linked to the % DM.

Climate challenges

Drought/heat stress, flooding/waterlogging, hail storms and early autumn frosts have become more frequent issues due to a changing climate and affect the growth of our forages. Under these conditions, the rules change on meeting the animal’s nutritional needs versus obtaining a harvestable crop.

Under growing conditions where the crop begins to die, particularly grain crops like maize and whole-crop cereals, then immediate harvest, irrespective of the stage of maturity, is strongly recommended. This is because the crop nutritional quality will only decline from this point, and mycotoxin load will increase. A double whammy!

Harvesting

Direct-cut crops (maize, sorghum, whole-crop cereals with grain)

The key factor here is to choose a cutting height that reduces the harvest of the dead stem near the soil. This region of the stem is high in both lignin and molds and, so, potential mycotoxins.

With a good maize crop, the stubble height can be increased to 30 centimeters (12 inches), leaving poorly digestible stem and potential mycotoxins in the field.

Crops that need wilting (grass, clover, lucerne and early harvest cereals with no grain)

These crops should be mown with a cutting height no less than 5 centimeters (2 inches), and with some crops, 10 centimeters (4 inches). Clean crops in good ground conditions can be cut at 5 centimeters (2 inches), but in poor ground conditions with dead material in the bottom of the sward, cutting should be higher.

Crops should also be conditioned appropriately; grass and cereals heavily conditioned; legumes lightly conditioned. They should then be spread in a wide swath and wilted to the optimum DM of 32–36%.

The wilt time should be no longer than 24 hours for grasses and 48 hours for legumes. Extended wilts can lead to a 10-fold increase in mold and yeast numbers. These serve to inoculate the entire silage crop and increase the risks of aerobic spoilage and mycotoxin load at feed-out.

Forage Harvesting Chop Length

The ideal chop length should only be varied depending on the % DM at harvest. For the ideal % DM, this is around 2 centimeters (0.8 inches). Drier forages should be chopped shorter, as this will aid consolidation in the clamp. Wetter crops should be chopped longer because low-DM crops chopped too short will increase the risk of clamp slippage during storage, increasing the risk of aerobic spoilage and mycotoxin load.

At the Clamp

Filling and consolidation

Air, or more correctly oxygen, is the ‘Achilles heel’ of silage making, as molds require oxygen to grow. Thus, once the forage is brought to the clamp, the quicker and better it is consolidated, the lower the oxygen concentration will be during the first few hours of storage and the less it will penetrate the feed-out face after opening.

The lower the oxygen, the less growth of yeasts and molds. Thus, the lower risk of mycotoxin levels increasing. Therefore, even layers no more than 15 centimeters (6 inches) thick should be loaded onto the forage mass and consolidated by the packing tractor before the next layer is loaded.

Proceeding in this way from the first to the last load is the most efficient packing methodology. This process needs to happen as quickly as possible while maintaining a minimum forage density of 720 kg FM/m³.

Sheeting

Side walls should be sheeted and overlap with the top sheet by at least 1 meter (39 inches). Oxygen barrier cling film should be used as the first top sheet, followed by adequate further sheeting and netting to prevent damage by wildlife.

Gravel bags should be placed touching each other around the entire periphery of the clamp. This will trap the CO2 produced in the first few hours during plant and microbial respiration and prevent further air ingress. Together, these processes will enable a rapid anaerobic environment to be attained and maintained for the entire storage procedure.

The processes of good consolidation and sealing of the silage clamp will be the biggest factors reducing aerobic spoilage and mycotoxin risk at feed-out. In contrast, a poorly compacted and sealed clamp allows molds to proliferate in the clamp. The clamp environment will then switch between aerobic and anaerobic at frequent intervals during the storage process. The molds will switch from growing (aerobic) to surviving (anaerobic).

During the surviving mode is when they would become stressed and are likely to increase their mycotoxin production as a defense and survival mechanism.

Feed-Out

If all the good management processes highlighted above have been followed to the letter, then feed-out management becomes easy. Use a sharp feed-out tool and as-rapid-as-possible feeding across the entire face.

Traversing the whole face should only take three days in summer and up to five days in winter. If the management practices before feed-out have been less than sufficient, then it becomes extremely difficult to keep management at feed-out ahead of yeast and mold growth, as they will already have built up extensive microbial biomass in the silage that will burst into life when oxygen becomes available. Alongside mold growth will come the significantly increased risk of excessive mycotoxin load.

Feed-Table

Make up the total mixed ration using silage freshly removed from the silo. Mix properly and feed immediately.

Do not remove and mix in advance of feeding, as it will significantly increase the mycotoxin load.

Clear any uneaten feed daily, prior to placing fresh feed in front of the livestock. Ensure all mixing and feed areas are kept clean and free of rotting and moldy feed residues.

In summing up, a little thought and attention to detail at harvesting and filling the silo will save weeks of anxiety at feed-out.

Post-Harvest Mycotoxin Risk Management

Dr. David Davies - Silage Solutions Ltd

Scroll to read more...

Introduction

This article aims to describe how to reduce mycotoxin risk from the point of harvest in the field to the point of presentation to livestock on the feeding table.

However, I will also take the liberty to include immediate preharvest decision-making on correct harvesting time, which can have a massive effect on initial, field-formed mycotoxin load.

When to Harvest

All forages for ensiling should be harvested when the nutritional quality is optimum for the livestock for which the crop is intended. Thus, for productive and growing animals, high energy and/or protein, depending on the forage.

For dry cows, low protein and high fiber. In terms of mycotoxin potential, the productive and growing stock criteria will, under normal growing conditions, result in relatively low mold and mycotoxin challenge in the field. The dry cow forages do, however, offer a greater potential challenge. Therefore, these types of crops need excellent post-harvest management to reduce the risks of mycotoxin challenges becoming a major problem during feed-out.

However, there is one golden rule that many miss and some climate challenges that would alter the rules.

All forages that are to be ensiled in a clamp, bunker or drive-over pile should be ensiled at between 32–36% dry matter (DM), without exception, if they are for feeding to any class of stock except the dry cow. This is because field-formed mycotoxins increase as the crop matures, which is closely linked to the % DM.

Climate challenges

Drought/heat stress, flooding/waterlogging, hail storms and early autumn frosts have become more frequent issues due to a changing climate and affect the growth of our forages. Under these conditions, the rules change on meeting the animal’s nutritional needs versus obtaining a harvestable crop.

Under growing conditions where the crop begins to die, particularly grain crops like maize and whole-crop cereals, then immediate harvest, irrespective of the stage of maturity, is strongly recommended. This is because the crop nutritional quality will only decline from this point, and mycotoxin load will increase. A double whammy!

Harvesting

Direct-cut crops (maize, sorghum, whole-crop cereals with grain)

The key factor here is to choose a cutting height that reduces the harvest of the dead stem near the soil. This region of the stem is high in both lignin and molds and, so, potential mycotoxins.

With a good maize crop, the stubble height can be increased to 30 centimeters (12 inches), leaving poorly digestible stem and potential mycotoxins in the field.

Crops that need wilting (grass, clover, lucerne and early harvest cereals with no grain)

These crops should be mown with a cutting height no less than 5 centimeters (2 inches), and with some crops, 10 centimeters (4 inches). Clean crops in good ground conditions can be cut at 5 centimeters (2 inches), but in poor ground conditions with dead material in the bottom of the sward, cutting should be higher.

Crops should also be conditioned appropriately; grass and cereals heavily conditioned; legumes lightly conditioned. They should then be spread in a wide swath and wilted to the optimum DM of 32–36%.

The wilt time should be no longer than 24 hours for grasses and 48 hours for legumes. Extended wilts can lead to a 10-fold increase in mold and yeast numbers. These serve to inoculate the entire silage crop and increase the risks of aerobic spoilage and mycotoxin load at feed-out.

Forage Harvesting Chop Length

The ideal chop length should only be varied depending on the % DM at harvest. For the ideal % DM, this is around 2 centimeters (0.8 inches). Drier forages should be chopped shorter, as this will aid consolidation in the clamp. Wetter crops should be chopped longer because low-DM crops chopped too short will increase the risk of clamp slippage during storage, increasing the risk of aerobic spoilage and mycotoxin load.

At the Clamp

Filling and consolidation

Air, or more correctly oxygen, is the ‘Achilles heel’ of silage making, as molds require oxygen to grow. Thus, once the forage is brought to the clamp, the quicker and better it is consolidated, the lower the oxygen concentration will be during the first few hours of storage and the less it will penetrate the feed-out face after opening.

The lower the oxygen, the less growth of yeasts and molds. Thus, the lower risk of mycotoxin levels increasing. Therefore, even layers no more than 15 centimeters (6 inches) thick should be loaded onto the forage mass and consolidated by the packing tractor before the next layer is loaded.

Proceeding in this way from the first to the last load is the most efficient packing methodology. This process needs to happen as quickly as possible while maintaining a minimum forage density of 720 kg FM/m³.

Sheeting

Side walls should be sheeted and overlap with the top sheet by at least 1 meter (39 inches). Oxygen barrier cling film should be used as the first top sheet, followed by adequate further sheeting and netting to prevent damage by wildlife.

Gravel bags should be placed touching each other around the entire periphery of the clamp. This will trap the CO2 produced in the first few hours during plant and microbial respiration and prevent further air ingress. Together, these processes will enable a rapid anaerobic environment to be attained and maintained for the entire storage procedure.

The processes of good consolidation and sealing of the silage clamp will be the biggest factors reducing aerobic spoilage and mycotoxin risk at feed-out. In contrast, a poorly compacted and sealed clamp allows molds to proliferate in the clamp. The clamp environment will then switch between aerobic and anaerobic at frequent intervals during the storage process. The molds will switch from growing (aerobic) to surviving (anaerobic).

During the surviving mode is when they would become stressed and are likely to increase their mycotoxin production as a defense and survival mechanism.

Feed-Out

If all the good management processes highlighted above have been followed to the letter, then feed-out management becomes easy. Use a sharp feed-out tool and as-rapid-as-possible feeding across the entire face.

Traversing the whole face should only take three days in summer and up to five days in winter. If the management practices before feed-out have been less than sufficient, then it becomes extremely difficult to keep management at feed-out ahead of yeast and mold growth, as they will already have built up extensive microbial biomass in the silage that will burst into life when oxygen becomes available. Alongside mold growth will come the significantly increased risk of excessive mycotoxin load.

Feed-Table

Make up the total mixed ration using silage freshly removed from the silo. Mix properly and feed immediately.

Do not remove and mix in advance of feeding, as it will significantly increase the mycotoxin load.

Clear any uneaten feed daily, prior to placing fresh feed in front of the livestock. Ensure all mixing and feed areas are kept clean and free of rotting and moldy feed residues.

In summing up, a little thought and attention to detail at harvesting and filling the silo will save weeks of anxiety at feed-out.