by Sally Colby
Once the leaves have fallen and cattle are grazing set-aside pasture or started on winter feed, there’s no turning back the clock. The weather conditions that determined how crops grew and when they were harvested have set the tone for winter feeding.
Forage may look good and have a decent nutritional analysis, but in some cases, off odors such as butyric acid can signal poor fermentation. While cattle will often eat what’s in front of them without any obvious deleterious effects, the long-term results aren’t good.
Dr. Garland Dahlke, Iowa State University Beef Center, said if spring harvest was rushed, forage may be less than optimum quality. Dahlke explained that protein in stored feed begins to break down during the fermentation process. “There’s NPN [non-protein nitrogen] because the protein is breaking down in fermentation,” he said. “We start getting some bacteria growth we don’t want – listeria, salmonella, E. coli can grow when the pH is over 5. Instead of haylage, you end up with something more like compost.”
Delayed harvest can also present problems in winter feeding due to higher dry matter levels that result in fermentation issues. “Be sure it’s covered and packed well,” said Dahlke, referencing bunker silos. “The saving grace of a delayed harvest is that cold weather comes quicker and there usually isn’t as much trouble. In March and April, when the weather warms up, it can become rotten.” Dahlke suggested feeding such silage before spring to avoid problems.
If crops were harvested after ideal maturity, crude protein levels drop. Dahlke said corn silage doesn’t have a lot of crude protein to begin with and over-maturity will reduce levels further. “Soluble protein is also going to be less than if it was put up at 38% dry matter,” he said. “Corn silage that’s made on time should have a pH of less than 4.”
Dahlke said good farming practices can initiate problems. Driving over the pack to achieve good compaction also inoculates the silage with whatever is on the tractor tires. Round bales that aren’t tight and left covered can introduce mold.
No-till and reduced tillage planting can introduce mycotoxins into crops because of pathogens in crop residue. Dahlke said today’s hybrids can handle the potential bacteria and fungi, but many molds inoculate plants as they emerge. “Before we ever harvest the feed, we can have mycotoxin problems,” he said. “Top-dressing with manure also introduces mycotoxins.”
Molds thrive in variety of conditions, such as aflatoxin, which is more likely an issue during drought. T2 toxin is a problem in wetter weather, and is usually the result of top-dressing fields with farm manure or sludge application. “It’s hit or miss,” said Dahlke, referring to T2, “but when you have it, it’s bad.” (T2 poisoning can be mistaken for salmonella because animals present with bloody diarrhea.)
Zearalenone, a mold that’s associated with ear and stalk rots in corn, acts like estrogen. Symptoms of zearalenone toxicity include poor reproductive performance, vaginal secretions and mammary gland enlargement in virgin heifers.
Dahlke related the story of a farm experiencing issues with stored feed. Standard lab analysis of a sample indicated high levels of zearalenone – more than 1,200 ppb (over 300 ppb is considered high). More specific testing for 400 different mycotoxins showed the sample had 71. Dahlke said that in a suspect sample, there is usually more than one toxin present, and each toxin has its own effects and causes different responses.
Toxin issues aren’t usually present throughout an entire crop – hot spots in various fields are the problem. Core samples in a bunker may indicate a particular toxin in one spot that reflects the loads coming in from one growing area, but the problem likely isn’t present throughout. “Molds and mycotoxins are growing on crops in the field,” said Dahlke. “Be aware of that, and take samples from different places – not just from one spot in the bunker or from one bale.”
Some toxins result in immediate death, while other toxins result in downed cows – usually due to neurological damage. Dahlke said toxins can lead to ketosis, impaired immune function, gut issues, reproductive problems, cancer, impaired milk production, sores, arthritis and overall poor performance. “Every mycotoxin has its own quirk and what it’s going to do,” said Dahlke. “It’s tough to diagnose, and some of them we never figure out.”
There are some fixes for mycotoxins in stored feed. Binders such as clays and yeast cell walls help in some cases, but shouldn’t be relied on as a fix-all. “Binders can tie up trace minerals,” he said. “If the immune system is already impaired, then copper and zinc are tied up and you’re going to add to the problem – especially if it’s the wrong binder. Not all mycotoxins will attach to the binder.” Other binders including chlorine, enzymes, ozone, UV light, microorganisms, prebiotics and probiotics sometimes work but are somewhat hit or miss. Additives to prevent mycotoxin issues include mild organic acids, inoculants, ammonia and sugars that enhance fermentation and reduce pH.
Dahlke said the no-cost mycotoxin fix is rumen protozoa because they’re much larger than bacteria and can denature and degrade mycotoxins. The problem is that protozoa are pH-sensitive, and in the case of subacute rumen acidosis (SARA), they don’t work. Another potential threat to protozoa working effectively is ionophores. Protozoa can become accustomed to cohabitation with ionophores, but that can take a while.
Another consideration for mycotoxin management is diet formulation. “Prevent acidosis or SARA, but you still need to provide adequate fermentable carbohydrates,” said Dahlke. “That becomes the glucose source for the animal for their brain, the developing calf and milk production. Don’t overdose rumen degradable protein – the liver may be straining out aflatoxin, and when the liver is compromised, protein metabolism is compromised as well. They can’t take all that excess nitrogen, so don’t use urea – balance it with natural proteins.”
Dahlke urged producers to minimize protein solubility. “Solubility and degradability aren’t the same thing,” he said. “Solubility just means it’s soluble in water. Formulate vitamins and minerals to be in line with requirements and don’t overdose. Keep dietary fat to a minimum.”
Choline, a B vitamin, can be used as a treatment for fatty liver. Dahlke said the ideal form to use is rumen bypass choline, which is expensive. “Choline is really needed in wintertime calving,” he said. “If the cow calves on pasture, there’s so much natural choline in the green grass that it doesn’t make any difference. If they’re eating stored feed and have a liver issue, that’s where the choline can work.”