Winter weather results in higher energy requirements for livestock. In the case of ruminant livestock a major portion of the diet is typically composed of forages. Forage nutrient content is affected by a number of factors, the major one being maturity at harvest, but also species composition, moisture content at harvest, and handling of the forage during the harvest and storage period. While most of our grain crops such as corn, soybeans, wheat, oats and barley have a fairly consistent quality and a narrow range of quality variance, forages can vary widely in nutritional quality. So while I can probably use book values for the nutritional content of corn no matter where it comes from, all first cut alfalfa hay or orchardgrass hay is not equal. To really know the nutrient content of forages, they should be sampled and sent to a lab for chemical analysis.
Recently I had an opportunity to attend a ruminant nutrition workshop sponsored by Rock River Lab. Dr. Bill Weiss, dairy and ruminant nutrition researcher at OARDC, was one of the presenters. His topic involved dairy cow diet composition variance and sampling. The focus was on forages, in particular haylage, corn silage and total mixed rations (TMR) that contain large portions of forage. One of the questions asked was; if a forage is resampled, for example corn silage or haylage from a bunker silo, and the result is different from a previous sample result, is that feedstuff really different or is the sample different? Research indicates that the largest variance between samples is likely to be due to sampling variance. In other words, how the sample is taken matters.
It is important to keep in mind that the small amounts of forage sent into the lab for analysis needs to accurately represent tons of forage. Accuracy and the confidence in the test results is improved when a number of subsamples is taken, combined and mixed together, and then a representative sample from that mixture sent into the lab. The actual process or technique used to gather a sample varies depending upon the forage to be sampled. Here are some general thumb rules to guide forage sampling:
- For dry hay, always use a forage probe to gather samples. Grabbing and pulling a sample from a hay bale will not provide you with a representative sample and test results will not accurately reflect the nutrient content of the bale.
- Sample lots of hay separately. A lot of hay could be defined as hay of similar species content, harvested at a similar maturity and ideally from the same field and/or from fields harvested on the same day or within a couple of day span. First cutting hay in particular can have large changes in forage quality within even a 2 to 3 day span.
- For small square bales, sample at least 20 separate bales within a lot. Use the forage probe to sample from the end of the bale, between the twine. Medium and large square/rectangular bales have a more uniform distribution of leaves and stems compared to small square bales so they can be sampled anywhere on the bale sides or ends. For large round bales, sample at least 8 to 10 bales per lot of hay. Sample on the curved side of the bale, inserting the forage probe perpendicular to the side of the bale. In all cases, if more samples can be taken and combined, this can increase the accuracy and reliability of the forage test results.
- Sampling ensiled forages such as haylage or corn silage: Taking hand grab samples from the face of the bunker silos is NOT recommended due to safety concerns. Use a loader bucket or face shaver to create a pile of silage on the floor of the bunker. If this forage is not going to be fed in a total mixed ration (TMR) then collect 5 to 8 samples. Using some type of scoop is better than using a hand grab sample, but if a hand grab sample is used, do so with your hand upturned to mimic a scoop. Combine samples into a 5 gallon pail, mix thoroughly and take a representative sample for analysis using a scoop.
- Sampling baleage or silage bags: Hand samples can safely be taken from the face of haylage or corn silage in bags. The best method is to knock down or remove the amount that would normally be fed and collect 4 to 5 scoop samples from that pile and then collect another 4 to 5 scoop samples from the newly exposed face. Combine all these subsamples into a bucket, mix thoroughly and then collect a representative sample to send in for analysis. Another way to sample wrapped baleage or forage in silo bags is to take at least 8 to 10 core samples at various locations, punching through the plastic. Holes must be taped shut after sampling. Core samples should be placed in a bucket, mixed and then a representative sample collected and sent for analysis.
- Sampling a TMR: At the nutrition workshop I mentioned at the beginning of this article, Bill Weiss presented results of his research work that had focused on TMR sampling and variance in sample results. Dr. Weiss told participants that there is large sampling variance with TMR rations and taking a single sample and sending it in for analysis is a waste of time and money. The way to decrease variance and increase the reliability of TMR analysis is to mix thoroughly, take smaller subsamples and send in duplicate samples to the lab. When results come back, average the lab results and use that figure.
All forages are not equal and forage quality book values are really not useful for on-farm ration balancing. Testing forages is the only way to be able to match and adjust forage rations to livestock nutrient needs. Proper sampling will increase the accuracy and reliability of test results.
For more information about forage sampling click on the link below to access a fact sheet from the University of Wisconsin Extension system: