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Forage testing is critical when using exotic feeds

Dennis Johnson, Dairy Production Systems, WCROC, Morris

January 18, 2008

"You were wrong" Jack said, sounding like my wife when I'd turned right instead of left as she'd directed. "The cattle love that weedy cover crop I baled in October and they're doing well on it too. You didn't think it would be much good. It's really helping stretch the expensive alfalfa I bought and it got good numbers from the lab, too." I remembered our discussion in November and recalled recommending that Jack sample all his forages and use the lab results to allocate the feed according to the needs of the different groups in his herd. At least I'd been part right.

"I just got $165 a ton for a load of grass hay at the hay auction. It went to a dairy. It was pure grass, it was just starting to come out of the boot when it was cut, it was baled and shedded with no rain and it was a beautiful green. I wish I had another load to sell. It was like getting a Christmas bonus." Lawrence had a big grin on his face as he planned to spend his quality bonus.

"This year I'm feeding my heifers corn stalks, distillers dried grains, wheat straw, a little grain, and vitamin mineral supplement in a TMR. My consultant balanced a ration that's saving me a lot of money and the heifers seem to be doing fine." Ray watches his margins closely. "If I had some good hay I'd probably sell it and just use the low cost ingredients."

Jack, Lawrence and Ray shared these comments with me the same day, at the same meeting. They were all satisfied with the performance of the forages they were using, but were all extremely dependent on making use of accurate forage analysis. Lawrence benefited when selling hay. Jack and Ray used the forage analysis to balance rations, determine which nutritional supplements to add to the diet, and to allocate feeds to livestock with different needs. With tight supplies of expensive forages available to purchase, the forage analysis is an essential tool for constructing diets.

Out wintered heifers fed TMR and hay to meet their needs.
Out wintered heifers fed TMR and hay to meet their needs.

No forage analysis is worth more than the sample it's based on. First, identify the lot as an allocation unit – species, date of harvest, maturity, weed content, etc. – that you consider an individual ingredient. If it is baled material, a core sampler that can penetrate 12 to 18 inches into the bales is needed. Fifteen to twenty bales should be cored and combined to assure that the sample is valid. Don't use flakes of hay as samples. Ten samples of ground hay combined should be adequate but watch that fine particles aren't lost in the sampling process. For silage, twenty grab samples across the face of the pile that are mixed and subsampled should make an adequate sample for the lab. Well-sealed freezer bags are ideal for sample transport. Freeze silage samples until they are sent to minimize sample deterioration.

Relative Feed Value (RFV) has been the standard for comparing forage samples. RFV is not a nutrient, but an index for ranking forages based on digestibility and intake potential. RFV is calculated from acid detergent fiber (ADF) and neutral detergent fiber (NDF). A RFV of 100 is considered the standard score and represents alfalfa hay containing 41% ADF and 53% NDF on a dry matter basis. The higher the RFV of the forage, the better the quality of the forage. A RFV of 150 is a frequent target value for "dairy" hay.

RFV is being replaced by Relative Forage Quality (RFQ). RFQ is an index for ranking forages based on a more complete analysis than RFV. RFQ is calculated using crude protein (CP), ADF, NDF, fat, ash and NDF digestibility measured after 48 hours in the reagent. RFQ is the better index, especially when grass forages are evaluated on the same scale as legume samples.

Ration balancing is more complex, combining feeds to meet requirements for energy, protein, a variety of expressions of fiber, fat, minerals and vitamins. Complex computer based programs also may draw on ingredients to produce a least cost ration.

Jack was concerned about combining expensive alfalfa with baled cover crop while meeting the needs of growing heifers. He was satisfied with a simple hand calculated ration that allocated the two ingredients to meet needs for growth while minimizing alfalfa in the diet.

Ray needed a more complex mixture as he wanted to generate a high performance diet with all bi-product ingredients. So he engaged a consultant with a strong nutritional background and a sophisticated computer program.

Jack, Lawrence and Ray all benefited from using forage analysis to improve the predictability of animal performance from diverse forages.

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