With an eye on the narrow margins between profit and loss, and another eye on sustainability, some Colorado lamb producers are able to take advantage of the culls of area onion growers. Though onions are approximately 92 percent moisture, on a dry matter basis, they’re similar in energy to corn. As no-cost byproducts as onion growers sort through their crops from about October to March, they can be a smart solution.

Brad Anderson has been feeding cull onions to bred ewes for nearly 10 years, feeding them on the ground along with about 1 pound per day per head of roughage like sub-par hay or corn stalks. Beginning in October, sheep can graze harvested fields, later returning closer to home where he feeds onions on the ground and supplements with roughage. The nearby onion processor stores onions through the winter, sorting as they meet demand, and giving Anderson a consistent feed source through the colder months. Unlike cattle, he said, sheep can eat onions even after they freeze.

A study conducted by Tom McBride, the late county Extension director in Adams County, and Anthony Knight at the Department of Clinical Sciences at Colorado State University, heralded the beneficial relationship between onion and lamb growers. Disposal of cull onions is an annual problem for growers, according to the study notes, due to the high water content, nitrate levels, and the smell of decomposing onions. Leaving them in the field is problematic due to the build up of plant pathogens that can affect future crop production. Removal and disposal of the onions by sheep producers has been the subject of several studies showing that sheep can use limited quantities of onions in their diet without suffering the toxic effects of onions as other species will.

McBride’s study included both a ewe and a lamb study. In the ewe study, bred ewes were fed a diet entirely of onions during the last 102 days of gestation while control ewes were fed alfalfa and grain. Study ewes had comparable body condition scores and fleece weights with no significant difference in pregnancy or lambing rate. Though onion-fed ewes developed Heinz body anemia, something a 2005 case report by M.R. Aslani in Iran associated with deaths, abortions, and clinical signs of toxicosis in a flock of onion-grazing sheep, McBride’s study suggested the ewes were not adversely affected when compared to the controls. Adaptation to the exclusive onion diet, according to the results, is probably due to increased rumen metabolism.

In the lamb study, 50 lambs were divided into five even subgroups and were fed either zero, 25 percent, 50 percent, 75 percent, or 100 percent of the ration in onions with the remainder of the ration fed in grain. After receiving a feedlot concentrate finishing ration, lambs were fed cull onions for 76 days at 3.5 percent of their body weight. Study lambs were weighed throughout the study and on day 76 when received for slaughter. Carcasses were chilled for 24 hours and then evaluated and graded. Meat samples were evaluated by a panel of 32 undergraduate animal science students for juiciness, tenderness, flavor intensity, flavor desirability and overall palatability.

The study conclusion, and Anderson’s experience, both indicate that when the percentage of onions exceeds 50 percent of the ration, there is a marked decrease in weight gains. Anderson, who has fed onions to as many as 400 ewes annually, said he returns ewes to a grain and hay ration a few weeks prior to lambing. As a portion of a ration, the onions offer a solution to both growers. ❖

— Gabel is an assistant editor and reporter for The Fence Post. She can be reached at rgabel@thefencepost.com or (970) 392-4410.