Graduate Thesis Or Dissertation
 

Evaluation of nutritional qualities of common ryegrass screenings

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  • This study was conducted to investigate the production and processing technology of common ryegrass screenings and to determine the nutritive value of these screenings for sheep. The animal response to them was assessed when the sheep were fed on the screenings alone and in combination with other feedstuffs. Four in vivo digestion trials were conducted using alfalfa pellets and a mixed steer ration fed alone and in combination with 40 and 60 percent light and heavy common ryegrass screenings. Corn silage was also fed in the same combination. Wether lambs weighing approximately 80 pounds were randomly assigned to metabolism stalls designed to collect feces quantitatively separate from the urine. Collection periods lasted for 5 days with a 15 day transition period between trials. Proximate analyses were done on representative sub-samples of each of the feedstuffs and feces. In vitro dry matter digestion studies were run on the same combination of feedstuffs utilized in the in vivo digestion trials. Combinations of common ryegrass screenings ranging from 20 to 80 percent of the mixture were used to determine the effects of increasing levels. In addition, 12 randomly selected common ryegrass screening samples were used for comparative weight and digestibility analyses. The in vitro procedure involved the digestion of feedstuffs by diluted rumen liquor in glass centrifuge bottles contained in a constant-temperature water-bath at 39° C for 24 hours. No apparent palatability or toxicity problems from weed seed contamination were observed during the 86 day in vivo study. In vivo apparent digestibility for heavy common ryegrass screenings fed alone and in combinations with other feedstuffs is relatively high, whereas that for light common ryegrass screenings fed in the same manner is relatively low. Favorable interactions are indicated from blending 40-60 and 60-40 combinations of alfalfa with heavy common ryegrass screenings and corn silage used in the same blend. Unfavorable interactions are indicated when common ryegrass screenings are blended with either alfalfa, steer ration #7, or corn silage; however, both are inconclusive. In vivo correlations indicate that organic matter and dry matter digestion, gross energy, and crude protein can be used with a high degree of confidence to predict digestible energy. Crude protein content of feedstuffs is a reasonably good indicator of in vivo dry matter digestibility. In vitro negative correlations are associated with increasing percentages of light and heavy common ryegrass screenings mixed with alfalfa and steer ration #7. Positive correlations are shown when corn silage is used in the blends. The highest in vitro dry matter digestion occurred between 40 and 70 percent heavy common ryegrass screenings blended with alfalfa; 30 to 70 percent blended with steer ration #7; and 60 to 70 percent blended with corn silage. A positive correlation (p < 0.05) indicates a close association between the comparative sample weights of 12 randomly selected common ryegrass samples and their in vitro dry matter digestion. Major differences in comparative proximate analyses are shown between light and heavy common ryegrass screenings. A significant (p < 0.01) correlation is indicated between pooled in vitro and in vivo measures of dry matter digestibility for alfalfa, steer ration #7, corn silage, and light and heavy common ryegrass screenings.
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