Graduate Thesis Or Dissertation
 

The effects of ryegrass straw and monensin on performance of feedlot lambs

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  • The objectives of this study were to investigate the effects of the by-product, ryegrass straw, and the feed additive, monensin, on the performance of feedlot lambs. Four pelleted rations were fed ad libitum: Ration 1 - 50% barley, 50% alfalfa hay; Ration 2 - 50% barley, 50% alfalfa hay and 25g/ton monensin; Ration 3 - 50% barley, 25% alfalfa hay and 25% ryegrass straw; Ration 4 - 50% barley, 25% Alfalfa hay, 25% ryegrass straw and 25g/ton monensin. The two levels of ryegrass straw (0 and 25%) and the two levels of monensin (0 and 25g/ton) were arranged factorially across the four rations. Sixty single-reared lambs sired by Hampshire rams started the trial shortly after weaning at an average weight of 29.15 kg. Fifteen lambs were fed each ration; five lambs in each of three pens. Lambs were weighed weekly and terminated from the trial when they reached 45.45 kg in unshrunk body weight. Two lambs from each pen were slaughtered and carcass traits obtained. A sample of the rumen fluid was taken from each slaughtered lamb to determine volatile fatty acid (VFA) concentrations. Some of the traits of interest were ration dry matter digestibility (DMD), lamb average daily gain (ADG), feed intake (FI) and feed efficiency (FE: feed/gain), carcass yield grade (YG), total volatile fatty acid content of rumen fluid (TVFA) and cost per unit of gain (CUG). Results indicated that monensin-fed lambs had a lower feed intake (-7.8%, P<.10), TVFA (-24%, P<.01), and ADG (-7.3%); an improved FE (+4.7%); an increased DMD (+1.7%) and a similar YG as non-monensin-fed lambs. Ryegrass straw fed-lambs had a lower DMD (-8.0% P<0.05), TVFA (-18.3%, P<0.01) and ADG (-7.3%); a poorer FE (-5.4%); an increased FI (+6.0%) and a similar YG as non-ryegrass straw-fed lambs. The acetic: propionic acid ratio was 2.72, 3.02, 3.07 and 2.67 for monensin, nonmonensin, ryegrass straw and non-ryegrass straw-fed lambs, respectively. CUG was lower (-1.8 for monensin than for non-monensin-fed lambs and lower (-8.0%) for ryegrass straw than for non-ryegrass straw-fed lambs. Estimated cost per kg carcass gain was lower (-1.1%) for monensin than for non-monensin-fed lambs and higher (12.6%) for ryegrass straw than for non-ryegrass straw-fed lambs.
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