Methionine Hydroxy Analog in Diets for Lactating Cows

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Abstract
In 2 trials in consecutive years 47 and 50 lactating Holstein cows were assigned to grain mixtures that contained 0, .1, .2 and .3% methionine hydroxy analog. Experimental diets were offered to the cows beginning 2 wk prepartum, and collection of data was begun 4 days postpartum. Grain was fed as a proportion of body weight. Individual intakes of dry matter [DM] were regulated by refusals maintained at 5 to 10% of intake. Alfalfa hay and corn silage were fed ad lib in a ratio of 1:1, dry basis. Milk fat test and yield were higher for cows supplemented with analog than for controls during early (4-116 days) lactation. Daily fiber intake was higher for cows fed .3% analog (2.2 kg) than for controls (1.9 kg) during early lactation in yr 1 but not in yr 2. Milk and solids-not-fat yields did not differ among treatments. Intakes of DM were not affected by treatment. From 117-256 days of lactation there were no differences in yields of milk, fat, or solids-not-fat. Milk from cows maintained on the same treatment both years changed little in fat test from yr 1 to yr 2, but cows that were changed from high analog during yr 1 to low during yr 2 decreased .48 percentage units in test. Those changed from no analog to analog increased .34 percentage units in test, and those changes from low analog to high analog increased .23 percentage units. Methionine hydroxy analog appears to be a useful supplement for increasing fat test of cows fed diets relatively high in concentrate.
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