ANNUAL REPORT, 1940 21 



with iron in milk was repeated during the winter of 1939-40. In the earlier 

 work done in 1938-39 only about as much supplemental iron was fed daily 

 as calculation showed to be already present in the ration. In this more 

 recent work from 3 to 4 times as much iron was added as occurred natural- 

 ly in the ration; as before, the supplement was the readily soluble iron 

 ammonium citrate. 



Results were very variable, with no definite trend. Average amounts 

 of iron were of the order of 0.3 mg. per kilo of milk or less, somewhat 

 less than was found in the earlier work, due it is thought to refinements in 

 method. As before, differences between individual cows in the same group 

 or between samples from the same cow in different months were much 

 greater than the average differences between the group receiving iron 

 and the group that did not receive it. Irrespective of method of statistical 

 handling of the results these average group differences were not signif- 

 icant. It is therefore concluded that the iron content of cows' milk cannot 

 be consistently changed by feeding an iron supplement. Workers in other 

 experiment stations have reached this same conclusion but with smaller 

 numbers of cows and over shorter periods of time. The element man- 

 ganese is being studied this year. 



Investigation of the Merits of Legume and Grass Silage for Massachu- 

 setts Agriculture. (J. G. Archibald and C. H. Parsons.) Further work 

 was done with phosphoric acid silage during the winter of 1939^0. In 

 double reversal feeding trials with fourteen cows over a period of 3^3 

 months, practically the same amount of milk was produced on this type 

 of silage as on corn silage (39.30 lbs. daily per cow as contrasted with 

 39.35 lbs. daily per cow). However, the observations in last year's report 

 regarding palatability and gains in live weight have been confirmed. 

 Phosphoric acid silage was somewhat less palatable to cows than either 

 corn silage or molasses silage, and gains in live weight were practically 

 negligible when it was fed. Again this year phosphoric acid silage has 

 produced milk of a finer flavor than that from cows on corn silage. 



Our first extensive trial of the suitability of molasses grass silage for 

 growing dairy heifers was inade during the past winter in comparison 

 with corn silage. In a double reversal trial 12 weeks in length, 18 heifers 

 gained 7.3 percent in live weight when fed corn silage, and 6.3 percent 

 when fed molasses grass silage. Average grade for condition, based on 

 general appearance and handling was: 



On corn Good+ + + + 



On grass Good + 



The molasses silage was readily eaten by the heifers. 



Results of this trial coupled with small weight gains noted when this 

 type of silage is fed to milking cows lead us to the tentative conclusion 

 that grass silage is better suited to milk production than to laying on of 

 flesh. 



A study of Urea as a Partial Substitute for Protein in the Ration of 

 Dairy Cows. (J. G. Arcliibald.) This project was organized the first of 

 the year in cooperation with the E. I. DuPont de Nemours Company of 

 Wilmington, Delaware, and the Massachusetts State Department of 

 Mental Health. Twenty-four cows in the herd of the Medfield State Hos- 

 pital are included in the feeding trial, eight of them on a double reversal 

 plan with periods eight weeks in length, and the other sixteen on a con- 

 tinuous feeding plan, eight to receive the regular herd ration for two 



