Calcium and Phosphorus Metabolism in Dairy Cows. V.—The Relative Assimilation of Calcium from Grades 1 and 3 Timothy Hay

Differences in the assimilation by dairy cows of calcium from alfalfa hay cured by different procedures, were first shown by H a r t and his collaborators in Wisconsin.They found that hay that had been " c u r e d under c a p s " gave a better assimilation than that which had been "exposed in windrows to air and light for four d a y s " (1, 2).The fact that the calcium of well-cured alfalfa hay is better assimilated by dairy cows than that of poorly-cured alfalfa hay was demonstrated in work conducted at this station (3).Alfalfa was cut and, after a few hours' drying in the field, spread loosely over racks in an open shed where it was exposed to the air but to no sun or rain.Another lot of the same hay was left in the field for more than a week where it was exposed to the sun and to one and one-half days of rainy weather.When these hays were fed the retention of calcium from the weathered hay was 14-15 grams per day less than that from the hay cured under cover.Assuming that the lesser calcium retention with the alfalfa exposed to sun and rain was probably due to a vitamin D deficiency, 1 an attempt was made to remedy this by the administration of cod-liver oil for a period of three weeks.No improvement in calcium assimilation was noted.I n fact there was a greater loss of calcium from the body when the cod-liver oil was fed.The question as to the effect of curing on the quality of hay is one of considerable practical as well as scientific interest.I t was therefore decided to investigate different grades of other hays and for this purpose grades 1 and 3 timothy hay were first chosen for comparison and a series of balance experiments initiated.In the first experiment., conducted during the winter months of 1929, conditions were not entirely satisfactory and the results were rather inconclusive.The experiment was, therefore, repeated with some variations in the spring of 1930. E X P E R I M E N T A LFor the 1929 experiment two pure-bred Holstein cows were used.Cow 200, 10 years old, had calved three months previous to the experiment and l~eceived for publication September 2, 1931.1 Steenbock et al later showed with rats that clover hay exposed to the sun contained more Vitamin D than that which was not so exposed (4).