Studies of the nutritive value of New Zealand dairy pastures

Abstract

The results of 89 mineral balance trials are reported, in which the intake and utilisation of potassium, sodium, calcium, phosphorus, and nitrogen have been examined with lactating dairy cows fed exclusively on fresh pasture herbage. Between September 1959 and April 1960 six Jersey crossbred cattle were stall-fed measured quantities of freshly cut herbage. The period covered by the trial extended from approximately the 10th week after calving until the cows were dried off. Excretion of each element was measured by total collection, representative sampling, and analysis of the dung and urine voided and the milk secreted. The mean intake of each element, the amounts voided in the milk, dung, and urine, and the amount of each retained, expressed in g per week, were as follows:— Mean availabilities of each element were: K, 88%; Na, 67%; Ca, 22%; P, 34%; N, 740%. Availability varied markedly between weeks and between animals, variation being greatest for Na and P. To assess the adequacy of the pasture herbages examined as sources of each element, intakes were compared with requirements derived from standard feeding tables. The only evidence of inadequate supply was of P, during a relatively short period in midsummer. Methods of deriving the maintenance requirements of these elements have been compared and discussed, and the results from the present trial are considered particularly in relation to the nature of the herbage fed and the chemical composition of herbages reported in previous studies.