Zinc Requirement of Holstein Bull Calves to Nine Months of Age

SUI~I~EARYFifteen Holstein bull calves were fed a semipractical type diet containing 8.6 ppm of zinc on an as-fed basis until 29 wk of age.Following this depletion phase, they were fed the same basal diet with the addition of various levels of zinc for 8 wk.As indicated by weight gains, feed consumption, testicle size and weight, testicle zinc content, blood zinc content, blood carbonic anhydrase activity, and clinical examination, calves fed the basal ration performed as well as those fed supplemental zinc.It was concluded that, under the conditions of this experiment, calves do not require more thau 8.6 ppm of zinc in their diet for normal performance to nine months of ~ge.Severe zinc deficiency symptoms developed by 12 wk oi' age in Holstein bull calves fed a purified diet containing 3.6 ppm zinc (8).These deficient animals responded very quickly to supplemental dietary zinc (8).Ill another study, calves fed a practical diet containing 25 ppm zinc performed as well for 15 wk as those fed the same diet supplemented with zinc (9).Thus, it appeared that the zinc requirement for normal growth of calves was well above 3.6 ppm, but not substantially above 25 ppm.It was suggested that a period much longer than 15 wk, a depletion phase, and a basal diet appreciably lower than 25 ppm zinc might be useful in further delineating the zinc requirement of cattle (9).The diet containing 3.6 ppm zinc which was used to develop and study zinc deficiency in calves (7, 8) was very expensive.Thus, it was reasoned that formulation of a ration which is relatively inexpensive, deficient in zinc, and which gives good perfornmnee when supplemented with zinc would be very helpful in zinc nutrition research.From analyses of various ingredients (10) and preliminary growth tests with calves a semi-practical~ reasonably economical diet was formulated containing 8.6 ppm zinc.This ration gave good performance when fed to calves.The purpose of this study was to further define the zinc requirement of calves and especially to determine whether the amount needed was above or below the level of zinc in the special semipractical basal ration (zinc content of 8.6 ppm).