gust: 38.9 vs.39.2◦C). Daily diurnal ranges and partial differences were lower for MYCW than NC cows in June (1.13 and 0.64 vs. 1.40 and 0.84◦C; P < 0.05) and August (1.11 and 0.54 vs. 1.29 and 0.70◦C; P < 0.05). Although not statistically significant, temperature differences between MYCW and PC cows also tended to support MYCW supplementation as a potential means of alleviating the problem of elevated body temperature associated with fescue toxicosis.

Three hundred multiparous Holstein cows (150 cows per treatment) were blocked according to calving date and randomly assigned to a study to determine the effect of trace mineral source on incidence and severity of claw lesions, reproduction, and lactation performance of dairy cattle. Treatments were 1) all trace minerals supplied by sulfates(ITM)or 2) 360mg Zn from Zn amino acid complex, 200mg Mn from Mn amino acid complex, 125mg Cu from Cu amino acid complex, and 12mg Co from Co glucoheptonate per day(CTM;Availa®; Zinpro Corporation, Eden Prairie, MN) replacing an equivalent amount of Zn, Mn, Cu, and Co from sulfates. Cows received assigned treatments from 21 d prior to calving through 250 d of lactation. Cows fed CTM produced 1.2kg more (P < 0.05) milk, energy-corrected milk, and 3.5% fat-corrected milk than cows supplemented with ITM. The CTM treatment reduced (P < 0.05) days open by 22 d and tended to increase (P < 0.15) percentage of cows pregnant by 150 d in milk (54.8% vs 42.7%) and first service conception rate (27.4% vs 18.4%). Cows fed CTM tended to have a lesser incidence (P < 0.15) of claw disorders than cows fed inorganic trace minerals at 75 d postpartum (23.6% vs 34.1%) and numerically lower incidence at 250 d postpartum (10.0% vs 17.7%). The CTM treatment increased yield of milk, decreased days open, and tended to increase first service conception rates, increase percentage of cows pregnant at 150 d in milk, and decrease claw disorders at 75 d postpartum.

influences of dietary NDF residuals (resNDF, sd = 3.0 ) was negative for kp (reskp = 0.059 resNDF, rsd = 0.4) and positive for MAST (resMAST = 0.088 resNDF, rsd = 0.9). For DMI the corresponding relationships were: reskp = 1.03 resDMI, rsd = 0.4; resMAST = 0.73 resDMI, rsd = 1.0. The influences of DMI and NDF remained similar among and within experiments for kp but not for MAST. When DMI decreased as dietary fill (as indicated by NDF and MAST) increased among experiments there was a mean decrease of kp of 0.26 %/h per hour of increase of MAST. In contrast, within the same experiments there was an increase of kp of 0.12 %/h per hour of increase of MAST.

The metabolism of intravenously dosed 75Se was studied in 10 Holstein bull calves fed for ad libitum access a control diet containing no added Pb or a control diet supplemented with 1000 ppm Pb as PbSO4 for 4 wk. The Pb-supplemented calves exhibited no clinical signs often ascribed to lead toxicity. Likewise, feed intake and body weight gains were not affected adversely. The lead content of rib, kidney, liver, and brain was increased. Serum glutamic oxaloacetate transaminase activity increased in the calves fed Pb during the last 2 wk of the experiment. The kidneys of the calves supplemented with lead were 34% larger than those of controls. The total endogenous 75Se in the feces over the 4-d collection period was not different between treatments (4.14% of dose versus 3.31% of dose). Likewise, urinary 75Se excretion values were similar. About 97% of the 75Se dose disappeared from the blood within 6 h after dosing four calves on both treatments. Tissue concentrations of 75Se were reduced in kidney, spleen, pancreas, brain, and spinal cord. In summary, ingested Pb had very little effect on the endogenous excretion of 75Se in urine and feces; therefore, the data are consistent with earlier research in which the main effect of Pb on Se occurs at the absorption site.

Thirty dairy cows, fed a control diet consisting of silage and concentrates, were given either 0, 1000, or 2000 ppm of supplemental Zn (DM basis), from zinc sulfate monohydrate (ZnSO4.H2O) for most of a lactation. Feeding 2000 ppm Zn decreased milk yield and feed intake after several weeks. Some cows were affected more severely than others. Generally, primiparous animals were more tolerant of the high Zn diet than multiparous cows. Milk Zn was materially higher for cows fed 1000 ppm added Zn than controls. With 2000 ppm Zn, milk Zn was elevated further but returned to control values when the high Zn diet was discontinued. Plasma Zn was higher in cows fed supplemental Zn with the increase from 1000 to 2000 greater than that for the first addition. Plasma Cu was lower in cows feed 2000 ppm Zn but milk Cu was not reduced. Milk fat content was not affected, but protein and SNF were reduced by the 12th wk with the 2000 ppm Zn diet. There was no apparent effect on long-term health or performance after the cows were removed from the 2000 ppm Zn diet. Except for lower calf weights with 2000 ppm Zn, reproductive performance was not measurably affected by the dietary treatments. The 1000 ppm added Zn diet had no adverse effect on the cows in any parameter measured.

Sixteen intact male Holstein calves averaging 86 kg and 63 d of age were assigned randomly to four treatment groups.The four treatment diets contained .17,.67,1.31, and 2.35% Ca on an as-fed basis.The resulting Ca:P ratios with P held constant at about .34%were .47:1,1.92:1, 3.83:1, and 7.20:1.Calves were fed diets at 3% of their body weights for 4 wk.Magnesium in the bone ash and serum was lowered by the 2.35% Ca treatment.Serum inorganic P was also reduced by the highest Ca diet during the last 2 wk of the experiment.Liver had the highest concentration of Zn in calves fed .67%Ca, and the muscle from calves fed 1.31% Ca diet had the lowest amount of Zn.Copper was reduced in pancreas for 1.31% Ca diet, but Ca was highest in the muscle and heart at the .67%Ca treatment.Weight gains and feed efficiencies were not affected by Ca.Fecal pH was different among treatments and increased as Ca intake increased.Young growing dairy calves can adapt to a wide range of Ca intakes and Ca:P ratios and maintain a moderate growth rate for 4 wk.It appears that excessive dietary Ca may affect concentrations of Zn, Fe, Cu, and Mn in some body tissues, but the magnitude of the effect is relatively small.

Bioavailability of P from defluorinated phosphate and dicalcium phosphate and the P requirement were studied with 63 male Holstein calves.A P depletion diet containing .08% total P on a dry matter basis was fed to all animals for 4 wk beginning at 6 wk of age and 61 kg weight.Calves developed typical signs of P deficiency.The depletion period was followed by a 6-wk experimental period in which the same depletion diet was used as a control.Phosphorus from each of the two sources was added to make diets containing .14, .20,and .32%total P. Source of supplemental P did not affect weight gains, feed consumption, feed efficiency, serum inorganic P, serum alkaline phosphatase, or bone ash.

Influence of dietary Ca on Se metabolism was studied with 16 intact male Holstein calves averaging 86 kg. Calves were assigned randomly and fed one of four diets containing, .17, .67, 1.31, and 2.35% Ca at 3% of their body weight for 4 wk. The diets contained .062 ppm Se and .34% P. Four days prior to the end of the experiment, calves were dosed orally with radioactive 75Se. Dietary Ca had no significant effect on 75Se absorption. There was a slight curvilinear relationship between apparent 75Se absorption and dietary Ca intakes. Urinary excretion of 75Se and stable Se tended to decrease with increasing dietary Ca, but differences were not significant. No significant differences were found in concentration of 75Se in several tissues. Kidney and liver had the highest concentration with that in kidney being about four times that of liver. Apparent 75Se absorption was decreased 10 to 6%, respectively, in calves fed extremely low and high amounts of Ca, compared with those receiving the requirement (.67% Ca). These small reductions along with a small R2 suggest that dietary Ca probably is of little practical importance relative to Se metabolism in calves.

Metabolism of orally dosed 75Se was studied in 10 intact male Holstein calves that were fed ad libitum a control diet containing no added Pb or supplemented with 1000 ppm Pb as PbSO4 for 4 wk. Lead-supplemented calves did not exhibit any clinical signs of Pb toxicity. Voluntary feed intake was reduced by 9.5% and average daily gain by 23%. Lead content of rib, liver, and kidney increased. Serum glutamic oxaloacetate transaminase activity was increased during the last 2 wk of the experiment in calves fed Pb. In calves receiving supplemental Pb, 75Se absorption, blood concentration, and urine concentration were reduced by 26, 21, and 42%, respectively. Tissue 75Se concentrations were significantly lower in kidney, liver, testicle, pancreas, small intestine, heart, spinal cord, and muscle in calves fed Pb. There was a significant negative correlation (r = -.78) between 75Se and stable Pb concentrations in the liver. It is not clear whether the ingestion of subclinical amounts of Pb could affect the absorption and utilization of Se in dairy calves to the extent of Se deficiency when dairy calves are kept in areas known to be low in Se.

Summary Fat is frequently added to ruminant diets to increase the energy density of the ration in an attempt to increase performance of animals such as high producing cows in early lactation. Often, problems have accompanied fat additions, including an adverse effect on rumen microbes, which may result in depressed fiber digestion and altered acetate to propionate ratio and depressed milkfat. Added dietary calcium can alleviate the adverse effects of feeding supplemental fats. Contrary to a widely held belief, recent research has shown that calcium absorption is not materially depressed by the addition of fat to cattle rations. Although the mechanisms involved in the calcium-fat interactions are not totally clear, evidence suggests the following as a working explanation. At the pH prevailing in an adequately buffered rumen, long chain fatty acids form insoluble soaps with calcium. In this form the fatty acids are not detrimental to the rumen microbes. At the lower pH of the abomasum and duodenum, the calcium soaps dissociate, with both the calcium and fatty-acids— being available for absorption. As the pH increases prior to excretion as feces, any unabsorbed calcium and fatty acids may recombine into calcium soaps.

Sixteen 10-wk-old, phosphorus (P)-depleted Holstein bull calves were fed for 6 wk a control diet containing .08% P or P-supplemented diets containing .14, .20 or .32% P with supplemental P from two sources (CDP and Dynafos). The diets contained .45, .56, .66 and .87% Ca. After 5 wk of the experiment, the calves were dosed orally with 65Zn, and daily total fecal collections were initiated. At the end of the experimental period, the calves were killed and tissue samples were taken for total Zn and 65Zn analyses. Growth, feed intake and feed efficiency improved with increasing dietary P levels. Level of dietary P and Ca had little or no effect (P greater than .05) on total Zn content of rib, tibia, liver, heart, kidney, muscle or blood. Likewise, 65Zn absorption and content in most tissues were not affected (P greater than .05). The results do not preclude the possibility of some minor effects of P levels on Zn metabolism. However, it is apparent that when adequate Zn is fed, any effects are likely to be of little or no practical importance.

Ten male Holstein calves were fed diets with or without 5% added animal fat in combination with low and high dietary calcium (.15 or .98%) for 4 wk. After 3 wk, the animals were orally dosed with calcium-45. One week later they were killed and tissue samples taken. Except for lower calcium-45 in bile, added dietary fat had no marked influence on calcium metabolism. Net absorption of calcium-45 (not excreted in feces) ranged from 82% for calves fed low calcium to 53% for those given high calcium. Calcium-45 in bone was substantially higher in calves fed .15% calcium. Tailbone biopsies revealed rapid uptake of calcium-45 with approximately as much incorporated during the 1st d as in the following 6 d. Calcium-45 in blood peaked 24 h following dosing. Calves fed .15% calcium had higher calcium-45 in blood and bile than those receiving .98% calcium. Calcium-45 values in soft tissue were low and did not differ materially among treatments. The decreases in radioactive calcium absorption and bone deposition with higher dietary calcium indicated that variable absorption was a major factor in calcium homeostasis. Added fat did not materially effect calcium metabolism with either low or high dietary calcium.