Effects of copper supplementation on the copper status of peripartum beef cows and their calves

The effects of copper supplementation on the copper status of 40 late-pregnant Aubrac beef cows grazing a copper-deficient pasture and later fed a marginally deficient diet were studied for five months. They were divided into four equal groups; the control group received no copper supplement, groups 1 and 2 received copper as copper sulphate at 10 and 30 mg/kg of diet dry matter (DM), respectively, for five months, and group 3 received 120 mg/kg of diet dry matter for 10 days. Plasma copper concentration and the activity of erythrocyte superoxide dismutase (eSOD) were measured at the beginning of the experiment, in the cows and calves during weeks 1 and 3 after calving, and in the calves before they were turned out to pasture at a mean (sd) age of 51 (26) days. In spite of the low dietary copper content (4.2 mg/kg of DM), the plasma copper concentration of the control cows increased during the winter. All the copper supplements resulted in normal and similar plasma copper concentrations in the cows after calving, but the concentration decreased slightly between weeks 1 and 3 after calving in the group supplemented for 10 days. The treatments did not affect the eSOD of the cows. The calves born to the four groups showed the same patterns of plasma copper and eSOD. Compared with the cows, the calves had low plasma copper concentrations at week 1 and values in the normal range at week 3; their eSOD was high at weeks 1 and 3 but decreased after week 3.     

Serum copper concentrations in beef cows and heifers

OBJECTIVE: To characterize serum copper status of cows and heifers in beef cow-calf herds throughout the United States and to evaluate use of copper supplements in those herds. DESIGN: Cross-sectional survey. ANIMALS: 2,007 cows and heifers from 256 herds in 18 states. PROCEDURES: Producers participating in a health and management survey conducted as part of the National Animal Health Monitoring System voluntarily allowed serum samples to be obtained from cows and heifers for determination of copper concentration. Results were categorized as deficient, marginally deficient, or adequate. The proportion of cattle and herds (on the basis of mean value of the tested cattle) in each category was determined. Copper concentrations were compared between herds that reportedly used copper supplements and those that did not. RESULTS: Overall, 34 of 2,007 (1.7%) cows and heifers were deficient in copper, and 781 (38.9%) were marginally deficient. In each region, at least a third of the cattle were deficient or marginally deficient. For herds, 92 of 256 (35.9%) were marginally deficient, and 22 (0.8%) were deficient. Approximately half of the producers reported use of copper supplements, but a sizeable proportion of those producers' cattle and herds were classified as marginally deficient or deficient. CONCLUSIONS AND CLINICAL RELEVANCE: Copper deficiency is not restricted to a single geographic region of the United States. Copper deficiency can persist despite reported use of supplements by producers. Veterinarians dealing with beef cow-calf herds that have problems consistent with copper deficiency should not rule out copper deficiency solely on the basis of geographic region or reported use of copper supplements for the herd.     

Nonstructural carbohydrate supplementation of yearling heifers and range beef cows

A digestion study with 28 yearling heifers (428 +/- 9.9 kg; Exp. 1) and a 2-yr winter grazing trial with 60 crossbred cows (552 +/- 6.9 kg; Exp. 2) were used to determine the effects of level of nonstructural carbohydrate (NSC) supplementation on intake and digestibility of low-quality forage. Treatments were as follows: 1) control, no supplement; 2) 0.32 kg of NSC (1.8 kg/d of soybean hulls and soybean meal; DM basis); 3) 0.64 kg of NSC (1.7 kg/d of wheat middlings; DM basis); and 4) 0.96 kg of NSC (1.7 kg/d of barley and soybean meal; DM basis). Supplements provided 0.34 kg of CP/d and 5.1 Mcal of ME/d. In Exp. 1, heifers were individually fed hay (5.5% CP, DM basis) and their respective supplements in Calan gates for 28 d. Data were analyzed as a completely randomized design. In Exp. 2, cows were individually fed supplement on alternate days, and grazed a single rangeland pasture stocked at 1.8 ha/ animal unit month. Two ruminally cannulated cows were used per treatment to obtain forage extrusa and to measure in situ DM disappearance (DMD) and carboxymethylcellulase (CMCase) activity of particle-associated ruminal microbes. Data were analyzed as a completely randomized design with the effects of treatment, year, and their interaction. In both experiments, Cr2O3 boluses were used to determine fecal output, individual animal was the experimental unit, and contrasts were used to test linear and quadratic effects of NSC level and control vs. supplemented treatments. In Exp. 1, hay and diet DM, NDF, and CP intakes and digestibilities were increased (P < 0.01) by NSC supplementation compared with the control. In Exp. 2, 72-h in situ DMD and CMCase were decreased linearly (P < 0.08) with increasing NSC supplementation. Intake of forage DM, NDF, and CP was decreased linearly (P < 0.01) with increasing NSC supplementation during both years. Supplementation with NSC decreased (P = 0.01) cow BW loss compared with the control in yr 1, whereas in yr 2, cow BW loss was linearly increased (P = 0.03) by increasing NSC supplementation. Supplements containing NSC improved forage digestion and intake when heifers consumed forage deficient in CP relative to energy (digestible OM:CP > 7), but decreased forage digestion and intake when cows grazed forage with adequate CP relative to energy (digestible OM:CP < 7). Forage and supplement digestible OM:CP seemed to be superior predictors of response to supplementation with NSC compared with forage CP levels alone.     

Effect of copper status, supplementation, and source on pituitary responsiveness to exogenous gonadotropin-releasing hormone in ovariectomized beef cows

The effect of Cu status, supplementation, and source on pituitary responsiveness to exogenous GnRH was evaluated using nine multiparous, nonpregnant, nonsuckling, ovariectomized Angus cows (7.1 +/- 3.3 yr; 622.9 +/- 49.8 kg; BCS = 6.0 +/- 0.5). Cows were considered Cu-deficient based on liver Cu concentrations (< 30 mg of Cu/kg of DM) after receiving a low-Cu, forage-based diet supplemented (DM basis) with 5 mg of Mo/kg and 0.3% S for 216 d. Copper-deficient cows were stratified based on age, BW, BCS, and liver Cu concentration and assigned randomly to repletion-phase treatments. Treatments included 1) control (no supplemental Cu); 2) organic (ORG; 100% organic Cu); and 3) inorganic (ING; 100% inorganic CuSO4). Treatments were formulated to meet all NRC recommendations, except for Cu, which was supplemented to ORG and ING cows at 10 mg of Cu/kg of dietary DM. During the 159-d repletion phase, Cu status was monitored via liver biopsy samples, and all cows received exogenous progesterone. A controlled intravaginal drug-release device (replaced every 14 d) was used to maintain luteal phase progesterone as a means to provide negative feedback on the hypothalamic-pituitary axis. During the repletion phase, liver Cu concentrations did not differ between ORG and ING cows at any time. By d 77 of the repletion phase, all supplemented cows were considered adequate in Cu, and liver Cu concentrations were greater in supplemented than in nonsupplemented control cows on d 77 (P < 0.05) and throughout (P < 0.01) the repletion phase. Beginning on d 99, exogenous GnRH was administered to all cows at low (0, 3, and 9 microg; Exp. 1) and high doses (0, 27, and 81 microg; Exp. 2) at six different times. Cows were catheterized every fifth day, and blood samples were collected every 15 min for 1 h before and 4 h after GnRH administration and analyzed for LH concentration. In Exp. 1, Cu status and supplementation did not affect basal or peak LH concentrations, but total LH released tended (P < 0.07) to be greater in Cu-supplemented vs. control cows when 3 microg of GnRH was administered. In Exp. 2, there was no effect of Cu supplementation or source on basal, peak, or total LH released, regardless of GnRH dose. Pituitary LH concentrations did not differ across treatments. In conclusion, Cu status, supplementation, and source did not affect GnRH-induced LH secretion or pituitary LH stores in ovariectomized, progesterone-supplemented cows in this experiment.     

Prevalence and effects of intramammary infection in beef cows

Prevalence and effects of intramammary infection in 322 beef cows was determined during three calving intervals. Intramammary infection was confirmed in 37% of cows and 18.1% of quarters. Coagulase-positive staphylococci accounted for 17.9% of infections with Staphylococcus aureus isolated from 7.1% of cows. Coagulase-negative staphylococci and micrococci accounted for the remainder of infectious organisms. Butterfat and total protein levels were reduced 27.3 (P less than .05) and 25.5% (P less than .01), respectively, in milk from quarters infected with S. aureus. Somatic cell counts were elevated (P less than .001) with 3,827 X 10(3) cells/ml for S. aureus-infected quarters as compared with 555 X 10(3) cells/ml for uninfected quarters. Somatic cell counts were negatively correlated with 210-d calf weaning weights. Staphylococcus aureus-infected cows weaned calves weighing 19.1 kg less (P less than .01) than uninfected cows. At a present market value of $1.65/kg, economic losses were placed at $31.43/calf from cows infected with S. aureus in one or more quarters.     

Mastitis in beef cows and its effects on calf weight gain.

Quarter milk samples from 51 purebred (Angus, Polled Hereford, and Simmental) and 69 crossbred (Angus x Simmental x Charolais three-way cross) beef cows were collected aseptically at three times during lactation to determine the prevalence of intramammary infection, milk somatic cell counts (SCC), and effects of infection on calf weight gain. Quarter infection prevalence was 13.1, 14.9, and 27.5% in early, mid, and late lactation; corresponding cow infection prevalence was 25.8, 29.2, and 54.4%. Staphylococcus aureus was isolated from 2.9, 2.7, and 3.2% of quarters in early, mid, and late lactation, respectively. Corynebacterium bovis, generally regarded as a minor pathogen, was isolated from 4.0, 7.6, and 18.2% of quarters at the three respective times. Geometric SCC means (10(3) cells/ml) were 1,522, 344, and 509 for S. aureus-infected quarters; 344, 899, and 221 for Staphylococcus hyicus-infected quarters; 65, 36, and 86 for C. bovis-infected quarters; and 20, 17, and 18 for uninfected quarters in early, mid, and late lactation, respectively. Adjusted 205-d weight gain for calves with S. aureus-infected dams was 9.6 kg less (P less than .05) than for calves with uninfected dams. Adjusted 205-d weight gain for calves with dams infected with any mastitis pathogen did not differ significantly from that of calves with uninfected dams. At weaning half of the infected cows and half of the uninfected cows were given an intramammary infusion product containing 300 mg of cephapirin benzathine in each quarter; the remaining cows were untreated controls. Quarter samples were collected aseptically from all cows 14 to 28 d after subsequent calving. Quarter prevalence of infection after calving was lower (P less than .05) in treated (8.2%) than in control (22.4%) cows. Significantly more infections present at weaning were eliminated in treated than in control cows, but the new infection rate during the dry period and early lactation did not differ between the two groups.     

Labile magnesium reserves in beef cows subjected to different prepasture supplementation regimens

Thirty pregnant beef cows were utilized to determine the effects of winter Mg supplementation regimen on blood minerals after cows were turned to a spring tetanigenic tall fescue pasture. The winter Mg treatments were (1) tall fescue hay with free access to a Mg-deficient salt-mineral mix, (2) 6.4 kg of corn silage dry matter plus 114 g MgO/d and (3) tall fescue hay with free access to a salt-mineral mix containing 40% MgO from January 1 to February 15. All cows were then placed on the same tetanigenic pasture from February 15 to April 17 with free access to a Mg-deficient salt-mineral supplement. Forage Mg remained below .2% during the experiment. Forage Ca, P and Al changed throughout the spring, attaining maximum values of .35%, .46% and 415 ppm, respectively. Forage N and K also increased throughout the spring, reaching values of 3.5 and 3.8%, respectively, at the April 3 sampling. The forage K:(Ca + Mg) ratio approached 2.2 by March 26, which coincided closely with the average tetany date (March 29). Serum Mg averaged 1.97, 3.58 and 2.06 mg/dl for treatments 1, 2 and 3, respectively, on February 15 before turning cows to pasture. There were no treatment differences for serum Ca, P and K during the experiment. Eight cows exhibited symptoms of grass tetany (collapse) on an average date of March 29. Winter Mg supplementation provided little long-term protection against hypomagnesemia after turning cows to tetanigenic pasture, indicating that cows must have a supplemental source of Mg during this critical period.     

Experimental copper deficiency, chromium deficiency and additional molybdenum supplementation in goats--pathological findings

Secondary copper (Cu) deficiency, chromium (Cr) deficiency and molybdenosis (Mo) has been suggested to cause the "mysterious" moose disease in the southwest of Sweden. The present experiment was performed on goats to investigate the clinical, chemical, and pathological alterations after 20 months feeding of a semi-synthetic diet deficient in Cu and Cr. Four groups were included in the study: control group (n = 4), Cu-deficient group (group 1, n = 4), Cr-deficient group (group 2, n = 2) and Cu + Cr-deficient group (group 3, n = 3). Group 3 was additionally supplemented with tetrathiomolybdate during the last 2 months of the experiment. Main histopathological findings in groups 1 and 3 were the lesions in the liver, characterised by a severe active fibrosis, bile duct proliferation, haemosiderosis and mild necroses. Additionally, degenerative alterations of the exocrine pancreas were prominent in groups 1 and 3. Lesions in group 3 were more pronounced than in group 1. In group 3, the skin showed an atrophic dermatosis, while in group 2 a crusty dermatitis caused by Candida spp. was observed. This study shows that liver, pancreas and skin are mainly affected by a long term deficiency of copper and the findings are complicated by molybdenum application while chromium deficiency produced no histomorphological effects in our study.     

Effects of selenium and copper supplementation on the growth of beef steers

During the grazing seasons of 1978 and 1979, 126 Hereford cross Friesian and 25 Charolais cross Friesian steers were used in controlled trials of the effects of injecting them with copper and, or, selenium. In both seasons the unsupplemented steers had low blood concentrations of copper, selenium and glutathione peroxidase, whereas the supplemented steers maintained their serum copper concentrations within the normal range and had significantly higher whole blood concentrations of selenium and glutathione peroxidase than the unsupplemented animals. Supplementing the steers with 400 mg copper during 1978 increased their growth rate by 0.032 kg/day and supplementing them with 200 mg copper during 1979 increased it by 0.080 kg/day. Supplementing the steers in each year with two doses of selenium, each of 0.15 mg selenium/kg bodyweight, increased their growth rate by 0.041 kg/day in 1978 and by 0.060 kg/day in 1979. There was no interaction between the selenium and copper treatments and the total increases in liveweight gains due to both supplements were around 11 kg in 1978 and 16 kg in 1979.     

Effects of copper oxide bolus administration or high-level copper supplementation on forage utilization and copper status in beef cattle

Two experiments were conducted to study effects of high-level Cu supplementation on measures of Cu status and forage utilization in beef cattle. In Exp. 1, eight steers randomly received an intraruminal bolus containing 12.5 g of CuO needles (n = 4) or no bolus (n = 4). Steers were individually offered free-choice ground limpograss (Hemarthria altissima) hay. On d 12 (Period 1) and d 33 (Period 2) steers were placed in metabolism crates, and total forage refused and feces produced were collected for 7 d. Daily samples of forage offered and refused and of feces excreted for each steer within period were analyzed for DM, ash, NDF, ADF, and CP. Liver biopsies were collected on d 0, 12, and 33. Copper oxide bolus administration resulted in greater (P < 0.03) liver Cu (DM basis) accumulation in Period 1 (556 vs. 296 mg/kg) and Period 2 (640 vs. 327 ppm). Apparent digestibilities of NDF and CP were greater (P < 0.04) for steers receiving no bolus in Period 2 (62.2 vs. 57.1% and 50.2 vs. 43.4% for NDF and CP digestibility, respectively). In Exp. 2, 24 crossbred heifers were assigned to individual pens and received a molasses-cottonseed meal supplement fortified with 0, 15, 60, or 120 ppm of supplemental Cu (Cu sulfate; six pens per treatment). All heifers were offered free-choice access to ground stargrass (Cynodon spp.) hay. Heifer BW and liver biopsies were collected on d 0, 42, and 84. Forage refusal was determined daily, and diet DM digestibility was estimated over a 21-d period beginning on d 42. Heifers consuming 120 ppm of supplemental Cu gained less (P < 0.05; 0.04 kg/d) than heifers consuming 15 (0.19 kg/d) and 60 ppm of Cu (0.22 kg/d), but their ADG did not differ from that by heifers consuming no supplemental Cu (0.14 kg/d; pooled SEM = 0.07). Heifers supplemented with 15 ppm of Cu had greater (P < 0.05) liver Cu concentrations on d 84 than those on the 0-ppm treatment and the high-Cu treatments (60 and 120 ppm). Forage intake was less (P = 0.07) by heifers receiving no supplemental Cu than by heifers on all other treatments (6.6 vs. 5.8 +/- 0.37 kg/d). Apparent forage digestibility was not affected by Cu treatment. These data suggest that high rates of Cu supplementation (Cu sulfate; > 60 ppm of total Cu) resulted in less liver Cu accumulation by beef heifers compared with heifers consuming diets supplemented with moderate dietary Cu concentrations (i.e., 15 ppm). As well, the administration of CuO boluses might depress the digestibility of forage nutrient fractions in steers.     

Copper deficiency and effects of copper supplementation in a herd of red deer (Cervus elaphus)

Copper (Cu) deficiency was diagnosed in a Norwegian red deer (Cervus elaphus) herd subsequent to deaths due to emaciation in late autumn 1999. The animals had free access to salt licks containing 3000 mg Cu/kg. An evaluation of the herd revealed poor calf growth rate, low weights of adult hinds, dull and light-coloured hair coats and cases of diarrhoea. The herd was subsequently monitored throughout a three-year period of Cu-supplementation. The monitoring regimen included clinical observation, copper serum examination, weighing, faecal parasitological examination, and reproduction control by ultrasound. During the period January 2000 to May 2001, the animals were treated with Cu oxid capsules (1 g CuO/10 kg liveweight) at 2–4 months intervals, with the exception of March to September 2000. The animals were fed continuously with Cu-enriched concentrates containing 300 mg Cu/kg, at a rate of 1/2 kg per head and day, from May 2001 to January 2003. Following both copper supplementation regimens adequate serum Cu concentrations were measured, and markedly improved body weights, coat quality and reproductive results were observed, except for the period from March to September 2000 when no treatment was given. The results showed that in a deer herd, with a diet low in Cu, supplementation with CuO capsules had to be given at intervals of a few months to maintain adequate serum Cu levels. Free access to Cu-containing salt licks did not meet the animals'' Cu demand. Good and stable results were achieved by the daily feeding of Cu-enriched concentrates.     

Switch hair as an indicator of magnesium and copper status of beef cows

Samples of switch hair, blood, and urine were obtained periodically over 5.5 months from 11 Angus and 13 Angus-Charolais cows grazing either all-grass or grass-legume swards. Liver samples were obtained at the end of the study. Hair growth rate and mineral concentrations in switch hair (magnesium [Mg], copper [Cu]), blood serum (Mg, Cu), urine (Mg), and liver (Cu) were determined. Significant (P less than 0.05) hair-growth rate differences were observed among sampling periods (daily mean = 0.58 +/- 0.01 mm). Angus black-pigmented switch hair contained more (P less than 0.001) Mg than did the light-pigmented Angus-Charolais hair. The effect of season was observed on hair Mg and Cu and on serum Mg (P less than 0.01). Serum and hair Mg concentration correlated in both breed groups after removal of individual cow treatment effects (Angus: r = 0.58, P less than 0.001, n = 64; Angus-Charolais: r = 0.46, P less than 0.001, n = 76). Likewise, urine Mg and hair Mg concentrations correlated (Angus: r = 0.35, P less than 0.05, n = 53; Angus-Charolais: r = 0.26, P less than 0.05, n = 63). Sward type had a pronounced effect on serum and urine Mg concentrations and a slight effect on hair Mg concentrations (P less than 0.10) only during midsummer. Cattle with switch hair Mg values less than 25 to 30 mg (light pigmentation) and 100 to 125 mg (black pigmentation)/kg of dry matter (DM) may be hypomagnesemic.(ABSTRACT TRUNCATED AT 250 WORDS)     

Whole soybean supplementation and cow age class: effects on intake, digestion, performance, and reproduction of beef cows

Two experiments were conducted to determine the effects of whole soybean supplementation on intake, digestion, and performance of beef cows of varying age. Treatments were arranged in a 2 x 3 factorial with 2 supplements and 3 age classes of cows (2-yr-old, 3-yr-old, and mature cows). Supplements (DM basis) included 1) 1.36 kg/d of whole raw soybeans, and 2) 1.56 kg/d of a soybean meal/hulls supplement. Supplements were formulated to provide similar amounts of protein and energy, but a greater fat content with the whole soybeans. Supplements were individually fed on Monday, Tuesday, Thursday, and Saturday mornings. During the treatment period, cows had free choice access to bermudagrass hay [Cynodon dactylon (L.) Pers.; 8.4% CP; 72% NDF; DM basis]. In Exp. 1, 166 spring-calving Angus and Angus x Hereford crossbred beef cows were individually fed supplements for an average of 80 d during mid to late gestation. During the first 50 d of supplementation, cows fed soybean meal/hulls gained more BW (10 kg; P < 0.001) and body condition (0.18 BCS units; P = 0.004) than cows fed whole soybeans. However, BW change (P = 0.87) and BCS change (P = 0.25) during the 296-d experiment were not different between supplements. Although calves from cows fed soybean meal/hulls were 2 kg heavier at birth, there was no difference in calf BW at weaning between supplements. Additionally, first service conception rate (68%; P = 0.24) and pregnancy rate (73%; P = 0.21) were not different between supplements. In Exp. 2, 24 cows from Exp. 1 were used to determine the effect of supplement composition on forage intake and digestion; cows remained on the same supplements, hay, and feeding schedule as Exp. 1. Crude fat digestibility was the only intake or digestibility measurement influenced by supplement composition; fat digestibility was higher for cows fed whole soybeans compared with cows fed the soybean meal/hulls supplement (58.1 vs. 48.8%). Hay intake and DMI averaged 1.63 and 1.92% of BW daily, respectively. Dry matter, NDF, and CP digestibility averaged 54.1, 55.1, and 63.2%, respectively. Compared with supplementation with soybean meal/ hulls, whole soybean supplementation during mid to late gestation resulted in reduced BW weight gain during supplementation, inconsistent effects on reproduction, no effect on calf weaning weight, and no effect on forage intake or digestion.     

Effect of fish meal supplementation on plasma and endometrial fatty acid composition in nonlactating beef cows

Seven nonlactating mature Angus cows (4 to 10 yr old) were used to examine the effects of fish meal supplementation on plasma and endometrial fatty acid composition. Cows were fed a corn silage-based diet supplemented with either fish meal, a rich source of the n-3 fatty acids, eicosapentaenoate and docosahexaenoate (n = 3; 5.1% of dietary DM), or corn gluten meal (n = 4; 8.5% of dietary DM) for approximately 64 d. Cows were given 25 mg of PGF2alpha (i.m.) on d 11 and 25 of supplementation to synchronize estrous cycles. On d 18 postestrus of the second estrous cycle, cows were slaughtered, and caruncular endometrium was dissected from uteri immediately after slaughter. Jugular blood samples were collected immediately before supplementation was initiated (d 0) and at 7-d intervals for 35 d of the study. Plasma eicosapentaenoic and docosahexaenoic acids did not differ between treatment groups on d 0 (P > 0.10); however, these fatty acids were greater in cows supplemented with fish meal over the first 35 d of supplementation compared with cows supplemented with corn gluten meal (P < 0.05). Endometrial docosahexaenoic acid did not differ (P = 0.12), whereas eicosapentaenoic acid was greater (P < 0.05) in cows supplemented with fish meal than in cows supplemented with corn gluten meal. These results indicate that dietary fish meal alters plasma and endometrial n-3 fatty acid composition in beef cows.     

Hypomagnesaemia in beef cows wintered in Ontario.

A field experiment was undertaken in northern Ontario in order to assess the magnesium status of beef cattle raised in the area. Magnesium status was assessed using several criteria including blood and urine magnesium levels, and bone biopsy samples. Eighteen groups each containing four pregnant Shorthorn beef cows were used. Each of the following three mineral feeds were offered to six groups throughout the experiment: a mineral feed without magnesium, a mineral feed containing 8% magnesium in the form of magnesium oxide and the third containing sequestered magnesium with a magnesium level of about a tenth of that in the mineral feed containing magnesium oxide. During the winter, when the cows were housed indoors, they were fed grass silage. Six groups, two of each mineral feed, remained indoors throughout the summer. The other 12 groups were turned out to pasture on May 25 and continued receiving the appropriate mineral feed. There were no differences in serum magnesium owing to magnesium-supplementation treatments observed at any time during any experiment. Serum magnesium levels fell drastically in all groups before the cows were released to pasture, implying that the hypomagnesaemic condition was attributable to the stress of yarding. The rate of recovery from hypomagnesaemia was slower in the cows released to pasture than in those kept indoors. Urine samples from cows returned to the pasture were indicative of low magnesium status. At the end of the experiment, the magnesium levels in the bones of the housed animals were higher than for those on pasture. In spite of severe cases of hypomagnesaemia, no clinical signs of this metabolic condition were observed.     

Effects of pre- or postpartum selenium supplementation on selenium status in beef cows and their calves

The effect of Se supplementation before or after calving on Se status in deficient cows and their calves was studied using 72 beef cows in two experiments. In Exp. 1, cows calving in February or March 1997 were supplemented orally for 15 d in late pregnancy with 13.0, 32.5, or 45.5 mg of Se/d as sodium selenite. Glutathione peroxidase (GSH-Px) activities were measured in red blood cells (RBC) or plasma of cows and calves at d 15 and between d 17 and 88 after calving. In Exp. 2, cows calving in January 1997 were supplemented orally with .0, 13.0, or 32.5 mg of Se/d for 15 d postpartum, and calves were injected with 1.38 mg of Se when 2 d old and at an average age of 49 d. The GSH-Px activities were measured in 30-d-old calves and in cows and calves between d 77 and 115 after calving. In both experiments, Se supplementation resulted in adequate Se status for the dams. The increase in RBC GSH-Px activity was faster with 45.5 mg of Se/d, and GSH-Px activities remained high for up to 98 d after the end of supplementation. The improvement in Se status in calves as a result of maternal supplementation was greater in Exp. 1 than in Exp. 2, suggesting that the placental transfer of Se is more efficient than milk transfer. Prepartum oral Se supplementation of deficient beef cows with 13.0 mg of Se/d for 15 d allowed adequate Se status of dams and calves, and 45.5 mg of Se/d resulted in a faster improvement of Se status. Parenteral administration of 1.38 mg of Se to newborn calves did not sustain normal Se status in calves issued from deficient cows.     

Nutritional management of grazing beef cows.

In grazing operations, forage quality and availability are sometimes limited, and cattle are unable to consume enough nutrients from pasture forage to fulfill requirements. During such situations, supplemental or replacement feeding is necessary to meet production goals. A fundamental understanding of ruminant nutrition and forage management is helpful in deciding which feed or supplement type (ie, energy versus protein) best fits the goals of a specific beef production system. It is important to choose a delivery method and supplement form that provide the targeted amount of desired nutrients to each animal in the herd and that minimize input costs. The objective of this article is to serve as a resource for veterinarians as they provide nutritional management support to beef cow producers.     

Streptozocin-induced pancreatic islet destruction in beef cows.

Streptozocin (STZ) induces diabetes mellitus in sheep and pigs. To test the effect of STZ in cattle, cows were given 75-150 mg STZ per kilogram of body weight. Cows receiving 150 mg/kg required euthanasia within 24 hours after infusion because of the severe systemic effects of STZ. Seven cows receiving doses of < or = 100 mg/kg had mild to marked decrease in islet immunoreactivity for insulin and in pancreatic islet density and mild to severe tubulointerstitial nephritis. Two cows receiving 75 and 85 mg/kg STZ regained their ability to produce insulin and return blood glucose to basal levels. One cow given 100 mg/kg STZ developed insulin insufficiency consistent with type I diabetes mellitus. These findings demonstrate the susceptibility of the bovine pancreas to STZ: however, severe systemic complications were encountered. Alternative dosages and methodologies should be considered in future attempts to induce diabetes in cattle using STZ.