Prepartum supplementation of selenium and vitamin E to dairy cows: assessment of selenium status and reproductive performance

Incidence of retained placenta in dairy cows was evaluated in 627 parturitions. The herd was divided prepartum into three groups: 1) control, no treatment (n = 217 cows); 2) cows injected intramuscularly (n = 190) 21 to 10 d prior parturition with 45 mg Se and 2040 IU of vitamin E; and 3) cows intraruminally administered (n = 220) with two 30-g pellets containing 10% elemental selenium 2 mo prior to expected calving. Incidence of retained placenta (22.1%) was not reduced by Se in combination with vitamin E injection or intraruminal Se pellet nor were other measures of reproduction improved for cows fed a prepartum diet adequate in Se. At parturition the blood plasma Se concentrations were higher in treated postpartum with Se than in untreated cows. No difference in blood plasma Se was observed at parturition between cows with or without placenta retention. Cows dosed intraruminally with Se had a significant increase in milk Se, but this was too small to be a danger to human health. The present results on placenta retention suggest that this disorder is not a Se responsive disease in the dairy cow.     

Effect of duration of supplementation of selenium and vitamin E on periparturient dairy cows

Cows were fed diets either supplemented with .2 ppm Se and 70 IU vitamin E/kg diet DM (21 cows) or unsupplemented (40 cows) during the dry period (approximately 60 d). From parturition to 21 d of lactation, cows were fed diets that were either supplemented with .3 ppm Se and 40 IU/kg vitamin E or unsupplemented. At d 21 following parturition, 18 cows fed the unsupplemented diet were switched to diets containing 0 or .3 ppm supplemental Se and 0 or 40 IU/kg supplemental vitamin E arranged factorially. These diets were fed for the next 32 d. The remaining cows continued their respective diets for 32 d. Plasma Se concentrations averaged .1 microgram/ml for supplemented cows but were .05 micrograms/ml for unsupplemented cows. Plasma Se concentration from cows fed supplemental Se from 21 to 53 d postpartum increased rapidly and were not different from long-term supplemented cows. Whole blood glutathione peroxidase activity was lower in unsupplemented than in supplemented cows. Short-term Se supplementation increased glutathione peroxidase activity above that for unsupplemented animals, but activity was still less than that in long-term supplemented animals. Plasma alpha-tocopherol concentrations at parturition and d 21 postpartum were lower in unsupplemented than in supplemented animals. On d 53 postpartum, no differences in plasma alpha-tocopherol concentrations were found between long-term supplemented and unsupplemented cows. Supplementing vitamin E during the dry period increased alpha-tocopherol content of colostrum.     

Meta-analysis of the effect of oral selenium supplementation on milk selenium concentration in cattle

Soils in many regions of the world have a low Se content. Consequently, forages and crops grown on these soils may provide inadequate dietary Se for humans and grazing animals. Selenium supplementation has been used to enhance Se status and milk Se concentration, but results conflict. Milk Se concentration appears to be a useful indicator of animal and herd Se status, and reflects the responsiveness to supplementation. A systematic review and meta-analysis were carried out to summarize all available scientific evidence for the effect of oral Se supplementation on milk Se concentration in cattle. The literature search was based on electronic and nonelectronic databases. Fixed- and random-effects models of meta-analysis were used, and a meta-regression was carried out to evaluate heterogeneity among studies. Random-effects meta-analysis was performed on 42 studies published between 1977 and 2007. Oral Se supplementation resulted in an average increase in milk Se content of 0.16 (95% confidence interval: 0.117, 0.207) μmol/L, with a significant heterogeneity among studies. Weak publication bias was evident, but it did not change the average effect. The continent where the study was performed, Se source, Se dose, and the interaction between source and dose explained 71% of the between-study variance. On average, American cows supplemented with Se yeast (e.g., 6 mg/h per day) had greater milk Se concentrations (approximately 0.37 μmol/L) 75 d after the beginning of supplementation when compared with those supplemented with inorganic forms of Se. This information provides a basis for tailoring daily animal requirements and for enhancing the Se intake of consumers of dairy products.     

Responses to controlling gastrointestinal parasitism in dairy cattle

Sixty-eight Holstein heifers, paired on milk production potential and season of birth, were randomly assigned within pairs to a control or treatment group to evaluate the effect of raising replacement heifers on a prophylactic anthelmintic regimen. The anthelmintic, thiabendazole (6.6 g/100 kg body weight), was administered orally as a paste at 2.5, 3.5, 6, 9, and 14 mo of age and at parturition. The control group received no thiabendazole. Fecal samples were collected from both groups at the time of thiabendazole treatment. Days to first service were 457.1 and 457.8 for the control and treatment groups. There were no differences in services per conception or days to first calving. Nematode eggs per 5 g of feces were similar at 2.5 mo (.6 and .8), 3.5 mo (38.6 and 22.4), 6 mo (40.2 and 43.1), 9 mo (39.0 and 22.4), 14 mo (55.2 and 22.4), or parturition (16.5 and .4). There were no differences in body weight changes over the first 18 mo of age. Subsequent first lactations were similar (9422 and 8710 kg 305-d mature equivalent, for twice daily milking) as was actual milk production for the first 120 d of lactation. Under these environmental conditions and apparently low parasitism in this herd, thiabendazole did not substantially influence nematode egg count and had no effects on body weight gains or milk production.     

Vitamin E supplementation during the dry period in dairy cattle. Part II: oxidative stress following vitamin E supplementation may increase clinical mastitis incidence postpartum

The aim of this study was to evaluate, retrospectively, which physiological states influenced the effect of vitamin E supplements during the dry period on the level of oxidative stress at 2 wk antepartum. Furthermore the effect of oxidative stress at 2 wk antepartum on the risk of clinical mastitis in early lactation was investigated. Cows experience oxidative stress around calving. Vitamin E is able to decrease oxidative stress by scavenging free radicals. Normally, vitamin E radicals formed when vitamin E reacts with free radicals are regenerated by a network of other antioxidants, termed the “vitamin E regeneration system” (VERS). In case of vitamin E supplementation, VERS should be sufficient to regenerate formed vitamin E radicals; if not, oxidative stress might increase instead of decrease. Additionally, the level of oxidative stress and vitamin E might be important physiological states to evaluate before supplementation. In a clinical trial, 296 cows on 5 farms were randomly divided into 2 groups, supplemented with a mineral mix between dry off and calving that supplied 3,000 or 135 IU/d, respectively. Blood samples collected at dry off and 2 wk antepartum were analyzed for vitamin E, reactive oxygen metabolites, ferric-reducing ability of plasma, glutathione peroxidase, and malondialdehyde. Cows were allocated retrospectively into 8 subgroups based on the level of oxidative stress, vitamin E, and VERS status at dry off. To evaluate whether differences in physiological states at dry off influenced the effect of vitamin E supplementation on the level of oxidative stress, group effects (supplemented vs. control) were studied with Student's t-test for all 8 subgroup at 2 wk antepartum. Differences in physiological states at dry off influenced the effect of vitamin E supplements. In 2 insufficient VERS subgroups, the supplemented group had higher levels of free radicals at 2 wk antepartum compared with the control group. Relative risk calculation was used to study the effect of oxidative stress at 2 wk antepartum on the incidence of mastitis in the first 100 d of lactation. Higher levels of oxidative stress at 2 wk antepartum were related to higher risk of clinical mastitis. In conclusion, not every dry cow responded well to high vitamin E supplementation. This subgroup analysis provides a possible explanation for the unexpected adverse effects observed in the clinical trial.     

Peripartum serum vitamin E, retinol, and beta-carotene in dairy cattle and their associations with disease

Peripartum decreases in serum concentrations of vitamins A and E may contribute to impaired immune function in dairy cows. The objectives of this study were to describe peripartum serum concentrations of alpha-tocopherol, beta-carotene, and retinol and their associations with disease risk. On 20 farms over 1 yr, blood samples were collected weekly from 1057 cows from 1 wk before expected calving until 1 wk postpartum. Serum concentrations of alpha-tocopherol, beta-carotene, and retinol, as well as several biochemical variables were measured. Their associations with the risk of retained placenta or clinical mastitis were modeled separately with logistic regression, and the factors associated with the concentration of each vitamin were modelled with mixed linear regression. Differences in vitamin concentrations between 2 batches of sera analyzed 6 mo apart required stratification of statistical analyses. Accounting for the effects of parity, season, and twins, an increase in alpha-tocopherol of 1 microg/mL in the last week prepartum reduced the risk of retained placenta by 20%, whereas serum nonesterified fatty acid concentration > or = 0.5 mEq/L tended to increase risk of retained placenta by 80%. In the last week prepartum, a 100 ng/mL increase in serum retinol was associated with a 60% decrease in the risk of early lactation clinical mastitis. There were significant positive associations of peripartum serum concentrations among each of alpha-tocopherol, beta-carotene, and retinol.     

Effect of vitamin E and selenium supplementation on incidence of clinical mastitis and duration of clinical symptoms

Incidence of clinical mastitis and duration of clinical symptoms for complete lactations were evaluated for 80 cows randomly assigned to one of four groups: vitamin E supplemented- and selenium injected, selenium injected, vitamin E supplemented, and controls. Vitamin E supplementation and selenium injection were during the dry period. Log-linear analysis of incidence data revealed a significant 37% reduction of clinical mastitis by vitamin E. Incidence was not affected by selenium alone, nor was there any evidence for interaction of vitamin E with selenium on incidence. However, duration of clinical symptoms (calendar months clinical/quarter lactating) was reduced by 46% for the selenium group, 44% for the vitamin E group, and 62% for the vitamin E-selenium group as compared to controls. We conclude that dairy cow diets deficient of vitamin E may elevate incidence of clinical mastitis. Selenium deficiency may result in greater duration of clinical symptoms, and selenium may interact with vitamin E. Coliform bacteria and species of streptococcus other than Streptococcus agalactiae were isolated from 70% of the clinical cases.     

Responses of high-producing dairy cows to long-term treatment with pituitary somatotropin and recombinant somatotropin

Thirty Holstein cows capable of high milk production were utilized to examine the effects of long-term administration of bovine somatotropin on lactational performance. Treatments were 0 (control), 13.5, 27, and 40.5 mg/day of recombinantly-derived bovine somatotropin and 27 mg/day of pituitary-derived bovine somatotropin. Hormone was injected intramuscularly, once daily beginning at 84 +/- 10 days postpartum and continuing for 188 days. Cows were fed ad libitum a total mixed diet throughout the lactation. Recombinant somatotropin treatments increased average fat-corrected milk yield in a dose-dependent fashion from 23 to 41% over the control production (27.9 kg/day. Pituitary somatotropin (27 mg/day) increased milk production by 16%. Milk lactose, protein, and fat composition was similar for all treatments. Control cows were in positive energy balance throughout the treatment period (4.7 Mcal net energy/day. Initially, the large increase in milk yield with somatotropin treatment caused cows to decrease in energy balance. However, voluntary intake gradually increased, and by week 10 of treatment all somatotropin treatment groups were in positive energy balance. Thus, the gain in body weight over the treatment period was similar for all groups, ranging from 17 to 22%. Gross lactational efficiency (milk per unit of net energy intake) was improved by exogenous somatotropin whether calculated as observed, corrected for body weight changes, or using the theoretical energy requirements for maintenance and milk production. Results are consistent with bovine somatotropin as a homeorhetic control that coordinates an array of physiological processes so that nutrients are partitioned for milk synthesis.     

Effect of niacin supplementation on milk production and ketosis of dairy cattle

In two experiments with Holstein cows effects of dietary supplementation of niacin to periparturient cattle on subsequent milk production and ketosis were examined. In Experiment 1, 20 cows were assigned to two groups. The treatment group received niacin at 6 g per head per day for 2 wk prepartum and 12 g per head per day for 4 wk postpartum. The control group received no niacin. In Experiment 2, 40 cows were assigned to four groups of 10 cows. One group served as the control and the other three received 3, 6, or 12 g niacin per head per day for 10 wk postpartum. In both experiments niacin-supplemented groups produced slightly more milk than controls. There were no consistent changes of milk composition with treatment. Glucose concentration in blood serum was higher for cows receiving niacin. Concentrations of beta-hydroxybutyrate and nonesterified fatty acids in blood and plasma were generally lower for niacin-supplemented groups. Niacin supplementation had no effect on feed intake or body weight changes. In Experiment 1 there was a significant reduction of niacin concentration in red blood cells of postpartum cows not receiving supplemental niacin. Insulin concentration in blood serum in Experiment 2 was unaffected by niacin supplementation.     

Long-term effects of feeding gossypol and vitamin E to dairy calves.

Male Holstein calves were used to test the effect of feeding 400 mg of free gossypol/kg of diet and to determine whether vitamin E could counteract gossypol toxicity. Fifty-two calves were allotted to treatments as follows: 1) soybean meal-based starter; 2) cottonseed meal-based starter; 3) cottonseed meal-based starter + 2000 IU of vitamin E/d per calf, and 4) cottonseed meal-based starter + 4000 IU of vitamin E/d per calf. Vitamin E supplementation (treatments 3 and 4) improved weight gain and feed intake over calves on treatment 1. Gossypol concentrations in plasma were higher in calves on treatments 2, 3, and 4 than in calves on treatment 1; however, no differences were observed among animals receiving the three cottonseed meal diets. Hemoglobin and hematocrit were decreased in calves receiving treatment 2, and vitamin E supplementation counteracted this effect (treatments 3 and 4). Plasma alpha-tocopherol concentrations were not affected by gossypol intake and followed the vitamin E supplementation pattern During the experimental period, 10 calves died, six from treatment 2 and two each from treatments 3 and 4. Necropsy findings from 4 of 10 calves were suggestive of gossypol toxicity. Histopathological examination revealed centrilobular necrosis in the liver and atrophy and vacuolation of cardiocytes. Feeding cottonseed meal caused death of some calves with gossypol related toxicity signs, but did not decrease plasma alpha-tocopherol; however, vitamin E supplementation increased performance and may have conferred some protection against gossypol toxicity.     

Comparing responses of dairy cows to short-term and long-term heat stress in climate-controlled chambers

Heat stress (HS) in dairy cows can be classified into short-term heat stress (STHS) and long-term heat stress (LTHS) according to the number of consecutive days in HS. The comparative study of these 2 types of HS is limited in terms of their effects on the production and energy metabolism of cows. In this study, 4 lactating Holstein cows (102.5 ± 12 days in milk, 605 ± 22 kg of body weight, second parity) fitted with rumen fistulae were randomly assigned to 1 of 2 groups in a 2 × 2 crossover design and allocated to 1 of 2 climate-controlled chambers. This study contained 2 periods, each with a control phase and a HS phase. There was a recovery phase between 2 periods. The HS phase comprised either STHS (3 d) or LTHS (7 d) treatments. Data collected from the 3 d of STHS and the last 3 d of LTHS were compared. The chambers were set at thermal neutral conditions (20°C, 50% humidity) during the control and recovery phases or cyclical HS conditions (26–38°C, 50% humidity) during the HS phase. Compared with STHS, LTHS decreased milk yield by 17.2% and dry matter intake by 12.6%, indicating that LTHS caused a more severe decline in milk production and feed intake. In addition, LTHS decreased milk protein concentration by 6.8% and milk protein yield by 22.4%. In comparison with STHS, LTHS decreased rumen liquor volatile fatty acid (29.7%), blood glucose (11.6%), and nonesterified fatty acid (13.6%) concentrations, but increased milk urea nitrogen by 15.1%, blood urea nitrogen by 8.6%, and creatine concentrations by 15.4%. Our results suggest that although reduced feed intake may be mainly responsible for reduced milk production during STHS, impaired rumen metabolism and suppressed mobilization of adipose tissue could be the main reasons for further reduction in milk yield during LTHS.     

Mammary transfer of vitamin E in dairy cows

Milk vitamin E from eight dairy cows was analyzed for vitamin E by HPLC during the 1st mo of lactation. Colostrum gave a mean value of 1.9 micrograms alpha-tocopherol/ml while concentrations of fresh milk averaged .3 microgram alpha-tocopherol/ml. D-gamma-tocopherol concentrations were observed in very small amounts. When six cows at the end of the 1st mo of lactation were injected intraperitoneally with an emulsion of dl-alpha-tocopherol acetate (5 g), plasma and milk concentrations of alpha-tocopherol were increased from their original values of 4.5 micrograms/ml plasma and .3 microgram/ml fresh milk to 10.9 micrograms/ml plasma and 1.6 micrograms/ml fresh milk, 12 h later. The results show that intraperitoneal administration of vitamin E to dairy cows in an effective way of increasing plasma and milk tocopherol concentration.     

Effect of dietary cobalt supplementation on cobalt metabolism and performance of dairy cattle

Three studies were conducted with dairy cattle fed diets with added Co. The first study examined cow age and added dietary Co on Co in liver and blood. Nonpregnant, nonlactating Holstein cows were blocked by age (2.5 or 6.5 yr) and assigned to either a control diet or a diet supplemented with 9 mg Co per day. The Co concentration of liver, taken on d 60, was not affected by dietary Co but was higher in the younger cows. The cytosolic fraction of liver contained the most Co, and the subcellular distribution of Co was not affected by total Co in liver. In a second study, Holstein cows were assigned to one of three treatments of dietary Co from 21 d prepartum until 120 d postpartum. There was an interaction of time x treatment x parity such that milk yield response to Co supplementation differed between multiparous cows and primiparous cows. Supplemental Co did not increase Co in serum, colostrum, milk, or liver. Primiparous cows secreted colostrum and milk with higher Co concentrations than did multiparous cows. Likewise, serum B12 levels were higher in primiparous than multiparous cows and declined with increasing days in milk (DIM). Serum Co also decreased from 7 to 120 DIM. In a final study, a Co supplement in the starter diet did not affect Co in serum or liver of young calves. In conclusion, supplemental dietary Co did not affect secretion of Co in milk, tissue retention, or subcellular distribution of Co within the liver. Primiparous and multiparous cows differed in their milk yield response to dietary Co supplementation.     

Effect of vitamin E supplementation on weight gain, immune competence, and disease incidence in barley-fed beef cattle

The aim of the study was to investigate whether vitamin E supplements in larger amounts than recommended could reduce incidence of disease, improve immune competence, and increase rate of weight gain of conventionally barley-fed beef cattle. Mean daily intake of vitamin E by individual calves in the experimental group was 200 mg during the first 2 mo, 400 mg during the next 2 mo, and 600 mg during the rest of the period. Corresponding daily intakes of vitamin E for the control group were 50, 100, and 150 mg. Mean plasma vitamin E of the experimental group increased from .49 mg/L at the start of the trial to 2.03 mg/L at the end, but that of the control group was lower at the end (.36 mg/L) than at the beginning (.53 mg/L). No significant differences were observed between the groups concerning incidence of disease or magnitude of lymphocyte stimulation. The results indicated that there was a surprisingly poor biological availability of the dietary vitamin. Therefore, a comparison in reality was made between calves with inadequate and normal vitamin E status. The differences in daily BW gain and time to reach slaughter weight thus probably were effects of the low vitamin E status rather than positive effects of additional vitamin in the diet.     

Combined use of Ovsynch and progesterone supplementation after artificial insemination in dairy cattle

The objective of this study was to evaluate the effects of different Ovsynch protocols combined with progesterone (P4) supplementation after artificial insemination (AI) of Holstein-Friesian cows. Cows were randomly synchronized at 52 to 63 d after parturition with either the classical Ovsynch protocol (GnRH on d 0, PGF(2α) on d 7, GnRH 48 h after PGF(2α)) or with a modified Ovsynch protocol (second GnRH 60 h after PGF(2α)). On d 4 after timed AI (TAI), the cows were blocked by parity and randomly divided into 2 groups. Half of the cows were supplemented with P4 (P4+) by applying a P4-releasing intravaginal device intravaginally for 14 d, whereas the other half remained untreated (P4-). In 50% of randomly chosen cows, plasma P4 was measured on d 4, 5, and 18 after TAI. Sonographic pregnancy diagnosis was performed on d 33 after TAI in a total of 398 cows. Health status and body condition score (BCS) of all cows were examined at several stages of the study. Cows in the modified Ovsynch protocol tended to have higher P4 values on d 4 after TAI than cows in the classical Ovsynch protocol (2.1 ± 0.2 vs. 1.6 ± 0.2 ng/mL), but no difference in pregnancy per AI (P/AI) was observed between the 2 Ovsynch protocols (38.4% vs. 44.1%). Independent of the Ovsynch protocols, P4+ cows tended to have higher P/AI compared with P4- cows (44.4% vs. 38.1%). The retention of fetal membranes and BCS at the time of insemination affected P/AI. Moreover, an interaction between BCS at the time of insemination and P4 supplementation was apparent; that is, the difference in P/AI between P4+ and P4- cows was significant in cows with BCS ≥3.25. Progesterone-supplemented cows showed higher P4 values on d 5 (4.9 ± 0.2 vs. 2.6 ± 0.2) and d 18 (7.8 ± 0.2 vs. 6.3 ± 0.2) after TAI, respectively. In conclusion, the elongation of the time interval between the injections of PGF(2α) and the second GnRH from 48 to 60 h had no effect on P/AI. Progesterone supplementation after insemination improved the P/AI of the Ovsynch protocols, but this effect was more apparent in cows with BCS ≥3.25.     

Effect of methionine hydroxy analog supplementation on dairy cattle hoof growth and composition

Fifty lactating Holstein cows were assigned randomly to one of two treatments, control and control plus approximately 30 g methionine hydroxy analog, and confined on concrete for 11 mo. The control diet consisted of sorghum silage and concentrate fed as a blended ration. Sulfur contents of dry matter were .12% and .16% for control and methionine hydroxy analog rations. Hoof growth and hardness were measured on front and rear right abaxial claws in the dorsal and lateral regions. Hoof growth rates were measured for four periods; summer-fall, fall-winter, winter-spring, and spring-summer, each 70 to 90 days. Hooves of cows fed methionine hydroxy analog grew faster than those of control cows during spring-summer in all regions. Variations of growth rates of hooves were seasonal and tended to follow variations in daily photoperiod. Wear rates were not affected significantly by treatment. Hooves of cows fed methionine hydroxy analog were softer in the top dorsal region at the end of winter-spring and in the dorsal toe region at the end of spring-summer. All other locations were not affected significantly by treatment. The toe region was harder than the top of the hoof. Cows fed methionine hydroxy analog had less cysteine and proline in hoof than control cows and greater percentages of methionine lysine, tyrosine, and glutamic acid. These results suggest that a decrease of disulfide bonding occurred in the hoof tissue of cows fed methionine hydroxy analog. Cows fed methionine hydroxy analog produced more actual milk, milk fat, and 4% fat-corrected milk during 180 days than did control cows.     

Production and health of pasture-fed dairy cattle following oral treatment with the ionophore lasalocid

The aim of the study was to evaluate the effect of feeding the ionophore lasalocid on the productivity and health of seasonally calving, pasture-fed dairy cows. Dairy cows (n = 1020) from 4 herds were enrolled in a split-herd, prospective intervention study. Cows were blocked by breed and age, ranked on previous production, and then assigned to 2 treatment groups. Treatment cows were each exposed to 300 to 350 mg of lasalocid/d commencing 3 wk before and ending 18 wk after the start of the seasonal calving period. Milk production was determined on 3 occasions for each cow at approximately monthly intervals (herd tests 1 to 3), body condition score was determined fortnightly, and all disease occurrences were recorded. Lasalocid treatment increased milk volume milk protein and milk fat production by approximately 2%, without altering milk composition. Fewer lasalocid-treated cows than control cows (7.3 vs. 11.6%, respectively) were diagnosed with clinical mastitis. Lasalocid treatment of pasture-fed dairy cows resulted in reduced mastitis incidence and increased milk production without changes in body condition or negative effects on metabolic processes as monitored by metabolite concentrations.     

Stability in the rumen and effect on plasma status of single oral doses of vitamin D and vitamin E in high-yielding dairy cows

The ruminal fate of the fat-soluble vitamins D and E was studied in dairy cows. Ten to 15 kg of ruminal contents was taken from each cow through a ruminal fistula. A sample was taken out (0-h sample) and the rest of the contents were mixed with 4,360 mg of all-rac-α-tocopheryl acetate (vitamin E; study 1) or 4,360 mg of all-rac-α-tocopheryl acetate, 250 mg of ergocalciferol (vitamin D₂), and 250 mg of cholecalciferol (vitamin D₃; study 2). After mixing, the ruminal contents were returned to the respective cows. Blood was collected 0, 6, 24, and 30 h after introducing the vitamins into the rumen. Samples of ruminal contents were collected at 0, 1, 2, 4, 6, 24, and 30 h (in vivo). From the 1-h sample, 6 subsamples from each cow were incubated at 37°C and taken out at 2, 4, 6, 12, 24, and 30 h (in vitro). In vivo concentrations of added α-tocopherol, ergocalciferol, and cholecalciferol in the rumen first increased and subsequently declined due to dilution effects of eating and passage out of the rumen. The level of the free-alcohol form of α-tocopherol from the natural content in feed was constant throughout the in vivo study, in contrast to the content of total α-tocopherol, which indicated that no hydrolysis of the acetate form into alcohol form happened in the rumen. In vitro, all added vitamins were found at constant levels; hence, none of the added vitamins were degraded in ruminal contents. The concentration of α-tocopherol in plasma increased at a rate per milligram of ruminally introduced α-tocopherol below the rate of the increase in plasma ergocalciferol or cholecalciferol metabolites per milligram of introduced ergocalciferol or cholecalciferol, respectively, over 24 h. In conclusion, ergocalciferol, cholecalciferol, and α-tocopheryl acetate proved to be stable in the rumen and in ruminal contents from high-yielding dairy cows. Changes in plasma concentrations of the vitamins relative to the amount of vitamin introduced to the rumen indicated a lower effect on plasma status of ergocalciferol than of cholecalciferol, and an even lower effect of α-tocopherol. The limited plasma response after a single dose of α-tocopheryl acetate led to the conclusion that oral single dose therapy with all-rac-α-tocopheryl acetate is of limited physiological value.     

Influence of dietary selenium and vitamin E on quality of veal

Three groups of six calves each were fed a milk replacer and a starter concentrate for 15weeks. Calves of the first group received the basal diet containing selenium (Se) and vitamin E at 0.095-0.128mg and 30-33mg per kg of total solids, respectively. Calves of the second group received the basal diet supplemented with Se-enriched yeast to increase dietary Se concentration to 0.50mg/kg. The third group of calves received the latter diet supplemented with vitamin E to increase its concentration to 100mg/kg. There was no effect of diet on growth rate, digestibility of dry matter and Se, chemical composition of meat (M. Longissimus thoracis et lumborum), meat colour and fatty acid profile of meat lipids. The Se supplementation significantly increased Se concentration in muscle from 0.21 to 0.43mg/kg. The activity of glutathione peroxidase (GSH-Px) in muscle and liver tissue of Se-supplemented animals was increased by 56% and 67%, respectively, compared to the control. The combined supplementation of vitamin E and Se significantly improved the lipid stability of meat compared to the control diet, but not compared to the Se-supplemented diet. It can be concluded that dietary Se supplementation increases the concentration of Se and the GSH-Px activity in meat, but has limited potential for improving meat oxidative stability.     

Effects of selenium and vitamin E on incidence of retained placenta

In a series of experiments over 3 yr, relatively low doses of selenium and vitamin E were injected intramuscularly 3 wk prepartum to pregnant Israeli-Holstein dairy cows in a high-producing herd (9000 kg milk/yr) with a history of retained placenta in 17% of the primiparous and 28% of the multiparous animals, as recorded for the 12 mo preceding the study. Selenium ranged from .035 to .109 ppm in the prepartum diet and from .160 to .200 ppm in the postpartum diet. Doses of selenium ranging from 2.3 to 23.0 mg reduced the incidence of retained placenta in 186 primiparous and in 428 multiparous to 7 and 15%, which was half of that of controls. Low doses of selenium (2.3 to 4.6 mg) tended to be more effective than higher ones. Selenium alone was at least as effective as a combination of selenium and vitamin E. Dosage, timing, mechanism, and interactions of selenium with other factors in reducing the incidence of retained placenta need clarification.