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Southwest Research and Extension Center, Department of Animal Science, University of Arkansas, Hope 71801-9729
2 Correspondence:
362 Highway 174 North, Hope, AR 71801-9729 (phone: 870-777-9702, ext. 107; fax: 870-777-8441; E-mail:
sgunter{at}uaex.edu).
| Abstract |
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0.19) on cow BW, BCS, conception rate, postpartum interval, or hay DMI. Birth date, birth weight, BW, total BW gain, mortality, and ADG of calves were not affected (P > 0.20) by Se or its source. Whole blood Se concentrations and glutathione peroxidase (GSH-Px) activity at the beginning of the trial did not differ (P
0.17) between cows receiving no Se and cows supplemented with Se or between Se sources. At the beginning of the calving and breeding seasons, cows supplemented with Se had greater (P < 0.01) whole blood Se concentrations and GSH-Px activities than cows receiving no supplemental Se; cows fed seleno-yeast had greater (P
0.05) whole blood Se concentrations than cows fed sodium selenite, but GSH-Px did not differ (P
0.60) between the two sources. At birth and on May 24 (near peak lactation), calves from cows supplemented with Se had greater (P
0.06) whole blood Se concentrations than calves from cows fed no Se. At birth, calves from cows fed seleno-yeast had greater (P
0.05) whole blood Se concentrations and GSH-Px activities than calves from cows fed sodium selenite. Although no differences were noted in cow and calf performance, significant increases were noted in whole blood Se concentrations and GSH-Px activities in calves at birth as a result of feeding of seleno-yeast compared to no Se or sodium selenite.
Key Words: Beef Cattle Forages Glutathione Peroxidase Selenium Yeasts
| Introduction |
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Studies with beef cattle in areas that are considered marginal or deficient in Se are limited (Hidiroglou and Jenkins, 1975; Spears et al., 1986; Ortman and Pehrson, 1999). In light of these facts, we designed an experiment to examine Se supplementation and source of Se utilized with gestating and lactating beef cows on growth, reproduction, and blood parameters when fed grass hay and pastured on forages that were marginally deficient in Se.
| Materials and Methods |
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On October 1, 1999, at the Southwest Research and Extension Center (33°42'N, 93°31'W), 120 pregnant, crossbred beef cows (average BW = 528 ± 10.2 kg) of mostly English (Angus and Hereford) and Continental (Simmental) breeding and bred to begin calving on February 1 were fed bermudagrass (Cynodon dactylon [L.] Pers.)/dallisgrass (Paspalum dilatatum Poir.) hay with ad libitum access to salt blocks (NaCl; Morton Salt Co., Salt Lake City, UT) as their only supplemental mineral source for 2 mo. This preliminary feeding period before the beginning of the experiment was an attempt to adjust the Se status of the cows to the Se level expected for cows maintained in the local environment without Se supplementation.
On December 2, 1999 (early December), the cows were weighed and their body condition scored (Wagner et al., 1988). Also, the cows were injected with a seven-way Clostridial antigen (Vision 7 Somnus; Bayer Corp., Shawnee Mission, KS) to increase Clostridial antibodies in the colostrum (Clarkson et al., 1985) and were dewormed with fenbendazole (Safeguard; Intervet, Inc., Millsboro, DE). Cows were sorted into six groups of 20 stratified by BCS, BW, breed, and age, and assigned randomly to one of six 5.1-ha dormant common bermudagrass pastures for 2 yr. Beginning in early December, cows had ad libitum access to a bermudagrass/dallisgrass hay (Table 1
); in addition, they were allowed limited access to a 2.4-ha winter-annual paddock planted in one-half of each pasture for a protein and energy supplement (Gunter et al., 2002). Treatments were randomly assigned to pastures (two pastures per treatment); cows had ad libitum access to one of the following three free-choice mineral supplements that contained (Table 1
): 1) no supplemental Se, 2) 26 mg of supplemental Se/kg of free-choice mineral from sodium selenite (Selenium Premix; Southeastern Minerals, Inc., Bainbridge, GA), or 3) 26 mg of supplemental Se/kg of a free-choice mineral from seleno-yeast (Sel-Plex; Alltech, Inc., Nicholasville, KY). A commercial feedmill (Sunbelt Custom Minerals, Inc., Sulphur Springs, TX) manufactured and delivered the mineral supplements in November of each year. Free-choice minerals were designed to be consumed at a rate of 113 g/cow daily; minerals were resupplied weekly by putting 1,000 g/cow in a weather-vane style mineral feeder. On alternate weeks, mineral feeders were cleaned and orts were weighed to determine mineral intake. After orts were weighed, if they appeared contaminated with feces or water, they were subsampled for DM determination and the remainder was discarded.
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Cows were restricted from winter-annual paddocks on nongrazing days using electric fences. Cows were allowed to graze winter-annual paddocks 1 d/wk (7 h/d) in December, 2 d/wk in January, 3 d/wk from February 1 to March 15, and 4 d/wk from March 15 to May 1. On 1 May, electric fences that divided pastures were removed and cows were allowed continuous access to the entire pasture until weaning. The grazing management used in the summer was continuous stocking because research at the Southwest Research and Extension Center showed no benefits to lactating cows or nursing calves on bermudagrass pasture when rotationally grazed compared with continuously stocked (Brown et al., 1997). Winter-annual paddocks were planted in October, and the forage was stockpiled until grazing began in December. Therefore, forage was not limiting for grazing in January and February when plant DM production was less than cattle demand. Hay was offered in the form of round bales in "ring"-type hay feeders, and technicians maintained records of the quantity of hay fed in each pasture. A trailer load of hay bales (14 bales/load) was weighed on a truck scale and the total weight of the bales was divided by the total number of bales to estimate the average bale weight at each hay cutting. To calculate estimated daily hay DMI per cow, quantities of hay offered in each pasture were corrected for wastage based on feeder type and the data of Buskirk et al. (2000), and then divided by the number of cows in each pasture. Chemical composition of the hay (core samples from 10% of the bales fed) and winter-annual pasture forage (hand plucked in January, March, and April, composited across pastures and times) was determined at a commercial laboratory (Dairy One, Ithaca, NY), DM and CP were determined as described by AOAC (1990), and TDN was determined as described by Weiss et al. (1992). Hay or pasture samples were composited across days and pastures and analyzed for Ca, P, Mg, K, Na, Fe, Zn, Cu, Mn, and Mo by inductively coupled plasma emission spectroscopy (Thermo Jerrell Ash Corp.; Franklin, MA) at DairyOne, Inc., as described by Sirois et al. (1991); Se concentration was conducted at Michigan State University, Animal Health Diagnostic Laboratory (East Lansing) by inductively coupled argon plasma emission spectroscopy using the improved fluorometric method (Olsen et al., 1975). On April 25 in both years, an Angus bull that had passed a breeding soundness examination was placed with each group of cows for a 60-d breeding season. Bulls were rotated weekly among cow groups to minimize the effect of individual bulls.
Cows and calves were weighed and body condition scored on February 8 (early February), May 24 (late May), June 29 (late June), and September 27 (late September) in 1999 and February 8 (early February), May 24 (late May), June 28 (late June), and October 16 (late September in 2000. The morning after calving, calves were weighed, tattooed in both ears with an individual number, and male calves were surgically castrated. Calves were also evaluated for calving ease, agility, and vigor scores. Calving ease scores were as follows: 1 = unassisted birth, 2 = minor assistance, 3 = mechanical assistance, 4 = cesarean section, and 5 = abnormal presentation (Vandervelde et al., 1990). Agility scores were assigned as follows: 1 = moves well and correct posture, 2 = moves showing slight stiffness in legs, 3 = significant stiffness in gate, 4 = significant stiffness in gate and slight arch in the topline, and 5 = significant stiffness in gate and arch in topline. Vigor scores were assigned as follows: 1 = alert and active, 2 = alert, 3 = appears healthy, but somewhat listless, 4 = listless, and 5 = listless and unresponsive. On May 24 in both years, cows were treated for internal and external parasites (Ivomec; Merck & Co., Inc., Whitehouse Station, NJ), vaccinated with a seven-way Clostridial antigen (Vision 7 Somnus), and vaccinated for infectious bovine rhinotracheitis, bovine viral diarrhea, parainfluenza-3, bovine respiratory syncytial virus, plus five strains of Leptospirosis (Triangle 4 + PH-K and TriVib L5; Fort Dodge Animal Health, Overland Park, KS).
Blood samples were collected from four randomly selected cows and their calves within each pasture via jugular venapuncture into a 10-mL tube containing EDTA (Vacutainer tube, No. 366457; Becton-Dickinson, Inc., Franklin Lakes, NJ) for determination of whole blood Se concentration and GSH-Px in the erythrocytes. Cows were bled on December 2 (trial initiation), February 8 (beginning of calving season), and April 19 (beginning of the breeding season) in 1999, and December 7, February 8, and April 19 in 2000; calves were bled at 0730 each morning after birth and on 24 May (near peak lactation) in both years. At bleeding, blood samples were immediately placed on ice and then frozen (-20°C) until overnight shipment on dry ice to the Michigan State University, Animal Health Diagnostic Laboratory for analysis. Blood samples were prepared for analysis and whole blood Se concentration was determined as described by Reamer and Veillon (1983). Glutathione peroxidase activity per gram of hemoglobin in the erythrocytes was determined using the procedure of Paglia and Valentine (1967) as modified by Lawrence et al. (1974). Cows were checked for pregnancy by rectal palpation on September 27, 1999 and October 16, 2000 by a veterinarian (Powell and Perry Veterinary Clinic, Hope, AR). In 1999, cows deemed not pregnant were replaced by mature pregnant cows (multiparis) in order to maintain 20 cows in each pasture. Postpartum interval was calculated by subtracting 283 d from the calving date of the following year to estimate conception date.
Body weight, BCS, conception rate, postpartum interval, and hay DMI were analyzed using PROC GLM (SAS Inst., Inc., Cary, NC) as a split-plot design with the effects of treatment (main plot), year (sub plot), treatment x year, and the covariates, cow age and calving date, in the model (Steel and Torrie, 1980). Pastures were considered the experimental units, so the treatment effects were tested with pasture within treatment, and year and year x treatment were tested with pasture within year x treatment as the error terms. Calf BW and calf total gain data were analyzed using PROC GLM as a split-plot design with the effect of treatment (main plot), year (subplot), and treatment x year and the covariates, cow age, calf gender, birth date, and birth weight in the model (Steel and Torrie, 1980). Models used to analyze birth date (Julian date) and birth weight were analyzed in a manner similar to the model previously described, except that calving date or birth weight, respectively, were excluded as a covariate. Because the experiment required a mixed model for analysis, year was considered a random effect and treatment was considered a fixed effect; all parameters discussed were averaged across years by treatment (Steel and Torrie, 1980). If a cow died during the course of the study, the affected cow and calf were immediately replaced with a spare cow-calf pair to equalize stocking rate; however, the data from replacement cows and calves were not used in the statistical analysis. Least squares means were separated using the following contrasts: 1) no supplemental Se vs. supplemental Se, and 2) sodium selenite vs. seleno-yeast with pasture within treatment as the error term (Steel and Torrie, 1980).
| Results and Discussion |
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Biweekly intake estimates of the free-choice minerals did not differ (P > 0.10) on any date between cows supplemented with Se and cows receiving no Se (Figure 1
); however, on wk 1 and 18, mineral intake by cows supplemented with seleno-yeast was greater (P < 0.05) than that by cows supplemented with sodium selenite. Each fall when we began to measure mineral intake, it required approximately 6 wk for cows to become accustomed to the feeder and to achieve the target intake of 113 g/d. Also, from week 6 to 28 (January to July), intake seemed to vary more by week than during weeks 30 to 42 (July to October), which probably resulted from inclement weather as a result of the frequent thundershowers that normally occur in the spring. The average daily intake per cow for no Se, sodium selenite, and seleno-yeast minerals was 108, 107, and 109 g, respectively.
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Body weight did not differ on any date between cows supplemented with Se and cows that received no Se (Table 2
) or between cows supplemented with sodium selenite and seleno-yeast. Other research has reported that cows consuming diets that were moderately deficient in Se (0.05 to 0.09 mg/kg) and were injected monthly with sodium selenite and vitamin E lost less BW during the winter than noninjected cows. However, the injected cows gained less BW during the summer than noninjected cows (Spears et al., 1986). Research in Alaska showed that cows administered an intraruminal Se bolus (sodium selenite) did not differ in BW from cows not given a Se bolus (Bruce, 1997). Body condition score did not differ on any date between cows supplemented with Se and cows receiving no Se (Table 2
) or between cows supplemented with sodium selenite and seleno-yeast. Research has also reported cows supplemented with sodium selenite did not differ in fat thickness compared to unsupplemented cows (Bruce, 1997).
Conception rates and postpartum intervals did not differ between cows supplemented with Se and cows receiving no Se (Table 2
), or between cows supplemented with sodium selenite and seleno-yeast. Research has reported that cows consuming diets that were moderately deficient in Se and that were injected with sodium selenite and vitamin E did not differ in conception rate, but they did experience a decrease in the postpartum interval compared to cows not injected with Se and vitamin E (Spears et al., 1986). However, Aréchiga et al. (1994) reported that Holstein dairy cows that were injected with a Se and vitamin E mixture had an increased conception rate and a decreased postpartum interval. Hay DMI did not differ between cows supplemented with Se and cows receiving no Se (Table 2
), or between cows supplemented with sodium selenite and seleno-yeast. In previous research at our location with cows limit-grazed on winter-annual pasture 3 d/wk, hay DMI was similar to hay DMI in the present study (Gunter et al., 2002).
Calf Performance
Birth date, birth weight, BW of calves, total BW gain, and ADG did not differ between calves nursing cows supplemented with Se and calves nursing cows supplemented with no Se, or between calves nursing cows supplemented with sodium selenite and seleno-yeast (Table 3
). Researchers have reported significant increases in ADG and/or total BW gain of calves with injectable sodium selenite and vitamin E (Hidirgoglou and Jenkins, 1975; Spears et al., 1986; Castellan et al., 1999). However, research conducted at this research center showed that when nursing calves were supplemented with Se from sodium selenite via constant-release bolus (Dura-Se, Schering-Plough Animal Health; Union, NJ), their ADG was similar to unsupplemented controls (Phillips et al., 1989). No differences (P > 0.16) were noted in mortality among treatments in the present study (data not shown).
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Whole blood Se concentrations in cows at the beginning of the experiment in December did not differ between cows supplemented with no Se and cows supplemented with Se. Initial whole blood Se concentrations were also unaffected by Se sources (Table 4
). The whole blood Se concentrations reported in December are suggested to be marginal (60 to 150 ng Se/mL) for optimal GSH-Px activity and immune function (Puls, 1989). At the beginning of the calving season (early February), cows fed Se-fortified minerals for approximately 64 d had higher (P = 0.003) whole blood Se concentrations than cows fed minerals with no Se. At this point in time (early February), the whole blood Se concentration of the Se-supplemented cows (average = 158 ng/mL) had been increased to a point (160 to 1,200 ng/mL) that is considered to be adequate for optimal GSH-Px activity and immune function (Puls, 1989). In early February, cows supplemented with sodium selenite had lower (P = 0.01) whole blood Se concentrations than cows supplemented with seleno-yeast. Whole blood Se concentrations in cows supplemented with seleno-yeast vs. sodium selenite were 23% greater than in cows supplemented with sodium selenite, suggesting that seleno-yeast was more available that sodium selenite. Research by Pehrson et al. (1989) showed that seleno-yeast was 1.8 times more available than sodium selenite in heifers. At the beginning of the breeding season in April, cows fed Se-fortified minerals had higher (P = 0.003) whole blood Se concentrations than cows fed minerals with no Se; cows supplemented with seleno-yeast had higher (P = 0.03) whole blood Se concentrations than cows supplemented with sodium selenite. As noted in early February, the difference between whole blood Se concentrations in cows supplemented with seleno-yeast and sodium selenite indicates that seleno-yeast is more available.
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Glutathione peroxidase activity in erythrocytes from cows at the beginning of the experiment in December did not differ between cows supplemented with no Se and cows supplemented with Se. Also, GSH-Px activity did not differ between Se sources (Table 4
). In early February and April, cows fed Se-fortified minerals for approximately 64 d had higher (P = 0.05) GSH-Px activity than cows fed minerals with no Se; however, the GSH-Px activity in cows supplemented with sodium selenite did not differ from cows supplemented with seleno-yeast.
Glutathione peroxidase activity in erythrocytes from calves at birth from cows fed Se-fortified minerals was higher (P = 0.11) than in calves from cows fed minerals with no Se (Table 4
); however, calves from cows supplemented with seleno-yeast had higher (P = 0.05) GSH-Px activity at birth than calves from cows supplemented with sodium selenite. In late May, GSH-Px activity in calves nursing cows fed Se-fortified minerals did not differ from calves nursing cows fed minerals with no Se; however, calves from cows supplemented with seleno-yeast had higher (P = 0.10) GSH-Px activity than calves nursing cows supplemented with sodium selenite. Activity of GTH-Px is expected to be between 45 and 85 nmol of reduced NAD phosphate oxidized per minute (EU)/g of hemoglobin (Hb) for cattle with adequate Se status, and a critically low activity is considered to be <15 EU/g of Hb (Erksine, 1993). Activity of GTH-Px was within the expected range for all cows and calves at all times during the study. Research comparing Se sources (Pehrson et al., 1999) demonstrated that Se from seleno-yeast is secreted via the milk in lactating beef cows, and cows supplemented with seleno-yeast were more able to maintain the GSH-Px activity in their nursing calves than cows supplemented with sodium selenite.
Selenium supplementation of gestating beef cows via fortified free-choice minerals benefited cows and calves by increasing whole blood Se concentrations and GSH-Px activity compared to no Se supplementation. Blood variables from cows supplemented with no Se did indicate a risk of clinical Se deficiency. The use of seleno-yeast as a Se supplement in free-choice minerals vs. sodium selenite increased the whole blood Se concentrations of both cows and their calves and increased GSH-Px activity. Also, seleno-yeast supplementation of nursing calves maintained whole blood Se concentration and GSH-Px activity, which sodium selenite failed to accomplish. No improvement was noted in performance of cows and calves.
| Implications |
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| Footnotes |
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Received for publication August 26, 2002. Accepted for publication December 9, 2002.
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