高效液相色谱法测定黄体酮、丙酸睾酮及苯甲酸雌二醇含量

采用高效液相色谱法测定复方丙酸睾酮注射液中黄体酮、丙酸睾酮及苯甲酸雌二醇含量。色谱柱为C18柱；流动相为甲醇-水(82：18)；检测波长为230nm,，在同一种检测条件下能同时测定3种组分的含量，在各自的浓度范围内均具有良好的线性关系(r=0．9999)。本法简便准确，可用于3种组分的含量测定。     

Effect of an implant of trenbolone acetate and estradiol on growth, feed efficiency, and carcass composition of Holstein and beef steers.

The effects of an implant of 140 mg of trenbolone acetate and 28 mg of estradiol (TBA + E2) on performance and carcass composition were evaluated with 72 individually fed steers. Holstein (n = 24), Angus (n = 24), and Angus x Simmental (n = 24) steer calves were allocated by breed and implant treatment to either an individual feeding pen (n = 36) or an electronic feeding door in a group pen (three pens with 12 animals per pen). Intake and refusal of the 85% concentrate diet were recorded daily. Animals were slaughtered when ultrasonic attenuation values of the longissimus muscle at the 12th rib reached .55, which is correlated with low Choice marbling. At slaughter, complete carcass measurements were taken and the right side of each carcass was separated into boneless wholesale cuts. Implanting with TBA + E2 improved (P less than .01) daily gain and feed efficiency. Daily gain was increased 17, 26, and 21% in Holstein, Angus, and crossbred steers, respectively. The implant increased overall daily protein and fat accretion 23%. Carcass conformation and dressing percentage were not affected (P greater than .05) by TBA + E2 treatment. Implantation with TBA + E2 had little effect on yield of wholesale boneless cuts when expressed as a percentage of carcass weight but increased absolute weight as a small degree of marbling by 6 to 40 kg.     

Concentration of progesterone and thyroxine in the luteal phase of the cycle in heifers after administration of estradiol benzoate

The effect of current 48-hour infusion of estradiol benzoate (EB) on the dynamics of the concentration of progesterone (P) and thyroxine (T4) was studied in four heifers in the luteal stage of their cycle. The parameters were evaluated in three intervals: infusion (A), post-infusion (B) and "uninfluenced" interval (C). In the course of infusion the concentrations of P in three animals had a markedly descending tendency. The P concentration increase in the 36th hour of infusion was maintained also during the post-infusion interval. The decrease in P in the third, "uninfluenced", interval was replaced by a new rise towards the end. One heifer showed an increase in P concentrations at the beginning of EB infusion. A decrease was recorded towards the end of the interval. The concentration decreased in the post-infusion period. A comparatively high concentration of P in the "uninfluenced" interval was again replaced by a drop towards the end in the 286th hour. The concentration of T4 in three heifers had a descending tendency in the infusion and post-infusion intervals. The decrease in the infusion interval was more pronounced. In the "uninfluenced" interval the T4 concentrations increased step by step. In one heifer the concentration of T4 slightly increased during infusion. A decrease was recorded in the post-infusion and "uninfluenced" interval. Rectal examination in the 172nd hour revealed the original corpus luteum in three animals and the production of the corpus luteum in the same ovary was found in this period in one heifer. In the 88th hour this animal showed clinical manifestations of oestrus. On the basis of the dynamics of the studied hormones and clinical studies, the thyroid hormones can be regarded as an important secondary factor involved in the permanent cyclic changes in reproduction process.     

Trenbolone acetate/estradiol combinations in feedlot steers: dose-response and implant carrier effects.

Two experiments were conducted at three locations to determine the correct dosage and carrier for trenbolone acetate (TBA) and estradiol (E2) implants in feedlot steers. In the dose-response experiment, 1,296 steers were allotted to six implant treatments (48 pens per location): control, 140 mg of TBA (140/0), 30 mg of E2 (0/30), 20 mg of TBA + 4 mg of E2(20/4), 80 mg of TBA + 16 mg of E2(80/16), and 140 mg of TBA + 28 mg of E2 (140/28). In the carrier experiment, 575 steers were allotted to five implant treatments (25 pens per location): control, 140 mg of TBA + 28 mg of E2 in lactose (140/28-LA), 140 mg of TBA + 28 mg of E2 in cholesterol (140/28-CH), 140 mg of TBA + 20 mg of E2 in LA (140/20-LA), and 200 mg of progesterone + 20 mg of E2 benzoate (SS, reimplanted). In both experiments steers were fed a finishing diet for 140 to 168 d. In the dose-response experiment, response to TBA alone (140/0) did not differ from control (P greater than .2). Estradiol alone (0/30) improved ADG by 7% (P less than .01) and tended to improve feed efficiency over control (3%, P = .17). The highest dosage (140/28) improved ADG by 18% (P less than .001) and feed efficiency by 10% (P less than .001) over control and 10% (P less than .001) and 7% (P less than .01) over E2 alone, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of weaning status and implant regimen on growth, performance, and carcass characteristics of steers

One hundred forty-three Angus x Simmental crossbred steers (initial BW = 155.1 +/- 4.5 kg) were used in a 2-yr study (yr 1, n = 67; yr 2, n = 76) to determine the effects of weaning age, implant regimen, and the weaning age x implant regimen interaction on steer growth and performance, organ mass, carcass characteristics, and cooked beef palatability. Steers were early-weaned at an average age of 108 d (EW) or normally weaned at an average age of 202 d (NW) and allotted by weight to an aggressive or nonaggressive implant regimen. On their respective weaning dates, EW and NW steers were penned individually and fed a grain-based diet until they were slaughtered at a final BW of 546 kg. A subsample of steers (n = 2 per treatment) were slaughtered at 254 kg. At 254 kg, EW steers implanted with the aggressive implant regimen had 64% greater backfat depth than those implanted with the nonaggressive implant regimen; conversely, NW steers implanted with the aggressive implant regimen had 52% lower backfat depth than those implanted with the nonaggressive implant regimen (weaning status x implant regimen interaction; P < 0.01). A similar interaction was observed for empty visceral organ weights. Early-weaned steers were younger (354.7 vs 372.4 d; P < 0.01) at final slaughter but were in the feedlot longer (246.5 vs 169.6 d; P < 0.01) than NW steers, whereas the aggressive implant regimen decreased days fed (203.3 vs 212.7; P < 0.07) compared to the nonaggressive implant regimen. Overall ADG was greater for EW than for NW steers (1.61 vs 1.50 kg/d; P < 0.01) and for the aggressive compared with the nonaggressive implant regimen (1.59 vs 1.52 kg/d; P < 0.02). Early-weaned steers consumed less DM per day (7.4 vs 8.5 kg/d; P < 0.01) and were more efficient (0.217 vs 0.208 kg/kg; P < 0.02) but consumed more total DM (1,817 vs 1,429 kg; P < 0.01) than NW steers while in the feedlot. Implant regimen did not affect DMI (P > 0.37) or feed efficiency (P > 0.15). Weaning status did not affect carcass characteristics (P > 0.14), final empty body composition (P > 0.25), or final longissimus muscle composition (P > 0.18); however, steaks from EW steers had higher (P < 0.05) taste panel tenderness and juiciness ratings than steaks from NW steers. The aggressive implant regimen decreased yield grade (P < 0.02), but did not affect quality grade (P > 0.86) compared to the nonaggressive implant regimen. Placing early-weaned steers on an aggressive implant regimen is a viable management option.     

Effects of residual and reapplied biosolids on performance and mineral status of grazing beef steers

An experiment was designed to assess the mineral status of 60 Angus yearling beef steers grazing bahiagrass pastures fertilized with large amounts of biosolids from three sources: Baltimore, MD; Tampa, FL; and Largo, FL. Biosolids were classified as exceptional quality and thus had no regulatory restrictions on loading rate. They differed primarily in concentration of Mo (12 to 56 mg/kg of DM). Residual treatments (biosolids applied only the previous year) for Baltimore biosolids were applied at 22.4 and 44.8 t/ha, and Tampa biosolids were either 16.8 or 33.6 t/ ha. The reapplied treatments (applied in consecutive years) for both Baltimore and Tampa sludges were applied at 22.4, 44.8, 16.8 , and 33.6 t/ha, respectively. The two Largo biosolids treatments were either 56 or 112 t/ha and were applied only in the 2nd yr. Liver biopsies and blood samples were collected on d 1, 95, and 180. Liver and plasma were analyzed for minerals and blood was analyzed for hemoglobin, hematocrit, and superoxide dismutase of polymorphonuclear neutrophils. Experimental animals were generally adequate in macromineral status and Co, Fe, and Mn throughout the experiment. Copper deficiency was evident based on the clinical signs of hair coat discoloration, very low plasma Cu at d 95, and the continuous decline in liver Cu over 180 d. A sharp decline in plasma Cu was observed for all treatments from d 1 to 95, after which Cu concentrations rebounded to normal concentrations (> 0.65 microg/mL) by d 180. Liver Mo was well below concentrations indicating toxicity (> 5.0 mg/kg). The steep decline in liver Cu over the first 95 d reflects the dietary Cu deficiency and the possibility of high forage S (0.26 to 0.52%) interfering with Cu metabolism. Biosolids application to bahiagrass pastures was not detrimental to mineral status except for declining Cu stores; however, the controls likewise declined, but to a lesser degree.     

Influence of thyroid status regulation and Synovex-S implants on growth performance and tissue gain in beef steers.

The separate and combined effects of Synovex-S (SYN) ear implants and thyroxine (T4)-5'-monodeiodinase inhibition (Trial 1) and T3 injection to create a mild elevation in circulating T3 concentrations (Trial 2) on BW gain and composition of gain were studied. Trial 1 used 24, 285-kg Angus steers in two experimental phases. Low-level feeding of propylthiouracil (PTU, 1.5 mg/kg BW daily) was used to achieve inhibition of T4-5'-monodeiodinase activity (TMA). Twelve steers received neither treatment (control) and 12 received SYN+PTU (hypothesized to maximize weight gain) from 0 to 56 d (phase 1) in a single factor treatment comparison. Subsequently, PTU was fed to six control steers and not fed to six of the original SYN+PTU steers from 56 to 175 d (phase 2) in a 2 x 2 arrangement of treatments. Trial 2 used 24, 302-kg Angus-Hereford steers. Treatments were without or with SYN and without or with sc injections of T3 in polyethylene glycol (2 micrograms/kg BW every 48 hr) in a 2 x 2 factorial arrangement of treatments. In both trials, all steers were individually fed a diet of a corn-based concentrate and silage mixture at an equal metabolizable energy intakes per unit of metabolic body weight (.25 Mcal/kg BW.75). Measurements of daily dry matter intakes, weekly BW, 28-d estimates of empty body components (measured by urea dilution), final TMA (trial 1) and plasma thyroid hormone concentrations were obtained. In both trials, SYN increased BW gain and protein accretion.(ABSTRACT TRUNCATED AT 250 WORDS)     

Performance of finishing beef steers in response to anabolic implant and zilpaterol hydrochloride supplementation

Our objectives were to evaluate the dose/payout pattern of trenbolone acetate (TBA) and estradiol-17β (E(2)) implants and feeding of zilpaterol hydrochloride (ZH) on performance and carcass characteristics of finishing beef steers. A randomized complete block design was used with a 3 × 2 factorial arrangement of treatments. British × Continental steers (n = 168; initial BW = 362 kg) were blocked by BW and allotted randomly to 42 pens (7 pens/treatment; 6 pens/block; 4 steers/pen). The main effects of treatment were implant [no implant (NI); Revalor-S (REV-S; 120 mg of TBA + 24 mg of E(2)); and Revalor-XS (REV-X; 200 mg of TBA + 40 mg of E(2))] and ZH (0 or 8.3 mg/kg of DM for 20 d with a 3-d withdrawal before slaughter). Blocks were split into 2 groups, and block groups were fed for either 153 or 174 d. No implant × ZH interactions were noted for cumulative performance data. Overall, shrunk final BW (567, 606, and 624 kg for NI, REV-S, and REV-X, respectively), ADG (1.25, 1.51, and 1.60 kg), and G:F (0.14, 0.16, and 0.17) increased (P < 0.05) as TBA and E(2) dose increased. Implanting increased (P < 0.05) DMI, but DMI did not differ (P > 0.10) between REV-S and REV-X (8.8 for NI vs. 9.4 kg/d for the 2 implants). From d 1 to 112 of the feeding period, implanting increased (P < 0.05) ADG and G:F, but REV-S and REV-X did not differ (P > 0.10). From d 112 to end, ADG increased by 19% (P < 0.05) and G:F was 18% greater (P < 0.05) for REV-X vs. REV-S. Carcass-adjusted final BW (29-kg difference), ADG (0.2-kg/d difference), and G:F (0.02 difference) were increased (P < 0.05) by ZH, but daily DMI was not affected by feeding ZH. Hot carcass weight was increased (P < 0.05) by ZH (19-kg difference) and implant, with REV-X resulting in the greatest response (HCW of 376 for NI vs. 404 and 419 kg for REV-S and REV-X, respectively; P < 0.05). An implant × ZH interaction (P = 0.05) occurred for dressing percent (DP). Without ZH, implanting increased DP, but DP did not differ (P > 0.10) between REV-X and REV-S. With ZH, REV-X increased (1.7%; P < 0.05) DP vs. NI and REV-S. Marbling score, 12th-rib fat, and KPH were not affected (P > 0.10) by implant or ZH. Overall, treatment increased steer performance and HCW in an additive fashion, suggesting different mechanisms of action for ZH and steroidal implants. In addition, a greater dose of TBA + E(2) and extended payout improved steer performance and HCW.     

Effect of the previously gravid uterine horn and postpartum interval on follicular diameter and conception rate in beef cows treated with estradiol benzoate and progesterone

An experiment was performed to evaluate the effect of the side of ovulation with respect to the previously gravid uterine horn on fertility of cows inseminated at one of two periods postpartum. All cows were treated with an intravaginal progesterone insert for 7 d and received estradiol benzoate (2 mg, i.m.) at the time of device insertion, prostaglandin F2alpha (25 mg, i.m.) at the time of device removal, and estradiol benzoate (1 mg, i.m.) 30 h after device removal. All cows were inseminated 28 to 30 h after the second treatment with estradiol benzoate, regardless of observed estrus. Cows treated in Period 1 received inserts at 16 to 20 d postpartum and were inseminated at 25 to 29 d postpartum. Cows treated in Period 2 received inserts at 26 to 30 d postpartum and were inseminated at 35 to 39 d postpartum. Diameter of the largest follicle at insert removal was greater in cows treated in Period 2 (10.1 +/- 0.3; mm +/- SEM) than in cows treated in Period 1 (9.1 +/- 0.3; P < .05). Diameter did not differ with the side of ovulation in respect to the previously gravid uterine horn. Diameter was greater in cows 5 to 9 (10.3 +/- 0.3) than in cows 3 to 4 (9.0 +/- 0.3) or 10 to 13 (9.4 +/- 0.6) yr of age (P < .01). The proportion of cows that ovulated from the ovary contralateral to the previously gravid uterine horn was greater (P < .05) than of those that ovulated from the ipsilateral ovary, and the incidence of ovulation was reduced in cows 3 to 4 yr of age (P < .01). Conception rate tended to be greater for ovulation from the ipsilateral compared with the contralateral ovary, relative to the previously gravid uterine horn (P < .10) and for ovulation from the right than the left ovary (P < .06). Conception rate was less if cows ovulated a follicle that was < 9 mm than a follicle > or = 9 mm in diameter at insert removal (P < .01) and was greater in cows inseminated in June than in April or May (P < .05). In conclusion, in cows in which estrus was synchronized at 25 to 39 d postpartum, ovulation from either the ovary ipsilateral to the previously gravid uterine horn, or the right ovary, tended to increase fertility.     

Effect of live weight gain of steers during winter grazing: I. Feedlot performance, carcass characteristics, and body composition of beef steers

Two experiments were conducted to examine the effect of previous BW gain during winter grazing on subsequent growth, carcass characteristics, and change in body composition during the feedlot finishing phase. In each experiment, 48 fall-weaned Angus x Angus-Hereford steer calves were assigned randomly to one of three treatments: 1) high rate of BW gain grazing winter wheat (HGW), 2) low rate of BW gain grazing winter wheat (LGW), or 3) grazing dormant tallgrass native range (NR) supplemented with 0.91 kg/d of cottonseed meal. Winter grazing ADG (kg/d) for HGW, LGW, and NR steers were, respectively, 1.31, 0.54, 0.16 (Exp. 1) and 1.10, 0.68, 0.15 (Exp. 2). At the end of winter grazing, four steers were selected randomly from each treatment to measure initial carcass characteristics and chemical composition of carcass, offal, and empty body. All remaining steers were fed a high-concentrate diet to a common backfat end point. Six steers were selected randomly from each treatment for final chemical composition, and carcass characteristics were measured on all steers. Initial fat mass and proportion in carcass, offal, and empty body were greatest (P < 0.001) for HGW, intermediate for LGW, and least for NR steers in both experiments. Live BW ADG and gain efficiency during the finishing phase did not differ (P = 0.24) among treatments, but DMI (% of mean BW) for NR and LGW was greater (P < 0.003) than for HGW steers. Final empty-body composition did not differ (P = 0.25) among treatments in Exp. 1. In Exp. 2, final carcass and empty-body fat proportion (g/kg) was greater (P < 0.03) for LGW and NR than for HGW steers. Accretion of carcass fat-free organic matter was greater (P < 0.004) for LGW than for HGW and NR steers in Exp. 1, but did not differ (P = 0.22) among treatments in Exp. 2. Fat accretion in carcass, offal, and empty body did not differ (P = 0.19) among treatments in Exp. 1, but was greater (P < 0.05) for LGW and NR than for HGW steers in Exp. 2. Heat production by NR steers during finishing was greater (P < 0.02) than by HGW steers in Exp. 1 and 2. Differences in ADG during winter grazing and initial body fat content did not affect rate of live BW gain or gain efficiency during finishing. Feeding steers to a common backfat thickness end point mitigated initial differences in carcass and empty-body fat content. However, maintenance energy requirements during finishing were increased for nutritionally restricted steers that were wintered on dormant native range.     

Effect of long- or short-term feeding of alpha-tocopheryl acetate to Holstein and crossbred beef steers on performance, carcass characteristics, and beef color stability.

Three experiments were conducted to examine the effects of vitamin E supplementation on feedlot cattle. Vitamin E supplementation did not affect feedlot performance or carcass characteristics of cattle fed a high-concentrate diet (P greater than .1). The major finding was the effectiveness of vitamin E in extending the color stability of displayed beef (P less than .01). Color stability during display of longissimus lumborum steaks from cattle supplemented with 300 IU/d for 266 d, 1,140 IU/d for 67 d, or 1,200 IU/d for 38 d was extended by 2.5 to 4.8 d. Gluteus medius steaks had an extended color display life of 1.6 to 3.8 d. The accumulation of lipid oxidation products, but not aerobic microbes, associated with displayed longissimus lumborum was suppressed for muscle from vitamin E-supplemented steers. Taste panelists detected no difference among longissimus lumborum steaks from control and vitamin E-supplemented steers but found (P less than .01) steaks aged for 21 d to be more tender than steaks aged for 7 d. Supplementing cattle with vitamin E should reduce economic losses associated with discolored beef during retail display.     

Reproductive performance of post-partum anoestrous dairy cows treated with progesterone and oestradiol benzoate

Abstract

Extract

Recent studies have shown that the anoestrous condition of post-partum dairy cows can be treated with a combination of progesterone (for 5–7 days) and oestradiol benzoate (ODB, 1 mg injected at 24 or 48 h after termination of the progesterone treatment)(1) McDougall, S, and Macmillan, KL. 1993. Follicle waves, ovulation and oestrus in the postpartum cow. Proceedings of the 13th Seminar for the Society of Dairy Cattle Veterinarians of the New Zealand Veterinary Association, : 33–47.  [Google Scholar]. However, published data on the performance of this anoestrus treatment programme in commercial dairy herds is limited(2) Macmillan, KL,, Taufa, VK,, Day, AM, and McDougall, S. 1995. Some effects of using progesterone and oestradiol benzoate to stimulate oestrus and ovulation m dairy cows with anovulatory anoestrus. Proceedings of the New Zealand Society of Animal Production, 55: 239–241.  [Google Scholar]. During the 1994–95 and 1995–96 breeding seasons, performance of this anoestrus treatment programme was determined in nine and six spring-calving herds, respectively. In each herd, cows that had not been detected in oestrus using the tailpainting technique by Day -7 (Day 0 = start of the breeding season) were examined per rectum by each herd owner's attending veterinarian for the presence of a palpable corpus luteum (CL) on the ovary. Cows with a palpable CL or with an enlarged or infected uterus were excluded. Throughout the trial period, anoestrous cows were managed together with the cycling cows.     

Reproductive performance in sows treated with estradiol benzoate/human chorionic gonadotrophin combination at weaning.

The effects of estradiol benzoate plus human chorionic gonadotrophin administered on the day of weaning on the reproductive performance in sows was studied. The treatment advanced the onset of estrus but the duration of estrus was slightly prolonged. Breeding on the post-weaning estrus was associated with poor pregnancy rate and smaller litters. The treatment did not cause permanent damage to the reproductive tract as the reproductive performance of the treated sows after subsequent breedings were unaffected. The possible causes of the poor fertility in the estradiol benzoate plus human chorionic gonadotrophin treated sows are discussed.     

Effects of biological type of beef steers on vitamin D, calcium, and phosphorus status

Feedlot steers (n = 36) from three biological types (Bos indicus, Bos taurus-Continental, and Bos taurus-English) were used to determine the Ca, P, and vitamin D3 status of feedlot cattle. The USDA yield and quality grade traits were measured at slaughter, and the concentrations of vitamin D3 (VITD) and the metabolites 25-hydroxyvitamin D3 (25-OH D) and 1,25-dihydroxyvitamin D3 (1,25-(OH)2 D) were determined in LM, liver, kidney, and plasma. Plasma and muscle Ca and P concentrations also were determined. Biological type of cattle affected a number of carcass traits. Carcasses from Bos taurus-English cattle had more marbling, resulting in higher quality grades (P < 0.05). Carcasses from Bos taurus-Continental cattle had lower calculated yield grades (P < 0.05) than did carcasses from cattle in the other biological types. In general, differences in carcass traits resulting from biological type were consistent with other reports. Plasma and LM Ca and P concentrations were not affected (P = 0.06) by biological type of cattle, indicating that Ca and P homeostasis is a conserved trait across the different types of cattle. Plasma VITD and 25-OH D concentrations were not affected (P = 0.41) by biological type, whereas plasma 1,25-(OH)2 D concentration was lower (P < 0.05) in Bos taurus-English cattle than in Bos taurus-Continental and Bos indicus cattle. Liver VITD and 25-OH D were not affected by biological type (P = 0.76), but liver 1,25-(OH)2 D concentration was greater (P < 0.05) in Bos indicus cattle than in Bos taurus-Continental cattle. Kidney vitamin D metabolite concentrations were not affected by biological type of cattle (P = 0.21). Muscle VITD concentration was greater (P < 0.05) in Bos taurus-English cattle than in the other two biological types, and muscle 25-OH D concentrations were greater (P < 0.05) in Bos taurus-English cattle than in Bos indicus cattle. Muscle 1,25-(OH)2 D concentration was less (P < 0.05) in the Bos taurus-Continental cattle than in the other two biological types. Cooking eliminated vitamin D metabolite differences among the biological types. Our results suggest that Bos indicus cattle had greater 1,25-(OH)2 D (the biologically active form) in tissues, and greater 1,25-(OH)2 D plasma concentrations than Bos taurus cattle. Thus, the need for VITD supplementation and optimal levels of Ca and P in feedlot diets might differ between Bos indicus and Bos taurus cattle.     

Association of serologic status for Neospora caninum and postweaning feed efficiency in beef steers.

OBJECTIVE: To determine the effects of serologic status for Neospora caninum on short-term weight gain, feed intake, and feed efficiency (feed intake/gain). DESIGN: Longitudinal observational study. ANIMALS: 34 weaned mixed-breed beef steers. PROCEDURE: Serologic status for N. caninum was determined for each steer on days 0 (weaning), 88, 116, 144, 172, and 200, using an agglutination test. Individual steer body weight was measured on days 0, 88, 116, 144, 172, 200, and 242 (slaughter). Daily feed intake was monitored from days 116 through 242. Serologic status was matched to animal performance for the period immediately following serum sample collection. A mixed mode, using repeated-measures with an unstructured covariance matrix, was used in the analysis. Breed, age, and pen effects were controlled for in the analysis. RESULTS: A reduction in average daily gain for the period following a positive serologic result was detected for the entire trial (6 measurements/steer). This may have been attributed to a significant impairment in feed efficiency rather than to an impairment in feed intake. Changes in serologic status in individual steers over time were common; additionally, the effects of serologic status on steer performance were also transitory. CONCLUSIONS AND CLINICAL RELEVANCE: Significant reductions in short-term weight gain and feed efficiency were associated with the presence of antibodies against N. caninum in postweaning beef steers.     

Effect of monensin, estradiol controlled release implants and supplement on performance in grazing steers

Five trials in five locations in the United States involving 512 steers were conducted to evaluate the effect of monensin [200 mg/d in .9 kg of supplement (Ru mensin )] and estradiol-controlled release implants ( Compudose ) administered alone and in combination on average daily gain (ADG) in steers on pasture. The effect of energy supplementation on rate of gain was also evaluated in these same trials. The initial weight of steers averaged 250 kg and the average duration of the five trials was 124 d. Estradiol-controlled release implants increased ADG by 15.6% (.095 kg/d; P less than .0001) and monensin increased ADG by 8.1% (.054 kg/d; P less than .05). The combination of estradiol-controlled release implant and monensin increased ADG by 27.4% (.168 kg/d). Treatment responses were additive relative to ADG response, with no interaction observed between the treatments. Nine-tenths kilograms of an energy supplement/d increased ADG by 12.4% (.073 kg/d; P less than .01).