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1.
Morphine (M), an opioid agonist, was administered to postpartum (PP) Angus cows to investigate opioid modulation of gonadotropin secretion. In Exp. 1, eight PP cows (36.9 +/- 2.3 d) received either M (1 mg/kg; n = 4) or saline solution (S) (n = 4) via i.v. injection 36 h after calf removal. Morphine decreased (P less than .01) the number of serum LH pulses (3.0 +/- 1.1 pre- vs .3 +/- .3 post-pulses/h) and, compared with pretreatment values (3.3 mg/ml), decreased (P less than .05) mean LH at 105 min (2.1 ng/ml) through 270 min 1.9 ng/ml +/- .4). Serum prolactin (PRL) increased (P less than .01) following M from 16.4 ng/ml to a peak of 59.3 ng/ml (+/- 3.9). Serum FSH concentrations were unaffected. In Exp. 2, M (.31 mg/kg i.v. injection followed by .15 mg/(kg.h) infusion; n = 6) or S (n = 6) treatments were given for 7 h beginning 36 h after calf removal. Serum LH was similar between groups during the pretreatment and the first 6 h of infusion, but M decreased (P less than .001) the number of serum LH pulses (.44 +/- .09 vs .06 +/- .04 pulses/h). Morphine increased (P less than .05) serum PRL. It is concluded that M differentially modulated gonadotropin secretion in the cow such that PRL increased, LH decreased and FSH was unchanged.  相似文献   

2.
Three experiments were conducted to evaluate effects of supplemental protein vs energy level on dormant forage intake and utilization. In Exp. 1, 16 ruminally cannulated steers were blocked by weight (avg wt = 242 kg) and assigned randomly to a negative control or to one of three isocaloric supplement treatments fed at .4% BW: 1) control, no supplement (NS); 2) 12% CP, low protein (LP); 3) 28% CP, moderate protein (MP); 4) 41% CP, high protein (HP). In Exp. 2 and 3, 16 ruminally cannulated steers were blocked by weight (avg wt = 332 kg, Exp. 2; 401 kg, Exp. 3) and assigned randomly to a 2 x 2 factorial arrangement of treatments. The treatments contrasted low (LP) and high (HP) levels of supplemental protein (.66 g CP/kg BW vs 1.32 g CP/kg BW) with low (LE) and high (HE) levels of supplemental ME (9.2 kcal/kg BW vs 18.4 kcal/kg BW). In Exp. 1, forage DMI as well as ruminal DM and indigestible ADF fill at 4 h postfeeding were greater (P less than .10) with the MP and HP steers than with control and LP steers. Total DM digestibility increased (P less than .10) for supplemented steers (35.5% for control vs 47.3 for supplemented steers); however, LP depressed (P less than .10) NDF digestibility. In Exp. 2, forage DMI, indigestible ADF flow and liquid flow were depressed (P less than .10) in LP-HE supplemented steers. In Exp. 3, HP steers had greater (P less than .10) forage DMI, indigestible ADF fill values (4 h postfeeding), liquid volume and tended (P = .11) to have greater ruminal DM fill (4 h postfeeding). In summary, increased levels of supplemental protein increased intake and utilization of dormant tallgrass-prairie forage (less than 3% CP). Increasing supplemental energy without adequate protein availability was associated with depressed intake and digestibility.  相似文献   

3.
A possible role for endogenous opioid peptides (EOP) in the control of luteinizing hormone (LH) and prolactin (PRL) secretion was studied by injecting the opioid antagonist, naloxone (NAL), into postpartum ewes and cows. Twelve ewes that lambed during the fall breeding season and nursed their lambs were injected iv with NAL (1.0 mg/kg) on d 10, 14, 18, 22 and 26 postpartum. Blood samples were collected at 15-min intervals from 2 h before to 2 h after NAL, and serum concentrations of LH and PRL were quantified. Following treatment on d 10, suckling lambs were removed from 6 of the 12 ewes, creating non-suckled (NS) and suckled (S) treatment groups for subsequent study on d 14 through 26. On d 10, NAL treatment increased LH (P less than .01) but concentrations of PRL were not affected. When averaged across d 14 to 26, post-NAL concentrations of LH were greater (P less than .001) than pre-NAL concentrations (6.5 +/- .7 vs 1.9 +/- .4 ng/ml). In contrast, concentrations of PRL in the post-NAL period were lower (P less than .001) than pre-NAL concentrations (129 +/- 15 vs 89 +/- 10 ng/ml). Compared with S ewes over d 14 to 26, those in the NS group had similar pre-NAL concentrations of LH, tendencies for higher (P less than .10) post-NAL concentrations of LH, lower (P less than .001) mean serum concentrations of PRL (pre- and post-NAL) and similar pre-NAL vs post-NAL differences in serum PRL. Six suckled beef cows on d 24 to 35 were injected iv with either saline or NAL (.5 mg/kg) in a replicated crossover design. Injections of NAL increased serum concentrations of LH (P less than .05), when averaged over all 12 injections in the six cows, but serum PRL was not changed. However, three of six cows did not respond to NAL with increases in serum LH. These non-responding cows were similar to the responding cows in their pre-injection concentrations of LH and PRL, but they tended (P = .10) to have higher serum concentrations of cortisol than responding cows.  相似文献   

4.
Two 160-d feedlot experiments, each consisting of 20 Angus-Hereford steers (216 +/- 5 kg BW, Exp. 1; 258 +/- 5 kg BW, Exp. 2) and 20 Angus-Hereford heifers (208 +/- 5 kg BW, Exp. 1; 236 +/- 5 kg BW, Exp. 2), were used to investigate the effects of supplementing diets with either roasted soybeans (RSB, roasted at 127 degrees C for 10 min) or soybean meal (SBM) and implanting or not implanting with an estrogenic growth promoter (SYN; Synovex-S, 20 mg of estradiol benzoate plus 200 mg of progesterone or Synovex-H, 20 mg of estradiol benzoate plus 200 mg of testosterone) on performance. The cattle were fed a basal diet of 15% orchardgrass silage, 15% corn silage, and 70% corn-based concentrate. Treatments were 1) no SYN and fed a SBM-supplemented diet, 2) no SYN and fed a RSB-supplemented diet, 3) SYN and SBM, and 4) SYN and RSB. Cattle in the SYN groups were reimplanted at 80 d. Four additional Angus-Hereford steers were used in a digestion and nitrogen balance experiment conducted during the first half of Exp. 1. For the total 160-d feedlot experiments, DMI for RSB compared with SBM was lower (P < .01; 8.5 vs 9.2 kg/d, SEM = .07) and ADG/DMI tended to be higher (P < .10; 165 vs 157 g/kg, SEM = 1.3). Final BW of steers fed RSB was similar (P > .10) to that of steers fed SBM (473 vs 478 kg, SEM = 5.6), as was ADG (1.39 vs 1.43 kg/d, SEM = .02). Dry matter intake for SYN-implanted steers was higher (P < .01) than for steers not implanted (9.2 vs 8.5 kg/d). Likewise, final BW (491 vs 460 kg) and ADG (1.49 vs 1.33 kg/d) were higher (P < .01), and ADG/DMI (166 vs 157 g/kg) tended to be higher (P < .10), for SYN-implanted steers than for steers not implanted. During the more rapid muscle growth period (0 to 80 d), DMI for RSB compared with SBM was lower (P < .01; 7.8 vs 8.6 kg/d, SEM = .07) and ADG/DMI was similar (P > .10; 181 vs 172 g/kg, SEM = 1.8). Dry matter intake for SYN-implanted steers was higher (P < .05) than for steers not implanted (8.4 vs 8.0 kg/d), as was ADG/DMI (P < .01, 182 vs 171 g/kg). During this more rapid growth period, the supplement x implant interaction for ADG was significant (P < .05; 1.35, 1.36, 1.59, and 1.44 kg/d for Treatments 1, 2, 3, and 4, respectively, SEM = .04). There were no differences in digestibilities or N balance. The results suggest that there is no improvement in performance under feedlot conditions when RSB replaces SBM in the diet of beef cattle, and, in young cattle, RSB may reduce the response expected by an estrogenic growth promoter.  相似文献   

5.
The objectives of our experiments were 1) to determine the effect of N-methyl-D,L-aspartate (NMA), an agonist of the neuroexcitatory amino acids aspartate and glutamate, on growth hormone (GH) release in ovariectomized ewes, and 2) to determine the effect of naloxone, an opioid antagonist, on the GH response to NMA. Jugular blood was collected via venipuncture at 12-min intervals for 2 h before and 2 h after i.v. injection of NMA. In Exp. 1, ewes received either 0, 6, 12 or 24 mg NMA/kg BW dissolved in .9% saline solution (n = 4 per treatment). Growth hormone concentrations were similar (P greater than .1) between groups prior to injection (9.8 +/- .7 ng/ml; mean +/- SEM) and were unaffected (P greater than .1) by saline treatment. In contrast, 6, 12 or 24 mg NMA/kg BW increased mean GH concentration by 210% (P less than .04), 273% (P less than .02) and 234% (P less than .02), respectively. In Exp. 2, ewes received NMA (6 mg/kg BW) 5 min after either saline (n = 4) or naloxone (1 mg/kg BW; n = 4) pretreatment. Serum GH concentrations averaged 7.0 +/- 1.1 ng/ml before pretreatment and increased similarly (238%; P greater than .1) in both groups following NMA. In summary, NMA increased GH concentrations in ovariectomized ewes by some mechanism that does not involve opioid receptors that are antagonized by naloxone.  相似文献   

6.
Endogenous opioid peptides mediate the effect of suckling on LH and PRL in the domestic pig. However, the role of opioids in modulating GH during lactation in swine is not known. Primiparous sows that had been immunized against GRF(1-29) conjugated to human serum albumin (GRF-HSA, n = 5) or HSA (n = 4) were used to determine changes in GH after naloxone. Treatments were imposed in all sows on day 21 of lactation when antibody titers were 9100 +/- 1629. All sows received (i.v.) naloxone (0.25 mg/kg) or saline (0.0125 ml/kg) at 15 min intervals for 165 min. Active immunization against GRF-HSA during lactation decreased (P less than 0.05) mean concentration (4.8 +/- 0.2 vs 2.6 +/- 0.1 ng/ml) and frequency (1.5 +/- 0.3 vs 0.4 +/- 0.2 peaks/4 hr). Concentrations of LH and PRL were similar in GRF-HSA and HSA immunized sows. Naloxone suppressed (P less than 0.05) GH in all sows. In HSA sows, naloxone abolished episodic release of GH and decreased average, but not basal, concentrations of GH. In sows immunized against GRF-HSA, naloxone decreased (P less than 0.05) average and basal GH but failed to decrease frequency of GH release. Naloxone failed to alter frequency of LH release. Concentrations of PRL decreased (P less than 0.05) after naloxone in all sows. In conclusion, immunization against GRF-HSA blocked most of the effect of lactation on GH. Blocking opioid receptors with naloxone decreased GH and PRL in all sows. In contrast to previous findings naloxone had no effect on LH. Opioids alter concentrations of GH through a GRF dependent and GRF independent pathway.  相似文献   

7.
The effects of n-methyl-d,l-aspartate (NMA), a neuroexcitatory amino acid agonist, on luteinizing hormone (LH), prolactin (PRL) and growth hormone (GH) secretion in gilts treated with ovarian steroids was studied. Mature gilts which had displayed one or more estrous cycles of 18 to 22 d were ovariectomized and assigned to one of three treatments administered i.m.: corn oil vehicle (V; n = 6); 10 micrograms estradiol-17 b/kg BW given 33 hr before NMA (E; n = 6); .85 mg progesterone/kg BW given twice daily for 6 d prior to NMA (P4; n = 6). Blood was collected via jugular cannulae every 15 min for 6 hr. Pigs received 10 mg NMA/kg BW i.v. 2 hr after blood collection began and a combined synthetic [Ala15]-h GH releasing factor (1-29)-NH2 (GRF; 1 micrograms/kg BW) and gonadotropin releasing hormone (GnRH; .2 micrograms/kg BW) challenge given i.v. 3 hr after NMA. NMA did not alter LH secretion in E gilts. However, NMA decreased (P < .02) serum LH concentrations in V and P4 gilts. Serum LH concentrations increased (P < .01) after GnRH in all gilts. NMA did not alter PRL secretion in P4 pigs, but increased (P < .01) serum PRL concentrations in V and E animals. Treatment with NMA increased (P < .01) GH secretion in all animals while the GRF challenge increased (P < .01) serum GH concentrations in all animals except in V treated pigs. NMA increased (P < .05) cortisol secretion in all treatment groups. These results indicate that NMA inhibits LH secretion and is a secretagogue of PRL, GH and cortisol secretion with ovarian steroids modulating the LH and PRL response to NMA.  相似文献   

8.
Four experiments evaluated the effect of implant dose and release pattern on performance and carcass traits of crossbred beef steers. In Exp. 1, steers (4 to 7 pens/treatment; initial BW = 315 kg) were fed an average of 174 d. Treatments were 1) no implant (NI); 2) Revalor-S [120 mg of trenbolone acetate (TBA) and 24 mg of estradiol 17β (E(2)); REV-S]; 3) Revalor-IS followed by REV-S (cumulatively 200 mg of TBA and 40 mg of E(2); reimplanted at 68 to 74 d; REV-IS/S); and 4) Revalor-XS (200 mg of TBA and 40 mg of E(2); REV-X). Carcass-adjusted final BW was greater (P < 0.05) for REV-X and REV-IS/S than for REV-S (610, 609, and 598 kg, respectively). Daily DMI did not differ (P > 0.10) among the 3 implants, but carcass-adjusted G:F was greater (P < 0.05) for REV-X and REV-IS/S than for REV-S (0.197 and 0.195 vs. 0.188). Both HCW and LM area were greater (P < 0.05) for REV-X and REV-IS/S than for REV-S. Marbling scores were greatest (P < 0.05) for REV-S and least (P < 0.05) for REV-IS/S; REV-X was intermediate to NI and REV-IS/S. In Exp. 2, steers (10 pens/treatment; initial BW = 391 kg) were fed 131 d, with treatments of REV-S, REV-IS/S (reimplanted at 44 to 47 d), and REV-X. Carcass-adjusted final BW (598 kg), ADG (1.6 kg), DMI (9.4 kg), G:F (0.17), and HCW did not differ (P > 0.10) among treatments. The percentage of Choice was less (P < 0.05) and percentage of Select greater (P < 0.05) for REV-IS/S than for REV-S and REV-X. In Exp. 3, steers (10 pens/treatment; initial BW = 277 kg) were fed 197 d and received either REV-IS/S (reimplanted at 90 to 103 d) or REV-X. Carcass-adjusted final BW (625 vs. 633 kg) and ADG (1.81 vs. 1.76 kg) were greater (P < 0.05) for REV-X-implanted steers. Daily DMI did not differ, but G:F tended (P < 0.10) to be increased and HCW was greater (P < 0.05) for REV-X than for REV-IS/S. In Exp. 4, steers (8 pens/treatment; initial BW = 238 kg) were fed 243 d and received either REV-IS/S (reimplanted at 68 to 71 d) or REV-X. Carcass-adjusted final BW (612 kg), ADG (1.54 kg), DMI (7.55), and G:F (0.21) did not differ (P > 0.10) for REV-IS/S and REV-X-implanted steers. Carcass traits did not differ among implants, but the percentage of Choice carcasses was greater (P < 0.05) and percentage of Select was less (P < 0.05) for REV-X than for REV-IS/S. These data indicate that when TBA/E(2) dose is equal, the altered release rate of REV-X can improve performance and quality grade, but these effects depend on duration of the feeding period and timing of initial and terminal implants.  相似文献   

9.
Two experiments were conducted to evaluate the effects of slow-release urea (SRU) versus feed-grade urea on portal-drained visceral (PDV) nutrient flux, nutrient digestibility, and total N balance in beef steers. Multi-catheterized steers were used to determine effects of intraruminal dosing (Exp. 1; n = 4; 319 +/- 5 kg of BW) or feeding (Exp. 2; n = 10; 4 Holstein steers 236 +/- 43 kg of BW and 6 Angus steers 367 +/- 46 kg of BW) SRU or urea on PDV nutrient flux and blood variables for 10 h after dosing. Intraruminal dosing of SRU (Exp. 1) prevented the rapid increase in ruminal ammonia concentrations that occurred with urea dosing (treatment x time P = 0.001). Although apparent total tract digestibilities of DM, OM, NDF, and ADF were not affected by treatment (P > 0.53, Exp. 2), SRU increased fecal N excretion (49.6 vs. 45.6 g/d; P = 0.04) and reduced apparent total tract N digestibility (61.7 vs. 66.0%; P = 0.003). Transfer of urea from the blood to the gastrointestinal tract occurred for both treatments in Exp. 1 and 2 at all time points with the exception for 0.5 h after dosing of urea in Exp. 1, when urea was actually transferred from the gastrointestinal tract to the blood. In both Exp. 1 and 2, both urea and SRU treatments increased arterial urea concentrations from 0.5 to 6 h after feeding, but arterial urea concentrations were consistently less with SRU (treatment x time P < 0.001, Exp. 1; P = 0.007, Exp. 2). Net portal ammonia release remained relatively consistent across the entire sampling period with SRU treatment, whereas urea treatment increased portal ammonia release in Exp. 1 and tended to have a similar effect in Exp. 2 (treatment x time P = 0.003 and P = 0.11, respectively). Urea treatment also increased hepatic ammonia uptake within 0.5 h (treatment x time P = 0.02, Exp. 1); however, increased total splanchnic release of ammonia for the 2 h after urea treatment dosing suggests that PDV ammonia flux may have exceeded hepatic capacity for removal. Slow-release urea reduces the rapidity of ammonia-N release and may reduce shifts in N metabolism associated with disposal of ammonia. However, SRU increased fecal N excretion and increased urea transfer to the gastrointestinal tract, possibly by reduced SRU hydrolysis or effects on digestion patterns. Despite this, the ability of SRU to protect against the negative effects of urea feeding may be efficacious in some feeding applications.  相似文献   

10.
Two experiments were conducted with the opioid antagonist naloxone to determine the effect of opioid receptor blockade on hormone secretion in postpartum beef cows. In Exp. 1, nine anestrous postpartum beef cows were used to measure the effect of naloxone on serum luteinizing hormone (LH), cortisol and prolactin concentrations. Cows received either saline (n = 4) or 200 mg naloxone in saline (n = 5) iv. Blood samples were collected at 15-min intervals for 2 h before and after naloxone administration. Serum LH concentrations increased (P less than .01) in naloxone-treated cows from 1.8 +/- .04 ng/ml before treatment to 3.9 +/- .7 ng/ml and 4.2 +/- .5 ng/ml at 15 and 30 min, respectively, after naloxone administration. In contrast, LH remained unchanged in saline-treated cows (1.6 +/- .3 ng/ml). Serum cortisol and prolactin concentrations were not different between groups. In Exp. 2, 12 anestrous postpartum beef cows were used to examine the influence of days postpartum on the serum LH response to naloxone. Four cows each at 14 +/- 1.2, 28 +/- .3 and 42 +/- 1.5 d postpartum received 200 mg of naloxone in saline iv. Blood samples were taken as in the previous experiment. A second dose of naloxone was administered 2 h after the first, and blood samples were collected for a further 2 h. Serum LH concentrations increased (P less than .01) only in cows at 42 d postpartum.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

11.
The dopamine antagonist metoclopramide (MC) was administered to steers grazing on endophyte-infected fescue. Yearling Angus steers (n = 24) were assigned randomly to pasture treatments including high (74%) and low (33%) endophyte levels and low (134 kg N.ha-1.yr-1) and high (335 kg N.ha-1.yr-1) N fertilization rates. One steer of the pair in each paddock (n = 12) received MC, whereas the other received sucrose (S) (15 mg/kg body weight, orally, three times a week for 10 wk). Blood for basal and maximal TRH-stimulated serum prolactin (PRL) concentrations was obtained before animals grazed fescue, after grazing for 1 mo, and after 3, 6 and 9 wk of animal treatment. Grazing endophyte-infected fescue decreased (P less than .05) basal serum PRL concentrations (less than 1.0 vs 5.3 ng/ml, high vs low endophyte). Basal serum PRL increased after 3, 6 and 9 wk of MC treatment (58.1 vs 5.4, 46.0 vs 12.0 and 50.8 vs 16.9 ng/ml, MC vs sucrose, respectively). After 6 wk of animal treatments, MC increased (P less than .05) serum cholesterol (84.7 vs 60.8 mg/dl, MC vs S). Animals treated with MC spent more (P less than .05) time between 1200 and 1600 grazing (22.4% vs 6.2%, MC vs S respectively) and had faster ADG (.314 vs .150 kg/d, MC vs S). The results implicate dopaminergic processes in fescue toxicosis.  相似文献   

12.
Three experiments were conducted to study the effects of lasalocid level on performance, intake, digestibility, ruminal fermentation and fluid flow of beef cattle grazing dormant, tallgrass prairie. In Exp. 1, 120 pregnant, mature beef cows of primarily Hereford breeding (avg wt = 471 kg) were randomly assigned to received 0, 100, 200 or 300 mg lasalocid X head-1 X d-1 in 1.82 kg supplement. Weight changes at 30, 60 or 90 d, condition score change and calf birth weight were not affected (P greater than .10) by lasalocid level. In Exp. 2, estimates of intake and digestibility were obtained with 40 pregnant, mature Hereford cows (avg wt = 474 kg) and 12 esophageal-cannulated, Hereford X Angus steers (avg wt = 225 kg), using Yb and indigestible acid detergent fiber as markers for fecal output and digestibility, respectively. Levels of lasalocid provided to cows and steers were similar, on a body weight (BW) basis, to those in Exp. 1 and corresponded to approximately 0, .22, .44 or .66 mg lasalocid/kg BW. Total diet and forage organic matter digestibility for beef cows decreased (P less than .01) at the .22 mg/kg BW level, but increased at the .44 and .66 mg/kg BW levels. Organic matter intake was not influenced (P greater than .10) by lasalocid addition. In Exp. 3, 16 ruminal-cannulated, Hereford X Angus steers (avg wt = 227 kg) were given the same lasalocid dosages per kg BW as in Exp. 2, and were used to study the effects of lasalocid on ruminal fermentation and fluid flow characteristics.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

13.
The objectives of this research were to determine the interaction of monensin and haylage supplementation for steers fed 60% dried distillers grains (DDGS) on 1) mineral status, performance, and carcass characteristics, and on 2) ruminal pH, H(2)S, and short-chain fatty acid concentrations. In Exp. 1, Angus-cross steers (n=168; BW=277 ± 67 kg) were blocked by BW and allotted in a 2 × 2 factorial arrangement of treatments to 24 pens. Dietary treatments were 1) 0 mg of monensin/kg of diet + 0% haylage, 2) 33 mg of monensin/kg of diet + 0% haylage, 3) 0 mg of monensin/kg of diet + 10% haylage, and 4) 33 mg of monensin/kg of diet + 10% haylage. The remainder of the diet was 60% DDGS, 10% corn silage, 15% supplement, and corn (either 5 or 15%) on a DM basis. When supplemented with 0 mg of monensin/kg of diet, added haylage increased ADG by 5.7%, whereas when supplemented with 33 mg of monensin/kg of diet, added haylage increased ADG by 13% (P < 0.01). No interactions of monensin and haylage were observed for DMI or G:F (P ≥ 0.36). Haylage inclusion increased (P < 0.01) DMI and decreased (P < 0.01) G:F. No interactions (P > 0.05) on plasma mineral concentrations were observed; however, over time, plasma Cu concentrations decreased (P < 0.01), whereas plasma ceruloplasmin and S concentrations increased (P < 0.01). There were no treatment effects (P ≥ 0.08) on carcass characteristics. Cattle fed the 60% DDGS diets benefitted from increased dietary forage, and the effects of monensin and forage were additive for ADG and final BW. In Exp. 2, ruminally fistulated steers (n=8; BW = 346 ± 34 kg) were used in a replicated 4 × 4 Latin square design and were randomly assigned to the diets used in Exp. 1. Haylage inclusion increased ruminal pH from 1.5 through 12 h postfeeding, and the effects of monensin supplementation were additive (P < 0.05). From 1.5 through 9 h postfeeding, steers fed 33 mg of monensin/kg of diet tended to have reduced (P ≤ 0.10) concentrations of H(2)S when compared with steers fed 0 mg of monensin/kg of diet. Acetate:propionate ratios at 6 h postfeeding were 0.94, 0.93, 1.29, and 1.35 for diets 1 to 4, respectively (P < 0.01); total lactate was decreased regardless of treatment (range: 0.94 to 1.42 μmol/mL). Sulfuric acid in DDGS, not ruminal short-chain fatty acids, may be responsible for the low rumen pH observed and may influence the maximum inclusion of DDGS in cattle diets. Monensin supplementation decreased H(2)S concentration and may decrease the risk of polioencephalomalacia for cattle fed high-DDGS diets.  相似文献   

14.
In each of two experiments, 70 crossbred steers were blocked by BW and assigned to initial slaughter groups or to treatments in a 2 x 2 design. In Exp. 1, treatments were 168 d of photoperiod (8 h of light [L]:16 h of dark [D] or 16L:8D) and plane of nutrition (high energy [HPN] or low energy [LPN]). On d -22, 67 and 155, blood was sampled every 20 min for 8 h. Relative to LPN, HPN increased (P less than .01) ADG by 28%, carcass weight by 26% and accretion of carcass fat by 109% and carcass protein by 20%. On d 155, compared with LPN, HPN increased (P less than .01) serum insulin (INS; 1.09 vs .64 ng/ml) and lowered (P less than .05) growth hormone (GH; 2.14 vs 3.70 ng/ml), but prolactin was not affected. Photoperiod did not affect BW gains, carcass composition or serum hormones. In Exp. 2, treatments were 113 d of photoperiod (8L:16D or 16L:8D) and Synovex-S implant (presence [IMP] or absence [NONIMP]). On d 93, blood was sampled every 30 min for 10 h. Relative to NONIMP, IMP increased (P less than .01) ADG by 12% and accretion of carcass protein by 16%. Implants did not affect carcass weight or accretion of fat. Compared with NONIMP, IMP increased (P less than .05) GH (3.16 vs 2.39 ng/ml) and INS (.68 vs .46 ng/ml) but did not affect PRL. Photoperiod did not affect BW gain, carcass composition or serum hormones. We conclude that photoperiod fails to influence growth and carcass composition of steers.  相似文献   

15.
We investigated the influence of DM and(or) energy intake and dietary CP levels on the performance and nitrogen (N) retention of beef steers with and without growth promoter implants. In Exp. 1, four implanted (Synovex-S, 200 mg of progesterone plus 20 mg of estradiol benzoate) Angus steers and four Angus steers that were not implanted were assigned to concurrent 4 x 4 Latin squares. Initial BW averaged 296 kg. Each square consisted of moderate and moderately high DM intake treatments (4 and 6 kg/d) and low and adequate CP intake treatments (450 and 600 g/d) in a 2 x 2 factorial arrangement. Periods were 2 wk of adaptation, 5 wk of growth, and 1 wk of balance collection. Experiment 2 consisted of two replicates of 32 Hereford steers each (initial BW 324 kg). Each replicate was a 4 x 2 factorial in which steers were individually fed for 63 d. All steers had ad libitum access to a 60% corn-based concentrate diet containing either 7.9, 10.0, 12.1, or 14.6% CP (DM basis), and steers were either implanted or not implanted with Synovex-S. Experiment 3 was similar to Exp. 2 except that all steers (initial BW 315 kg) received a low-protein diet (7.6% CP) with calculated energy densities of either 1.86, 2.04, 2.22, or 2.42 Mcal ME/kg DM, and steers were limited to an equalized DM intake of 9.5 kg daily. In Exp. 1, gains for the low CP, moderate and moderately high DM intakes and the adequate CP, moderate and moderately high DM intakes were 240, 555, 208, and 730 g/d, respectively, for steers not implanted and 333, 643, 488, and 988 g/d, respectively, for implanted steers (SEM = 102 g/d). Respective values for retained N were .13, .18, .16, and .26 g/kg BW.75 and .13, .15, .22, and .29 g/kg BW.75 (SEM = .04 g/kg BW.75). Implant response was greater (CP x implant, P < .01) for both gain and retained N when adequate CP compared to low CP diets were fed. For Exp. 2, the lowest CP diet reduced ADG (.97 vs 1.27 kg/d) and efficiency of gain (100 vs 120 g gain/kg DM). Synovex-S was less effective in improving efficiency for the lowest protein diet than for the other diets (11.7 vs 20.2%). During Exp. 3, neither Synovex-S nor dietary energy influenced gain and efficiency. We concluded that adequate dietary protein is necessary to optimize the response to estrogenic growth promoters and that the low response under inadequate protein and energy intake is not improved by increasing the energy density of the diet.  相似文献   

16.
This study was conducted to investigate regulation of LH release by opioid peptides during puberal development in beef heifers. Fourteen heifers were randomly assigned to receive naloxone (opioid antagonist) i.v. at dosages of either 1 mg.kg BW-1.wk-1 (Dose 1) or .25 mg.kg BW-1.wk-1 (Dose 2) for 13 wk or until puberty. Blood was sampled (one sample every 15 min) 6 h before (prenaloxone) and 2 h after naloxone administration. Two hours after naloxone administration, GnRH (10 ng/kg BW) was administered and blood was sampled for 1 h. Nine heifers attained puberty during the study. There were no differences between naloxone dosage groups for any measured variables. Therefore, heifers were grouped dependent on the attainment of puberty. Prenaloxone concentrations of serum LH and LH pulse frequency were normal for prepuberal heifers. Serum LH concentrations increased within 30 min after naloxone 135 of 139 times it was administered (P less than .05). Serum LH concentrations during the hour after naloxone were higher (P less than .05) than those during the hour before naloxone in both puberal and nonpuberal heifers. In puberal heifers, serum LH pulse height during the hour after naloxone was greater (P less than .02) at 5 wk before puberty and lower (P less than .02) the week before puberty than at other times during the trial. There was no effect of week on serum LH pulse height after naloxone in heifers that failed to attain puberty during the study. Response of LH to GnRH was similar between groups.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

17.
The dopamine antagonist metoclopramide monohydrochloride (MC) and the serotonin agonist quipazine maleate (Q) were administered to steers by both the oral and intravenous (i.v.) routes. Dose-response studies were designed to determine the effects of these drugs on serum prolactin (PRL) concentrations. Parameters subjected to analysis included maximal serum PRL concentrations within 1 h and the areas under the PRL response curves over time. At 1, 4, and 8 mg/kg i.v., and at 15, 30, 45, and 60 mg/kg orally, MC increased (P less than 0.05) serum PRL concentrations (difference between maximal and basal serum PRL concentrations) and increased (P less than 0.05) areas under the PRL response curves except for 1.0 mg/kg i.v. Doses of MC greater than 60 mg/kg and Q at all dosage rates were considered toxic. These studies determined a dose-response to MC in terms of serum PRL concentration and indicate that MC is well tolerated and effective for elevating serum PRL concentrations in steers. Furthermore, 4 mg/kg i.v. and 15 mg/kg orally could be considered the preferred dosage rates due to a plateau in the response above those rates.  相似文献   

18.
Sixteen ovariectomized (OVX) mature gilts, averaging 139.6 ± 3.1 kg body weight (BW) were assigned randomly to receive either progesterone (P, 0.85 mg/kg BW, n=8) or corn oil vehicle (OIL, n=8) injections im twice daily for 10 d. On the day of experiment, all gilts received either the EAA agonist, N-methyl-d,l-aspartate (NMA; 10 mg/kg BW, iv) alone or NMA plus the EOP antagonist, naloxone (NAL, 1 mg/kg BW, iv), resulting in the following groups of 4 gilts each: OIL-NMA, OIL-NMA-NAL, P-NMA and P-NMA-NAL. Blood samples were collected via jugular cannula every 15 min for 6 hr. All pigs received NMA 5 min following pretreatment with either 0.9% saline or NAL 2 hr after blood collection began and a GnRH challenge 3 hr after NMA. Administration of NMA suppressed (P<0.03) LH secretion in OIL-NMA gilts and treatment with NAL failed to reverse the suppressive effect of NMA on LH secretion in OIL-NMA-NAL gilts. Similar to OIL-NMA gilts, NMA decreased (P<0.03) mean serum LH concentrations in P-NMA gilts. However, in P-NMA-NAL gilts, serum LH concentrations were not changed following treatment. All gilts responded to GnRH with increased (P<0.01) LH secretion. Additionally, administration of NMA increased (P<0.01) growth hormone (GH) and prolactin (PRL) secretion in both OIL-NMA and P-NMA gilts, but this increase in GH and PRL secretion was attenuated (P<0.01) by pretreatment with NAL in OIL-NMA-NAL and P-NMA-NAL gilts. Serum cortisol concentrations increased (P<0.01) in all gilts and the magnitude of the cortisol response was not different among groups. In summary, results of the present study confirmed previous findings that NMA suppresses LH secretion in both oil- and P-treated OVX gilts, but we failed to provide definitive evidence that EOP are involved in the NMA-induced suppression of LH secretion. However, NMA may, in part, activate the EOP system which in turn increased GH and PRL secretion in the gilt.  相似文献   

19.
The influence of the suckling stimulus and ovarian secretions on LH response to naloxone was studied in 16 postpartum anestrous beef cows that were assigned randomly to one of four groups (n = 4/group): intact suckled (IS), intact nonsuckled (IN), ovariectomized suckled (OS) or ovariectomized nonsuckled (ON). Ovariectomy (OS + ON) and calf removal (IN + ON) were performed on d 2, 3 or 4 after parturition. Jugular venous blood was collected at 15-min intervals for 4 h before and 4 h after administration of naloxone (1 mg/kg BW, i.v.) on d 14 and d 28 after parturition. Gonadotropin-releasing hormone (5 micrograms, i.v.) was given 3 h after naloxone. Both IN and OS increased (P less than .05) mean pretreatment LH above IS values (mean +/- SE, ng/ml; IS 1.6 +/- .1 vs IN 2.5 +/- .3 and OS 2.7 +/- .4; P less than .01), whereas ON increased (P less than .01) LH (3.7 +/- .3 ng/ml) even further. Mean LH increased (P less than .05) after naloxone administration in all treatment groups. However, magnitude of this response was variable and dependent on ovarian status. Amplitude of the naloxone-induced LH response was greater (P less than .05) for ovariectomized (5.9 +/- 1.1 ng/ml) than for intact groups (2.7 +/- .5 ng/ml). Gonadotropin-releasing hormone increased mean LH concentrations in all groups. We suggest that ovarian secretions and the suckling stimulus contribute to endogenous opioid inhibition of LH during the postpartum interval.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

20.
Effects of bovine respiratory disease (BRD) on stocker cattle systems are unknown under extensive rangeland environments. Three experiments were conducted to test the hypothesis that BRD-based morbidity is a major factor affecting the productivity and profitability of stocker cattle grazing Southern Plains rangelands. In Exp. 1 (658 male calves; average BW = 231 kg), 17% of the cattle were treated for BRD <8 d, 6% for 8 to 14 d, and 8% for >14 d. Morbid cattle had lower ADG than did healthy cattle (P < 0.10). Cattle requiring 14 d of pharmaceutical therapy gained less than cattle having <14 d therapy (P < 0.01). In Exp. 2, (279 steers and bulls; average BW = 216 kg), the ADG by steers (0.74 kg x animal(-1) x d(-1)) was greater (P < 0.05) than by bulls castrated after arrival (0.64 kg x animal(-1) x d(-1)). Castration after arrival led to a 13.5% loss in daily gain and a 10.3% loss in season-long gain. More (P < 0.05) bulls castrated after arrival (60%) were morbid compared with steers (28%). In Exp. 3, 633 heifers (average BW = 251 kg) were used to test the effects of morbidity on weight gain and reproduction. Heifers with lower initial weights exhibited increased (P < 0.05) morbidity. Heifers requiring two or more antibiotic treatments gained 0.03 kg/d less (P < 0.10) than did healthy heifers and had lower (P < 0.05) conception rates (66 vs. 81%). Conception rate in twice-treated heifers was 19% less than healthy heifers. Morbid heifers conceived 0.6 mo later (P < 0.05) than healthy heifers. Under the conditions of Exp. 1 and Exp. 2, morbidity decreased net returns 9.7 to 21.3% per animal. Adjusted gross returns per animal in Exp. 3 for replacement heifers were 3 to 7.8% less for morbid heifers.  相似文献   

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