Effects Of Lasalocid Research Articles

Effects of lasalocid, narasin, or virginiamycin supplementation on rumen parameters and performance of beef cattle fed forage-based diet.

Two experiments were designed to evaluate the impacts of supplementing lasalocid (LAS), narasin (NAR), or virginiamycin (VRM) on rumen fermentation parameters, apparent nutrient digestibility, and blood parameters (Exp. 1), as well as feed intake and performance (Exp. 2) of Nellore cattle consuming a forage-based diet. In Exp. 1, 32 rumen-fistulated Nellore steers (initial shrunk body weight [BW] = 355 ± 4.4 kg) were assigned to a randomized complete block design. Within block, animals were randomly assigned to one of four treatments: 1) forage-based diet without feed additives (CON), 2) CON diet plus 13 mg/kg of dry matter (DM) of NAR, 3) CON diet plus 20 mg/kg of DM of sodium LAS, or 4) CON diet plus 20 mg/kg of DM of VRM. No treatment effects were detected (P ≥ 0.32) for intake and apparent digestibility of nutrients. Steers fed NAR had the lowest (P ≤ 0.01) molar proportion of acetate on day 28, 56, and 112 vs. CON, LAS, and VRM steers, whereas acetate did not differ (P ≥ 0.25) between LAS, VRM, and CON steers from day 28 to 84. On day 112, steers fed LAS had a lower (P < 0.02) molar proportion of acetate vs. VRM and CON, whereas it did not differ between CON and VRM (P > 0.33). Steers receiving NAR had a greater (P ≤ 0.04) ruminal propionate vs. CON, LAS, and VRM, whereas LAS steers had greater (P < 0.04) propionate vs. CON and VRM steers on day 28 and 112, and it did not differ (P > 0.22) between CON and VRM. In Exp. 2, 160 Nellore bulls were blocked by initial shrunk BW (212 ± 3.1 kg) in a 140-d feedlot trial. Diets contained the same treatments used in Exp. 1. Bulls fed NAR had greater (P < 0.02) average daily gain (ADG) vs. CON and VRM, and similar (P = 0.17) ADG between NAR and LAS, whereas ADG did not differ (P > 0.28) between LAS, VRM, and CON bulls. A treatment effect was detected (P = 0.03) for dry matter intake, being greater in NAR vs. CON, LAS, and VRM bulls, and similar (P > 0.48) between CON, LAS, and VRM bulls. A tendency was detected (P = 0.09) for feed efficiency, which was greater (P < 0.02) in NAR bulls vs. CON and VRM, and similar (P = 0.36) between NAR and LAS bulls. From day 112 to 140, bulls receiving NAR were heavier (P < 0.03) vs. CON, LAS, and VRM bulls, but no differences were observed (P > 0.51) between CON, LAS, and VRM bulls. Collectively, ruminal fermentation profile and intake were impacted by NAR supplementation, which partially contributed to the enhanced performance of Nellore bulls receiving a forage-based diet.

1368 A meta-analysis of lasalocid effects on rumen measures, beef and dairy performance, and carcass traits in cattle

1368 A meta-analysis of lasalocid effects on rumen measures, beef and dairy performance, and carcass traits in cattle

A meta-analysis of lasalocid effects on rumen measures, beef and dairy performance, and carcass traits in cattle.

The effects of lasalocid on rumen measures, beef and dairy performance, and carcass traits were evaluated using meta-analysis. Meta-regression was used to investigate sources of heterogeneity. Ten studies (20 comparisons) were used in the meta-analysis on rumen measures. Lasalocid increased total VFA and ammonia concentrations by 6.46 and 1.44 m, respectively. Lasalocid increased propionate and decreased acetate and butyrate molar percentage (M%) by 4.62, 3.18, and 0.83%, respectively. Valerate M% and pH were not affected. Meta-regression found butyrate M% linearly increased with duration of lasalocid supplementation (DUR; = 0.017). When >200 mg/d was fed, propionate and valerate M% were higher and acetate M% was lower ( = 0.042, = 0.017, and = 0.005, respectively). Beef performance was assessed using 31 studies (67 comparisons). Lasalocid increased ADG by 40 g/d, improved feed-to-gain ratio (F:G) by 410 g/kg, and improved feed efficiency (FE; combined measure of G:F and the inverse of F:G). Lasalocid did not affect DMI, but heterogeneity in DMI was influenced by DUR ( = 0.004) and the linear effect of entry BW ( = 0.011). The combination of ≤100 vs. >100 d DUR and entry BW ≤275 vs. >275 kg showed that cattle ≤275 kg at entry fed lasalocid for >100 d had the lowest DMI. Heterogeneity of ADG was influenced by the linear effect of entry BW ( = 0.028) but not DUR. Combining entry BW ≤275 vs. >275 kg and DUR showed that cattle entering at >275 kg fed ≤100 d had the highest ADG. The FE ( = 0.025) and F:G ( = 0.015) linearly improved with dose, and entry BW >275 kg improved F:G ( = 0.038). Fourteen studies (25 comparisons) were used to assess carcass traits. Lasalocid increased HCW by 4.73 kg but not dressing percentage, mean fat cover, or marbling score. Heterogeneity of carcass traits was low and not affected by DUR or dose. Seven studies (11 comparisons) were used to assess dairy performance but the study power was relatively low and the evidence base is limited. Lasalocid decreased DMI in total mixed ration-fed cows by 0.89 kg/d but had no effect on milk yield, milk components, or component yields. Dose linearly decreased DMI ( = 0.049). The DUR did not affect heterogeneity of dairy measures. This work showed that lasalocid improved ADG, HCW, FE, and F:G for beef production. These findings may reflect improved energy efficiency from increased propionate M% and decreased acetate and butyrate M%. Large dairy studies are required for further evaluation of effects of lasalocid on dairy performance.

Effect of lasalocid or salinomycin administration on performance and immunity following coccidia vaccination of commercial broilers

Coccidiosis vaccines and feed medications have traditionally been used in the poultry industry to control or prevent coccidiosis; however, little information exists on the use of these products jointly to reduce the deleterious effects of coccidiosis on bird performance. Vaccination allows preferential cycling of drug-sensitive strains and development of immunity to coccidiosis, whereas medications halt or minimize intestinal damage due to this parasitic disease and help control secondary bacterial infections. The goal of using both products is to allow the bird's immunity to be established while optimizing performance. Lessening the effect of coccidiosis on bird performance could result in substantial economic benefits to the poultry industry. This study was designed to investigate the potential benefits of giving the ionophores, lasalocid or salinomycin, to in ovo coccidia-vaccinated chickens. Utilizing either of these medications in conjunction with the vaccine resulted in improved feed conversion while maintaining immunity to coccidia challenge, with performance and economic advantages seen when the ionophores were included in the finisher diet or in both the grower and finisher diets.

Administration of lasalocid-NA is preventive against cryptosporidiosis of newborn calves

Cattle are major hosts of Cryptosporidium (Santin and Trout 2008). Cryptosporidiosis in neonatal calves is associated with weight loss and mortality, as well as with zoonotic infections in humans (de...

Effects of lasalocid and intermittent feeding of chlortetracycline on the growth of prepubertal dairy heifers

Forty Holstein heifers entered the 12-wk study at approximately 12 wk of age. At enrollment, heifers were blocked by birth date and assigned to 1 of 4 treatments: (1) carrier (30 g; control); (2) lasalocid + carrier (1 mg/kg of body weight; L); (3) chlortetracycline + carrier (22 mg/kg of body weight; CTC); (4) L + CTC + carrier (CTCL). Heifers on CTC and CTCL were provided treatment Monday through Friday and carrier only on Saturday and Sunday. These heifers were provided their respective treatment during wk 1 to 4, 6, and 10; wk 5, 7 to 9, and 11 to 12 heifers were provided the nonmedicated carrier. Heifers were individually fed a total mixed ration with treatments top-dressed at 1200 h daily. Dry matter intake was monitored for each heifer and feed provided was adjusted according to individual intakes. Skeletal measurements were taken weekly and blood samples were obtained every Monday, Wednesday, and Friday. Blood samples were analyzed for thyroxine concentration via radial immunoassay. Heifers supplemented with L had lower average daily gain , overall body weight gain, and trends for lower daily body length gain and overall girth gain compared with CTC heifers, but similar to control and CTCL heifers. Heifers fed L had lower hip height gain and overall hip height gain compared with CTCL heifers, but similar to control and CTC heifers. Heifers fed L had lower overall withers height gain compared with control heifers, but similar to CTC and CTCL heifers. No treatment effect on thyroxine concentrations was observed. These data indicate that L did not increase growth. Results from this experiment indicate that supplementing heifers with L was not beneficial and no benefits to supplementing heifers with CTC or the combination of CTC and L were evident compared with control heifers. Heifers in this study experienced minimal health problems and were regarded to be under low stress levels. Supplementing CTC and L may be beneficial to growing heifers under conditions where disease exposure and stressors are greater.

Toxicity of the ionophore antibiotic lasalocid to soil-dwelling invertebrates: Avoidance tests in comparison to classic sublethal tests

Lasalocid is a veterinary ionophore antibiotic used for prevention and treatment of coccidiosis in poultry. It enters the environment with the use of contaminated manure on agricultural land. Despite its extensive use, the effects of lasalocid on non-target soil organisms are poorly explored. We used classical subleathal ecotoxicity tests to assess the effects of lasalocid on earthworms (Eisenia andrei) and isopods (Porcellio scaber) and compared the results with tests using avoidance behaviour as the endpoint. The results showed that avoidance is a much more sensitive endpoint. For earthworms, EC50 for avoidance (12.3mgkg−1 dry soil) was more than five times lower than EC50 for reproduction (69.6mgkg−1 dry soil). In isopods the sensitivity of the behavioural response test was even higher. While the highest lasalocid concentration 202mgkg−1 had no significant effects on isopod growth or survival, already the lowest used concentration in the behavioural assay (4.51mgkg−1) caused significant impact on isopod behaviour. Using the avoidance test results for calculating the predicted no-effect concentration (PNEC) of lasalocid to soil invertebrates, the value is close to the predicted environmental concentration (PEC). This indicates that the use of lasalocid-contaminated manure could potentially impair the habitat function of agricultural soils.

Lasalocid induces apoptosis via the cell cycle arrest and ROS‐mediated mitochondrial pathway in prostate cancer PC‐3 cells

Lasalocid is an antibiotic from the group of carboxylic ionophores and is produced by Streptomyces lasaliensis. But there is limited information on the effect of lasalocid on human prostate cancer cells. In the present studies, the lasalocid was examined to better understand its effect on apoptosis and associated signal pathways in vitro in human prostate cancer cells. Using PC‐3 cells, we demonstrate that lasalocid triggers apoptosis by elevating the intracellular ROS level, which was accompanied by increased mitochondrial membrane potential, prompted the levels of Bax and caspase‐3 and reduced the level of Bcl‐2, and cleavage of PARP‐1, a caspase‐3 substrate. These results are the first to link elevated oxidative stress and mitochondrial membrane hyperpolarization to caspase‐dependent apoptosis of lasalocid‐treated prostate cancer cells.

Effects of lasalocid or monensin on in situ biohydrogenation of flaxseed and sunflower seed unsaturated fatty acids

The objective of this study was to compare the effects of two ionophores, lasalocid and monensin (24 mg kg-1 dry matter), on in situ biohydrogenation of C18:2 and C18:3 from whole sunflower seed and flaxseed, respectively. There were no treatment effects on biohydrogenation of C18:2. Ionophore supplementation did not affect the lag time, but monensin decreased the rate of biohydrogenation of C18:3 compared with control and lasalocid. Key words: Ionophore, monensin, lasalocid, biohydrogenation (in situ), sunflower seed, flaxseed

Effects of Lasalocid or Monensin Supplementation on Digestion, Ruminal Fermentation, Blood Metabolites, and Milk Production of Lactating Dairy Cows

Six ruminally fistulated midlactating multiparous Holstein cows were used in a double 3×3 Latin square design (35-d periods) to study the effects of lasalocid (LAS) and monensin (MON) supplemented at 24 mg/kg of dry matter on digestion, ruminal fermentation, blood metabolites, and milk production. Cows were blocked according to milk production and fed a red clover silage-based total mixed ration (17.8% crude protein) without supplementation or supplemented with LAS or MON. Daily dry matter intake, milk production, and milk fat and protein concentrations were similar among treatments and averaged 23.5kg, 36.6kg, 3.36%, and 3.38%, respectively. Rumen lipogenic:glucogenic volatile fatty acids and NH3-N concentration were lower, and apparent digestibility of dry matter, organic matter, crude protein, and gross energy were higher with than without ionophore supplementation. Compared with LAS, MON increased concentrations of plasma urea-N and milk urea-N, and excretion of urinary urea-N and total N. Monensin also decreased N retention and tended to reduce plasma concentration of nonessential AA in comparison with LAS. Both ionophores reduced daily fecal excretion of N by 13g compared with the control, but MON increased daily losses of urinary N by 36g compared with LAS. Results from this study suggest that postabsorptive metabolism of N might be altered by the type of ionophore fed.

An Alternative to Antibiotic-Based Drugs in Feed for Enhancing Performance of Broilers Grown on Eimeria Spp.-Infected Litter

Three trials were conducted to evaluate the effects of lasalocid, an anticoccidial feed additive (90.7 kg/ton); bacitracin, a growth-promoter (50 g/ton); and yeast culture residue (YCR) (1 kg/ton) on the performance of broiler chicks reared to 42 d of age on recycled litter. Recycled litter consisted of pine wood shavings containing droppings from chicks infected with 3 select strains of coccidia (Eimeria tenella, Eimeria maxima, and Eimeria acervulina). Response variables (BW, intestinal tract and litter coliform counts, cecal and liver relative weights, and litter moisture content) were recorded biweekly. Mean BW of chicks fed the diet supplemented with YCR was higher than that of the controls (P < 0.05) and comparable to that of the lasalocid-treated birds in all 3 trials. Mean BW of chicks in all treatment groups decreased uniformly as the litter aged and moisture content increased. The mean intestinal coliform population from YCR-treated chicks was lower (P < 0.05) than those of the control and lasalocid populations. The coliform count was consistently lower than that in chicks on a bacitracin-supplemented diet. Coliform counts from the control and lasalocid-treated birds did not differ. The litter coliform counts increased with increased use of the litter. Cecal and liver relative weights calculated from the chicks in trial 3 showed that only the liver was significantly affected by treatments. YCR appeared to be a viable alternative to bacitracin and lasalocid medication in enhancing growth of broiler chicks reared on recycled litter.

Effect of lasalocid on growth, blood gases, and nutrient utilization in dairy goats fed a high forage, low protein diet.

This study investigated the effect of lasalocid on weight gain, blood gases, nutrient digestibility, and nitrogen utilization in growing dairy goats. In a growth experiment, 24 crossbred dairy does were assigned to diets without or with lasalocid (approximately 30 mg per head per day) for 12 wk. Goats were group fed bermudagrass hay for free choice plus concentrate at a fixed level (approximately 0.264 kg DM per head per d). Goats grew faster when fed lasalocid than those fed the control diet. Jugular blood partial pressure of O2 was lower when goats were supplemented with lasalocid. In contrast, goats fed lasalocid tended to have a higher partial pressure of CO2 than control goats. Percent O2 saturation tended to increase, and concentrations of total CO2 tended to decrease in goats fed lasalocid. Serum glucose and urea N did not differ between treatments. In a metabolism experiment, 8 castrated male goats were fed hay and concentrate identical to those of the growth experiment to determine whole tract nutrient digestibility and N utilization. Lasalocid did not affect feed intake or nutrient digestion coefficients. Daily urinary N output was reduced by lasalocid supplementation. In spite of this, N retention was not significantly affected. With use of ionophore, the proportion of urinary N relative to digested N tended to decrease, and the retained N as a proportion of digested N tended to increase.

Effects of lasalocid on circulating concentrations of leptin and insulin-like growth factor-I and reproductive performance of postpartum Brahman cows.

Objectives were to determine effects of lasalocid on reproductive performance and serum concentrations of leptin and IGF-I, and to correlate concentrations of leptin and IGF-I with reproductive performance of beef cows. Forty-one purebred, multiparous Brahman cows were blocked to control (C; n = 20) or lasalocid (L; n = 21) treatments by BW, BCS, and predicted calving date. Treatment began 21 d before expected calving. Cows were each fed 1.4 kg daily of an 11:1 corn:soybean meal supplement, with the L group receiving 200 mg of lasalocid/cow daily. Cows and calves were weighed, and cow BCS was assessed at calving and at 28-d intervals thereafter. Blood samples were collected weekly precalving, at parturition, and twice weekly thereafter. Sterile marker bulls were maintained with cows for estrous detection. Six days after estrus, ovaries were evaluated for corpus luteum formation, and blood samples from d 6, 7, and 8 after estrus were collected. Serum samples were assayed for progesterone (P4), IGF-I, and leptin concentration. Progesterone concentrations > 1 ng/mL were considered indicative of a functional corpus luteum. Treatment ended after completion of a normal estrous cycle, and cows removed from treatment were placed with a fertile bull equipped with a chinball marker. There were no treatment differences in calving date, calf sex, cow BW, BCS, calf BW, calf ADG, or in serum concentrations of P4, IGF-I, or leptin. Prepartum cow ADG was increased (P < 0.01) in L cows and tended (P < 0.011) to be increased from calving to d 56 after calving in L cows. Postpartum interval (PPI) was not affected by treatment; however, a greater percentage (P < 0.05) of L cows conceived by 90 d after calving (43% L vs. 15% C). First-service conception rate tended (P < 0.08) to be greater in L vs. C cows (68 vs. 40%), but pregnancy rate was not different (P < 0.12; 86% for L vs. 65% for C). There were no treatment differences (P > 0.18) for serum IGF-I concentrations. At calving, leptin was positively correlated with IGF-I (P < 0.04; r = 0.32), BCS (P < 0.06; r = 0.29), and cow BW (P < 0.02; r = 0.36), and was negatively correlated with PPI (P < 0.06; r = -0.29). These results provide evidence that feeding an ionophore before calving and during the postpartum period may increase the number of cows that rebreed to maintain a yearly calving interval. Cows with higher concentrations of leptin postpartum may exhibit shorter PPI.

Lasalocid Supplementation of Dairy Cow Diets in Early Lactation11Supported by the Illinois Agricultural Experiment Station (Hatch 35-397) and a gift from Hoffmann-LaRoche, Inc., Nutley, NJ 07110.

<h2>Abstract</h2> A 36-cow study was conducted to evaluate the effects of lasalocid on feed intake, milk production and composition, and various blood metabolites in early lactation. Multiparous Holstein cows were assigned at parturition to a total mixed diet containing 33% corn silage, 17% chopped alfalfa hay, and 50% concentrate mix on a DM basis for 10 wk. An additional 2.3kg of alfalfa hay was fed during the first 7 d in milk (DIM). Diets were supplemented with 0, 180, or 360 mg/d of lasalocid in a completely randomized design. Covariant-adjusted mean (the covariate was mature equivalent milk production from the previous lactation) DMI; milk and fat-corrected milk (FCM) production; percentages of milk fat, protein, and solids-not-fat; milk somatic cell count; BW; body condition score; and concentrations of glucose, β-hydroxybutyrate, and non-esterified fatty acid (NEFA) in blood were unaffected by supplementation with lasalocid. A dose of 360 mg/d of lasalocid may not be enough to significantly affect high-producing cows consuming >20 kg/d of DM.

Effects of lasalocid and protein levels on the performance of Awassi lambs

A 2×2 factorial experiment was carried out to evaluate the effects of adding lasalocid (25 ton −1 active ingredient) to the diets of 94 fattened lambs of mixed sexes. The lambs were offered complete diets at two dietary protein levels (12.8 and 15.4% dry matter (DM) basis) on feed intake, lamb growth rate and feed conversion efficiency (FCE) over a 70-day experimental period. The mean body weight (BW in kg±standard deviation (SD)) of the lambs at the start of the experiment was 23.5±3.7 kg. The diets consisted of grain (barley), soybean meal and 20% straw with minerals and vitamins. The inclusion of lasalocid lowered the feed intake by 6.4% ( P<0.01) over the whole experimental period. Feed intake was highest in the high-protein treatment when lasalocid was not included ( P<0.01). The inclusion of lasalocid did not increase growth rate (g day −1±standard error (SE)) in either the high-protein (226±8.9 vs. 230±8.9 g) or low-protein (183±9.1 vs. 187±9.2 g) treatments ( P>0.05). However, the lambs on the high-protein diet had a 23% higher ( P<0.01) growth rate compared to those on the low-protein diet (228±8.9 vs. 185±9.1 g day −1±SE). Male lamb growth rate was 44% higher ( P<0.01) than that of females (244±5.8 vs. 169±7.3 g day −1±SE). At the end of the 70-day experimental period, the average BW (kg±SD) of male and female lambs was 41.4±6.4 and 33.9±5.1 kg, respectively. Overall, the inclusion of lasalocid resulted in an improved FCE, feed/BW gain of 4.2% (5.75 and 5.51 for without and with lasalocid, respectively). The FCE was higher ( P<0.01) when the lambs were fed the high-protein diet rather than the low-protein diet (5.41±0.065 vs. 5.85±0.065). Lasolocid could be incorporated into fattening lamb ration to improve feed efficiency.

Effects of Lasalocid in Milk Replacer or Calf Starter on Health and Performance of Calves Challenged with Eimeria Species

Holstein bull calves (n = 48) were purchased from local sale barns at 3 to 7 d of age and were assigned randomly to a 2×2 factorial arrangement of lasalocid in milk replacer (0 or 80 mg/kg) and in calf starter (3 or 44 mg/kg of dry matter). On d 10 after arrival, calves were orally dosed with 100,000 Eimeria oocysts. Intakes of calf starter and milk replacer, body weight (BW), BW gain, excretion of fecal oocysts, and fecal scores were determined. Calves fed lasalocid in milk replacer consumed more calf starter, had greater BW gain, shed fewer oocysts in feces, and scoured less frequently and less severely than did calves fed no lasalocid or those fed lasalocid in calf starter alone. The combination of lasalocid in milk replacer and in calf starter did not improve performance above that of calves fed lasalocid in milk replacer alone. Low intake of calf starter prior to weaning may provide an insufficient amount of lasalocid to control effectively the effects of coccidiosis when calves are infected with Eimeria at an early age. Use of coccidiostats in milk replacers may reduce the effects of coccidiosis in young calves that are infected with Eimeria at an early age.

Efeitos da lasalocida sobre a produção de vacas leiteiras em sistema semi-intensivo

Foram estudados os efeitos da lasalocida sobre a produção de leite, teor e percentagem de gordura no leite, variações de peso e condições corporais de 18 vacas leiteras do ecótipo Mantiqueira, com média de 75 dias pós-parto ao início do experimento, alimentadas com 1,0 kg de mistura de concentrados para cada 2,5 kg de leite produzidos acima dos primeiros 4,0 kg, capim elefante (Pennisetumpurpureum, var. Napier) picado, fornecido no cocho, e pastagem de Bracharia brizantha. Utilizou-se um delineamento em blocos casualizados e os tratamentos consistiram na administração diária de 0,200 e 300 mg de lasalocida/animal. O experimento teve duração de 17 semanas, sendo as quatro primeiras destinadas ao período de adaptação. Independente da dose empregada a lasalocida não alterou significativamente a produção de leite e a produção de leite corrigida a 4% de gordura, porém o grupo tratado com 200 mg apresentou maior porcentagem de gordura no leite (P &lt; 0,05). Os grupos tratados com 200 e 300 mg apresentaram ganhos de peso, porém não estatisticamente menores em relação aos animais controle, quando os dados foram analisados como percentagem de peso vivo. Não foi observada alteração na condição corporal dos animais.

Effect of ionophores on in vitro caecal fermentation in rabbits

Experiments were carried out at Uhříněves, Czech Republic, in 1995 and 1996 to evaluate the effect of salinomycin, monensin, lasalocid and maduramicin on in vitro rabbit caecal fermentation. In cultures supplied with starch, hemicellulose and pectin, all ionophores in the range of concentrations tested (1–10 μg/ml) stimulated methanogenesis. Ionophores at 5 μg/ml increased the production of methane by 26–35% and decreased the production of acetate (P&lt;0·05). Significantly more acetate was produced in mixotrophic acetogenic cultures of caecal micro-organisms with glucose (2 mg/ml) under hydrogen atmosphere than under nitrogen. The H2-dependent formation of acetate was blocked in cultures with ionophores. The stimulation of methanogenesis by salinomycin, monensin, lasalocid and maduramicin can thus be related to the inhibition of acetogenesis, which is an alternative method of H2 utilization in the rabbit caecum.

Effects of lasalocid and protein levels on feed intake and growth rate of Awassi lambs

Lasalocid is a polyether antibiotic derived from the fermentation of streptomyces lasaliensis used as a coccidiostat in sheep. There are varying literature reports on lamb growth rate and feed intake when lasalocid is included in the diet of feedlot lambs. While some reports have shown that lasalocid enhances feed efficiency in ruminants by decreasing feed intake and either maintaining or improving rate of gain others indicate that lasalocid did not have any effect on lamb growth rates or feed efficiency (Stobart et al., 1987). Also, when lasalocid was fed to Chios lambs, growth rate was increased but there was no improvement in feed conversion efficiency (Hadjipanayiotou et al., 1988). There are no published data in the literature relating to the use of lasalocid as a growth promoter in the Awassi breed of sheep fed complete diets and the purpose of this study was to investigate the effect of lasalocid with two levels of protein on the growth rate and feed efficiency of weaned male and female Awassi lambs.

Lasalocid Effects on Ruminal Degradation of Protein and Postruminal Supply of Amino Acids in Holstein Steers

Five ruminally and duodenally cannulated Holstein steers (305kg) were used in a switchback experiment with three periods to evaluate two experimental treatments: a basal diet with or without 45ppm of lasalocid. The basal diet contained approximately 43% rolled corn, 45% alfalfa hay, and 10% soybean meal (DM basis). Lasalocid did not affect feed intake or ruminal digestion of OM and NDF. Ruminal digestion of ADF tended to increase with supplemental lasalocid. Total tract digestion of OM, NDF, ADF, and N and intestinal flow of amino acids were not affected by lasalocid. Also, the ratio of microbial to nonmicrobial N fractions at the duodenum remained unchanged. Ruminal pH and concentrations of NH3, VFA, peptides, and amino acids were not affected by lasalocid. Ruminal protease activity decreased with supplemental lasalocid, but this decrease was not reflected in other variables, such as ruminal concentrations of peptides and amino acids. Ruminal deaminase activity remained unchanged. Thus, we concluded that dietary lasalocid did not alter ruminal protein degradation or postruminal flow of amino acids.