Evaluation of decoquinate, lasalocid, and monensin against experimentally induced sarcocystosis in calves

Effects of decoquinate, lasalocid, and monensin against experimentally induced sarcocystosis (Sarcocystis bovicanis) were evaluated in 12 calves, 3 of which were inoculated, nontreated controls. Three additional calves were noninoculated, nontreated controls. Drugs were administered in the feed (33 mg/kg of feed) of the treated calves (3 calves/group) for 87 days. Eight of the 12 inoculated calves died from acute sarcocystosis during the experiment (the 3 inoculated, nontreated controls, the 3 calves given decoquinate, and 2 of the 3 calves given lasalocid). Large numbers of sarcocysts were found in tissues from inoculated calves that survived in the experiment (1 of the 3 calves given lasalocid and the 3 calves given monensin). Although large numbers of sarcocysts developed in the muscles of monensin-treated calves, monensin may have an ameliorating effect on acute sarcocystosis.     

Effect of pretreatment with selenium-vitamin E on monensin toxicosis in cattle

Ten female beef calves weighing approximately 180 kg each were allotted to 2 groups of 5 each before they were given (orally) monensin (50 mg/kg of body weight). In group A, the calves were given (IM) a commercial selenium-vitamin E (Se-E) preparation (0.25 mg of Se and 17 IU of alpha-tocopherol/kg of body weight) at 72 and 24 hours before monensin was given. The calves in group B were injected at the 2 times with isotonic saline solution. Clinical signs of monensin toxicosis, including lethargy and recumbency, appeared on day 2 in the calves given the Se-E pretreatment, compared with the onset on day 1 in the saline solution-pretreated calves. All calves in the 2 groups died, but mean survival time was longer in group A (4.4 vs 2.2 days). Lesions of monensin toxicosis were myocardial necrosis, skeletal myonecrosis, pulmonary congestion, and rumenitis. The frequency and severity of the lesions were similar for both groups of calves. The results of the present study indicate that Se-E pretreatment modifies the development of monensin toxicosis in cattle.     

Monensin toxicosis in water buffaloes (Bubalus bubalis).

The consumption of monensin-containing feed resulted in deaths of water buffaloes from a feedlot in which cattle and buffaloes were kept together. The monensin formulation was recommended only for use in cattle. Anorexia, muscular weakness, dyspnea, and recumbency were the major clinical findings. The most significant gross lesions were focal pale areas in semitendinosus and semimembranosus muscles, in which segmental necrosis of myofibers was seen microscopically. To compare susceptibilities of species to monensin, 3 bovine calves and 3 buffalo calves were orally dosed. At 5, 7.5, and 10 mg/kg of monensin, only the buffaloes became ill and died. Clinical signs initiated 18-20 h postdosing and were comparable to those from field cases. Gross changes consisted of ascites, hydrothorax, hydropericardium, hepatomegaly, and focal pale areas in the myocardium and to a lesser degree in semitendinosus and semimembranosus muscles. Histopathological changes also resembled those from the field cases, but were especially pronounced in the myocardial cells. The hypothesis that buffaloes could have a lower tolerance to monensin than cattle has been supported by experimental cases.     

Effect of monensin on rumen fermentation and performance of young calves

The effect of monensin on the growth and rumen metabolism of young calves (30 days old initially) was followed in 70-day experiment. Calves diet consisted of a milk substitute (4 1 per day), a concentrate mixture (13 g per 1 kg of live weight per day) and meadow hay ad libitum. Ten calves were fed 0.65 mg of monensin (SPOFA, Czechoslovakia) per 1 kg of live weight per day. Ten calves served as a control. The non-glucogenic/glucogenic ratio of VFA, mol-% acetate and butyrate were significantly lower and propionate higher in monensin-treated calves. Monensin-fed calves gained non significantly more (+ 7.2%) than control calves. A possible mode of action of monensin in young calves is discussed.     

Control of bovine coccidiosis with monensin: in nonresistant newborn calves

Newborn Holstein male calves were purchased within 3 days after birth and were removed from the local farms to the Dixon Springs Agricultural Research Center. They were hand-fed for 7 weeks and then weaned to a prepared feed. Eight groups, each of 4 calves, were housed in separate pens. In each of 4 pens (pens 2 to 5), 1 calf was inoculated with sporulated oocysts of Eimeria bovis (and was not medicated); 1 calf was inoculated and given feed with added monensin at the dosage level of 10 g/906 kg of feed; and 2 calves were inoculated and given medicated feed with added monensin at the dosage level of 20 g/906 kg or 30 g/906 kg. In the 4 other pens (6 to 9), the calves were inoculated with E zuernii and otherwise were given feed without or with added monensin as in pens 2 through 5. Another group of 5 calves (all kept in 1 pen), served as noninoculated, nonmedicated controls. At 14 days after inoculations with E bovis, the single calves in each of the 4 pens that were given the nonmedicated feed began to show clinical signs of coccidiosis and discharged increasing numbers of oocysts. The other inoculated calves (given monensin) had fewer clinical signs and discharged fewer oocysts in the feces as the level of medication in the feed increased. The calves inoculated with E zuernii developed only moderately severe infections when compared with those inoculated with E bovis. Inoculated (with E bovis) nonmedicated calves had severe reductions in feed consumption and weight, and 3 of 4 died.(ABSTRACT TRUNCATED AT 250 WORDS)     

Experimental bovine coccidiosis: control with monensin

Young Holstein-Friesian bull calves were used in a controlled experiment to evaluate the efficacy of monensin against coccidiosis. The calves were given oocysts of Eimeria bovis and/or E. zurnii. Medication was started 3 days prior to inoculation and continued during the 30-day experimental period. Oocyst shedding was quantified prior to and throughout the experiment and demonstrated that monensin at the rate of 20 or 30 g ton-1 of feed significantly reduced oocyst shedding and clinical coccidiosis. Clinical infection with E. zurnii was very difficult to establish, even when calves were treated with 20 mg dexamethasone IM on Days 12, 15, and 16 post-inoculation.     

The effects of increasing garlic powder and monensin supplementation on feed intake,nutrient digestibility,growth performance and blood parameters of growing calves

The objective of this study was to evaluate the effects of increasing garlic powder and monensin supplementation on feed intake, nutrient digestibility, growth performance and blood metabolites of growing calves. Forty Holstein calves (BW = 100 ± 11 kg) were randomly assigned to four dietary treatments (n = 10) in a complete randomized design. Experimental treatments consisted of the following: (i) basal diet (control), (ii) basal diet supplemented with 0.0003% of dietary dry matter (DM) sodium monensin, (iii) low level of garlic powder (Low‐GAR; 0.5% of dietary DM) and (iv) high level of garlic powder (High‐GAR; 1% of dietary DM). DM intake (DMI) and DM digestibility were (p < 0.05) decreased by High‐GAR. However, calves supplemented with Low‐GAR had a similar DMI to the control calves and similar DM digestibility to the control and monensin groups. The digestibility of other nutrients were not affected by the treatments. Although supplementing monensin relative to Low‐GAR increased the DMI (p < 0.05), average daily gain was similar between Low‐GAR and monensin supplemented calves, which were higher than the control and High‐GAR groups (p < 0.05). As a result, feed conversion ratio was improved in the Low‐GAR group versus other treatment groups (p < 0.05). Administrating garlic powder decreased the blood low‐density lipoprotein (LDL) and non‐esterified fatty acids (p < 0.05) without affecting the blood triglyceride, high‐density lipoprotein and beta‐hydroxybutyric acid concentrations. In conclusion, the calves fed the Low‐GAR showed an improved FCR and blood metabolites without changing the DMI and nutrient digestibility. It suggests that garlic powder could be used as an alternative to monensin for growing calves under the current feeding conditions.     

Evaluation of lasalocid as a coccidiostat in calves: titration, efficacy, and comparison with monensin and decoquinate

Two experiments were conducted to evaluate lasalocid as a coccidiostat in Holstein calves and to compare lasalocid with monensin and decoquinate. In experiment 1, calves in 3 groups (6 calves/group) were each inoculated with 500,000 sporulated oocysts, 88% of which were Eimeria bovis and 12% were E zuernii. Calves in each group were given lasalocid-medicated feed at 0.50 (group 3), 0.75 (group 4), or 1 mg/kg (group 5) of body weight/day for 45 days. Two control groups (6 calves/group) were also evaluated; calves in control group 2 were inoculated and nontreated, and calves in control group 1 were noninoculated and nontreated. At 0.50, 0.75, or 1 mg/kg/day, lasalocid was equally effective in preventing induced coccidiosis (E bovis and E zuernii) in calves. Compared with inoculated nontreated controls, treated calves had significantly (P less than 0.05) fewer oocysts in feces and had fewer clinical signs of coccidiosis from days 16 to 30 after inoculation. Experiment 2 was conducted to compare the effectiveness of monensin, lasalocid, and decoquinate for the prevention of experimentally induced coccidiosis. Calves (n = 48) were allotted into 4 groups (12 calves/group); each was inoculated orally with 275,000 sporulated oocysts, predominantly E bovis and E zuernii, and each was given nonmedicated feed (group 6) or feed medicated with 33 mg of lasalocid (group 7), decoquinate (group 8), or monensin (group 9)/kg of feed for 46 days. Calves given medicated rations had significantly (P less than 0.05) fewer oocysts in their feces and fewer clinical signs of coccidiosis than did calves given nonmedicated rations.(ABSTRACT TRUNCATED AT 250 WORDS)     

Nitrogen utilization by ruminants during restricted intake of high-concentrate diets

A series of experiments was conducted to determine the effects of limit-feeding high-concentrate (LFHC) diets on dietary CP requirements of steer calves. When steer calves were fed 80% concentrate diets at 78 g/kg of BW.75, increasing dietary CP resulted in increased ADG (P less than .001). Average daily gain was increased in steers as daily monensin dosage increased from 120 to 180 mg (P less than .05). Increasing the daily monensin dosage to 240 mg did not increase ADG further. There were no (P greater than .10) CP X monensin interactions, suggesting that the monensin response was caused by improved energy utilization and not be the possible protein-sparing effects of ionophores. Steer calves in the second feedyard experiment expressed similar ADG when provided equal NEg as limit-fed, high-moisture ear corn (HMEC) or when given ad libitum access to corn silage. The basal diet did not affect the steers' daily N requirement for growth. Gain per unit of protein intake declined quadratically (P less than .05) with increasing CP intake, indicating that CP requirements were near NRC estimates on both diets. The corn silage-based diet was less digestible (70.3 vs 77.4%; P less than .01) than the HMEC diet when fed to lambs. Fecal output differed (P less than .10) substantially (342 g/d of corn silage vs 205 g/d of HMEC), whereas fecal N output was only slightly higher (6.97 vs 6.34 g/d, respectively; P less than .10). Limited feeding of higher-concentrate diets to steer calves seemed to be an effective management procedure and did not cause acute digestion upset.(ABSTRACT TRUNCATED AT 250 WORDS)     

Concurrent use of the oxfendazole pulse release bolus and the monensin rumen delivery device in young grazing cattle

When they were turned out to grass in May 1987 for their first season, 10 calves were dosed with a 5 x 750 mg oxfendazole pulse release bolus (OPRB) and a monensin sodium rumen delivery device (RDD); eight calves received one OPRB; 10 calves received one RDD and eight calves received neither bolus. Each group was set-stocked on individual paddocks which had been grazed during the previous season by cattle which developed clinical parasitic gastroenteritis and bronchitis (husk). In July, before they were due to be moved to new pastures in mid-summer, and before they were dosed strategically with levamisole HCl, some of the calves not dosed with an OPRB succumbed to clinical parasitic gastroenteritis and husk and received emergency anthelmintic treatment, after which no further clinical episodes occurred. The 'dose and move' strategy was implemented in early August after which both groups not dosed with an OPRB were set-stocked together until the trial ended on October 14, 147 days after turn out. The two groups of calves which had received the OPRB were also moved to new pasture and set-stocked together until the end of the trial. No evidence of clinical helminthiases developed in either of the two groups of calves dosed with OPRBs and their faecal worm egg and larval counts, and plasma pepsinogen activities remained low. They gained significantly more weight than the two groups of calves not dosed with OPRBs (P less than 0.001). The bolus types were compatible and induced no untoward side-effects when used together.     

Resistance to Eimeria zuernii produced after chemotherapy of experimental infection in calves

Nineteen Holstein-Friesian bull calves were inoculated with 2.4 × 10⁶ sporocysts of Eimeria zuernii by stomach tube. The calves were divided into three groups 10 days after infection. The first group (seven calves) was treated with monensin (1 mg/kg body weight daily) from the 10th–20th day after infection; the second group (six calves) with amprolium (10 mg/kg body weight daily) for the same period of time and the third group (six calves) acted as infected controls. Both drugs were effective in preventing clinical signs, in reducing rates of weight gain and in suppressing oocyst production. The calves were reinfected with E. zuernii 35 days after the initial infection. The calves of all three groups were resistant to the second infection with E. zuernii as measured by rates of weight gain, fecal oocyst output and lack of clinical signs.     

The effect of monensin on performance and selected biochemical and hematological parameters in the blood of calves]

The aim of this study was to find out the influence of monensin, a ionophore antibiotic, on calf performance and selected physiological parameters. Monensin is a product of Streptomyces cinnamonensis. It has effects on all Gram-negative microbes, such as Escherichia coli, salmonellas, pseudomonads and vibria. It has a small effect on Gram-positive microbes. At the beginning of the experiment eight young crossbred bulls (C x N) at the age of three weeks were weighted and divided into two groups, experimental and control ones. Calves were kept in individual boxes and fed acidified whole milk (2 ml of 85% formic acid per 1 litre of milk). They had a free access to concentrates (COT), hay and drinking water. The calves received 3 lt. of whole milk twice a day until the age of eight weeks. 0.5 mg of monensin per 1 kg live weight were served orally to calves of the experimental group every day. Monensin was made by the Spofa Corporation, Prague. Daily intake of feed was recorded and the calves were weighted once a week. Blood samples were taken from the jugular vein before the beginning of the experiment, and in the period from the fifth to the tenth week of age, always before morning feeding. The average daily live weight gain was 0.452 kg and 0.471 kg for the control and experimental group, respectively, during the milk feeding period, the index being 104.2 (Tab. I). Tab. II shows the average feed intake per 1 kg live weight gain.(ABSTRACT TRUNCATED AT 250 WORDS)     

Performance,rumen fermentation and blood metabolites of dairy calves fed starter mixtures supplemented with herbal plants,essential oils or monensin

This study evaluated the supplementation effects of three herbal plants (thyme [THY], eucalyptus [EUC] and celery [CEL]), a commercial phytogenic additive ?containing essential oils (PFA‐EO, Digestarom^® P.E.P.) and monensin (MON) in calf starter on performance, rumen fermentation and blood metabolites during pre‐ (days 3–55) and post‐weaning (days 56–70). Sixty‐six Holstein dairy calves (3 days of age, 41.2 ± 3 kg of BW) were allocated to one of six starters supplemented with: (i) no additives (CON), (ii) MON (30 mg/kg), (iii) THY (23 g/kg), (iv) CEL (23 g/kg), (v) EUC (23 g/kg) and (vi) PFA‐EO (3 g/kg). All the calves were offered starters ad libitum plus 6 L of whole milk daily. Starter intake tended to be the highest in calves fed PFA‐EO and THY; intermediate in calves fed CON, MON and EUC; and the lowest in those fed CEL. Average daily gain (ADG) and feed efficiency (FE) remained unaffected by dietary treatments during the pre‐weaning. During the post‐weaning period, ADG and FE ?were greatest in calves fed EUC followed by those fed CON, MON, PFA‐EO and THY, and then in those fed CEL. No differences were observed among the treatments in skeletal growth, faecal score, rumen pH or ammonia‐N concentration. Compared to calves fed CON and MON, those fed the herbal plants or PFA‐EO tended to recorded higher molar proportions of acetate and butyrate, and the acetate: propionate ratio. Blood malondialdehyde level did not differ among treatments, but calves on CON had the highest glucose concentration, and those fed PFA‐EO recorded the highest value for β‐hydroxyl butyrate on day 70. In conclusion, the results indicate that the three herbs and PFA‐EO are capable of modulating some of the rumen fermentation parameters and blood metabolites as well as eucalyptus could potentially be a better alternative to monensin for improving post‐weaning performance.     

Biochemical studies on the fate of monensin in animals and in the environment

Extensive studies have been conducted with monensin in target animals and laboratory animals to determine monensin concentrations in tissues, route of elimination, metabolism and pharmacokinetics of monensin. These studies indicate that monensin administered orally is absorbed, extensively metabolized, excreted in the bile and eliminated in the feces by the several species examined. Monensin did not accumulate in the tissues of orally dosed animals. When fed to cattle and chickens according to recommended practices, monensin was not detected (less than .05 ppm) in edible tissues. Environmental studies indicate that monensin is biodegradable in manure and soil.     

Monensin toxicity in cattle

Monensin has been tested to determine its toxicity and safety in cattle. Single dose acute toxicity and signs associated with toxicity were determined by oral gavage, 7-d oral gavage and feeding experiments with high concentrations of monensin in feed. Oral feeding studies indicated a near complete anorexia resulting from intake of sublethal amounts of monensin. In these cases, cattle recovered from the insulting dose and resumed growth and feed intake. In long-term chronic feedlot, pasture supplement, and reproduction safety studies conducted with monensin administered in the feed, the high concentrations caused cattle to show signs of mild monensin intoxication. Mortality resulted from feeding groups of cattle large quantities of monensin in small quantities of feed. Furthermore, these studies have demonstrated no detrimental effects upon reproduction. Collectively, these studies indicate that the greatest risk of intoxication occurs when cattle first receive a feed containing monensin. Mixing errors and misuse situations under actual use conditions have resulted in cases of cattle mortality. In most cases the mortality was predictable based upon the exposure in controlled studies.     

Influence of monensin on the performance of cattle

Performance data on nearly 16,000 head of cattle that were used in trials to document effects of monensin on feedlot cattle were summarized. Cattle fed monensin-containing diets gained 1.6% faster, consumed 6.4% less feed and required 7.5% less feed/100 kg gain than cattle fed control diets. Monensin resulted in the greatest improvement in feed/gain at 2.9 Mcal metabolizable energy (ME)/kg diet dry matter (DM). Within the range of monensin concentrations used in the trials that were summarized (31.8 +/- 7.5 mg/kg DM), high monensin concentrations did not improve feed/gain over that obtained with lower concentrations. Carcass characteristics were not significantly influenced by monensin. Responses of cattle to monensin and implants were additive. Energy metabolism data suggested that monensin improved digestibility of DM, reduced fasting heat production and increased dietary net energy maintenance (NEm) values more than it increased net energy gain (NEg) values. Data showing the response of cattle to monensin when fed various dietary protein concentrations or sources of supplemental N suggested that monensin had a protein sparing effect. Monensin has also been shown to reduce lactic acid production, aid in the control of coccidia and bloat and to be toxic to face and horn fly larva in feces of monensin-fed cattle. In pasture trials, monensin improved daily gains. When fed to beef cows, monensin reduced amounts of feed required to maintain cow weight.     

L’utilisation du prémélange de monensin chez les vaches laitières : un suivi simple et essentiel pour s’assurer d’une utilisation adéquate

The use of monensin premix in dairy cows: Simple and essential steps for ensuring its proper use. Dietary monensin, containing monensin sodium as active ingredient, is frequently used on dairy farms in Canada. Although the use of monensin is safe, some overdose situations have been reported following consumption of higher than recommended doses. A regular monitoring of bulk tank milk fat percentage should be performed to ensure quick detection of a potential overdose situation. Diarrhea and sudden drop in dry matter intake are other potential clinical signs of monensin overdose. Quick detection of such cases will allow rapid correction of the situation.(Translated by the authors)     

Efficacy of ionophores in cattle diets for mitigation of enteric methane

Use of ionophores in cattle diets has been proposed as a strategy for mitigation of enteric CH4 emissions. Short- and long-term effects of feeding a single ionophore (monensin) or rotation of 2 ionophores (monensin and lasalocid) on enteric CH4 emissions were evaluated in 36 Angus yearling steers (328 +/- 24.9 kg of BW) over a 16-wk period. Steers were randomly assigned to 6 dietary treatments of 6 steers each. The 6 diets were low-concentrate without ionophore supplementation, low-concentrate with monensin supplementation, low-concentrate with a 2-wk rotation of monensin and lasalocid supplementation, high-concentrate without ionophore supplementation, high-concentrate with monensin supplementation, and high-concentrate with a 2-wk rotation of monensin and lasalocid supplementation. Daily enteric CH4 emissions, as measured using the SF(6) tracer gas technique, ranged from 54.7 to 369.3 L/steer daily. Supplementing ionophores decreased (P < 0.05) enteric CH4 emissions, expressed as liters per kilogram of DMI or percentage of GE intake, by 30% for the first 2 wk and by 27% for the first 4 wk, for cattle receiving the high-concentrate and low-concentrate diets, respectively. Cattle fed a rotation of ionophores did not (P > 0.05) exhibit a greater decrease and did not (P > 0.05) have a longer period of depressed enteric CH4 emissions compared with cattle receiving monensin only. Ionophore supplementation did not (P > 0.05) alter total ruminal fluid VFA concentration; however, the acetate:propionate ratio and ammonia-N concentration in ruminal fluid were decreased (P < 0.001) from the time that ionophores were introduced to the time they were removed from the diets. Both monensin and the rotation of monensin and lasalocid decreased (P < 0.001) total ciliate protozoal populations by 82.5% in the first 2 wk and by 76.8% in the first 4 wk during which they were supplemented in the high-concentrate and low-concentrate diets, respectively. Original ciliate protozoal populations were restored by the fourth and sixth week of supplementation when cattle were fed the high- or low-concentrate diets, respectively. No significant change was observed thereafter. These data suggest that the effects of ionophores on enteric CH(4) production are related to ciliate protozoal populations and that ciliate protozoal populations can adapt to the ionophores present in either low- or high-concentrate diets. Rotation of monensin and lasalocid did not (P > 0.05) prevent ciliate protozoal adaptation to ionophores.     

Herd-level risk factors associated with fecal shedding of Shiga toxin-encoding bacteria on dairy farms in Minnesota,USA

This study aimed to identify herd-level risk factors associated with fecal shedding of Shiga toxin-encoding bacteria (STB) on dairy cattle farms in Minnesota, USA. After adjustment for farm size, risk factors included: use of total mixed ration (TMR) for lactating dairy cows [odds ratio (OR) = 3.0; 95% confidence interval (CI): 1.8 to 5.1], no use of monensin for weaned calves (OR = 4.8, 95% CI: 2.5, 9.3), and no use of decoquinate for preweaned calves (OR = 2.2, 95% CI: 1.4, 3.6). Fecal shedding of STB was more common in small herds (< 100 cows, OR = 3.6, 95% CI: 2.1, 6.2) than in large herds (≥ 100 cows). Herd management factors related to cattle feeding practices were associated with fecal shedding of STB.     

饲粮中添加牛至精油和莫能菌素对荷斯坦犊牛血清生化指标、消化酶活性及瘤胃微生物区系的影响

旨在研究牛至精油（oregano essential oil,OEO）与莫能菌素（monensin,MON）对荷斯坦犊牛血清生化指标、消化酶活性以及瘤胃微生物区系的影响。本试验前期阶段选用了体重相近（（41.31±2.23）kg）,体况良好的荷斯坦初生犊牛80头,随机分为4组,每组20头,采用单栏饲养。对照组饲喂全脂牛乳和颗粒饲料,其他3个试验组在饲喂全脂牛乳和颗粒饲料的基础上分别添加4 g·kg^-1牛至精油、3.6 g·kg^-1莫能菌素和7.6 g·kg^-1牛至精油和莫能菌素的混合物,饲喂至56、70日龄时,从每组中选取6头体重相近的公犊,颈静脉采血测定血清指标,并通过口腔导管的形式采集犊牛的瘤胃液,检测消化酶活性以及瘤胃微生物区系。结果表明：1）添加牛至精油显著提高了56日龄犊牛血清中TP、SOD、GSH和GSH-Px的浓度（P ≤ 0.05）;莫能菌素对56、70日龄犊牛BUN浓度有降低的趋势（P<0.10）。2）牛至精油显著降低了56、70日龄犊牛瘤胃中产琥珀酸丝状杆菌的数量（P<0.05）,显著提高了白色瘤胃球菌的数量（P ≤ 0.05）;莫能菌素显著降低了56、70日龄犊牛瘤胃中原虫的数量（P ≤ 0.05）,并有降低白色瘤胃球菌数量的趋势（P<0.10）,在56日龄时,莫能菌素有降低犊牛瘤胃中黄色瘤胃球菌数量的趋势（P<0.10）;牛至精油和莫能菌素对56、70日龄犊牛瘤胃中溶纤维丁酸弧菌有显著的交互作用（P ≤ 0.05）;在56日龄时,牛至精油和莫能菌素对栖瘤胃普雷沃氏菌有交互作用的趋势（P<0.10）,而在70日龄时则呈显著的交互作用（P ≤ 0.05）。3）牛至精油和莫能菌素对56、70日龄犊牛瘤胃中胃蛋白酶浓度有显著的交互作用（P ≤ 0.05）。综上所述,饲粮中添加牛至精油可提高犊牛的免疫力和抗氧化能力。莫能菌素在抑制瘤胃内原虫数量上强于牛至精油,牛至精油对提高主要蛋白质降解菌数量的作用效果优于莫能菌素。总之,牛至精油可改善犊牛的健康状况以及调控瘤胃微生物区系,牛至精油作为天然植物抗生素可替代犊牛期预防性治疗的其他类抗生素生长促进剂。