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A meta-analysis of the impact of monensin on health and reproductive outcomes in dairy cattle was conducted. A total of 16 papers were identified with sufficient data and quality to evaluate health and reproductive outcomes for monensin. The available trials provided approximately 9,500 cows with sufficient data for analysis. This provided good statistical power to examine the effects of monensin on health and reproduction. Over all the trials analyzed, monensin decreased the risk of ketosis [relative risk (RR) = 0.75], displaced abomasums (RR = 0.75), and mastitis (RR = 0.91). No significant effects of monensin were found for milk fever, lameness, dystocia, retained placenta, or metritis. Monensin had no effect on first-service conception risk (RR = 0.97) or days to pregnancy (hazard ratio = 0.93). However, the impact of monensin on dystocia, retained placenta, and metritis was heterogeneous for all 3 outcome measures and random effect models were utilized. Causes of the heterogeneity were explored with meta-regression. Days of treatment with monensin before calving increased the risk of dystocia. Delivery method of monensin influenced the incidence of retained placenta and metritis, with risk being lower with controlled release capsule treatment compared with delivery in either topdress or in a total mixed ration. Days of treatment before calving also influenced retained placenta with an increase in risk with more days treated before calving. Improvements in ketosis, displaced abomasums, and mastitis with monensin were achieved. Exposure to prolonged treatment in the dry period with monensin may increase the risk of dystocia and retained placenta. [ABSTRACT FROM AUTHOR]

A meta-analysis of the impact of monensin on metabolism of dairy cattle was conducted following a search of the literature. A total of 59 studies with monensin feeding in dairy cattle were identified in which 30 papers and 45 trials contained metabolic data. The phydroxybutyrate (BHBA) data were obtained from over 4,000 cows and 115 trial sites. Data for each trial were extracted and analyzed using meta-analysis software in Stata. Estimated effect sizes of monensin were calculated on blood concentrations of BHBA, acetoacetate, nonesterified fatty acids (NEFA), glucose, cholesterol, urea, calcium, insulin, and milk urea. Monensin use in lactating dairy cattle significantly reduced blood concentrations of BHBA 13%, acetoacetate 14%, and NEFA 7%. Monensin increased glucose 3% and urea 6%. Monensin had no significant effect on cholesterol, calcium, milk urea, or insulin. Heterogeneity was significant for BHBA and cholesterol [I2 (measure of variation beyond chance) = 37 and 54%, respectively]; therefore, random effects models were used for those analytes. Publication bias existed with the monensin effect on BHBA, with a tendency for studies to be published if there was a significant reduction in this ketone. Meta-regression analysis of the effect sizes obtained from the metabolic data showed that method of delivery, timing of administration, stage of lactation, and diet were influential in modifying effect size of monensin treatment. Use of top dress or delivery via a controlled release capsule reduced the magnitude of effect on BHBA (coefficient +0.353); however, top dress use compared with controlled release capsule or total mixed ration enhanced the monensin effect on glucose (coefficient +0.296). There was a greater impact with monensin on reducing BHBA in early lactation (coefficient -0.151) and in pasture-based trials (coefficient -0.194). Use of monensin in both the pre- and postcalving periods was associated with an enhanced impact on NEFA (coefficient -0.254). Monensin had less impact on serum glucose in the precalving time period (coefficient -0.237). These findings demonstrate an improvement in the energy metabolism of dairy cows supplemented with monensin. [ABSTRACT FROM AUTHOR]

A meta-analysis of the impact of monensin on production outcomes in dairy cattle was conducted using the 36 papers and 77 trials that contained eligible data. Statistical analyses were conducted in STATA and included a consideration of fixed or random effects models, assessment of publication bias, and impact of influential studies. Meta-regression was used to investigate sources of heterogeneity of response. There were 71 trials containing data from 255 trial sites and 9,677 cows examining milk production and composition. Monensin use in lactating dairy cattle significantly decreased dry matter intake by 0.3 kg, but increased milk yield by 0.7 kg and improved milk production efficiency by 2.5%. Monensin decreased milk fat percentage 0.13%, but had no effect on milk fat yield; however, there was significant heterogeneity between studies for both of these responses. Milk protein percentage was decreased 0.03%, but protein yield was increased 0.016 kg/d with treatment. Monensin had no effect on milk lactose percentage. Monensin increased body condition score by 0.03 and similarly improved body weight change (0.06 kg/d). Analysis of milk fatty acid profile data indicated that monensin was associated with a reduction of short-chain fatty acids (from 1 to 12% reduction) and stearic acid (-7.8%). The impact of monensin on linoleic and linolenic acids was variable, but monensin significantly increased conjugated linoleic acid (22%). Meta-regression of the effect of monensin on milk component percentages and yields indicated an influence of delivery method, stage of lactation, dose, and diet. Increasing concentrations of C18:1 in the diet enhanced the effect of monensin on decreasing milk fat yield, whereas increasing the rumen peptide balance increased the effect of monensin on milk protein yield. These findings indicate a benefit of monensin for improving milk production efficiency while maintaining body condition. The effect of monensin on milk fat percentage and yield was influenced by diet. [ABSTRACT FROM AUTHOR]

Choline and monensin may be supplemented during the transition period with the objectives of aiding in fat metabolism and improving energy balance, respectively. The objectives of this study were to determine the effects of supplementing rumen-protected choline (RPC) and monensin in a controlled-release capsule (CRC) on metabolism, dry matter intake, milk production, and liver function in transition dairy cattle. Three weeks before expected calving, 182 Holsteins were randomly assigned to receive one of the following: a monensin CRC, 56 g/d of RPC until 28 d in milk, CRC + RPC, or neither supplement (control). Blood samples were collected at enrollment, 1 wk before calving, and in the first and second weeks after calving. Liver biopsies were obtained from multiparous cows randomly selected from each treatment group within 24 h and again 3 wk postpartum. Daily milk production was recorded through 60 d in milk. There were no interactions of the effects of RPC and CRC on any of the outcomes measured. Overall, cows that received RPC produced 1.2 kg/d more milk in the first 60 d of lactation, but this effect was attributable to an increase in milk production of 4.4 kg/d among cows with a body condition score ≥4 at 3 wk before calving; fat cows that received RPC ate 1.1 kg of DM/d more from wk 3 before calving through wk 4 after calving. Monensin supplementation significantly increased serum concentrations of glucose and urea, lowered concentrations of β-hydroxybutyric acid and aspartate aminotransferase in the peripartum period, and increased liver glycogen content at 3 wk into lactation. The metabolic effects of CRC are consistent with previous studies, and the effects on liver are novel. The mechanism by which RPC increased milk production was not revealed in this study and merits further research. [ABSTRACT FROM AUTHOR]

The objective of this study was to determine effects of monensin on ovarian follicular development and reproductive performance in postpartum dairy cows. Forty-eight multiparous Holstein cows were randomly assigned to receive either a control total mixed ration (n = 24) or the same diet plus 22 mg of monensin/kg (n = 24) from 21 d before anticipated calving until cows were either confirmed pregnant or were >180 d postpartum. Monensin had no effect on development of the first dominant follicle postpartum or the numbers of class 1 (3 to 5 mm), 2 (6 to 9 mm), or 3 (10 to 15 mm) follicles. Control cows had more class 4 (>15 mm) follicles at 10 to 13 d postpartum than cows in the monensin group. The first dominant follicle postpartum ovulated, regressed, or became cystic unrelated to differences between diets. However, the first ovulation postpartum occurred earlier in monensin-fed cows than in the control group (27.2 ± 2.1 d vs. 32.4 ± 1.5 d), with no dietary effects on the diameter of the ovulating follicle. Similarly, treatments did not differ in the proportion of cows with 2 or 3 waves of ovarian follicular development per cycle, nor in the number of follicles of all classes during the breeding period. Times of ovulation following treatment with prostaglandin F[sub2α] were not different between dietary groups. Pregnancy rates after timed artificial insemination were similar between diets. Supplementation with monensin resulted in a shorter postpartum interval to first ovulation but did not affect other reproductive measures in healthy, lactating dairy cows. [ABSTRACT FROM AUTHOR]

The objective of this study was to investigate the effect of monensin (MN) and dietary soybean oil (SBO) on milk fat percentage and milk fatty acid (FA) profile. The study was conducted as a randomized complete block design with a 2 x 3 factorial treatment arrangement using 72 lactating multiparous Holstein dairy cows (138 ± 24 d in milk). Treatments were [dry matter (DM) basis] as follows: 1) control total mixed ration (TMR, no MN) with no supplemental SBO; 2) MN-treated TMR (22 g of MN/kg of DM) with no supplemental SBO; 3) control TMR including 1.7% SBO; 4) MN-treated TMR including 1.7% SBO; 5) control TMR including 3.4% SBO; and 6) MN-treated TMR including 3.4% SBO. The TMR (% of DM; corn silage, 31.6%; haylage, 21.2%; hay, 4.2%; high-moisture corn, 18.8%; soy hulls, 3.3%; and protein supplement, 20.9%) was offered ad libitum. The experiment consisted of a 2-wk baseline, a 3-wk adaptation, and a 2-wk collection period. Monensin, SBO, and their interaction linearly reduced milk fat percentage. Cows receiving SBO with no added MN (treatments 3 and 5) had 4.5 and 14.2% decreases in milk fat percentage, respectively. Cows receiving SBO with added MN (treatments 4 and 6) had 16.5 and 35.1% decreases in milk fat percentage, respectively. However, the interaction effect of MN and SBO on fat yield was not significant. Monensin reduced milk fat yield by 6.6%. Soybean oil linearly reduced milk fat yield and protein percentage and linearly increased milk yield and milk protein yield. Monensin and SBO reduced 4% fat-corrected milk and had no effect on DM intake. Monensin interacted with SBO to linearly increase milk fat concentration (g/100 g of FA) of total trans-18:l in milk fat including trans-6 to 8, trans-9, trans-10, trans-11, trans-12 18:1 and the concentration of total conjugated linoleic acid isomers including cis-9, trans-11 18:2; trans-9, cis-11 18:2; and trans-10, cis-12 18:2. Also, the interaction increased milk concentration of polyunsaturated fatty acids. Monensin and SBO linearly reduced, with no significant interaction, milk concentration (g/100 g of FA) of short- and medium -chain fatty acids (

An investigation was conducted to compare the effects of the monensin controlled-release capsule, monensin sodium in feed, and a negative control on feed intake and metabolic parameters in a randomized and blinded clinical trial. A total of 136 Holstein cows and heifers were assigned to a negative control group, administered a monensin controlled-release capsule (CRC) or administered 22 mg/kg of dry matter of monensin sodium in the total mixed ration (premix). Cows were enrolled 3 wk prior to expected calving; at this time monensin treatment began. Cows were located at the Elora Dairy Research Centre (Elora, Ontario, Canada). Blood samples were obtained at enrollment, at 1 wk prior to expected calving date, at calving, and at 1 and 2 wk postpartum. Sera from these samples were analyzed for/%hydroxybutyrate (BHBA), nonesterified fatty acids, glucose, urea, bilirubin, aspartate aminotransferase activity, insulin, and cortisol. Cows were assigned a body condition score upon enrollment and upon completion of the trial. The dry matter intake was measured for all cows for the entire experimental period (12.0, 11.7, and 11.3 kg/d for control, premix, and CRC groups, respectively). However, no differences in dry matter intake between treatment groups were noted. The interaction of experimental group and sampling time was significant for serum concentration of BHBA and urea. Both monensin delivery methods significantly decreased serum BHBA postpartum. Urea concentrations were increased in the postpartum period compared with the prepartum samples. The CRC group had a significant impact on reducing the loss in body condition over the study period. Serum concentrations of all measured metabolic parameters varied over the peripartum period. Calving season, parity, and body condition score at the start of the study period influenced many of the measured metabolic parameters. [ABSTRACT FROM AUTHOR]

Effects of prepartum administration of a monensin controlled release capsule (CRC) and stage of lactation on variation of blood metabolites within 24 h were determined in 16 dairy cows. Cows were fed a total mixed ration ad libitum twice daily at 0700 and 1300 h. At calving, cows were switched from a close-up dry cow diet to a lactating cow diet. Cows were blood sampled every 3 h for 24 h at 3 stages of lactation, including 1 wk before calving (wk -1), 1 wk after calving (wk 1), and 6 wk after calving (wk 6). Serum concentrations of glucose, β-hydroxybutyrate (BHBA), nonesterified fatty acids (NEFA), and urea exhibited significant variation within 24 h. Glucose and NEFA were, respectively, 0.09 and 0.08 mM lower between 1030 and 2230 h than between 2230 and 1030 h. β-Hydroxybutyrate and urea were, respectively, 95.1 and 0.49 mM higher between 1030 and 2230 h than between 2230 and 1030 h. Monensin did not significantly affect glucose, NEFA, and urea in this study. Monensin reduced BHBA at wk 1, but not at wk -1 or wk 6. Glucose was lower and BHBA and NEFA were higher at wk 1 compared with wk -1 and wk 6. Urea was higher at wk 6 compared with wk -1. The variation within 24 h of glucose, BHBA, and NEFA were not affected by monensin and stage of lactation. Diurnal variation of urea was affected by stage of lactation, but not by monensin. [ABSTRACT FROM AUTHOR]

The effects of monensin premix supplementation on ruminal pH characteristics and forage degradability, and total tract diet digestibility during grain-induced subacute ruminal acidosis (SARA) in lactating dairy cows receiving a total mixed ration were investigated. Six multiparous, rumen-fistulated Holstein cows were used in a 2-treatment, 2-period (5 wk per period) crossover design. During wk 5 (d 29 to 35) of each period, SARA was induced using a grain challenge model, and ruminal pH was measured continuously using indwelling pH probes. Ruminal degradation of corn silage and alfalfa haylage was determined using the in situ (nylon bag) technique, and total tract diet digestibility was determined by total fecal collection during wk 5. Monensin supplementation did not affect dry matter intake, milk yield, and composition, and ruminal pH characteristics under these experimentally induced SARA conditions. Rates of ruminal forage fiber degradability were similar between control and monensin-treated cows; however, monensin supplementation increased total tract fiber digestion. This study indicates that monensin altered total tract nutrient digestion by increasing fiber digestion at postruminal sites. [ABSTRACT FROM AUTHOR]

The effects of a monensin premix on milk fatty acid content during grain-induced subacute ruminal acidosis (SARA) in Holstein cows receiving a total mixed ration was investigated. Six multiparous, rumen-fistulated Holstein cows were used in a two-treatment, two-period crossover design with 6-wk periods. Experimental treatments were either a monensin premix or a placebo premix. At the beginning of wk 4, SARA was induced in experimental cows for a 10-d period using a grain challenge model. The administration of a monensin premix elevated milk fat proportion of total short-chain saturated fatty acids (sum of C[sub4] to C[sub15]). Milk fat proportions of conjugated linoleic acid isomers were unaffected. Linolenic acid (C[sub18:3n3]) proportion in milk fat of monensin-treated cows were lower when compared with placebo-treated cows during the SARA period. Results from this study indicate that dietary supplementation with monensin during SARA had little effect on milk fatty acid content. [ABSTRACT FROM AUTHOR]