Meta-analysis of the effects of monensin on performance of beef replacement heifers and beef cows.

Although performance benefits of monensin have been extensively studied in finishing cattle, growing cattle, and dairy cows, considerably less published work is available evaluating response to monensin supplementation in cow-calf production systems. This meta-analysis investigated the impacts of monensin on performance of beef cows and developing replacement heifers. The replacement heifer analysis was conducted using data from 18 different peer-reviewed publications and experiment station reports. The mature cow analysis included 21 different publications and experiment station reports. The metaphor package (version 2.4-0; Viechtbauer, 2010) for R (version 4.0.3; www.r-project.org) was used to determine the overall effect size of monensin compared to a negative control. Each study's n, means, and SEM or P value was used to calculate the mean difference and estimate of within study variance for responses of interest. In replacement heifers, monensin treatment increased (P < 0.01); average daily gain (+0.03 ± 0.008 kg/d), feed efficiency (+0.013 ± 0.008 gain:feed), and percentage cycling before the breeding season (+15.9 ± 5.13%); while decreasing (P < 0.01): dry matter intake (0.293 ± 0.081 kg), and age at puberty (-8.9 ± 1.48 d). Six studies reporting ad libitum forage intake for mature cows showed decreased (P = 0.008) DMI by 0.85 ± 0.32 kg/d. Six studies reported milk yield and revealed an increase (P = 0.01) of 0.39 ± 0.15 kg/d when cows were supplemented with monensin. Monensin supplementation resulted in a reduction (P = 0.02) in days to first estrus by 18 ± 8.2 d and percentage of cows exhibiting estrus prior to the breeding season was increased by 19 ± 8% (P = 0.03). There were no differences in artificial insemination pregnancy nor total pregnancy for either the heifer or mature cow data sets. This analysis indicates potential for use of monensin in heifer development and beef cow production systems. Further research is needed to elucidate the effects on reproductive efficiency, DMI, milk production, weight, and body composition change.

Meta-analysis of the effects of monensin on growth and bloat of cattle on pasture.

Monensin has been part of the beef production landscape for over 45 years. Although first approved for use in finishing cattle, it has since been approved for cattle in extensive production systems and has been an economical way to increase performance of forage-fed animals. This meta-analysis investigated the impacts of monensin on performance of stocker cattle on high-forage diets. The stocker performance analysis resulted from 38 experiments with 73 mean comparisons; bloat analysis was conducted with 12 experiments with 23 mean comparisons. The metaphor package (version 2.4-0) for R (version 4.0.3; www.r-project.org) was used to determine the overall effect size of monensin compared to a negative control. Each study's n, means, and SEM or P-value was used to calculate the mean difference and estimate of within-study variance for responses of interest. Moderators of monensin response considered in the analysis were delivery method, dose, study duration, initial calf BW, diet ME and CP, and forage category. Initial BW and basal ADG averaged 236 ± 45.9 kg and 0.72 ± 0.28 kg, respectively. In the ADG analysis, the only significant moderator of those considered was length of the study (P < 0.01); as duration of the study increased, the ADG response to monensin decreased by 0.0007 kg/day. For the average 112-day length of study, the average monensin response was estimated to be 0.0784 kg/day increase in ADG, approximately 10% above controls. Sufficient information was presented in 18 citations representing 40 mean comparisons for determining the effect of monensin on BW at the end of the experiment. The response model (P < 0.01) for ending BW, kg = 22.3-0.05 (initial calf BW, kg). Thus, for the average initial BW of 235 kg the average monensin response was estimated to be 10.6 kg increase in average ending BW. The incidence (-20%) and severity (-0.7 bloat score) of bloat was found to be reduced in bloat-prone pastures. There is ample evidence that monensin increases performance of growing calves on high forage diets along with reducing the incidence and severity of bloat.

Influence of an immune-modulatory feed supplement on performance and immune function of beef cows and calves preweaning.

The ability to positively alter immune and stress response with nutritional compounds is of great interest and importance to the beef industry. There is a proprietary product (OmniGen-AF [OG]; Phibro Animal Health, Quincy, IL) reported to have performance-enhancing benefits by altering animal response to stress and immune challenges. The objective of this 2-yr research project was to study the effect of supplementing OG to beef cows and their calves on breeding and growth performance. One hundred and twelve multiparous beef cows and 48 primiparous cows were randomly assigned to treatment in year 1; control (CON, no OG; n = 56 multiparous and 24 primiparous) or treatment (OG fed at 8.8 g/100 kg body weight [BW]; n = 56 multiparous and 24 primiparous). Multiparous cows (mean ± SD = 6.4 ± 0.4 yr; BW = 589 ± 9.2 kg; body condition score [BCS] 6.2 ± 0.07) were used in both years of the experiment and primiparous cows (mean ± SD = 2.1 ± 0.04 yr of age, weighed 400 ± 7.5 kg, and BSC of 5.6 ± 0.06) were only used in the first year of the experiment. CON and OG supplements were offered over two production cycles beginning in December approximately 60 d prior to projected calving through pre-breeding in May of each year. Calves from treatment cows were offered treatments in a creep supplement limited to a daily rate of 1% as-fed of BW prorated for 3-d/wk feeding from mid-July through weaning with OG offered at 8.8 g/100 kg BW. Primiparous cow's BW, BCS, and calf performance were not affected by treatment (P ≥ 0.15) in year 1. BW of multiparous OG cows tended (P = 0.10) to be heavier at weaning in year 1 and was greater (P = 0.05) at the onset of the experiment in year 2. Body condition of OG cows was greater (P ≤ 0.02) at weaning in both years 1 and 2, as well as at the onset of the experiment in year 2. Calves fed OG from the mature cows gained more (P = 0.05) BW during the creep feeding period than CON. Core body temperatures of OG heifers measured during the late summer with intravaginal temperature data loggers tended (P ≤ 0.10) to be less at 1400 and 1700 hours and were less (P = 0.05) at 1800 hours than CON heifers. Feeding OG did not result in changes (P = 0.25) in serum titer response to the BVD virus of calves during year 2. The results of the current experiment indicate feeding OG to beef cows and calves can result in improvement in BCS of cows, enhance weight gain of calves preweaning, and reduce heat loads in heifer calves during the late summer.

Diurnal variation in fecal concentrations of acid-detergent insoluble ash and alkaline-peroxide lignin from cattle fed bermudagrass hays of varying nutrient content.

BACKGROUND: The effect of time of fecal sampling on the accuracy of acid-detergent insoluble ash (ADIA) and alkaline-peroxide lignin (APL) for the prediction of fecal output (FO) in cattle was evaluated. Eight ruminally cannulated cows (594 ± 35.5 kg) were allocated randomly to 4 bermudagrass [Cynodon dactylon (L.) Pers.] hay diets markedly different in crude protein concentration (79-164 g/kg) with 2 replicates per diet for 3 periods. Cows were offered hay individually at 20 g DM/kg of body weight daily in equal feedings at 08:00 and 16:00 h for a 10-d adaptation period followed by 5-d of total fecal collection. Fecal grab samples also were taken each day during the fecal collection period at 06:00, 12:00, 18:00, and 24:00 h either directly from the rectum or from freshly voided feces. Samples were composited within cow and time across the 5 d total fecal collection period. Additionally, forage, ort, and fecal samples were analyzed for concentrations of APL and ADIA. RESULTS: Fecal concentrations of ADIA and APL were not affected by sampling time (P ≥ 0.22), even though diet affected (P < 0.01) fecal ADIA and APL concentrations. There were no diet × sampling time interactions (P ≥ 0.60). Estimates of FO and dry matter digestibility (DMD) from ADIA and APL were not affected (P ≥ 0.16) by sampling time or the diet × sampling time interaction (P ≥ 0.74). Estimates of FO and DMD from markers from different sampling times or all different combinations of sampling time were not different (P ≥ 0.72) from those of total collection among internal markers. CONCLUSION: Little variation in concentrations of ADIA and APL in daily fecal excretion across time increases flexibility in fecal grab sampling schedules for predicting FO and DMD.

Comparison of acid-detergent lignin, alkaline-peroxide lignin, and acid-detergent insoluble ash as internal markers for predicting fecal output and digestibility by cattle offered bermudagrass hays of varying nutrient composition.

BACKGROUND: The potential for acid-detergent insoluble ash (ADIA), alkaline-peroxide lignin (APL), and acid-detergent lignin (ADL) to predict fecal output (FO) and dry matter digestibility (DMD) by cattle offered bermudagrass [Cynodon dactylon (L.) Pers.] hays of different qualities was evaluated. Eight ruminally cannulated cows (594 ± 35.5 kg) were allocated randomly to 4 hay diets: low (L), medium low (ML), medium high (MH), and high (H) crude protein (CP) concentration (79, 111, 131, and 164 g CP/kg on a DM basis, respectively). Diets were offered in 3 periods with 2 diet replicates per period and were rotated across cows between periods. Cows were individually fed 20 g DM/kg of body weight in equal feedings at 08:00 and 16:00 h for a 10-d adaptation followed by a 5-d total fecal collection. Actual DM intake (DMI), DMD, and FO were determined based on hay offered, ort, and feces excreted. These components were then analyzed for ADL, APL, and ADIA concentration to determine marker recovery and marker-based estimates of FO and DMD. RESULTS: Forage DMI was affected by diet (P = 0.02), and DMI from MH and H was greater (P < 0.05) than from L. Apparent DMD tended (P = 0.08) to differ among diets while FO (P = 0.20) was not affected by diet treatments. Average ADL recovery (1.16) was greater (P < 0.05) than that of ADIA (1.03) and APL (1.06), but ADIA and APL did not differ (P = 0.42). Estimates of FO and DMD derived using APL and ADIA were not different (P ≥ 0.05) from total fecal collection while those using ADL differed (P < 0.05). There was no diet by marker interaction (P ≥ 0.22) for either FO or DMD. CONCLUSION: Acid-detergent insoluble ash and APL accurately predicted FO and DMD of cattle fed bermudagrass hay of varying nutrient composition. These internal markers may facilitate studies involving large numbers of animals and forages. Results from such studies may be used to develop improved equations to predict energy values of forages based on the relationship of dietary components to digestibility across a wide range of forages.