Performing Department
Range Cattle Research and Education Center
Non Technical Summary
Concentrate supplementation is one of the most costly management practices in beef cattle production. Monensin is a feed additive that has potential to increase the efficiency of concentrate supplementation in beef cattle. However, most of the information published in the literature are with the utilization of monensin on beef cattle receiving high quality diets. Most of beef cattle production in Florida is on grazing systems with warm-season perennial grasses with limited quality. Therefore, the objective of these studies is to generate information about the responses of monensin on beef cattle receiving low-quality warm-season perennial grasses.
Animal Health Component
100%
Research Effort Categories
Basic
(N/A)
Applied
100%
Developmental
(N/A)
Goals / Objectives
In Florida, grasslands cover approximately 4.5 million hectares, most of which is utilized by beef cattle (Chambliss, 1999). The beef industry is a very important component of Florida's agriculture industry. Florida ranks 12th in number of beef cows in the USA and has a herd of more than 870 thousand animals. In 2015 and 2016, Florida's calf crops were 800 and 810 thousand calves, respectively (USDA, 2017). In 2015, the beef cattle business in Florida generated cash receipts of more than $867 million dollars, a total that represented 10.3% of all agricultural products (Florida Department of Agriculture and Costumer Service, 2015).Warm-season perennial grasses are the main forage used for beef cattle production in the southeastern USA (Ball et al. 1991). Although warm-season grass monocultures require a minimum level of N fertilization to maintain sustainable biomass growth and nutritive value to ruminants, forage-based cow-calf systems in Florida are characterized by extensive grazing with low input levels.Monensin is a feed additive that may induce positive responses in growth and feed efficiency in ruminants receiving diets with high concentrate inclusion (Duffield et al., 2012). However, there have been several articles promoting the use of monesin in beef cattle on pasture with limited levels of supplementation. It is known that monensin select microorganisms in the rumen and enhance fermentation efficiency by increasing propionic acid and decreasing methane production. In beef cattle grazing warm-season perennial grasses, the animals will be consuming limited amount of propionic acid precursors, such as starch and sugars, and therefore, it is expected that monensin may not be an efficient feed additive to be used under those conditions. Conversely, beef cattle supplemented on pasture with significant levels of concentrate may consume considerable amount of starch and sugars, which may enhance the effects of monensin and result in increased animal performance.Therefore, this project has the overall objective to identify the efficiency of monensin on beef cattle grazing warm-season perennial grasses and receiving different levels of supplementation.The specifics objectives are: 1) to investigate the effects of monensin supplementation on animal performance grazing warm-season perennial pastures, and 2) to evaluate the effects of monensin on cattle receiving different levels of concentrate supplementation.
Project Methods
Experiment 1: Effects of monensin supplementation on performance of early-weaned beef calves grazing bahiagrass pasturesBrangus crossbred calves (n = 48; 24 steers and 24 heifers) will be weaned and randomly allocated into 1 of 8 bahiagrass (Paspalum notatum; 0.4 ha each) pastures using a fixed and continuous stocking rate (3 steers and 3 heifers/pasture).Calves will be supplemented with 2% BW concentrate daily and the treatments will be monensin (20 mg/kg of the expected dry matter intake) or control (no monensin) in a completely randomized design with four replicates. The treatment will be added to the supplement at the time of feeding.Individual calf BW will be obtained every 28 days from day 0 to 84, after 16 hours of feed and water withdrawal. From day 0 to 84, calves will be provided daily concentrate supplementation (80% soybean hulls and 20% cottonseed meal, as-fed basis; Table 1) at 2.0% of BW (DM basis). Supplementation rate was selected based on previous studies from our group and according to differences on nutritive value of each forage type (Vendramini et al., 2006; Vendramini and Arthington, 2008). Supplemental amount offered will be adjusted every 28 days using average BW of each pasture. Calves will be offered free choice access to water and commercial mineral, mineral mix (Cattle Select Essentials Range; Lakeland Animal Nutrition, Lakeland, Florida, USA; 6.0, 0.10, 0.10, 0.30, 63, and 1.0% of Ca, K, Mg, S, NaCl, and P, respectively, and 50, 1,500, 800, 210, 500, 40, and 3,000 mg/kg of Co, Cu, Fe, I, Mn, Se, and Zn, respectively) throughout the study.Rectal fecal samples will be collected at 28-day intervals, from day 0 to 84, for total fecal worm egg counts (FEC). Individual fecal samples will be collected and sealed in plastic bags, identified, and sent in an insulated container with ice to a commercial laboratory (Myers Parasitology Services, Magnolia, Kentucky, USA) for analysis of coccidia egg count using the Modified Wisconsin Sugar Flotation Technique (Cox and Todd, 1962). The laboratory staff was blinded to treatment assignments. Egg counts (observed total egg count + 1) of each calf will be log-transformed before statistical analyses, and reported as log10 FEC (DeRouen et al., 2009).Herbage mass (HM) will be determined from day 0 to 84 at 14-day intervals, as described by Vendramini and Arthington (2008), but reported as the average HM obtained every 28 days. Average herbage allowance (HA) will be calculated as the average HM (kg of DM/ha) multiplied by the area of each experimental unit (ha) and divided by total calf BW (kg) on the experimental unit (Sollenberger et al., 2005), and reported as the average HA obtained every 28 days. Hand-plucked samples of pastures will be collected every 28 days from day 0 to 84. These samples will be dried at 60°C in a forced-air oven for 72 h and ground in a Wiley mill (model 4, Thomas-Wiley Laboratory Mill; Thomas Scientific, Swedesboro, New Jersey, USA) to pass a 1-mm stainless steel screen. Forage CP concentration will be calculated as 6.25 × N concentration, which will be measured using modifications of the aluminum block digestion technique (Gallaher et al., 1975). In vitro OM digestibility (IVOMD, % of total OM) concentration will be determined by the 2-stage procedure developed by Tilley and Terry (1963) and modified by Moore and Mott (1974).Statistical analyses. Data will be analyzed using pasture as the experimental unit and Satterthwaite approximation to determine the denominator degrees of freedom for the tests of fixed effects. The response variables will be ADG, fecal egg count, HM, HA, CP and IVDOM concentration. Data will be analyzed using PROC MIXED of SAS (SAS Institute Inc., 2006) with monensin and month as fixed effects. Month will be analyzed as a repeated measure using the unstructured covariance structure. Treatments and interactions will be considered different when P ≤ 0.05 and tendencies will be determined if P > 0.05 and ≤ 0.10. Interactions not discussed in the Results and Discussion sections will not be significant (P > 0.10). The means reported will be least squares means and will be compared using PDIFF (SAS Institute Inc., 2006).Experiment 2: Effects of monensin on rumen and blood metabolites of beef cattle receiving warm-season perennial grasses with different levels of concentrate supplementationThe study will be conducted at the University of Florida Range Cattle Research and Education Center, Ona, FL (27o26' N 82o55' W) from May to August 2019.Treatments will be two levels of concentrate (0.5 or 1% BW) and two levels of monensin (0 and 20 mg/kg of the DM intake) tested in a 4 x 4 Latin square design. Four rumen-cannulated steers (500 ± 34 kg of initial BW) will be allocated to individual metabolic stalls and will receive ground stargrass hay (6.3% CP and 52% IVDOM) with 10% refusals during the experimental period. The hay will be processed through a hay chopper (Balebuster 2100, Haybuster Jamestown, ND) to an approximately 5-cm particle size and will be fed 4 times daily.The adaptation period will be from d 0 to 10, and blood and rumen fluid collection periods from d 11 to 12. Blood and rumen fluid will be collected a 12-h interval.Animal measurements. Blood will be collected from the jugular vein into sodium heparin-containing blood collection tubes (Vacuntainer, 10 mL, Becton Dickinson, Franklin Lakes, NJ), placed on ice and then centrifuged (2000 × g for 30 min). The plasma urea nitrogen (PUN) will be determined using a colorimetric kit (Kit B-7551-120, Pointe Scientific, Inc., Detroit, MI).Rumen fluid will be collected (50 mL) and filtered through four layers of cheesecloth into a 200 mL plastic container and pH will be measured [OrionpHmeter(Model330) Perphect LOgROrionResearch, Boston, MA]. Rumen fluid will be transferred into a plastic container and 0.5 mL of a 20% (vol/vol) sulfuric acid solution was added. The container will be placed in ice and then frozen at -20°C until further analysis. For VFA and NH3-N concentration analyses, rumen fluid will be transferred to a plastic container and centrifuged (Beckman Coultier, Avanti JE - rotor JA-20) for 15 min at 10,000 x g at 10°C and 3 mL of the solution will be transferred into a glass tube. Rumen fluid will be analyzed for NH3-N concentrations using the phenol-hypochlorite technique described by Broderick and Kang (1980) with the following modification: absorbance will be read at 620 nm in flat-bottom 96-well plates using a plate reader (DU-500, Beckman Coulter Inc.). Ruminal VFA concentrations will be analyzed using an Agilent 7820A Gas Chromatograph (Agilent Technologies, Palo Alto, CA, 2.5 m x 0.32 mm x 0.45 mm glass column) equipped with a flame ionization detector and a capillary column (CP-WAX 58 FFAP 25 m 0.53 mm, Varian CP7767, Varian Analytical Instruments, Walnut Creek, CA), using crotonic acid as an internal standard.Statistical analysis. Data will be analyzed using steer as the experimental unit and Satterthwaite approximation to determine the denominator degrees of freedom for the tests of fixed effects. The response variables will be pH, PUN, VFA concentrations, and ruminal NH3-N. Data will be analyzed using PROC MIXED of SAS (SAS Institute Inc., 2006) with treatment (main plot), year (subplot) and period and time after feeding (h) as fixed effects. Time after feeding will be analyzed as a repeated measure using the unstructured covariance structure. Steer (treatment x period) and its interactions were considered random effects. Treatments and interactions will be considered different when P ≤ 0.05 and tendencies will be determined if P > 0.05 and ≤ 0.10. Interactions not discussed in the Results and Discussion sections will not be significant (P > 0.10). The means reported will be least squares means and will be compared using PDIFF (SAS Institute Inc., 2006).