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Effect of supplementation of developing replacement heifers with monensin or bambermycins on gain and pregnancy rates1
The Professional Animal Scientist 32 (2016):619–626; http://dx.doi.org/10.15232/pas.2016-01525 ©2016 American Registry of Professional Animal Scientists. All rights reserved.
E foffectdeveloping of supplementation replacement heifers with monensin or bambermycins on gain and pregnancy rates1
P. Beck,*2 PAS, W. Galyen,† PAS, D. Galloway,† E. B. Kegley,† PAS, R. Rorie,† D. Hubbell,‡ J. Tucker,‡ T. Hess,‡ M. Cravey,§3 PAS, J. Hill,# and C. Nichols,§ PAS *Southwest Research and Extension Center, Division of Agriculture, University of Arkansas, Hope 71807; †Department of Animal Science, Division of Agriculture, University of Arkansas, Fayetteville 72701; ‡Livestock and Forestry Research Station, Division of Agriculture, University of Arkansas, Batesville 72501; §Huvepharma Inc., Peachtree City, GA 30269; and #ADM Alliance Nutrition Inc., Quincy, IL 62301
ABSTRACT Medicated feed additives have been shown to increase BW gain and decrease age at puberty; therefore, heifers were provided nonmedicated control (CNTRL), bambermycins (BAMB, Gainpro, Huvepharma Inc., Sofia, Bulgaria), or monensin (MON, Rumensin, Elanco Animal Health, Greenfield, IN) supplements to determine effects on growth performance and reproductive development. Spring-calving (block 1; n = 70 heifers; BW = 208 ± 21.7 kg; age = 231
This project was conducted with funding from the University of Arkansas Agricultural Experiment Station, Hatch Project No. AR 002434, gifts from ADM Alliance Nutrition Inc. (Quincy, IL), and a grant from Huvepharma Inc. (Peachtree City, GA). 2 Corresponding author: [email protected] 3 Current address: Phileo Animal Care, Amarillo, TX 79101. 1
± 17.0 d) and fall-calving (block 2; n = 72 heifers; BW = 225 ± 31.7 kg; age = 276 ± 12.8 d) heifers were allotted to treatments [n = 4 groups in CNTRL and 5 groups in BAMB and MON (block 1), 4 groups per treatment (block 2)] by breed, BW, and source. Heifers in block 1 grazed tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] for 188 d; heifers in block 2 grazed bermudagrass (Cynodon dactylon) pasture and tall fescue for 161 d. The BW at breeding and ADG of CNTRL (323 ± 4.8 kg and 0.68 ± 0.0167 kg/d, respectively) was less (P ≤ 0.04) than medicated, yet MON (346 ± 4.6 kg and 0.73 ± 0.0163 kg/d) and BAMB (344 ± 4.6 kg and 0.74 ± 0.0163 kg/d) did not differ (P ≥ 0.69). Prebreeding reproductive tract scores (3.5 ± 0.60), cycling activity (61 ± 12.3%), and AI (30 ± 12.3%) and total pregnancy rates (82 ± 11.5%) did not differ (P ≥ 0.25) among treatments. This experiment indicates that BAMB and MON effectively increased growth performance
of heifers but did not affect reproductive development or pregnancy rates. Key words: bambermycins, beef heifer, monensin, reproduction
INTRODUCTION Medicated feed additives, such as lasalocid, monensin, and bambermycins, have been used for years to effectively increase BW gain of growing cattle on pasture or fed hay (Bretschneider et al., 2008). Replacement heifer development is an expensive endeavor with lifetime implications on productivity of the cowherd. To optimize production and lifetime profitability, heifers should be bred at 15 mo of age to calve at 24 mo of age (Clark et al., 2005; Stygar et al., 2014). Furthermore, heifers that calve early in the calving season tend to calve early in subsequent calving seasons (Short and Bellows, 1971), which may have ef-
620 fects on the ability to get primiparous cows to rebreed with their second calf within a short subsequent breeding season. Producers have increasingly become interested in forage-based programs that will cost-effectively supply required nutrients to growing beef cattle without daily feeding of mixed diets. Ionophores and ruminally active antibiotic growth promoters function by increasing the production of propionate and decreasing the acetate:propionate ratio, increasing DM and protein digestibility, and increasing gluconeogenesis and glucose turnover (Schelling, 1984). McCartor et al. (1979) found that heifers fed diets containing monensin that resulted in increased propionate production were pubertal 30 d earlier and 17 kg lighter in BW than heifers fed nonmedicated diets. There are data available that indicate that supplying monensin to developing replacement heifers improves fertility and decreases age at puberty (Lalman et al., 1993), but there is limited research investigating the utility of bambermycins in similar production systems. Therefore, this research was conducted to determine the effects of supplementation of growing replacement heifers with monensin (Rumensin, Elanco Animal Health, Greenfield, IL) or bambermycins (Gainpro, Huvepharma Inc., Sofia, Bulgaria) on BW gain, puberty, and pregnancy rates of developing replacement heifers.
MATERIALS AND METHODS Animal procedures in the experiments were approved by the University of Arkansas Institutional Animal Care and Use Committee (Protocol #12042). Heifers from spring-calving (block 1; n = 70 heifers; mean BW 208 ± 21.7 kg; mean age 231 ± 17.0 d) and fall-calving (block 2; n = 72 heifers; mean BW 225 ± 31.7 kg; mean age 276 ± 12.8 d) cowherds were used to test the effects of bambermycins or monensin fed in 1 kg/d corn gluten feed–based supplements (22.1% CP, 11.8% ADF, 30.7% NFC, and 72% calculated TDN;
Beck et al.
DM basis) on pasture in comparison with nonmedicated supplement. The 3 treatments were (1) CNTRL— supplement included a mineral and vitamin premix only; (2) BAMB— supplement included a mineral and vitamin premix designed to supply 15 mg per heifer of bambermycins daily; (3) MON—supplement included a mineral and vitamin premix designed to supply 200 mg per heifer of monensin daily. Following weaning and preconditioning, heifers were allocated into 14 groups (n = 5 heifers per group) for block 1 and 12 groups (n = 6 heifers per group) in block 2 by breed, BW, and source. These groups were then assigned randomly to pastures, and pastures were assigned randomly to treatments [n = 4 groups in CNTRL and 5 groups in BAMB and MON (block 1), 4 groups per treatment (block 2)]. Heifers from the Livestock and Forestry Research Station cowherd (n = 56 in block 1 and n = 60 in block 2) were crossbreds of English (Angus) and Continental (Gelbvieh and Charolais) origin. Heifers from the Southwest Research and Extension Center cowherd (n = 14; block 1) were predominantly of Angus origin (87%) with slight Bos indicus influence (13%). Heifers used from the Southeast Research and Extension Center cowherd (n = 12; block 2) were predominantly of Beefmaster breeding. Treatment supplements were offered daily at a rate of 1.0 kg per heifer (as-fed basis). Supplements contained (DM basis) 89% corn gluten feed and 11% of the respective mineral premix. The mineral premix for CNTRL (Control Mineral G0771AAA, ADM Alliance Nutrition Inc., Quincy, IL) was designed to contain (as-fed basis) 17.5% Ca, 7% P, 18.5% salt, 2.7% Mg, 0.1% K, 1,200 mg of Cu/kg, 1.25 mg of Se/kg, 4,200 mg of Zn/kg, and 440,000 IU of vitamin A/kg. The mineral premix for BAMB (GAINPRO Test Mineral G0771AOZ, ADM Alliance Nutrition Inc.) was designed to contain (as-fed basis) 17.5% Ca, 7% P, 18.5% salt, 2.7% Mg, 0.1% K, 1,200 mg of Cu/kg, 1.25 mg of Se/ kg, 4,200 mg of Zn/kg, 440,000 IU of
vitamin A/kg, and 132 mg of bambermycins/kg. The MON mineral supplement (MoorMan’s Grower Mineral RU-1620; ADM Alliance Nutrition Inc.) was designed to contain (as-fed basis) 9.2% Ca, 6% P, 21.6% salt, 0.3% Mg, 0.8% K, 1,120 mg of Cu/kg, 26 mg of Se/kg, 3,840 mg of Zn/kg, and 441,000 IU of vitamin A/kg.
Study Site and Pasture Management This research was conducted at the University of Arkansas Livestock and Forestry Branch Station located near Batesville, Arkansas. Heifer calves in block 1 were housed in fourteen 2-ha pastures consisting primarily of nontoxic endophyte–infected [Epichloë coenophiala (Morgan-Jones and W. Cams) C.W. Bacon & Schardl, comb. Nov.] tall fescue [Lolium arundinaceum (Schreb.) Darbysh. Duramax Gold, DLF International Seeds, Halsey, OR]. Pastures were fertilized with 168 kg of ammonium nitrate/ ha (56 kg of N/ha) in September and February. Pastures were allowed to accumulate forage mass from fertilization in September until October 29, 2013, at which time 5 heifers were placed on each pasture. Each pasture was divided into 4 paddocks and rotationally grazed by the heifers assigned to that particular pasture. Residence time on each paddock was 7 d, allowing for 21 d of rest for each paddock before grazing of regrowth. Heifers remained on the study from October 29, 2013, to May 5, 2014 (188 d). From February 3, 2014, to March 17, 2014 (35 d), slow regrowth of tall fescue and ice and snow cover made it necessary that nontoxic endophyte tall fescue hay be fed (14.4% CP and 56.6% TDN, DM basis). During the hay feeding period heifers were placed on a single paddock in each pasture and resided there until grazing was reinitiated for the spring-grazing season. Heifer calves in block 2 grazed twelve 2-ha common bermudagrass (Cynodon dactylon) pastures from June 24, 2014, to October 2, 2014, at which time heifers were moved to twelve 2-ha tall fescue pastures (Dura-
Growth promoting technologies for replacement heifers
max Gold) until breeding on December 2, 2014. Bermudagrass pastures were fertilized with 168 kg of ammonium nitrate per hectare (56 kg of N/ ha) in June, July, and October. While heifers were on bermudagrass pastures, continuous grazing management was used. After heifers were moved to tall fescue pastures, grazing was managed using rotational grazing as described previously for block 1.
Cattle Management Heifers were AI bred beginning on May 6, 2014 (block 1), or December 2, 2014 (block 2), at which time the heifers, within block, were commingled on a single pasture. Heat detection patches (Estrotect Heat Detector, Western Point Inc., Apple Valley, MN) were placed on the tailhead of each heifer to assist with heat detection. Heifers were observed for heat for 7 d, then heifers not AI bred by d 7 were injected (i.m.) with 5 mL of prostaglandin F2α (Lutalyse, Zoetis, Florham Park, NJ) and were bred 8 h following observed standing heat for an additional 72 h. Heifers not observed in heat were not exposed to AI. A single low-birthweight Angus sire was used for AI. Two lowbirthweight bulls that had passed a breeding soundness exam were placed with the heifers 14 d following final AI for a 46-d breeding season. One month following AI, pregnancy was determined via transrectal ultrasonography, using an Ibex Pro ultrasound (E.I. Medical Imaging, Loveland, CO) with an 8–5 MHz linear transducer to determine first service AI pregnancy rates, respectively. The AI pregnancy rate for each pasture was defined as the number of heifers pregnant from AI breeding divided by the total number of heifers in each pasture. Heifers were palpated via rectal palpation by an experienced licensed veterinarian in October (block 1) and May (block 2) to determine total pregnancy rates. Heifers were weighed full on 2 consecutive dates at the initiation and termination of the study and at 28-d intervals. Heifers were weighed (full) at weekly intervals, from March
10 through AI breeding in May in block 1 and from October 14 through AI breeding in December in block 2. At each date, blood was collected via jugular venipuncture in 15-mL Vacutainer tubes (BD Inc., Franklin Lakes, NJ) for analysis of progesterone, BUN, and nonesterified fatty acid (NEFA) content. Following collection, blood was allowed to stand at room temperature for 1 h and then placed on ice at 4°C for 2 h after collection, and serum was separated by centrifugation at 1,000 × g for 30 min at 23°C. Serum was then decanted and stored at −20°C for subsequent analysis. Serum was analyzed for urea N using a commercially available colorimetric assay kit (Teco Diagnostics, Anaheim, CA). Nonesterified fatty acid concentrations were analyzed using commercially available colorimetric assay kits (Wako Chemicals USA Inc., Richmond, VA). Serum progesterone was determined by radioimmunoassay using a commercially available radioimmunoassay kit (MP Biomedicals LLC, Santa Ana, CA). Date of first estrus was defined as the first day of 2 consecutive samples with ≥1 ng of progesterone/mL of serum or when a single sample was analyzed to contain >2 ng of progesterone/mL of serum. Before breeding, reproductive tract scores (1 to 5 scale; Pence et al., 1999) were determined by transrectal ultrasonography, using an Ibex Pro ultrasound (E.I. Medical Imaging) with an 8–5 MHz linear transducer in block 1 and by rectal palpation in block 2. The reproductive tract scores were based on development of uterine horns and ovarian structures. A reproductive tract score of 1 would consist of uterine horns that are immature, <20 mm diameter with no palpable follicles or tone to the ovary, whereas a reproductive tract score of 5 would have uterine horns >30 mm in diameter and follicles on the ovaries >10 mm, an erect corpus luteum, and good tone to the ovary (Pence et al., 1999). Heifers were maintained at the Livestock and Forestry Research Station through the subsequent calving season; the calving day was calculated using the
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calving date for each heifer past the first theoretically possible calving due date.
Herbage Sampling and Analysis Herbage yield and chemical composition were measured at the beginning of each month. Forage mass in each field was estimated during the grazing season using a calibrated rising-plate meter with 20 sampling points per pasture (Michell and Large, 1983). Calibration samples were collected by clipping all forage within a single 0.1 m2 frame in each pasture at each sampling to 2.5-cm stubble height with hand shears. Clipped calibration samples were dried to a constant weight under forced air at 60°C for 48 h. Dry weights of these clippings were used to relate forage mass (kg of DM/ha) to plate height within each treatment using linear regression for forage mass prediction. Forage mass prediction equations for the rising plate data were generated using the regression procedure of SAS (SAS Institute Inc., Cary, NC) using the clipping data for each collection period. The regression of rising plate reading on clipped DM yield resulted in equations that explained 80% of the variation in forage mass (forage mass, kg of DM/ha = 25.5 × rising plate height, mm; R2 = 0.80; P < 0.01) for the tall fescue pastures and 93% of the variation in forage mass (forage mass, kg of DM/ ha = 27.8 × rising plate height, mm; R2 = 0.93; P < 0.01) for bermudagrass pastures. Additional forage samples were collected to be representative of diets consumed by grazing heifers from all pastures by clipping forage to mimic forage selected by grazing heifers. Samples were dried to constant weight at 60°C in a forced-air oven for 48 h and ground to pass a 2-mm screen (Thomas A. Wiley Laboratory Mill, Model 4, Thomas Scientific, Swedesboro, NJ) for analysis using near infrared reflectance spectroscopy (Feed & Forage Analyzer model 6500, FOSS North America, Eden Prairie, MN). The CP calibration equation
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Beck et al.
had a SE of calibration of 0.92, a SE of cross validation of 0.93, and R2 of 0.96. The NDF calibration equation had a SE of calibration of 2.63, a SE of cross validation of 2.73, and R2 of 0.95. The ADF calibration equation had a SE of calibration of 1.66, a SE of cross validation of 1.70, and R2 of 0.93. Total digestible nutrient content of the forages was calculated based on species specific equations (bermudagrass TDN, % = 111.8 + 0.95 × % CP − 0.36 × % ADF − 0.70 × % NDF; tall fescue TDN, % = 58.4 + 1.034 × % CP − 0.42 × % ADF) presented by Davis et al. (2002) that were developed using Arkansas forages. Herbage mass and nutritive composition were characterized for each month of grazing in each block, using the Means procedure of SAS (SAS Institute Inc.).
Statistical Analysis Animal performance was analyzed as a randomized complete block design using the mixed procedures of SAS (SAS Institute Inc.). Reproductive data (AI conception, pregnancy percentage, percentage of heifers cyclic before breeding) were analyzed using the GLIMMIX procedure of SAS (SAS Institute Inc.). Pasture group within each block was deemed
the experimental unit, heifer within pasture served as the sampling unit, and block was used in the random statement. Least squares means for animal performance and reproduction were separated using contrasts (1) CNTRL versus medicated feed additives and (2) BAMB versus MON. Treatment comparisons with P ≤ 0.05 were considered significantly different, with tendencies discussed at P > 0.05 and <0.10. Statistical analysis of serum NEFA and BUN was conducted as a randomized complete block design using the mixed procedure of SAS (SAS Institute Inc.) with repeated measures. For repeated measures analyses, the repeated statement was month and fixed effects included treatment, month, and the treatment × month interaction. Least squares means for NEFA were separated using contrasts (1) CNTRL versus medicated feed additives and (2) BAMB versus MON. In the presence of a treatment × month interaction (P = 0.07) for BUN, treatment least squares means of BUN were separated within month using the predicted differences option of SAS (SAS Institute Inc.). Treatment comparisons with P ≤ 0.05 were considered significantly different, with tendencies discussed at P > 0.05 and <0.10.
RESULTS AND DISCUSSION Herbage Mass and Nutritive Content The mean (±SD) CP (% DM basis), ADF (% DM basis), NDF (% DM basis), TDN (% DM basis), and herbage mass (kg of DM/ha) are presented by month in Tables 1 and 2 for blocks 1 and 2, respectively. Forage mass at all times was managed so that there was adequate herbage (>1,500 kg/ha) for heifers to exhibit selective grazing and acquire ad libitum DMI for heifers grazing tall fescue (Tables 1) in block 1 as well as the bermudagrass and tall fescue (Table 2) in block 2. The forage nutritive quality of tall fescue during block 1 and bermudagrass and tall fescue in block 2 closely agrees with the synthesis of forage characteristics presented by Beck et al. (2013). As presented by Beck et al. (2013), forage in the present study contained CP concentrations that would not limit performance of growing heifers in this experiment (NRC, 1996). The seasonal changes in CP, ADF, NDF, and subsequently TDN from the tall fescue in block 1 (Table 1) and the bermudagrass and tall fescue in block 2 (Table 2) agree with the seasonal changes presented by Beck et al. (2013).
Heifer Performance Table 1. Mean (±SD) forage mass and nutritive quality of tall fescue pastures grazed by developing heifers during block 1 from October 29, 2013, to May 5, 2014 % DM basis
Item
Forage mass, kg/ha
CP
ADF
NDF
TDN1
October November December January March April May
2,654 (420.6) 2,555 (420.6) 1,870 (285.8) 1,848 (221.8) 1,808 (194.5) 1,585 (308.9) 3,940 (427.9)
19.5 (1.22) 17.6 (2.25) 15.5 (1.38) 14.3 (1.49) 17.7 (1.52) 22.4 (3.21) 19.8 (1.54)
24.0 (2.28) 25.3 (2.39) 29.4 (1.99) 35.0 (1.78) 33.1 (2.41) 28.4 (4.79) 26.7 (1.28)
47.2 (3.65) 49.4 (3.68) 55.3 (2.74) 62.9 (2.42) 60.4 (3.39) 53.9 (6.84) 50.0 (1.93)
75.6 (2.53) 74.2 (2.66) 69.6 (2.21) 63.3 (1.99) 65.5 (2.68) 70.6 (5.33) 72.6 (1.43)
Total digestible nutrient content of the forages was calculated based on species specific equations (bermudagrass TDN, % = 111.8 + 0.95 × % CP − 0.36 × % ADF − 0.70 × % NDF; tall fescue TDN, % = 58.4 + 1.034 × % CP − 0.42 × % ADF) presented by Davis et al. (2002) that were developed using Arkansas forages.
1
The BW at breeding for heifers fed BAMB (343 ± 4.6) and MON (346 ± 4.6) did not differ (P = 0.69) and were 12.5 kg greater (P = 0.04) than those of CNTRL (332 ± 4.6) heifers (Table 3). Bodyweight is a major factor on timing of puberty in developing heifers (Patterson et al., 1992) and heifers of lighter BW tend to attain puberty at an older age than heavier heifers (Wiltbank et al., 1985). The heifers averaged 67% of their estimated mature BW across treatments at breeding, which is slightly above the target BW (65% of mature BW) often promoted for developing heifers before breeding (Short and Bellows, 1971), indicating that the development systems used were adequate
Growth promoting technologies for replacement heifers
Table 2. Mean (±SD) forage mass and nutritive quality of bermudagrass (from June 24, 2014, to October 2, 2014) and tall fescue (from October 2, 2014, to December 2, 2014) pastures grazed by developing heifers during block 2
Item
Forage mass, kg/ha
% DM basis CP
ADF
NDF
TDN1
Bermudagrass June 1,603 (203.0) 20.9 (2.30) 33.7 (2.88) 60.7 (4.88) 64.8 (3.21) July 2,874 (697.8) 14.7 (1.64) 35.1 (2.00) 63.9 (2.10) 63.2 (2.22) August 2,858 (421.9) 11.3 (1.24) 38.5 (1.60) 69.1 (1.91) 59.5 (1.78) September 2,043 (335.8) 11.6 (1.56) 40.4 (2.94) 72.1 (3.04) 57.4 (3.28) October 1,783 (248.1) 12.5 (2.20) 39.4 (3.84) 71.4 (3.33) 58.5 (4.28) Tall fescue October 1,951 (334.9) 19.7 (2.03) 29.8 (3.33) 55.7 (4.41) 69.2 (3.71) November 1,888 (327.1) 18.1 (2.40) 25.6 (4.06) 49.4 (5.58) 73.9 (4.52) December 1,589 (294.1) 18.0 (1.78) 28.8 (3.18) 53.1 (3.93) 70.3 (3.54) Total digestible nutrient content of the forages was calculated based on species specific equations (bermudagrass TDN, % = 111.8 + 0.95 × % CP − 0.36 × % ADF − 0.70 × % NDF; tall fescue TDN, % = 58.4 + 1.034 × % CP − 0.42 × % ADF) presented by Davis et al. (2002) that were developed using Arkansas forages.
1
for reproductive success regardless of treatment. Average daily gains of developing replacement heifers were 10% greater (P < 0.01) for MON and
BAMB than CNTRL during the prebreeding development period. In agreement with the current study, Hammond et al. (2002) re-
Table 3. Effect of medicated feed additives bambermycins (BAMB) or monensin (MON) on performance and development of replacement heifers from blocks 1 and 2 combined Treatment1 Item BW, kg Initial Final ADG, kg/d Reproductive tract score Pregnancy, % AI pregnancy, % Cycling prebreeding, % Age at puberty, d BW at puberty, kg Calving day3
CNTRL
214 332 0.68 3.4 84 36 64 339 312 29.7
Contrast2
BAMB
215 343 0.74 3.6 81 31 65 340 298 26.0
MON
218 346 0.73 3.5 83 23 76 336 301 31.8
SE
8.9 4.6 0.02 0.29 5.5 6.8 0.07 6.8 18.4 5.2
1
0.71 0.04 <0.01 0.34 0.77 0.17 0.42 0.84 0.24 0.83
2
0.55 0.69 0.89 0.40 0.83 0.19 0.28 0.42 0.77 0.15
CNTRL = supplement included a mineral and vitamin premix only; BAMB = supplement included a mineral and vitamin premix designed to supply 15 mg per heifer of bambermycins daily; MON = supplement included a mineral and vitamin premix designed to supply 200 mg per heifer of monensin daily. 2 Treatment least squares means were separated using the contrasts 1 (CNTRL vs. BAMB and MON) and 2 (MON vs. BAMB). 3 Average days past the first theoretically possible calving due date. 1
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ported that gains of dairy heifers fed forage-based diets in drylot pens did not differ whether diets included monensin, bambermycins, or lasalocid. Rush et al. (1996) reported that gains of calves grazing crested wheatgrass (Agropyron cristatum) pastures during the summer in Nebraska were increased by 13 to 22% for calves supplied MON or BAMB, respectively, compared with nonmedicated controls. Similar to the results in the current research, a meta-analysis conducted by Bretschneider et al. (2008) found that the average gain response from antibiotic growth promoters did not differ among compounds, and the increased gain response averaged 0.08 kg/d for MON and 0.07 kg/d for BAMB, which were 12 and 8% greater than the control groups in the respective studies. In contrast to the present research, Hubbell et al. (2000) reported that ADG of steers grazing tall fescue were not affected when supplements contained chlortetracycline or bambermycins compared with nonmedicated corn-based supplement. Also in contrast with the current research, Galyen et al. (2015) reported that when growing steers grazing wheat (Triticum aestivum L.) pasture were offered BAMB in a selffed mineral free choice, BW gains did not differ from steers fed nonmedicated minerals. Galyen et al. (2015) also reported that gains of steers offered MON in self-fed free-choice mineral supplement were increased by 11% compared with CNTRL, which is slightly greater than the results in the current research. Before breeding, reproductive tract scores (1 to 5 scale) did not differ (P ≥ 0.34), averaging 3.5 ± 0.29 across all treatments, indicating that, on average, most heifers were on the cusp of their cycling activity at the time of this assessment before the breeding season. Age and BW at first puberty (of those heifers cycling before breeding) were not affected by treatment (P ≥ 0.70); the percentage of heifers determined to be cyclic before breeding was 76% for MON, 64% for CNTRL, and 65% for BAMB. Across treatments, the heifers reached
624 puberty at an average BW of 304 kg, which is approximately 60% of their average estimated mature BW and was greater than the 51% of mature BW at breeding observed by Martin et al. (2008) and the 56% of mature BW at breeding observed for extensively raised heifers by Funston and Larson (2011). Ionophores and ruminally active antibiotic growth promoters function by increasing the production of propionate and decreasing the acetate:propionate ratio, increasing DM and protein digestibility, and increasing gluconeogenesis and glucose turnover (Schelling, 1984), leading to the hypothesis that feeding MON and BAMB would increase prebreeding puberty rates. In contrast to the present research, McCartor et al. (1979) found that heifers fed diets containing monensin that resulted in increased propionate production were pubertal at 30-d-earlier age and 17-kg-lighter BW. Lalman et al. (1993) reported that heifers fed monensin during development entered puberty at 21-dearlier age even though BW gains were held constant by dietary manipulation. There were no differences (P ≥ 0.17) in AI pregnancy rate (30%) or total pregnancy rate (82%). Because of the limited number of cattle used in the current experiment, it is unlikely there is sufficient statistical power to detect differences in pregnancy rates related to treatment. Similar to the current research, feeding monensin to mature cows and heifers before calving and during early lactation was not found to affect pregnancy rates (Linneen et al., 2015). The low percentage of heifers pregnant to AI is likely related to the fact that only heifers in observed standing estrus were AI bred. The BUN concentration (Figure 1) was affected (P = 0.07) by an interaction between sampling date and treatment. The change in BUN concentration over time is likely related to the change in forage CP (Tables 1 and 2) during the grazing period. In general, BAMB heifers had BUN concentrations that were less (P = 0.02) than
Beck et al.
Figure 1. Effect of sampling day and BAMB or MON on serum BUN concentration (SE = 0.26) in developing replacement heifers (sampling date × treatment interaction, P = 0.07). CNTRL = supplement included a mineral and vitamin premix only; BAMB = supplement included a mineral and vitamin premix designed to supply 15 mg per heifer of bambermycins daily; MON = supplement included a mineral and vitamin premix designed to supply 200 mg per heifer of monensin daily. *BAMB less than MON (P < 0.05); **BAMB less than CNTRL and MON (P < 0.05); †MON greater than CNTRL and BAMB (P < 0.05).
MON on d 0 and 28 and less (P < 0.01) than both MON and CNTRL on d 56. On d 112 and 140 heifers fed MON had greater (P ≤ 0.01) BUN than both CNTRL and BAMB. One of mode of action of monensin in increasing animal performance is the sparing of ruminal protein and increased flow of AA N to the lower gut (Schelling, 1984) and thus more efficient protein utilization. The surplus protein escaping ruminal degradation and reaching the small intestine because of this mode of action of monensin may have been in excess of needs for growth, and thus contributed to the elevation of BUN in MON. The increase in BUN with MON is consistent with previous literature (Poos et al., 1979; Lalman et al., 1993; Duffield et al., 2008; Linneen et al., 2015). Serum NEFA was not affected by a treatment × sampling day interaction (P = 0.16), thus the serum
NEFA concentrations are presented in Figure 2, pooled across sampling day. Serum NEFA concentrations were 17% greater (P = 0.02) for MON (503 ± 23.8 μg/dL) and BAMB (488 ± 23.8 μg/dL) than for CNTRL (423 ± 25.7 μg/dL). The greater NEFA concentrations for MON and BAMB indicate that these heifers were in a more positive energy balance than CNTRL because of reduced NEFA clearance by tissues (Grummer and Carroll, 1991), which is supported by the observations of increased weight gain for MON and BAMB compared with CNTRL.
IMPLICATIONS These results indicate that BAMB and MON improve the growth performance of heifers grazing bermudagrass or tall fescue pastures when offered in a hand-fed supplement. The increase in growth performance from
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in 2015 Arkansas Anim. Sci. Dept. Rep. No. RS 628. Arkansas Agric. Exp. Stn., Fayetteville, AR. Grummer, R. R., and D. J. Carroll. 1991. Effects of dietary fat on metabolic disorders and reproductive performance of dairy cattle. J. Anim. Sci. 69:3838–3852. Hammond, A., J. E. Shirley, M. Scheffel, E. C. Tigemeyer, and J. S. Stevenson. 2002. Performance of dairy heifers fed high forage diets supplemented with bambermycins, lasalocid, or monensin. Pages 66–70 in Dairy Day 2002 Conf. Proc. Kansas State Univ., Manhattan, KS. Hubbell, D. S., III, L. B. Daniels, K. F. Harrison, and Z. B. Johnson. 2000. The production of stocker cattle supplemented with Aueromycin or Gain Pro while grazing fescue during the fall and winter. Pages 51–52 in 2000 Arkansas Anim. Sci. Dept. Rep. No. RS 478, Arkansas Agric. Exp. Stn., Fayetteville, AR.
Figure 2. Effect of BAMB and MON on serum nonesterified fatty acid (NEFA) concentration (SE = 23.8) in developing replacement heifers (sampling date × treatment interaction, P = 0.16) from blocks 1 and 2 combined. CNTRL = supplement included a mineral and vitamin premix only; BAMB = supplement included a mineral and vitamin premix designed to supply 15 mg per heifer of bambermycins daily; MON = supplement included a mineral and vitamin premix designed to supply 200 mg per heifer of monensin daily. a,bCNTRL versus medicated feed additives (P = 0.02), BAMB versus MON (P = 0.66).
supplying MON and BAMB resulted in heavier BW at puberty, even though there were no improvements in puberty rates, reproductive tract scores, or pregnancy rates. The increase in BUN observed in heifers fed MON indicates that sparing of ruminal protein and increased flow of AA N to the lower gut resulted in more efficient protein utilization. Serum NEFA was also increased in MON and BAMB, indicating improved energy balance of heifers fed these growth promoting technologies. The increased BW achieved from using MON or BAMB can provide economic advantages for beef production even though reproductive development was unaffected.
LITERATURE CITED Beck, P. A., M. Anders, B. Watkins, S. A. Gunter, D. Hubbell, and M. S. Gadberry. 2013. Improving the production, environmental, and economic efficiency of the stocker cattle industry in the southeastern United
States. J. Anim. Sci. 91:2456–2466. http:// dx.doi.org/10.2527/jas.2012-5873. Bretschneider, G., J. C. Elizalde, and F. A. Perez. 2008. The effect of feeding antibiotic growth promoters on the performance of beef cattle consuming forage-based diets: A review. Livest. Sci. 114:135–149. Clark, R. T., K. W. Creighton, H. H. Patterson, and T. N. Barrett. 2005. Symposium Paper: Economic and tax implications for managing beef replacement heifers. Prof. Anim. Sci. 21:164–173. Davis, G. V., M. S. Gadberry, and T. R. Troxel. 2002. Composition and nutrient deficiencies of Arkansas forages for beef cattle. Prof. Anim. Sci. 18:127–134. Duffield, T. F., A. R. Rabiee, and I. J. Lean. 2008. A meta-analysis of the impact of monensin in lactating cattle. Part 1. Metabolic effects. J. Dairy Sci. 91:1334–1346. http:// dx.doi.org/10.3168/jds.2007-0607. Funston, R. N., and D. M. Larson. 2011. Heifer development systems: Dry-lot feeding compared with grazing dormant winter forage. J. Anim. Sci. 89:1595–1602. http:// dx.doi.org/10.2527/jas.2010-3095. Galyen, W., T. Hess, D. Hubbell, S. Gadberry, B. Kegley, M. Cravey, J. Powell, and P. Beck. 2015. Effects of Gainpro or Rumensin on steers grazing wheat pasture. Pages 48–49
Lalman, D. L., M. K. Petersen, R. P. Ansotegui, M. W. Tess, C. K. Clark, and J. S. Wiley. 1993. The effects of ruminally undegradable protein, propionic acid, and monensin on puberty and pregnancy in beef heifers. J. Anim. Sci. 71:2843–2852. Linneen, S. K., A. L. McGee, J. R. Cole, J. S. Jennings, D. R. Stein, G. W. Horn, and D. L. Lalman. 2015. Supplementation of monensin and Optimase to beef cows consuming lowquality forage during late gestation and early lactation. J. Anim. Sci. 93:3076–3083. http:// dx.doi.org/10.2527/jas.2014-8406. Martin, J. L., K. W. Creighton, J. A. Musgrave, T. J. Klopfenstein, R. T. Clarke, D. C. Adams, and R. N. Funston. 2008. Effect of prebreeding body weight or progestin exposure before breeding on beef heifer performance through the second breeding season. J. Anim. Sci. 86:451–459. http://dx.doi. org/10.2527/jas.2007-0233. McCartor, M. M., R. D. Randel, and L. H. Carroll. 1979. Dietary alteration of ruminal fermentation on efficiency of growth and onset of puberty in Brangus heifers. J. Anim. Sci. 48:488–494. Michell, P., and R. V. Large. 1983. The estimation of herbage mass of perennial ryegrass swards: A comparative evaluation of a risingplate meter and a single probe capacitance meter calibrated at or above ground level. Grass Forage Sci. 38:295–300. NRC. 1996. Nutrient Requirements of Beef Cattle. 7th ed. Natl. Acad. Press, Washington, DC. Patterson, D. J., R. C. Perry, G. H. Kiracofe, R. A. Bellows, R. B. Staigmiller, and L. R. Corah. 1992. Management considerations in heifer development and puberty. J. Anim. Sci. 70:4018–4035. Pence, M. R. BreDahl, and J. U. Thompson. 1999. Clinical use of reproductive tract scor-
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Beck et al.
ing to predict pregnancy outcome. 1999 Beef Res. Rep., A. S. Leaflet R1656. Iowa State Univ., Ames.
Pages 69–70 in 1996 Nebraska Beef Cattle Report, Rep. No. MP66-A. Univ. Nebraska, Lincoln.
Poos, M. I., T. I. Hanson, and T. J. Klopfenstein. 1979. Monensin effects on diet digestibility, ruminal protein bypass and microbial protein synthesis. J. Anim. Sci. 48:1516–1524. http://dx.doi.org/10.2134/jas1979.4861516x.
Schelling, G. T. 1984. Monensin mode of action in the rumen. J. Anim. Sci. 58:1518– 1527.
Stygar, A. H., A. R. Kristensen, and J. Mukulska. 2014. Optimal management of replacement heifers in a beef herd: A model for simultaneous optimization of rearing and breeding decisions. J. Anim. Sci. 92:3636– 3649. http://dx.doi.org/10.2527/jas.20107535.
Short, R. E., and R. A. Bellows. 1971. Relationships among weight gains, age at puberty and reproductive performance in heifers. J. Anim. Sci. 32:127–131. http://dx.doi. org/10.2134/jas1971.321127x.
Wiltbank, J. N., S. Roberts, J. Nix, and L. Rowden. 1985. Reproductive performance and profitability of heifers fed to weigh 272 or 318 kg at the start of the first breeding season. J. Anim. Sci. 60:25–34.
Rush, I., B. Weichenthal, and B. Van Pelt. 1996. Effects of Bovatec, Rumensin, or GainPro fed to yearling summer grazing steers.
E foffectdeveloping of supplementation replacement heifers with monensin or bambermycins on gain and pregnancy rates1
P. Beck,*2 PAS, W. Galyen,† PAS, D. Galloway,† E. B. Kegley,† PAS, R. Rorie,† D. Hubbell,‡ J. Tucker,‡ T. Hess,‡ M. Cravey,§3 PAS, J. Hill,# and C. Nichols,§ PAS *Southwest Research and Extension Center, Division of Agriculture, University of Arkansas, Hope 71807; †Department of Animal Science, Division of Agriculture, University of Arkansas, Fayetteville 72701; ‡Livestock and Forestry Research Station, Division of Agriculture, University of Arkansas, Batesville 72501; §Huvepharma Inc., Peachtree City, GA 30269; and #ADM Alliance Nutrition Inc., Quincy, IL 62301
ABSTRACT Medicated feed additives have been shown to increase BW gain and decrease age at puberty; therefore, heifers were provided nonmedicated control (CNTRL), bambermycins (BAMB, Gainpro, Huvepharma Inc., Sofia, Bulgaria), or monensin (MON, Rumensin, Elanco Animal Health, Greenfield, IN) supplements to determine effects on growth performance and reproductive development. Spring-calving (block 1; n = 70 heifers; BW = 208 ± 21.7 kg; age = 231
This project was conducted with funding from the University of Arkansas Agricultural Experiment Station, Hatch Project No. AR 002434, gifts from ADM Alliance Nutrition Inc. (Quincy, IL), and a grant from Huvepharma Inc. (Peachtree City, GA). 2 Corresponding author: [email protected] 3 Current address: Phileo Animal Care, Amarillo, TX 79101. 1
± 17.0 d) and fall-calving (block 2; n = 72 heifers; BW = 225 ± 31.7 kg; age = 276 ± 12.8 d) heifers were allotted to treatments [n = 4 groups in CNTRL and 5 groups in BAMB and MON (block 1), 4 groups per treatment (block 2)] by breed, BW, and source. Heifers in block 1 grazed tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] for 188 d; heifers in block 2 grazed bermudagrass (Cynodon dactylon) pasture and tall fescue for 161 d. The BW at breeding and ADG of CNTRL (323 ± 4.8 kg and 0.68 ± 0.0167 kg/d, respectively) was less (P ≤ 0.04) than medicated, yet MON (346 ± 4.6 kg and 0.73 ± 0.0163 kg/d) and BAMB (344 ± 4.6 kg and 0.74 ± 0.0163 kg/d) did not differ (P ≥ 0.69). Prebreeding reproductive tract scores (3.5 ± 0.60), cycling activity (61 ± 12.3%), and AI (30 ± 12.3%) and total pregnancy rates (82 ± 11.5%) did not differ (P ≥ 0.25) among treatments. This experiment indicates that BAMB and MON effectively increased growth performance
of heifers but did not affect reproductive development or pregnancy rates. Key words: bambermycins, beef heifer, monensin, reproduction
INTRODUCTION Medicated feed additives, such as lasalocid, monensin, and bambermycins, have been used for years to effectively increase BW gain of growing cattle on pasture or fed hay (Bretschneider et al., 2008). Replacement heifer development is an expensive endeavor with lifetime implications on productivity of the cowherd. To optimize production and lifetime profitability, heifers should be bred at 15 mo of age to calve at 24 mo of age (Clark et al., 2005; Stygar et al., 2014). Furthermore, heifers that calve early in the calving season tend to calve early in subsequent calving seasons (Short and Bellows, 1971), which may have ef-
620 fects on the ability to get primiparous cows to rebreed with their second calf within a short subsequent breeding season. Producers have increasingly become interested in forage-based programs that will cost-effectively supply required nutrients to growing beef cattle without daily feeding of mixed diets. Ionophores and ruminally active antibiotic growth promoters function by increasing the production of propionate and decreasing the acetate:propionate ratio, increasing DM and protein digestibility, and increasing gluconeogenesis and glucose turnover (Schelling, 1984). McCartor et al. (1979) found that heifers fed diets containing monensin that resulted in increased propionate production were pubertal 30 d earlier and 17 kg lighter in BW than heifers fed nonmedicated diets. There are data available that indicate that supplying monensin to developing replacement heifers improves fertility and decreases age at puberty (Lalman et al., 1993), but there is limited research investigating the utility of bambermycins in similar production systems. Therefore, this research was conducted to determine the effects of supplementation of growing replacement heifers with monensin (Rumensin, Elanco Animal Health, Greenfield, IL) or bambermycins (Gainpro, Huvepharma Inc., Sofia, Bulgaria) on BW gain, puberty, and pregnancy rates of developing replacement heifers.
MATERIALS AND METHODS Animal procedures in the experiments were approved by the University of Arkansas Institutional Animal Care and Use Committee (Protocol #12042). Heifers from spring-calving (block 1; n = 70 heifers; mean BW 208 ± 21.7 kg; mean age 231 ± 17.0 d) and fall-calving (block 2; n = 72 heifers; mean BW 225 ± 31.7 kg; mean age 276 ± 12.8 d) cowherds were used to test the effects of bambermycins or monensin fed in 1 kg/d corn gluten feed–based supplements (22.1% CP, 11.8% ADF, 30.7% NFC, and 72% calculated TDN;
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DM basis) on pasture in comparison with nonmedicated supplement. The 3 treatments were (1) CNTRL— supplement included a mineral and vitamin premix only; (2) BAMB— supplement included a mineral and vitamin premix designed to supply 15 mg per heifer of bambermycins daily; (3) MON—supplement included a mineral and vitamin premix designed to supply 200 mg per heifer of monensin daily. Following weaning and preconditioning, heifers were allocated into 14 groups (n = 5 heifers per group) for block 1 and 12 groups (n = 6 heifers per group) in block 2 by breed, BW, and source. These groups were then assigned randomly to pastures, and pastures were assigned randomly to treatments [n = 4 groups in CNTRL and 5 groups in BAMB and MON (block 1), 4 groups per treatment (block 2)]. Heifers from the Livestock and Forestry Research Station cowherd (n = 56 in block 1 and n = 60 in block 2) were crossbreds of English (Angus) and Continental (Gelbvieh and Charolais) origin. Heifers from the Southwest Research and Extension Center cowherd (n = 14; block 1) were predominantly of Angus origin (87%) with slight Bos indicus influence (13%). Heifers used from the Southeast Research and Extension Center cowherd (n = 12; block 2) were predominantly of Beefmaster breeding. Treatment supplements were offered daily at a rate of 1.0 kg per heifer (as-fed basis). Supplements contained (DM basis) 89% corn gluten feed and 11% of the respective mineral premix. The mineral premix for CNTRL (Control Mineral G0771AAA, ADM Alliance Nutrition Inc., Quincy, IL) was designed to contain (as-fed basis) 17.5% Ca, 7% P, 18.5% salt, 2.7% Mg, 0.1% K, 1,200 mg of Cu/kg, 1.25 mg of Se/kg, 4,200 mg of Zn/kg, and 440,000 IU of vitamin A/kg. The mineral premix for BAMB (GAINPRO Test Mineral G0771AOZ, ADM Alliance Nutrition Inc.) was designed to contain (as-fed basis) 17.5% Ca, 7% P, 18.5% salt, 2.7% Mg, 0.1% K, 1,200 mg of Cu/kg, 1.25 mg of Se/ kg, 4,200 mg of Zn/kg, 440,000 IU of
vitamin A/kg, and 132 mg of bambermycins/kg. The MON mineral supplement (MoorMan’s Grower Mineral RU-1620; ADM Alliance Nutrition Inc.) was designed to contain (as-fed basis) 9.2% Ca, 6% P, 21.6% salt, 0.3% Mg, 0.8% K, 1,120 mg of Cu/kg, 26 mg of Se/kg, 3,840 mg of Zn/kg, and 441,000 IU of vitamin A/kg.
Study Site and Pasture Management This research was conducted at the University of Arkansas Livestock and Forestry Branch Station located near Batesville, Arkansas. Heifer calves in block 1 were housed in fourteen 2-ha pastures consisting primarily of nontoxic endophyte–infected [Epichloë coenophiala (Morgan-Jones and W. Cams) C.W. Bacon & Schardl, comb. Nov.] tall fescue [Lolium arundinaceum (Schreb.) Darbysh. Duramax Gold, DLF International Seeds, Halsey, OR]. Pastures were fertilized with 168 kg of ammonium nitrate/ ha (56 kg of N/ha) in September and February. Pastures were allowed to accumulate forage mass from fertilization in September until October 29, 2013, at which time 5 heifers were placed on each pasture. Each pasture was divided into 4 paddocks and rotationally grazed by the heifers assigned to that particular pasture. Residence time on each paddock was 7 d, allowing for 21 d of rest for each paddock before grazing of regrowth. Heifers remained on the study from October 29, 2013, to May 5, 2014 (188 d). From February 3, 2014, to March 17, 2014 (35 d), slow regrowth of tall fescue and ice and snow cover made it necessary that nontoxic endophyte tall fescue hay be fed (14.4% CP and 56.6% TDN, DM basis). During the hay feeding period heifers were placed on a single paddock in each pasture and resided there until grazing was reinitiated for the spring-grazing season. Heifer calves in block 2 grazed twelve 2-ha common bermudagrass (Cynodon dactylon) pastures from June 24, 2014, to October 2, 2014, at which time heifers were moved to twelve 2-ha tall fescue pastures (Dura-
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max Gold) until breeding on December 2, 2014. Bermudagrass pastures were fertilized with 168 kg of ammonium nitrate per hectare (56 kg of N/ ha) in June, July, and October. While heifers were on bermudagrass pastures, continuous grazing management was used. After heifers were moved to tall fescue pastures, grazing was managed using rotational grazing as described previously for block 1.
Cattle Management Heifers were AI bred beginning on May 6, 2014 (block 1), or December 2, 2014 (block 2), at which time the heifers, within block, were commingled on a single pasture. Heat detection patches (Estrotect Heat Detector, Western Point Inc., Apple Valley, MN) were placed on the tailhead of each heifer to assist with heat detection. Heifers were observed for heat for 7 d, then heifers not AI bred by d 7 were injected (i.m.) with 5 mL of prostaglandin F2α (Lutalyse, Zoetis, Florham Park, NJ) and were bred 8 h following observed standing heat for an additional 72 h. Heifers not observed in heat were not exposed to AI. A single low-birthweight Angus sire was used for AI. Two lowbirthweight bulls that had passed a breeding soundness exam were placed with the heifers 14 d following final AI for a 46-d breeding season. One month following AI, pregnancy was determined via transrectal ultrasonography, using an Ibex Pro ultrasound (E.I. Medical Imaging, Loveland, CO) with an 8–5 MHz linear transducer to determine first service AI pregnancy rates, respectively. The AI pregnancy rate for each pasture was defined as the number of heifers pregnant from AI breeding divided by the total number of heifers in each pasture. Heifers were palpated via rectal palpation by an experienced licensed veterinarian in October (block 1) and May (block 2) to determine total pregnancy rates. Heifers were weighed full on 2 consecutive dates at the initiation and termination of the study and at 28-d intervals. Heifers were weighed (full) at weekly intervals, from March
10 through AI breeding in May in block 1 and from October 14 through AI breeding in December in block 2. At each date, blood was collected via jugular venipuncture in 15-mL Vacutainer tubes (BD Inc., Franklin Lakes, NJ) for analysis of progesterone, BUN, and nonesterified fatty acid (NEFA) content. Following collection, blood was allowed to stand at room temperature for 1 h and then placed on ice at 4°C for 2 h after collection, and serum was separated by centrifugation at 1,000 × g for 30 min at 23°C. Serum was then decanted and stored at −20°C for subsequent analysis. Serum was analyzed for urea N using a commercially available colorimetric assay kit (Teco Diagnostics, Anaheim, CA). Nonesterified fatty acid concentrations were analyzed using commercially available colorimetric assay kits (Wako Chemicals USA Inc., Richmond, VA). Serum progesterone was determined by radioimmunoassay using a commercially available radioimmunoassay kit (MP Biomedicals LLC, Santa Ana, CA). Date of first estrus was defined as the first day of 2 consecutive samples with ≥1 ng of progesterone/mL of serum or when a single sample was analyzed to contain >2 ng of progesterone/mL of serum. Before breeding, reproductive tract scores (1 to 5 scale; Pence et al., 1999) were determined by transrectal ultrasonography, using an Ibex Pro ultrasound (E.I. Medical Imaging) with an 8–5 MHz linear transducer in block 1 and by rectal palpation in block 2. The reproductive tract scores were based on development of uterine horns and ovarian structures. A reproductive tract score of 1 would consist of uterine horns that are immature, <20 mm diameter with no palpable follicles or tone to the ovary, whereas a reproductive tract score of 5 would have uterine horns >30 mm in diameter and follicles on the ovaries >10 mm, an erect corpus luteum, and good tone to the ovary (Pence et al., 1999). Heifers were maintained at the Livestock and Forestry Research Station through the subsequent calving season; the calving day was calculated using the
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calving date for each heifer past the first theoretically possible calving due date.
Herbage Sampling and Analysis Herbage yield and chemical composition were measured at the beginning of each month. Forage mass in each field was estimated during the grazing season using a calibrated rising-plate meter with 20 sampling points per pasture (Michell and Large, 1983). Calibration samples were collected by clipping all forage within a single 0.1 m2 frame in each pasture at each sampling to 2.5-cm stubble height with hand shears. Clipped calibration samples were dried to a constant weight under forced air at 60°C for 48 h. Dry weights of these clippings were used to relate forage mass (kg of DM/ha) to plate height within each treatment using linear regression for forage mass prediction. Forage mass prediction equations for the rising plate data were generated using the regression procedure of SAS (SAS Institute Inc., Cary, NC) using the clipping data for each collection period. The regression of rising plate reading on clipped DM yield resulted in equations that explained 80% of the variation in forage mass (forage mass, kg of DM/ha = 25.5 × rising plate height, mm; R2 = 0.80; P < 0.01) for the tall fescue pastures and 93% of the variation in forage mass (forage mass, kg of DM/ ha = 27.8 × rising plate height, mm; R2 = 0.93; P < 0.01) for bermudagrass pastures. Additional forage samples were collected to be representative of diets consumed by grazing heifers from all pastures by clipping forage to mimic forage selected by grazing heifers. Samples were dried to constant weight at 60°C in a forced-air oven for 48 h and ground to pass a 2-mm screen (Thomas A. Wiley Laboratory Mill, Model 4, Thomas Scientific, Swedesboro, NJ) for analysis using near infrared reflectance spectroscopy (Feed & Forage Analyzer model 6500, FOSS North America, Eden Prairie, MN). The CP calibration equation
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had a SE of calibration of 0.92, a SE of cross validation of 0.93, and R2 of 0.96. The NDF calibration equation had a SE of calibration of 2.63, a SE of cross validation of 2.73, and R2 of 0.95. The ADF calibration equation had a SE of calibration of 1.66, a SE of cross validation of 1.70, and R2 of 0.93. Total digestible nutrient content of the forages was calculated based on species specific equations (bermudagrass TDN, % = 111.8 + 0.95 × % CP − 0.36 × % ADF − 0.70 × % NDF; tall fescue TDN, % = 58.4 + 1.034 × % CP − 0.42 × % ADF) presented by Davis et al. (2002) that were developed using Arkansas forages. Herbage mass and nutritive composition were characterized for each month of grazing in each block, using the Means procedure of SAS (SAS Institute Inc.).
Statistical Analysis Animal performance was analyzed as a randomized complete block design using the mixed procedures of SAS (SAS Institute Inc.). Reproductive data (AI conception, pregnancy percentage, percentage of heifers cyclic before breeding) were analyzed using the GLIMMIX procedure of SAS (SAS Institute Inc.). Pasture group within each block was deemed
the experimental unit, heifer within pasture served as the sampling unit, and block was used in the random statement. Least squares means for animal performance and reproduction were separated using contrasts (1) CNTRL versus medicated feed additives and (2) BAMB versus MON. Treatment comparisons with P ≤ 0.05 were considered significantly different, with tendencies discussed at P > 0.05 and <0.10. Statistical analysis of serum NEFA and BUN was conducted as a randomized complete block design using the mixed procedure of SAS (SAS Institute Inc.) with repeated measures. For repeated measures analyses, the repeated statement was month and fixed effects included treatment, month, and the treatment × month interaction. Least squares means for NEFA were separated using contrasts (1) CNTRL versus medicated feed additives and (2) BAMB versus MON. In the presence of a treatment × month interaction (P = 0.07) for BUN, treatment least squares means of BUN were separated within month using the predicted differences option of SAS (SAS Institute Inc.). Treatment comparisons with P ≤ 0.05 were considered significantly different, with tendencies discussed at P > 0.05 and <0.10.
RESULTS AND DISCUSSION Herbage Mass and Nutritive Content The mean (±SD) CP (% DM basis), ADF (% DM basis), NDF (% DM basis), TDN (% DM basis), and herbage mass (kg of DM/ha) are presented by month in Tables 1 and 2 for blocks 1 and 2, respectively. Forage mass at all times was managed so that there was adequate herbage (>1,500 kg/ha) for heifers to exhibit selective grazing and acquire ad libitum DMI for heifers grazing tall fescue (Tables 1) in block 1 as well as the bermudagrass and tall fescue (Table 2) in block 2. The forage nutritive quality of tall fescue during block 1 and bermudagrass and tall fescue in block 2 closely agrees with the synthesis of forage characteristics presented by Beck et al. (2013). As presented by Beck et al. (2013), forage in the present study contained CP concentrations that would not limit performance of growing heifers in this experiment (NRC, 1996). The seasonal changes in CP, ADF, NDF, and subsequently TDN from the tall fescue in block 1 (Table 1) and the bermudagrass and tall fescue in block 2 (Table 2) agree with the seasonal changes presented by Beck et al. (2013).
Heifer Performance Table 1. Mean (±SD) forage mass and nutritive quality of tall fescue pastures grazed by developing heifers during block 1 from October 29, 2013, to May 5, 2014 % DM basis
Item
Forage mass, kg/ha
CP
ADF
NDF
TDN1
October November December January March April May
2,654 (420.6) 2,555 (420.6) 1,870 (285.8) 1,848 (221.8) 1,808 (194.5) 1,585 (308.9) 3,940 (427.9)
19.5 (1.22) 17.6 (2.25) 15.5 (1.38) 14.3 (1.49) 17.7 (1.52) 22.4 (3.21) 19.8 (1.54)
24.0 (2.28) 25.3 (2.39) 29.4 (1.99) 35.0 (1.78) 33.1 (2.41) 28.4 (4.79) 26.7 (1.28)
47.2 (3.65) 49.4 (3.68) 55.3 (2.74) 62.9 (2.42) 60.4 (3.39) 53.9 (6.84) 50.0 (1.93)
75.6 (2.53) 74.2 (2.66) 69.6 (2.21) 63.3 (1.99) 65.5 (2.68) 70.6 (5.33) 72.6 (1.43)
Total digestible nutrient content of the forages was calculated based on species specific equations (bermudagrass TDN, % = 111.8 + 0.95 × % CP − 0.36 × % ADF − 0.70 × % NDF; tall fescue TDN, % = 58.4 + 1.034 × % CP − 0.42 × % ADF) presented by Davis et al. (2002) that were developed using Arkansas forages.
1
The BW at breeding for heifers fed BAMB (343 ± 4.6) and MON (346 ± 4.6) did not differ (P = 0.69) and were 12.5 kg greater (P = 0.04) than those of CNTRL (332 ± 4.6) heifers (Table 3). Bodyweight is a major factor on timing of puberty in developing heifers (Patterson et al., 1992) and heifers of lighter BW tend to attain puberty at an older age than heavier heifers (Wiltbank et al., 1985). The heifers averaged 67% of their estimated mature BW across treatments at breeding, which is slightly above the target BW (65% of mature BW) often promoted for developing heifers before breeding (Short and Bellows, 1971), indicating that the development systems used were adequate
Growth promoting technologies for replacement heifers
Table 2. Mean (±SD) forage mass and nutritive quality of bermudagrass (from June 24, 2014, to October 2, 2014) and tall fescue (from October 2, 2014, to December 2, 2014) pastures grazed by developing heifers during block 2
Item
Forage mass, kg/ha
% DM basis CP
ADF
NDF
TDN1
Bermudagrass June 1,603 (203.0) 20.9 (2.30) 33.7 (2.88) 60.7 (4.88) 64.8 (3.21) July 2,874 (697.8) 14.7 (1.64) 35.1 (2.00) 63.9 (2.10) 63.2 (2.22) August 2,858 (421.9) 11.3 (1.24) 38.5 (1.60) 69.1 (1.91) 59.5 (1.78) September 2,043 (335.8) 11.6 (1.56) 40.4 (2.94) 72.1 (3.04) 57.4 (3.28) October 1,783 (248.1) 12.5 (2.20) 39.4 (3.84) 71.4 (3.33) 58.5 (4.28) Tall fescue October 1,951 (334.9) 19.7 (2.03) 29.8 (3.33) 55.7 (4.41) 69.2 (3.71) November 1,888 (327.1) 18.1 (2.40) 25.6 (4.06) 49.4 (5.58) 73.9 (4.52) December 1,589 (294.1) 18.0 (1.78) 28.8 (3.18) 53.1 (3.93) 70.3 (3.54) Total digestible nutrient content of the forages was calculated based on species specific equations (bermudagrass TDN, % = 111.8 + 0.95 × % CP − 0.36 × % ADF − 0.70 × % NDF; tall fescue TDN, % = 58.4 + 1.034 × % CP − 0.42 × % ADF) presented by Davis et al. (2002) that were developed using Arkansas forages.
1
for reproductive success regardless of treatment. Average daily gains of developing replacement heifers were 10% greater (P < 0.01) for MON and
BAMB than CNTRL during the prebreeding development period. In agreement with the current study, Hammond et al. (2002) re-
Table 3. Effect of medicated feed additives bambermycins (BAMB) or monensin (MON) on performance and development of replacement heifers from blocks 1 and 2 combined Treatment1 Item BW, kg Initial Final ADG, kg/d Reproductive tract score Pregnancy, % AI pregnancy, % Cycling prebreeding, % Age at puberty, d BW at puberty, kg Calving day3
CNTRL
214 332 0.68 3.4 84 36 64 339 312 29.7
Contrast2
BAMB
215 343 0.74 3.6 81 31 65 340 298 26.0
MON
218 346 0.73 3.5 83 23 76 336 301 31.8
SE
8.9 4.6 0.02 0.29 5.5 6.8 0.07 6.8 18.4 5.2
1
0.71 0.04 <0.01 0.34 0.77 0.17 0.42 0.84 0.24 0.83
2
0.55 0.69 0.89 0.40 0.83 0.19 0.28 0.42 0.77 0.15
CNTRL = supplement included a mineral and vitamin premix only; BAMB = supplement included a mineral and vitamin premix designed to supply 15 mg per heifer of bambermycins daily; MON = supplement included a mineral and vitamin premix designed to supply 200 mg per heifer of monensin daily. 2 Treatment least squares means were separated using the contrasts 1 (CNTRL vs. BAMB and MON) and 2 (MON vs. BAMB). 3 Average days past the first theoretically possible calving due date. 1
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ported that gains of dairy heifers fed forage-based diets in drylot pens did not differ whether diets included monensin, bambermycins, or lasalocid. Rush et al. (1996) reported that gains of calves grazing crested wheatgrass (Agropyron cristatum) pastures during the summer in Nebraska were increased by 13 to 22% for calves supplied MON or BAMB, respectively, compared with nonmedicated controls. Similar to the results in the current research, a meta-analysis conducted by Bretschneider et al. (2008) found that the average gain response from antibiotic growth promoters did not differ among compounds, and the increased gain response averaged 0.08 kg/d for MON and 0.07 kg/d for BAMB, which were 12 and 8% greater than the control groups in the respective studies. In contrast to the present research, Hubbell et al. (2000) reported that ADG of steers grazing tall fescue were not affected when supplements contained chlortetracycline or bambermycins compared with nonmedicated corn-based supplement. Also in contrast with the current research, Galyen et al. (2015) reported that when growing steers grazing wheat (Triticum aestivum L.) pasture were offered BAMB in a selffed mineral free choice, BW gains did not differ from steers fed nonmedicated minerals. Galyen et al. (2015) also reported that gains of steers offered MON in self-fed free-choice mineral supplement were increased by 11% compared with CNTRL, which is slightly greater than the results in the current research. Before breeding, reproductive tract scores (1 to 5 scale) did not differ (P ≥ 0.34), averaging 3.5 ± 0.29 across all treatments, indicating that, on average, most heifers were on the cusp of their cycling activity at the time of this assessment before the breeding season. Age and BW at first puberty (of those heifers cycling before breeding) were not affected by treatment (P ≥ 0.70); the percentage of heifers determined to be cyclic before breeding was 76% for MON, 64% for CNTRL, and 65% for BAMB. Across treatments, the heifers reached
624 puberty at an average BW of 304 kg, which is approximately 60% of their average estimated mature BW and was greater than the 51% of mature BW at breeding observed by Martin et al. (2008) and the 56% of mature BW at breeding observed for extensively raised heifers by Funston and Larson (2011). Ionophores and ruminally active antibiotic growth promoters function by increasing the production of propionate and decreasing the acetate:propionate ratio, increasing DM and protein digestibility, and increasing gluconeogenesis and glucose turnover (Schelling, 1984), leading to the hypothesis that feeding MON and BAMB would increase prebreeding puberty rates. In contrast to the present research, McCartor et al. (1979) found that heifers fed diets containing monensin that resulted in increased propionate production were pubertal at 30-d-earlier age and 17-kg-lighter BW. Lalman et al. (1993) reported that heifers fed monensin during development entered puberty at 21-dearlier age even though BW gains were held constant by dietary manipulation. There were no differences (P ≥ 0.17) in AI pregnancy rate (30%) or total pregnancy rate (82%). Because of the limited number of cattle used in the current experiment, it is unlikely there is sufficient statistical power to detect differences in pregnancy rates related to treatment. Similar to the current research, feeding monensin to mature cows and heifers before calving and during early lactation was not found to affect pregnancy rates (Linneen et al., 2015). The low percentage of heifers pregnant to AI is likely related to the fact that only heifers in observed standing estrus were AI bred. The BUN concentration (Figure 1) was affected (P = 0.07) by an interaction between sampling date and treatment. The change in BUN concentration over time is likely related to the change in forage CP (Tables 1 and 2) during the grazing period. In general, BAMB heifers had BUN concentrations that were less (P = 0.02) than
Beck et al.
Figure 1. Effect of sampling day and BAMB or MON on serum BUN concentration (SE = 0.26) in developing replacement heifers (sampling date × treatment interaction, P = 0.07). CNTRL = supplement included a mineral and vitamin premix only; BAMB = supplement included a mineral and vitamin premix designed to supply 15 mg per heifer of bambermycins daily; MON = supplement included a mineral and vitamin premix designed to supply 200 mg per heifer of monensin daily. *BAMB less than MON (P < 0.05); **BAMB less than CNTRL and MON (P < 0.05); †MON greater than CNTRL and BAMB (P < 0.05).
MON on d 0 and 28 and less (P < 0.01) than both MON and CNTRL on d 56. On d 112 and 140 heifers fed MON had greater (P ≤ 0.01) BUN than both CNTRL and BAMB. One of mode of action of monensin in increasing animal performance is the sparing of ruminal protein and increased flow of AA N to the lower gut (Schelling, 1984) and thus more efficient protein utilization. The surplus protein escaping ruminal degradation and reaching the small intestine because of this mode of action of monensin may have been in excess of needs for growth, and thus contributed to the elevation of BUN in MON. The increase in BUN with MON is consistent with previous literature (Poos et al., 1979; Lalman et al., 1993; Duffield et al., 2008; Linneen et al., 2015). Serum NEFA was not affected by a treatment × sampling day interaction (P = 0.16), thus the serum
NEFA concentrations are presented in Figure 2, pooled across sampling day. Serum NEFA concentrations were 17% greater (P = 0.02) for MON (503 ± 23.8 μg/dL) and BAMB (488 ± 23.8 μg/dL) than for CNTRL (423 ± 25.7 μg/dL). The greater NEFA concentrations for MON and BAMB indicate that these heifers were in a more positive energy balance than CNTRL because of reduced NEFA clearance by tissues (Grummer and Carroll, 1991), which is supported by the observations of increased weight gain for MON and BAMB compared with CNTRL.
IMPLICATIONS These results indicate that BAMB and MON improve the growth performance of heifers grazing bermudagrass or tall fescue pastures when offered in a hand-fed supplement. The increase in growth performance from
Growth promoting technologies for replacement heifers
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in 2015 Arkansas Anim. Sci. Dept. Rep. No. RS 628. Arkansas Agric. Exp. Stn., Fayetteville, AR. Grummer, R. R., and D. J. Carroll. 1991. Effects of dietary fat on metabolic disorders and reproductive performance of dairy cattle. J. Anim. Sci. 69:3838–3852. Hammond, A., J. E. Shirley, M. Scheffel, E. C. Tigemeyer, and J. S. Stevenson. 2002. Performance of dairy heifers fed high forage diets supplemented with bambermycins, lasalocid, or monensin. Pages 66–70 in Dairy Day 2002 Conf. Proc. Kansas State Univ., Manhattan, KS. Hubbell, D. S., III, L. B. Daniels, K. F. Harrison, and Z. B. Johnson. 2000. The production of stocker cattle supplemented with Aueromycin or Gain Pro while grazing fescue during the fall and winter. Pages 51–52 in 2000 Arkansas Anim. Sci. Dept. Rep. No. RS 478, Arkansas Agric. Exp. Stn., Fayetteville, AR.
Figure 2. Effect of BAMB and MON on serum nonesterified fatty acid (NEFA) concentration (SE = 23.8) in developing replacement heifers (sampling date × treatment interaction, P = 0.16) from blocks 1 and 2 combined. CNTRL = supplement included a mineral and vitamin premix only; BAMB = supplement included a mineral and vitamin premix designed to supply 15 mg per heifer of bambermycins daily; MON = supplement included a mineral and vitamin premix designed to supply 200 mg per heifer of monensin daily. a,bCNTRL versus medicated feed additives (P = 0.02), BAMB versus MON (P = 0.66).
supplying MON and BAMB resulted in heavier BW at puberty, even though there were no improvements in puberty rates, reproductive tract scores, or pregnancy rates. The increase in BUN observed in heifers fed MON indicates that sparing of ruminal protein and increased flow of AA N to the lower gut resulted in more efficient protein utilization. Serum NEFA was also increased in MON and BAMB, indicating improved energy balance of heifers fed these growth promoting technologies. The increased BW achieved from using MON or BAMB can provide economic advantages for beef production even though reproductive development was unaffected.
LITERATURE CITED Beck, P. A., M. Anders, B. Watkins, S. A. Gunter, D. Hubbell, and M. S. Gadberry. 2013. Improving the production, environmental, and economic efficiency of the stocker cattle industry in the southeastern United
States. J. Anim. Sci. 91:2456–2466. http:// dx.doi.org/10.2527/jas.2012-5873. Bretschneider, G., J. C. Elizalde, and F. A. Perez. 2008. The effect of feeding antibiotic growth promoters on the performance of beef cattle consuming forage-based diets: A review. Livest. Sci. 114:135–149. Clark, R. T., K. W. Creighton, H. H. Patterson, and T. N. Barrett. 2005. Symposium Paper: Economic and tax implications for managing beef replacement heifers. Prof. Anim. Sci. 21:164–173. Davis, G. V., M. S. Gadberry, and T. R. Troxel. 2002. Composition and nutrient deficiencies of Arkansas forages for beef cattle. Prof. Anim. Sci. 18:127–134. Duffield, T. F., A. R. Rabiee, and I. J. Lean. 2008. A meta-analysis of the impact of monensin in lactating cattle. Part 1. Metabolic effects. J. Dairy Sci. 91:1334–1346. http:// dx.doi.org/10.3168/jds.2007-0607. Funston, R. N., and D. M. Larson. 2011. Heifer development systems: Dry-lot feeding compared with grazing dormant winter forage. J. Anim. Sci. 89:1595–1602. http:// dx.doi.org/10.2527/jas.2010-3095. Galyen, W., T. Hess, D. Hubbell, S. Gadberry, B. Kegley, M. Cravey, J. Powell, and P. Beck. 2015. Effects of Gainpro or Rumensin on steers grazing wheat pasture. Pages 48–49
Lalman, D. L., M. K. Petersen, R. P. Ansotegui, M. W. Tess, C. K. Clark, and J. S. Wiley. 1993. The effects of ruminally undegradable protein, propionic acid, and monensin on puberty and pregnancy in beef heifers. J. Anim. Sci. 71:2843–2852. Linneen, S. K., A. L. McGee, J. R. Cole, J. S. Jennings, D. R. Stein, G. W. Horn, and D. L. Lalman. 2015. Supplementation of monensin and Optimase to beef cows consuming lowquality forage during late gestation and early lactation. J. Anim. Sci. 93:3076–3083. http:// dx.doi.org/10.2527/jas.2014-8406. Martin, J. L., K. W. Creighton, J. A. Musgrave, T. J. Klopfenstein, R. T. Clarke, D. C. Adams, and R. N. Funston. 2008. Effect of prebreeding body weight or progestin exposure before breeding on beef heifer performance through the second breeding season. J. Anim. Sci. 86:451–459. http://dx.doi. org/10.2527/jas.2007-0233. McCartor, M. M., R. D. Randel, and L. H. Carroll. 1979. Dietary alteration of ruminal fermentation on efficiency of growth and onset of puberty in Brangus heifers. J. Anim. Sci. 48:488–494. Michell, P., and R. V. Large. 1983. The estimation of herbage mass of perennial ryegrass swards: A comparative evaluation of a risingplate meter and a single probe capacitance meter calibrated at or above ground level. Grass Forage Sci. 38:295–300. NRC. 1996. Nutrient Requirements of Beef Cattle. 7th ed. Natl. Acad. Press, Washington, DC. Patterson, D. J., R. C. Perry, G. H. Kiracofe, R. A. Bellows, R. B. Staigmiller, and L. R. Corah. 1992. Management considerations in heifer development and puberty. J. Anim. Sci. 70:4018–4035. Pence, M. R. BreDahl, and J. U. Thompson. 1999. Clinical use of reproductive tract scor-
626
Beck et al.
ing to predict pregnancy outcome. 1999 Beef Res. Rep., A. S. Leaflet R1656. Iowa State Univ., Ames.
Pages 69–70 in 1996 Nebraska Beef Cattle Report, Rep. No. MP66-A. Univ. Nebraska, Lincoln.
Poos, M. I., T. I. Hanson, and T. J. Klopfenstein. 1979. Monensin effects on diet digestibility, ruminal protein bypass and microbial protein synthesis. J. Anim. Sci. 48:1516–1524. http://dx.doi.org/10.2134/jas1979.4861516x.
Schelling, G. T. 1984. Monensin mode of action in the rumen. J. Anim. Sci. 58:1518– 1527.
Stygar, A. H., A. R. Kristensen, and J. Mukulska. 2014. Optimal management of replacement heifers in a beef herd: A model for simultaneous optimization of rearing and breeding decisions. J. Anim. Sci. 92:3636– 3649. http://dx.doi.org/10.2527/jas.20107535.
Short, R. E., and R. A. Bellows. 1971. Relationships among weight gains, age at puberty and reproductive performance in heifers. J. Anim. Sci. 32:127–131. http://dx.doi. org/10.2134/jas1971.321127x.
Wiltbank, J. N., S. Roberts, J. Nix, and L. Rowden. 1985. Reproductive performance and profitability of heifers fed to weigh 272 or 318 kg at the start of the first breeding season. J. Anim. Sci. 60:25–34.
Rush, I., B. Weichenthal, and B. Van Pelt. 1996. Effects of Bovatec, Rumensin, or GainPro fed to yearling summer grazing steers.