Performance assessment of feedlot cattle receiving two or three implants

Our objective was to evaluate two implant strategies on feedlot cattle performance. A total of 45 pens were randomly assigned to one of two implant strategies (two or three implants) in a randomized complete block experimental design. Each pen had 60 bulls with average initial weight of 277.6 ± 8.1 kg (range = 255–289 kg) and fed for 180 days. Bulls were implanted (100 mg trenbolone acetate–14 mg 17β-estradiol benzoate; Synovex^® Choice) at the start of the experiment and re-implanted (200 mg trenbolone acetate–20 mg 17β-estradiol; Revalor^® H) after 90 days (two implants; Synovex^® Choice–Revalor^® H) or at 60 and 120 days (three implants; Synovex^® Choice–Revalor^® H–Revalor^® H) on feed. The measured performance indicators were the average daily gain (ADG), the dry matter intake (DMI), and the feed efficiency expressed as the gain-to-feed (G/F) ratio or the feed conversion ratio (FCR). Linear mixed model analyses included the treatment (implant strategy) and the covariate average initial weight as the fixed effects and block (2-week feedlot entry period) as the random effect. Treatment affected all performance measures (p < 0.01) except for ADG (p = 0.08). Pens of cattle administered two implants had greater DMI (9.54 ± 0.09 vs. 9.16 ± 0.10 kg/day p < 0.01) than pens of cattle administered three implants. Pens of cattle administered three implants had greater G/F ratio (0.160 ± 0.002 vs. 0.172 ± 0.002, p < 0.01) and smaller FCR (6.25 ± 0.08 vs. 5.82 ± 0.08, p < 0.01) than pens of cattle administered two implants. For cattle fed approximately 180 days in feedlot, a strategy with three instead of two implants increased the feed efficiency (~7.4%) without affecting the ADG, helping to improve profitability.

1 Introduction

Anabolic implants are an efficient technology to improve feedlot cattle growth rate, feed efficiency, and lean tissue accretion. The most likely mechanisms of anabolic implants are increased growth hormone and insulin-like growth factor-1 secretion, increased satellite cell proliferation, and enhanced response of skeletal muscle satellite cells to growth factors (Preston, 1999). Anabolic implants are approved as safe for both cattle and consumers by the Food and Drug Administration (FDA) in the United States and the Veterinary Drug Directorate in Canada (NASEM, 2016). In feedlot cattle, anabolic implants, dependent on the type and number, have the potential to increase the growth rate by up to 28% and improve the feed efficiency by up to 20% (Duckett and Andrae, 2001; Smith and Johnson, 2020; Nichols et al., 2002). In general, the dry matter intake (DMI) and the average daily gain (ADG) are increased in implanted cattle. Proportionally, ADG is increased to a greater degree than DMI; hence, the feed efficiency is enhanced (NASEM, 2016).

The active ingredients in implants include estrogens, androgens, and progesterone. Guiroy et al. (2002) concluded that combining estradiol with trenbolone acetate in implants is the most effective combination; therefore, this combination is widely used. The optimal implant strategy is dependent on the targeted performance and the carcass quality objectives. Because implants increase lean tissue accretion, the proportion of carcasses grading USDA Low Choice or higher typically decreases (Martinez et al., 2023). This reduction in quality grade becomes more pronounced with an increased number of implants or with higher anabolic agent doses (Guiroy et al., 2002). Reinhart and Wagner (2014) conducted a meta-analysis and reported that anabolic implants increased the dressing percentage by 0.10% and decreased the proportion of carcasses grading Choice or Prime by 10.1% relative to the non-implanted controls.

Central Mexico consumers prefer lean beef; therefore, producers are incentivized to utilize implants because they improve the feedlot performance and produce lean carcasses. We hypothesize that employing three instead of two implants would increase the growth rate and feed efficiency in cattle fed for 180 days. The objective of this research study was to assess the feedlot performance of cattle fed for 180 days and receiving two or three anabolic implants.

2 Materials and methods

All experimental procedures were approved by the Corrales el 3 Animal Care and Use Committee (protocol 003) and followed the standards described by the Guide for the Care and Use of Animals in Research and Teaching, third edition (FASS, 2010).

2.1 Data

The bulls in this study were bought from a single stocker in Southern Mexico in August and September 2017. Two-week feedlot entry periods were treated as blocking factors in the analyses. The bulls were weighed at the origin location (full initial weight) and shipped 9 h to a feedlot in Central Mexico (Belem, Estado de Mexico, Mexico), where the experiment was conducted. Upon feedlot arrival, the bulls were weighed (to estimate the weight shrinkage due to the trip). A total of 2,700 bulls weighing between 255 and 289 kg were allocated to pens based on random chute order, and a total of 45 pens were grouped over 2 months (August–September 2017). All bulls were implanted (100 mg trenbolone acetate/14 mg 17β-estradiol benzoate; Synovex^® Choice, Zoetis, Florham Park, NJ, USA) at the first day on feed, and that same day, pens were randomly assigned to one of two treatments: re-implanted (200 mg trenbolone acetate/20 mg 17β-estradiol benzoate; Revalor^® H, Merck & Co., Inc., Kenilworth, NJ, USA) on day 90 (two-implant treatment; Synovex^® Choice–Revalor^® H) or re-implanted on day 60 and day 120 (three-implant treatment; Synovex^® Choice–Revalor^® H–Revalor^® H). In summary, the data were generated from an unbalanced randomized completely block design with two treatments. There were 23 pens assigned to the two-implant treatment and 22 pens to the three-implant treatment.

Cattle were initiated on the feeding program on the same day of arrival. Bulls were fed alfalfa hay for the first 3 days on feed. Thereafter, the bulls were gradually adapted over a 4-week period to a high-energy ration based on steam-flaked corn. Three rations were used during the adaptation period, and each ration was provided to the bulls approximately during 10 days. All rations were formulated to fulfill or exceed the National Academies of Sciences, Engineering, and Medicine (2016) energy, protein, mineral, and vitamin guidelines. The net energy for maintenance (NEm) [net energy for gain (NEg)] of the finishing diet was 1.98 (1.30) Mcal kg⁻¹, which contained 35 ppm monensin (Rumensin; Elanco Animal Health, Inc., Greenfield, IN, USA), 500 ppb chromium propionate (Phi-Chrome 10×; Phibro Animal Health Corporation, Guadalajara, JA 44130, Mexico), and 250 ppm virginiamycin (Stafac 500; Phibro Animal Health Corporation, Guadalajara, Mexico).

The total mixed rations were delivered twice daily. The first feeding service (morning), conducted between 0700 and 0900 hours, provided 30% of the total daily allotment. The second feeding service (afternoon) supplied the remaining 70% of the daily allotment and was performed from 1600 to 1800 hours. A slick feed bunk feeding strategy was used, and feed bunk scores were evaluated visually and recorded every day from 0600 to 0700 hours. All pens were equipped with feed bunks covered by galvanized metal roofing, offering approximately 10 m of linear shade at a height of ~5 m. The flooring was solid, with 2 m of concrete floor around the waterers and feed bunks. In all pens, the stocking density was 10 m² per bull, the feed bunk space was 40 cm per bull, and automatic waterers (two per pen) always had potable and fresh water.

After 24 h of arrival at the feedlot, bulls received a vaccine for infectious bovine rhinotracheitis (IBR), bovine viral diarrhea (BVD) types 1 and 2, bovine respiratory syncytial virus (BRSV), parainfluenza 3 (PI3), and Mannheimia haemolytica (Bovi-Shield Gold One Shot; Zoetis, Florham Park, NJ, USA). An intranasal vaccine for IBR and PI3 (TSV-2; Zoetis, Florham Park, NJ, USA) and a vaccine for Clostridium chauvoei, Clostridium septicum, Clostridium novyi, Clostridium sordellii, and Clostridium perfringens types C and D plus Haemophilus somnus (Ultrabac 7/Somubac; Zoetis, Florham Park, NJ, USA) were also given. Cattle were also treated for internal and external parasites (Baymec Prolong; Elanco Animal Health, Inc., Greenfield, IN, USA), injected with vitamins A, D, and E (Vigantol ADE; Elanco Animal Health, Inc., Greenfield, IN, USA), and implanted as previously mentioned.

The following variables were recorded per pen: the average daily DMI (in kilograms per day), the ADG per animal (in kilograms per day, calculated based on the full initial and final weights), the gain-to-feed (G/F) ratio (ADG/DMI), and the feed conversion ratio (FCR; DMI/ADG). Pens were fed for 180 days and harvested in February and March 2018.

2.2 Statistical analysis

Data were analyzed using a linear mixed model with pen as the experimental unit. Treatment and average initial weight were the fixed effects, and the 2-week feedlot entry periods were the blocking factors fitted as random effects. Data were analyzed with the GLIMMIX procedure of SAS (SAS Institute Inc., Cary, NC, USA). Pairwise comparisons between the least squares means were computed using the PDIFF option of the LSMEANS statement. Differences were considered statistically significant at p < 0.05. The following statistical model was fitted to the response variables analyzed:

$$y_{ijkl}={\beta }_0+{\beta }_1{x}_{ijk}+{\tau }_i+b_j+e_{ijkl}$$

where $y_{ijkl}$ is the $l^{\text{th}}$ record (i.e., DMI, ADG, G/F ratio, and FCR) for pen $k$ in block $j$ receiving treatment $i$; ${\beta }_0$ is the intercept; ${\beta }_1$ is the regression coefficient associated with the average initial weight; $x_{ijk}$ is the covariate average initial weight for pen $k$ in block $j$ receiving treatment $i$; ${\tau }_i$ is the fixed effect of treatment $i$; $b_j$ is the random effect of block ~NIID (0, ${\sigma }_b^2$); and $e_{ijk}$ is the residual ~NIID (0, ${\sigma }_e^2$).

3 Results

Pens assigned to the two treatments did not differ in average initial weight (p = 0.81). There were no treatment effects on the average final weight or ADG (p ≥ 0.06). Pens of cattle receiving two implants had greater DMI (9.54 ± 0.09 vs. 9.16 ± 0.10 kg/day) and FCR (6.25 ± 0.08 vs. 5.82 ± 0.08) than pens of cattle receiving three implants (p < 0.01). The G/F ratio (0.160 ± 0.002 vs. 0.172 ± 0.002) was greater (p < 0.01) for pens of cattle implanted three times compared with that of pens of cattle implanted twice. The least squares means are presented in Table 1.

Table 1

Table 1. Results of the statistical analyses.

The contrasts of the least squares means between the two- and three-implant treatments (i.e., 2 − 3 implants) were 0.38 ± 0.14 ($df$ = 38.2, $t$ = 2.78, CI = 0.11–0.65, p < 0.01), −0.04 ± 0.03 ($df$ = 38.2, $t$ = −1.72, CI = −0.10 to 0.01, p = 0.09), 0.43 ± 0.09 ($df$ = 38.1, $t$ = 4.63, CI = 0.25–0.61, p < 0.01), and −0.011 ± 0.002 ($df$ = 38.1, $t$ = −4.88, CI = −0.02 to −0.01, p < 0.01) for the DMI, ADG, FCR, and G/F ratio, respectively. Figure 1 summarizes the raw data, least squares means, and contrasts.

Figure 1

Figure 1. Distribution of raw data in box plots; least squares means, with lines representing 95% confidence intervals; and estimates for contrasts (2 − 3 implants) of the least squares means, with lines representing 95% confidence intervals for the dry matter intake (A), average daily gain (B), feed conversion ratio (C), and the gain- to-feed (G/F) ratio (D).

4 Discussion

Numerous studies have reported that anabolic implant administration increases the growth rate, protein deposition, and cattle value while, at the same time, reducing the production costs (Montgomery et al., 2001; Duckett and Andrae, 2001) and environmental impacts (Lean et al., 2018; Crawford et al., 2022). Implanting technology can be applied in different phases of beef production. However, growth-promoting technology use is very common during the finishing phase, the aim of which is to maximize the productivity, efficiency, and return on investment (Duckett and Andrae, 2001; Montgomery et al., 2001). To meet the global beef demand, it is necessary for the production systems to become more efficient (Parr et al., 2016) while, at the same time, producing a high-quality product. In this way, the use of anabolic implants can contribute to improving animal efficiency and to meeting the global demand.

In the current study, feedlot cattle fed 180 days and administered three instead of two doses of anabolic growth promoters had better production efficiency. Specifically, pens of cattle receiving three implants had a reduced DMI (~4.1%) and a greater feed efficiency (~7.4%) than pens of cattle with two implants. In previous studies, implanted animals showed greater ADG (Guiroy et al., 2002; Smith and Johnson, 2020) and G/F ratio (Smith and Johnson, 2020) when compared with non-implanted animals. In general, improvements ranging from 8% to 28% for ADG and from 5% to 20% for the G/F ratio (Duckett et al., 1996; Smith and Johnson, 2020; Nichols et al., 2002) were reported. The observed response in feed efficiency in our study agrees with results from previous research. Nevertheless, in the current study, the treatment effect was not significant for the average final weight or the ADG. However, a possible explanation is that we compared two vs. three implants, while the majority of the previous studies contrasted implanted vs. non-implanted cattle.

In a study with steers, Martinez et al. (2023) compared a single (S1) extended-release implant (Revalor-XS; 40 mg of 17β-estradiol and 200 mg of TBA; Merck Animal Health, Rahway, NJ, USA) with two re-implant programs [the extended-release implant plus a second conventional implant (Revalor-200; 20 mg of 17β-estradiol and 200 mg of TBA; Merck Animal Health, Rahway, NJ, USA)] at either 120 days on feed (S2) or 80 days before slaughter (S3). In the study by Martinez et al. (2023), the single extended-release program (S1) is similar to our two-implant program, and their re-implant scenarios (S2 and S3) are similar to our three-implant program. In their study, the ADG did not differ among pens with different implant strategies [1.73 (S1) vs. 1.76 (S2) vs. 1.76 (S3) kg/animal per day, p = 0.98], while the G/F ratio was improved [0.167 (S1) vs. 0.173 (S2) vs. 0.172 (S3), p > 0.01] and the DMI was decreased [10.37 (S1) vs. 10.20 (S2) vs. 10.21 (S3) kg/animal per day, p > 0.01] in pens of cattle receiving the re-implant strategies compared with the pens of cattle with an extended-release implant, in agreement with our results.

Elaborating on the theory developed by Lobley et al. (1985); Martinez et al. (2023) concluded that, as trenbolone acetate minimizes protein degradation, a greater hormone supply improved the energy efficiency and, thus, the G/F ratio. This supports our results: even when the pens of cattle with two or three implants did not differ in terms of the average final weight or ADG, the G/F ratio and FCR were improved for the pens of cattle receiving three implants.

Similar outcomes were reported by Schumacher et al. (2019) in heifers when comparing two implant strategies: a single delayed- and extended-release implant containing 200 mg of trenbolone acetate and 28 mg of estradiol benzoate (Synovex One Feedlot, ONE; Zoetis, Florham Park, NJ, USA) and a two-implant program consisting of an initial implant containing 100 mg of trenbolone acetate and 14 mg of estradiol benzoate (Synovex Choice; Zoetis, Florham Park, NJ, USA), followed by a terminal implant containing 200 mg of trenbolone acetate and 28 mg of estradiol benzoate (Synovex Plus, CHO/PLU; Zoetis, Florham Park, NJ, USA). The carcass-adjusted final weight [618 (ONE) vs. 622 kg/day (CHO/PLU), p = 0.13] or the ADG [1.69 (ONE) vs. 1.71 kg/day (CHO/PLU), p = 0.13] did not differ between strategies; however, the DMI was reduced [11.6 vs. 11.3 kg/day, p < 0.01] and the carcass-adjusted G/F ratio improved (0.157 vs. 0.161, p < 0.01) for heifers receiving the two-implant strategy, which delivered a greater overall hormonal dose.

Kayser et al. (2022) reported that the implant dose affected the steer and heifer G/F ratio more than the ADG. Similarly, Lean et al. (2018) concluded that the effect on cattle productivity and efficiency was dependent on the type and number of implants used, as well as on the nutritional status of cattle. The type of implant differs in relation to the hormone category used: androgens, estrogens, and progestins (Motsinger and Gonzalez, 2023). In general, the use of estrogenic implants is recommended for bulls and that of androgenic implants for heifers (Dikeman, 2007). In this study, cattle were administered implants containing a combination of trenbolone acetate and 17β-estradiol benzoate, with the doses specified in Section 2.

The need to increase the number of re-implants primarily stems from the limited duration of action of growth promoters, which typically lasts between 60 and 120 days (Hilscher et al., 2016), being insufficient to sustain its effect on performance throughout the entire finishing period required to reach target slaughter weights. In addition, consumers in Central Mexico prefer lean beef, incentivizing the use of more implants as this will favor muscle deposition and reduce fat deposition.

5 Conclusions

In this study, pens of cattle fed approximately 180 days in feedlot and implanted three times had a decreased DMI (~4.1%) and an improved feed efficiency (~7.4%), but without a difference on the ADG, compared with pens of cattle implanted twice. The improvement in feed efficiency could help to increase the profitability in feedlots.

Data availability statement

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

Ethics statement

The animal study was approved by Corrales el 3 Animal Care and Use Committee. The study was conducted in accordance with the local legislation and institutional requirements.

Author contributions

JH: Formal analysis, Data curation, Methodology, Visualization, Conceptualization, Writing – original draft, Writing – review & editing, Investigation, Software. JG: Visualization, Formal analysis, Conceptualization, Methodology, Data curation, Writing – review & editing, Writing – original draft. ML: Writing – review & editing, Writing – original draft. AC: Writing – review & editing, Writing – original draft. AA: Writing – review & editing, Writing – original draft. ME: Writing – original draft, Writing – review & editing. RS: Writing – original draft, Writing – review & editing. ET: Writing – original draft, Writing – review & editing. JG: Formal analysis, Methodology, Writing – review & editing, Writing – original draft, Conceptualization.

Funding

The author(s) declared that financial support was not received for this work and/or its publication.

Acknowledgments

We gratefully acknowledge the data availability from Corrales el 3. Mention of trade names or commercial products in this article solely provides specific information and does not imply recommendation or endorsement by the authors.

Conflict of interest

Author ME was employed by the company Corrales el 3, S. A. de C. V. Author RS was employed by company Nutrientes Basicos de Monterrey, S.A. de C.V.

The remaining author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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The author(s) declare that Generative AI was not used in the creation of this manuscript.

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