Farmer, C. 2013. Review: Mammary development in swine: effects of hormonal status, nutrition and management. Can. J. Anim. Sci. 93: 1-7. There are three phases of rapid mammary accretion in swine, namely, from 90 d of age until puberty, during the last third of gestation and throughout lactation. Nutrition, endocrine status and management of gilts or sows during those periods can affect mammary development. More specifically, in growing gilts, feed restriction as of 90 d of age hinders mammary development and either supplying the phytoestrogen genistein or increasing circulating concentrations of prolactin stimulates mammogenesis. In late gestation, inhibition of relaxin or prolactin drastically diminishes mammary development and overly increasing dietary energy has a detrimental effect on mammogenesis. It also appears that feeding of the gestating sow can affect the mammary development of her offspring once it reaches puberty. Various management factors such as litter size, nursing intensity and use or non-use of a teat in the previous lactation will affect the amount of mammary tissue present at the end of lactation. Mammary development is followed by the essential process of involution whereby a rapid and drastic regression in parenchymal tissue takes place. It can occur either after weaning or in early lactation when teats are not being regularly suckled. Despite our current knowledge, much remains to be learned in order to develop the best management strategies for replacement gilts, and gestating and lactating sows that will maximize their milk production.

Woyengo, T. A. and Nyachoti, C. M. 2013. Review: Anti-nutritional effects of phytic acid in diets for pigs and poultry - current knowledge and directions for future research. Can. J. Anim. Sci. 93: 9-21. Plant feedstuffs contain phytic acid (PA), which is a storage form of phosphorus. Phytic acid is, however, poorly hydrolyzed by pigs and poultry, and it has a capacity to complex dietary nutrients, thereby reducing nutrient digestibility. Reduced nutrient digestibility by PA implies reduced efficiency of utilization of the nutrients and increased discharge of the unabsorbed nutrients to the environment. Phytic acid has also recently been shown to increase the endogenous nutrient losses (ENL) in pigs and poultry. Because the increased ENL in the gastrointestinal tract are associated with increased maintenance requirement for the lost nutrients and of energy spent on their secretion, an increase in ENL due to PA implies that there are other adverse effects of PA on nutrient utilization in addition to reducing nutrient digestibility. In this review, the effects of PA on performance of pigs and poultry, and on the digestibility and ENL in these animals are discussed in detail. Also, the mechanisms by which PA reduces nutrient digestibility and increases gastrointestinal ENL in pigs and poultry are discussed, and areas that need further research to gain more insight into these mechanisms are suggested.

Barge, P., Gay, P., Merlino, V. and Tortia, C. 2013. Radio frequency identification technologies for livestock management and meat supply chain traceability. Can. J. Anim. Sci. 93: 23-33. Animal electronic identification could be exploited by farmers as an interesting opportunity to increase the efficiency of herd management and traceability. Although radio frequency identification (RFID) solutions for animal identification have already been envisaged, the integration of a RFID traceability system at farm level has to be carried out carefully, considering different aspects (farm type, number and species of animals, barn structure). The tag persistence on the animal after application, the tag-to-tag collisions in the case of many animals contemporarily present in the reading area of the same antenna and the barn layout play determinant roles in system reliability. The goal of this paper is to evaluate the RFID identification system performance and determine the best practice to apply these devices in livestock management. RFID systems were tested both in laboratory, on the farm and in slaughterhouses for the implementation of a traceability system with automatic animal data capture. For this purpose a complete system for animal identification and tracking, accomplishing regulatory compliance as well as supply chain management requirements, has been developed and is described in the paper. Results were encouraging for identification of calves both in farms and slaughterhouses, while in swine breeding, identification was critical for small piglets. In this case, the design of a RFID gate where tag-to-tag collisions are avoided should be envisaged.

Bøe, K. E. and Ehrlenbruch, R. 2013. Thermoregulatory behavior of dairy goats at low temperatures and the use of outdoor yards. Can. J. Anim. Sci. 93: 35-41. The aim of this experiment was to investigate the effect of roof cover and location of feed on thermoregulatory behavior and the goat's use of an outdoor yard under different weather conditions. A total of four groups of five pregnant dairy goats (20 goats in total) were allocated to a 4×4 Latin square experiment with four groups, four treatments and four experimental periods. Each treatment period lasted for 7 d. The goats were exposed to the following treatments: roof covering of outdoor yard (yes or no) and location of feed (indoors or in yard). The goats were video recorded for two 24-h periods at the end of each experimental period (totally 32, 24-h periods). When the air temperature dropped and when there was rain or snow, the goats spent less time in the outdoor yard (P<0.0001), but total lying time (P=0.47) and time spent feeding (P=0.77) were not affected by weather conditions. Lying in the outdoor yard was reduced as the air temperature decreased (P<0.001) and time spent standing/walking inside increased (P<0.001). Irrespective of weather conditions, the goats spent significantly more time in the outdoor yard in pens when the outdoor yards were covered with a roof (P <0.01), but time spent lying was not affected by roof cover (P=0.12) or feed location (P=0.40). We conclude that even if the outdoor yard was less used at decreasing temperatures, the time spent lying and feeding was not affected by inclement weather. Hence, a housing system with an inside resting area and an outside activity area provides adequate environmental protection for the goats even at low temperatures. A roof covering the outdoor yard had only a limited positive effect.

Correa, J. A., Gonyou, H. W., Torrey, S., Widowski, T., Bergeron, R., Crowe, T. G., Laforest, J. P. and Faucitano, L. 2013. Welfare and carcass and meat quality of pigs being transported for two hours using two vehicle types during two seasons of the year. Can. J. Anim. Sci. 93: 43-55. A total of 3756 pigs were transported for 2 h in summer and winter using a “pot-belly” trailer (PB) and a hydraulic double-decked truck (DD) in order to assess the effect of vehicle design on animal welfare and carcass and meat quality. Animal welfare was assessed in randomly selected barrows by measuring heart rate of pigs and lactate and creatine phospho-kinase (CPK) concentrations in exsanguination blood. Skin damage was scored and meat quality was evaluated in the longissimus dorsi (LD), semimembranosus (SM) and adductor (AD) muscles. Heart rates in winter were higher (P< 0.01) during transport, at unloading and in lairage. Blood CPK and lactate concentrations at slaughter were higher (P<0.05 and P<0.01, respectively) in pigs transported on the PB trailer. Bruises increased in winter (P<0.001) and in pigs from the DD truck (P<0.05). The pHu was higher (P< 0.01) in all muscles and L* value was lower (P<0.05) in the LD muscle from pigs transported in the PB trailer. Overall, the results of this study indicate that the type of vehicle, animal location in the truck and the season affect the welfare of pigs during transport with clear consequences on skin bruises and pork quality variation.

Li, Y. Z., Phillips, C. E., Wang, L. H., Xie, X. L., Baidoo, S. K., Shurson, G. C. and Johnston, L. J. 2013. Effects of distillers' dried grains with solubles on behavior of sows kept in a group-housed system with electronic sow feeders or individual stalls. Can. J. Anim. Sci. 93: 57-66. A study was conducted to investigate the effects of diets that contained distillers' dried grains with solubles (DDGS) on stereotypic behaviors of gestating sows housed in stalls and aggression in a group-housed system. Sows were fed corn-soybean-based control (CON) or treatment (DDGS) diets starting from their previous breeding cycle (40% and 20% DDGS as-fed basis during gestation and lactation, respectively). Group-housed sows were mixed in pens with an electronic sow feeder within 1 wk after mating. Behaviors of focal sows (n=27 in stalls, n=40 in pens) were video-recorded for a period of 24 h between 4 and 8 d after mating. Salivary cortisol levels were measured on 32 focal sows (n=16 in stalls, n=16 in pens) during the week before mating (week 0), 1 wk and 12 wk after mating. In pens, DDGS sows fought for longer periods (P=0.05), tended to fight more frequently (P=0.06), and had greater cortisol concentrations (P<0.001) at mixing compared with CON sows. In stalls, DDGS sows spent more time resting (P=0.02), less time performing stereotypies (P=0.05), and had lower cortisol concentrations (P=0.03) in week 12 compared with CON sows. These results indicate that DDGS diets may compromise the welfare of sows in pens, but improve the welfare of sows in stalls.

Maniatis, G., Demiris, N., Kranis, A., Banos, G. and Kominakis, A. 2013. Model comparison and estimation of genetic parameters for body weight in commercial broilers. Can. J. Anim. Sci. 93: 67-77. The availability of powerful computing and advances in algorithmic efficiency allow for the consideration of increasingly complex models. Consequently, the development and application of appropriate statistical procedures for model evaluation is becoming increasingly important. This paper is concerned with the application of an alternative model determination criterion (conditional Akaike Information Criterion, cAIC) in a large dataset comprising 203 323 body weights of broilers, pertaining to 7 (BW₇) and 35 (BW₃₅) days of age. Seven univariate and seven bivariate models were applied. Direct genetic, maternal genetic and maternal environmental (c²) effects were estimated via REML. The model evaluation criteria included conditional Akaike Information Criterion (cAIC), Bayesian Information Criterion (BIC) and the standard Akaike Information Criterion (henceforth marginal; mAIC). According to cAIC the best-fitting model included direct genetic, maternal genetic and c² effects. Maternal heritabilities were low (0.10 and 0.03) compared to the direct heritabilities (0.17 and 0.21), while c² was 0.05 and 0.04 for BW₇ and BW₃₅, respectively. BIC and mAIC favoured a model that additionally included a direct-maternal genetic covariance, resulting in highly negative direct-maternal genetic correlations (-0.47 and -0.64 for BW₇ and BW₃₅, respectively) and higher direct heritabilities (0.25 and 0.28 for BW₇ and BW₃₅, respectively). Results suggest that cAIC can select different animal models than mAIC and BIC with different biological properties.

Durunna, O. N., Mujibi, F. D. N., Nkrumah, D. J., Basarab, J. A., Okine, E. K., Moore, S. S. and Wang, Z. 2013. Genetic parameters for production and feeding behaviour traits in crossbred steers fed a finishing diet at different ages. Can. J. Anim. Sci. 93: 79-87. Because cattle can be raised postweaning under several feeding regimes, this study examined the consistency of phenotypic and genetic parameters of some production and feeding behaviour traits between two feeding periods that beef cattle received a finisher diet. Crossbred steers (n=851) were used for feeding trials from 2002 to 2009 where the steers received a finisher diet either during the fall-winter season (FP1) or during the winter-spring season (FP2). The steers evaluated in FP2 received a backgrounding diet in FP1. Traits examined include dry matter intake (DMI), average daily gain (ADG), gain: feed ratio (G:F), residual feed intake (RFI), and ultrasound measures of backfat thickness (UBF), rib-eye area (UREA) and marbling (UMB). Others include feeding duration (FD), headdown time (HDT) and feeding frequency (FF). As expected, there was no difference (P=0.90) between the RFI measured in the two periods. The two periods were similar for UBF (P=0.87) and UREA (P=0.25),while DMI, ADG and UMB were greater (P<0.04) in FP2 than in FP1. The FD, HDT and FF were greater (P<0.0001) in FP1 compared with FP2. Heritability estimates were calculated in FP1 and FP2, respectively, for ADG (0.38, 0.28), DMI (0.52, 0.42), RFI (0.16, 0.27), G:F (0.18, 0.33), HDT (0.35, 0.18) and FF (0.26, 0.46). More importantly, genetic correlations between FP1 and FP2 were estimated for DMI (0.61), RFI (0.65) and G:F (0.60). The results may indicate the influence of age or feeding period or both on these traits, which may suggest the need for multi-environment genetic evaluations to identify superior animals.

Juárez, M., Larsen, I. L., Klassen, M. and Aalhus, J. L. 2013. Canadian beef tenderness survey: 2001-2011. Can. J. Anim. Sci. 93: 89-97. A large survey across Canada was developed collecting retail beef samples in 2001 (702 steaks) and 2011 (602 steaks). The samples (strip loin, top sirloin, inside round and cross-rib steaks) were evaluated for instrumental tenderness using standard procedures for sampling, storage, cooking and texture evaluation. New equations were also developed in order to compare the results obtained in these studies with consumer thresholds developed in Canada and the United States of America. In general, retail steaks collected in 2011 weighed less and showed higher fat thickness than those from 2001. Regarding tenderness, a significant improvement was observed, especially for strip loin and top sirloin steaks between 2001 and 2011. Using US threshold categories, the percentage of “tender” samples improved for the strip loin (2001=89%; 2011=99%), top sirloin (2001=70%; 2011=87%), inside round (2001=52%; 2011=61%) and cross-rib (2001=65%; 2011=76%) steaks. Similarly, the percentage of “tough” samples shifted from 5, 8 27 and 13% for the strip loin, top sirloin, inside round and cross-rib steaks in 2001 to 1, 5, 13, and 8%, respectively, in 2011. Similar improvements were observed when using the more descriptive four-category Canadian threshold system. These improvements may be due to changes in the animal population, production systems, carcass processing and distribution/handling prior to display in Canada.

Rodas-González, A., Juárez, M., Robertson, W. M., Larsen, I. L. and Aalhus, J. L. 2013. Characterization of Canadian grade standards and lean yield prediction for cows. Can. J. Anim. Sci. 93: 99-107. Commercial carcasses (n=120) were selected to benchmark the current Canadian grading system for cows (D1, D2, D3, D4;>50% ossification) in comparison to A/AA grades youthful carcasses [over (OTM) and under (UTM) 30 mo of age based on dentition but <50% ossification]. With the exception of the D3 and D4 grades, D1 and D2 carcass grades had similar carcass yield attributes compared with OTM and UTM carcasses; however, rib-eye area from UTM carcasses was the largest (P<0.05), followed by D1, D2 and OTM. As expected, both OTM and UTM grades had lower ossification scores (P<0.05); however, D4 grade showed the highest marbling score (P<0.05). For carcass composition, compared with all other grades, the D3 grade had the highest proportion of lean (P<0.05) due to a lower proportion of dissectible fat (P<0.05); however, it had the lightest carcass weight (P<0.05). Using simple measures of carcass characteristics (grade fat, rib-eye area, marbling and ossification) a prediction equation to estimate lean yield (R²=0.825; Cp=4.31) could be used to more accurately assess carcass value in cows; however, validation of the equation on a separate population would be required before its application.

Quesnel, H., Ramaekers, P., van Hees, H. and Farmer, C. 2013. Short Communication: Relations between peripartum concentrations of prolactin and progesterone in sows and piglet growth in early lactation. Can. J. Anim. Sci. 93: 109-112. Postpartum hypogalactia has been suggested to be related to an impaired secretion of prolactin or to elevated concentrations of progesterone around farrowing. In the current study, peripartum circulating concentrations of prolactin and progesterone were determined in 50 multiparous sows (parities 1 to 5) and related to the Na K^-1 ratio and lactose in colostrum and to piglet growth in early lactation. An effect of parity (P<0.001) was observed for prolactin, with sows from parity 1 having lower concentrations than sows from parities 2, 3, 4 and 5, and sows from parities 4 and 5 having the greatest concentrations. Piglet growth from day 1 to day 5 was negatively correlated with progesterone concentrations in sows on day 1 (r=-0.36, P=0.01). The present study supports the hypothesis of a negative impact of high concentrations of progesterone after farrowing on early growth of piglets and also shows a clear effect of sow parity on the peripartum concentrations of prolactin suggesting that younger sows are more vulnerable to reduced milk yield due to lower prolactin concentrations.

Schinckel, A. P., Einstein, M. E., Ajuwon, K. M. and Adeola, O. 2013. Characterization of whole body compositional growth of male ducks during the twenty-nine day post-hatch period. Can. J. Anim. Sci. 93: 113–122. Changes in whole body dry matter, lipid, ash, energy, crude protein, and amino acids were evaluated during a 29 d post-hatch period in White Pekin ducks. Drakes were assigned to slaughter 1, 8, 15, 22, or 29 d post-hatch with four replicates of four ducks per slaughter period. The body weight (BW) data were fitted to the Weibull function with the form:

where BW_it is the BW of the ith duck at t days of age and A, B, C, and IP are parameters. The value of IP, the inflection point, which minimized the residual SD, was 40 d. Values of A (8591 g, SE=190), B (42.87, SE=11.5), and C (1.7399, SE=0.050) resulted in an R² of 0.9836 and residual SD of 83.7 g. Allometric (Y=A BW^B), linear-quadratic and exponential (Y=exp (b₀+b₁BW+b₂ (BW)²) functions of BW were fitted to the chemical component and amino acid mass data. Dry matter percentage of the ducks increased (P<0.01) with age. The protein content of the dry matter decreased (P<0.01) from day 1 to day 8 (69 to 58.2%) and then increased to 60% by d 29. Concentrations of several amino acids were affected (P<0.05) by age. The predicted accretion rates of Lys, Trp, and Met relative to protein accretion increased as age increased. The predicted daily accretion rates for major indispensable amino acids increased rapidly the first 5 d post-hatch and subsequently increased but at a decreasing rate to day 29 post-hatch. The relative growth rates of chemical components and indispensable amino acids were affected by age indicating that the nutrient requirements of ducks differ from day 1 to day 29 post-hatch. Compositional growth and amino acid accretion data can be used to model the nutrient requirements of ducks.

Davies, K. L., McKinnon, J. J. and Mutsvangwa, T. 2013. Effects of dietary ruminally degradable starch and ruminally degradable protein levels on urea recycling, microbial protein production, nitrogen balance, and duodenal nutrient flow in beef heifers fed low crude protein diets. Can. J. Anim. Sci. 93: 123-136. The objective was to determine the effects of ruminally degradable starch (RDS; 28.6 and 69.2% of total starch) and ruminally degradable protein [RDP; 48.0 and 55.0% of crude protein (CP)] content on urea recycling, nitrogen (N) balance, duodenal nutrient flow, and microbial protein production in beef heifers fed low CP (10%) diets. Four ruminally and duodenally cannulated beef heifers (723±57 kg body weight) were used in a 4×4 Latin square design with a 2×2 factorial arrangement of dietary treatments with 23-d periods. Jugular infusions of [¹⁵N¹⁵N]-urea (220 mg d^-1; 98 atom percent) were conducted for 4 d (days 18-22) to estimate urea kinetics, with total collection of faeces and urine. Proportions of [¹⁵N¹⁵N]- and [¹⁴N¹⁵N]-urea in urinary urea, and ¹⁵N enrichment in faeces were used to calculate urea kinetics. Ruminal microbial N production was estimated using ¹⁵N as a marker. Ruminal ammonia-N concentration was greater (P=0.01) in heifers fed high RDP as compared with those fed low RDP, and it was also greater (P=0.01) in heifers fed low RDS as compared with those fed high RDS. Microbial N flow to the duodenum increased as RDP level increased on the high RDS diet, but was not affected by RDP level on the low RDS diet (interaction; P=0.04). Urea-N entry rate and urea-N transfer to the gastrointestinal tract were similar (P>0.05) across diets. The amount of recycled urea-N incorporated into microbial N increased as RDP level increased on the high RDS diet, but the opposite was observed on the low RDS diet (interaction; P=0.008). These results indicate that at a low CP level (10%), increasing both RDS and RDP levels can increase microbial N flow to the duodenum and improve the efficiency of use of recycled urea-N for microbial N synthesis.

Chibisa, G. E., Christensen, D. A. and Mutsvangwa, T. 2013. Replacing canola meal as the major protein source with wheat dried distillers' grains alters omasal fatty acid flow and milk fatty acid composition in dairy cows. Can. J. Anim. Sci. 93: 137-147. Wheat dried distillers' grains with solubles (W-DDGS) has a high fat content and is now commonly fed to dairy cows in western Canada. The objective was to determine the effects of replacing canola meal (CM) with W-DDGS on omasal fatty acid (FA) flow and milk FA composition. Four ruminally-cannulated lactating dairy cows were used in a 4×4 Latin square design with 28-d periods. Cows were fed either a standard barley silage-based total mixed ration (TMR) (0% W-DDGS, control) or TMR containing 10, 15 and 20% W-DDGS, with W-DDGS replacing CM as the major protein source. The omasal flow of C18:1 trans-10, C18:1 trans-11, C18:2n-6, C18:3n-3, conjugated linoleic acid (CLA) cis-9, trans-11, and total CLA increased linearly with increasing levels of W-DDGS. There were quadratic changes in milk concentrations of total C18:2, C18:3n-3, total n-3 polyunsaturated fatty acid (PUFA), and total n-6 PUFA as the level of W-DDGS increased. Feeding increasing amounts of W-DDGS resulted in a linear increase in milk concentrations of CLA cis-9, trans-11, CLA trans-11, trans-13, and total CLA, whereas milk concentrations of C18:1 trans-11 tended to increase linearly when level of W-DDGS increased. Feeding increasing amounts of W-DDGS resulted in quadratic changes in milk concentrations of C18:2n-6 and C18:3n-3. In summary, feeding increasing amounts of W-DDGS increased milk concentrations of key FA like C18:2n-6, C18:3n-3, CLA cis-9, trans-11, and total CLA, which can potentially improve human health.

Mapiye, C., Dugan, M. E. R., Turner, T. D., Rolland, D. C., Basarab, J. A., Baron, V. S., McAllister, T. A., Block, H. C., Uttaro, B. and Aalhus, J. L. 2013. Short Communication: Erythrocytes assayed early ante mortem can predict adipose tissue and muscle trans-18:1 isomeric profiles of steers fed red clover silage supplemented with flaxseed. Can. J. Anim. Sci. 93: 149-153. Steers were fed a red clover silage-based diet with or without flaxseed to evaluate over time the effects of flaxseed supplementation on erythrocytes (ERC) trans(t)18:1 isomers composition and their relationships to adipose tissue and muscle t18:1 profiles at slaughter. Concentrations of most ERC t18:1 isomers in steers fed flaxseed increased (P<0.01) markedly in the first 2 mo and increased gradually thereafter. Strong (P<0.01) correlations of t9-, t10- and t11-18:1 isomers were observed from month 2 to 6 between ERC and beef tissues collected at slaughter from steers fed flaxseed. Findings suggest that ERC sampled as early as 2 mo into the feeding period can be indicative of variation in beef t18:1 isomeric profile at a later slaughter date when feeding red clover silage with flaxseed.

Jin, L., Wang, Y., Iwaasa, A. D., Xu, Z., Schellenberg, M. P., Zhang, Y. G. and McAllister, T. A. 2013. Short Communication: Effect of condensed tannin on in vitro ruminal fermentation of purple prairie clover (Dalea purpureaVent)-cool- season grass mixture. Can. J. Anim. Sci. 93: 155–158. Four purple prairie clover [Dalea purpurea Vent (PPC)]-/grass mixtures containing 7.3, 14.0, 29.3 and 42.1 g kg^-1 dry matter (DM) of condensed tannin (CT) were incubated with rumen fluid. As the CT increased, in vitro true dry matter disappearance (IVTDMD), production of volatile fatty acids (VFA) and microbial protein synthesis were linearly increased (P<0.05) at 12 h, and IVTDMD and VFA were quadratically increased (P<0.01) at 48-h incubation. Molar proportion of acetate was linearly increased (P<0.01) but propionate and butyrate were decreased (P<0.05) at both 12 and 48-h incubation. Incorporation of PPC into cool-season grass pasture up to CT content of 42 g kg^-1 DM improved ruminal fermentability and microbial protein synthesis in mixed forages.

Flesch, T. K., Vergé, X. P. C., Desjardins, R. L. and Worth, D. 2013. Methane emissions from a swine manure tank in western Canada. Can. J. Anim. Sci. 93: 159-169. The emission rate of methane (CH₄) to the atmosphere was measured from a concrete manure tank at a farrow-to-finish swine facility in western Canada. Measurements were made during four seasonal campaigns using a bLS inverse-dispersion technique. Emission rates were highest in summer and lowest in winter, with intermediate rates in spring and fall. Annual emissions were estimated at 7600 kg CH₄, or 6.3 kg CH₄ m^-2 of tank surface area. Site-specific factors used for estimating CH₄ emissions were calculated from our measurements. A simple methane conversion factor, used by the Intergovernmental Panel on Climate Change to relate emissions to the volatile solids content of the manure, was calculated as 0.23. This value may be unrepresentatively high due to the long duration (15 mo) that manure was stored in the tank. A more sophisticated calculation methodology considers the influence of manure storage duration and temperature, and includes a critical management design practices (MDP) factor. The MDP factor was calculated as 0.31 for our tank. This MDP value implies that emissions from our manure tank were lower than expected given the results from other studies.

López-Campos, Ó., Aalhus, J. L., Okine, E. K., Baron, V. S. and Basarab, J. A. 2013. Effects of calf- and yearling-fed beef production systems and growth promotants on production and profitability. Can. J. Anim. Sci. 93: 171–184. In each of 2 yr, 112 spring-born steers were used to evaluate the effect of calf-fed vs. yearling-fed with and without growth implant and ß-adrenergic agonist on production parameters and economic potential. Steers were grouped into: (1) non-implanted feeders harvested at 11-14 mo of age, (2) growth implanted feeders harvested at 11-14 mo of age, (3) non-implanted feeders harvested at 19-23 mo of age, and (4) growth implanted feeders harvested at 19-23 mo of age. Production data were collected and economic evaluation was performed. Calf-fed steers grew slower (1.21 vs. 1.99±0.07 kg d^-1) and had a poorer feed conversion ratio [5.32 vs. 4.99±0.34 kg dry matter intake (DMI) kg^-1 gain] during the feedlot dietary adjustment period than yearling-fed. Calf-fed steers were more efficient than yearling-fed during the first 76-83 d (5.16 vs. 7.33±0.11 kg DMI kg^-1 gain) and latter 48-79 d (5.69 vs. 14.28±1.50 kg DMI kg^-1 gain) of the finishing period. Implanted steers were more efficient than non-implanted during the dietary feedlot adjustment period (4.80 vs. 5.52±0.15 kg DMI kg^-1 gain), and during the first 76-83 d (6.05 vs. 6.44±0.11 kg DMI kg^-1 gain) and latter 48-79 d of the finishing period (9.29 vs. 10.69±1.50 kg DMI kg^-1 gain). Implanted steers grew 11.4-19.6% faster than non-implanted throughout the finishing period, while yearling-fed grew 11.1-12.9% faster during the first 76-83 d, but 49.1-64.4% slower during the last 48-79 d of the finishing period compared with calf-fed. Quality grade was improved for non-implanted steers, with 43.6% of yearling-fed and 35.7% calf-fed steers grading AAA. Adjusted net return was best for calf-fed implanted ($17.52 head^-1), followed by calf-fed non-implanted ($-41.92 head^-1), yearling-fed implanted ($-73.77 head^-1), and yearling-fed non-implanted ($-99.65 head^-1) production strategies. The results of the present study suggest that reducing age at slaughter combined with growth implant can increase profit and reduce risk, but growth implants can negatively affect the carcass quality.