Effect of ractopamine on digestible-lysine requirement for finishing barrows under thermoneutral conditions

The purpose of the present study was to determine the digestible-lysine (Lys) requirement in diets supplemented or not with ractopamine (RAC), so as to maximise performance and carcass characteristics for finishing barrows reared at thermoneutral conditions. In total, 128 high-lean commercial hybrid barrows with an initial bodyweight of 78.2 ± 4.3 kg were distributed in a completely randomised block design, in a 4 × 2 factorial arrangement (four Lys concentrations: 0.730%, 0.830%, 0.930% and 1.030% and two RAC inclusions: 0 and 10 mg/kg), with two animals per pen and eight pens per treatment. Lys concentrations tested significantly (P < 0.05) affected digestible-lysine intake, and the absolute (g) and relative (%) lean meat content, regardless of RAC inclusion. When diets were RAC-supplemented, feed conversion rate of animals was improved and, in addition, final bodyweight, daily bodyweight gain, loin eye area, loin eye depth, and absolute (g) and relative (%) carcass lean meat content increased (P < 0.05). RAC inclusion also decreased (P < 0.05) backfat thickness and the colour values a* and b* of finishing pigs. Therefore, on the basis of our results, it can be inferred that the best performance and carcass characteristics for finishing barrows reared at thermoneutral conditions were obtained at 1.030% and 0.730% Lys respectively, corresponding to an estimated daily Lys intake of 34.3 g and 24.2 g, independently of the diet RAC concentration.

A multivariate approach to determine the factors affecting response level of growth, carcass, and meat quality traits in finishing pigs fed ractopamine

The effect of ractopamine (RAC) supplementation on growth, carcass, and meat quality traits of finishing pigs was studied using a meta-analytical approach. The database was composed of 57 studies published from 2004 to 2016. The dependent variables extracted for the meta-analysis included final BW, ADG, ADFI, feed:gain ratio, HCW, dressing percentage, carcass length, lean yield, back fat thickness, loin muscle area, loin depth, postmortem pH, meat brightness, redness, and yellowness. The studies were grouped by similarity in 3 clusters (C1, C2, and C3) by hierarchical clustering on principle components. The main differences observed between clusters were those of animal initial weight, which increased from C1 through C3. Linear mixed models were used to analyze the data, where studies were assumed as random effect, whereas the total amount of RAC in the diet, cluster, and sex category were considered fixed effects. The interactions between cluster and sex category (barrows, gilts, and mixed sex) and RAC level were also evaluated. Dietary RAC was effective in improving final weight ( < 0.0001), ADG ( < 0.0001), and feed:gain ratio ( < 0.0001) and had a positive effect on HCW ( < 0.0001), lean yield ( = 0.0081), loin muscle area ( = 0.0190), and loin depth ( < 0.0001). In addition, a relatively limited effect on pork quality was observed in the current study. The RAC supplementation was more effective, mainly when pigs started supplementation with higher initial weight, although different responses were observed according to sex category ( < 0.05). There is ample indication that growth and carcass traits could be improved by dietary RAC supplementation. Ractopamine supplementation did not influence the pork quality.

Physical meat quality and chemical composition of the Longissimus thoracis of entire and immunocastrated pigs fed varying dietary protein levels with and without ractopamine hydrochloride

Physical and chemical attributes of the Longissimus thoracis (LT) of 96 PIC(©) entire (E) and immunocastrated (C) pigs were evaluated. The study followed a 2 × 2 × 3 factorial design where three diets of low, medium and high proteins (7.50, 9.79 and 12.07 g digestible lysine/kg) were fed either with (10mg/kg) or without ractopamine (RAC) for the last 28 days of growth. Vaccination of C occurred at 16 and 20 weeks and slaughtering at 24 weeks of age. The LTs were analysed for moisture, protein, fat and ash contents as well as CIE L*, a*, b* colour, drip loss, cooking loss and Warner-Bratzler shear force (WBSF). Various sex and protein interactions were observed for LT protein content, L* values and WBSF. Cooking loss was decreased in C and by the medium protein diet. Feeding RAC increased WBSF values, whilst decreasing a* and b* values. However, the differences observed are minor and might be considered negligible when evaluated by a consumer.

Effect of dietary zinc and ractopamine hydrochloride on pork chop muscle fiber type distribution, tenderness, and color characteristics

A total of 320 finishing pigs (PIC 327 × 1050; initially 98 kg) were used to determine the effects of adding Zn to diets containing ractopamine HCl (RAC) on muscle fiber type distribution, fresh chop color, and cooked meat characteristics. Dietary treatments were fed for approximately 35 d and consisted of a corn-soybean meal-based negative control (CON), a positive control diet with 10 mg/kg of RAC (RAC+), and the RAC+ diet plus 75, 150, or 225 mg/kg added Zn from either ZnO or Availa-Zn. Loins randomly selected from each treatment (n = 20) were evaluated using contrasts: CON vs. RAC+, interaction of Zn level × source, Zn level linear and quadratic polynomials, and Zn source. There were no Zn source effects or Zn source × level interactions throughout the study (P > 0.10). Pigs fed RAC+ had increased (P < 0.02) percentage type IIX and a tendency for increased (P = 0.10) percent type IIB muscle fibers. Increasing added Zn decreased (linear, P = 0.01) percentage type IIA and tended to increase (P = 0.09) IIX muscle fibers. On d 1, 2, 3, 4, and 5 of display, pork chops from pigs fed the RAC+ treatment had greater (P < 0.03) L* values compared to the CON. On d 0 and 3 of display, increasing added Zn tended to decrease (quadratic, P = 0.10) L* values and decreased (quadratic, P < 0.03) L* values on d 1, 2, 4, and 5. Pigs fed RAC+ had decreased (P < 0.05) a* values on d 1 and 4 of display and tended to have decreased (P < 0.10) a* values on d 0 and 2 compared to CON pork chops. Pork chops from the RAC+ treatment had a tendency for increased (P < 0.08) oxymyoglobin percentage compared to CON pork chops on d 1, 2, 4, and 5. On d 0, as dietary Zn increased in RAC+ diets, there was a decrease (linear, P < 0.01) in the formation of pork chop surface oxymyoglobin percentage. Metmyoglobin reducing ability (MRA) of pork chops on d 5 was decreased in the RAC+ group. Chops from pigs fed added Zn had increased (quadratic, P < 0.03) MRA on d 3 and 5 of the display period. There was a trend for increased (linear, P = 0.07) cooking loss with increasing Zn in RAC diets and treatments did not affect tenderness as measured by Warner-Bratzler shear force (P > 0.07). In conclusion, RAC+ diets produced chops that were lighter and less red but maintained a greater percentage of surface oxymyoglobin throughout a 5-d simulated retail display. Ractopamine reduced MRA at the end of the display period, but supplementing Zn to RAC diets restored MRA to near CON treatment levels at the end of the display period.