The use of different anabolic agents in gilts
Dias, Geraldo Paulino
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24 Crossbred gilts (Large White x Landrace) purchased as weaners were randomly allocated to four treatment groups (n = 6) and submitted for an observation period of three phases: Phase I, in which the animals were treated with anabolic agents (nandrolone, clenbuterol, zeranol); Phase 2, could be seen as the anabolic agent clearance period; and Phase 3, in which certain carcass characteristics and meat quality parameters were measured. The trial was aimed to compare the effect of the different anabolic agents zeranol (implants of 36 mg/pig, every three weeks, for 9 weeks), clenbuterol (daily oral dose of 0.5 mg/pig, for 9 weeks) and nandrolone (intramuscularly injected, 50 rng/pig, every ,3 weeks, for a period of 9 weeks), on growth rate parameters, carcass and meat characteristics, visceral organ growth and blood concentrations of urea, glucose, creatinine, oestradiol and the hematocrit. The gilts were individually housed and fed a pig growth diet (16% crude protein) ad libitum, with free access to water. Body weight of all animals were recorded every 48 hours to monitor the average daily gain (ADG) and the growth rate up to the target liveweight of 85 kg. Weekly feed intake was monitored and the feed conversion rate (FCR) determined for the individual animals and the mean of the groups. Backfat thickness (P2) and eye muscle diameter were measured weekly with the aid of a sonar apparatus in all animals, to monitor the deposition of fat and lean muscle. Blood was sampled weekly from 4 specific animals per group for the determination of hematocrit, blood urea, blood glucose, blood creatinine and blood oestradiol concentrations. The clearance rate of the anabolic agents was monitored in the urine sampled every second day from all anabolic agent treated animals following cessation of treatment. At slaughter (85 kg liveweight), several carcass measurements were done. Visceral organ weights were noted and meat quality parameters (water loss, cutting resistance, pH) were determined. Zeranol treatment revealed an improved growth rate (ADG of 727 g/d and 147.3 days to attainment of 85 kg) compared to the control and the other treatment groups. None of the three anabolic agents improved the FCR significantly, although the control showed the lowest mean value (2.76 kg feed/kg liveweight gain). A tenclency for an increase in this parameter was observed over time, in all the groups, the highest mean value being encountered in the group treated with zeranol (3.32 kg feed/kg liveweight gain). Overall average daily feed intake was significantly (P<0.05) greatest in the zeranol treated animals (2.03 kg/cl). Backfat thickness (P2) deposition assessed through ultrasonic measurements, showed no significant differences between the treatments and the control. The diameter of the eye muscle, weekly monitored by the same method, from the P2 site, showed significant (P<0.05) differences - the control having the highest value (4.43 mm/week). The clearance rate of the anabolic agents was faster in clenbuterol treated animals than in the zeranol group, while for nandrolone group this could not be. assessed, because its metabolites in swine are still unknown. Zeranol treated animals had a significantly (P<0.05) improved cold carcass weight and dressing percentage (68.8 kg and 79.8% respectively). Mean values for backfat thickness were generally high in carcasses from zeranol treated animals (PI = 13.5 mm; Pi = 14.8 mm; P3 = 16.6 mm) which leaner carcasses were obtained in the clenbuterol group (PI = 6.7 m; P2 = 7.4 mm; P3 = 8.6 mm). The eye muscle area (physically measured) was significantly (P<0.05) higher in the nandrolone group (34.3 cm2) compared to the Zeranol group (30.6 cm2), but not statistically different from the control and the nandrolone group. Zeranol, clenbuterol and nandrolone treatments did not significantly alter carcass conformation indicators. However, carcass weight was recorded to be positively (P< 0.05) correlated to ham circumference (r = 0.52); chest depth (r = 0.64) and chest diameter (r = 0.56). With the exception of cutting resistance values, in which the zeranol treatment group produced more tender meat (3.74 kg shear force) than the control and the other two treatments, the rest of meat quality parameters measured (muscle pH; cooking loss of water holding capacity) were not affected by the treatment with anabolic agents. No significant differences in the weights of digesta, digestive tract and the visceral organs (liver, kidneys, lungs, heart and spleen) were found following anabolic agent treatment. Suppressed ovary growth (0.6 g of weight) and over-growth of the reproductive tract (134 g uterus weight) and increased size of the vulvas were observed following zeranol implantation of gilts. The reproductive organs from clenbuterol and nandrolone groups were functional and apparently unaffected. The determination of blood urea, blood glucose, blood creatinine and blood oestradiol levels using specific kits to assess the concentrations of the metabolites and hormones generally did not result in definite trends of increases or decreases over time. These determinations could thus not be accurately used as possible indicators of the metabolic status following the use of zeranol, clenbuterol and nandrolone in gilts. It was concluded that the use of clenbuterol and nandrolone in gilts yielded no improvements in the growth parameters. In gilts treated with zeranol, overall growth rate was higher. Ultrasonic measurements of backfat thickness and eye muscle diameter proved to be an inaccurate and unreliable predictor of fat thickness or leanness of the carcass. A longer withdrawal period is necessary after an implantation of pigs with zeranol compared to the rapid clearance realised after an oral dose of clenbuterol. The faster growth rate obtained following the use of zeranol implants is counteracted by higher feed costs of lean meat production and the yield of poorer ratio of lean-to-fat content in the carcass when compared to the clenbuterol and nandrolone treatments. The growth of the digestive tract, liver, heart, kidneys, spleen and lungs were not affected by anabolic agent treatment, and thus the anabolic effect of zeranol concerning growth characteristics is not through an increased gastrointestinal capacity. The assessment of growth performance and feed utilisation efficiency through blood levels of glucose and urea appear to be time consuming and not always practical. Further investigations regarding blood biochemistry, ideal doses of the anabolic agents, their metabolism and clearance rate in swine, as well as the margin of consumer's safety, is still of crucial importance for the future legal and safe use of anabolic agents in the pig industry. From the results obtained, it would seem that the use of these anabolic agents for the respective treatment periods and doses in gilts are not justified.