Effects of the use of ractopamine in pregnant sows on reproductive and blood parameters

The effects of the use of ractopamine (20 ppm per sow and day) in sows were evaluated during three different pregnancy stages (T1: 25 to 50; T2: 50 to 80; T3: 25 to 80 days of gestation, and T4: control-no ractopamine), assessing possible effects on reproduction, litter performance up to weaning, blood parameters, as well as on some of the biochemistry parameters at 20, 40, 60, 80, and 100 days of pregnancy. Forty sows were included in the trial for the evaluation of reproductive measures and litter performance. As to blood counts, a total of 10 sows were used. The use of 20 ppm of ractopamine during the three pregnancy stages had no effects on reproductive measures, litter performance or blood values, when compared to the control. However, total cholesterol, high density lipids and triglyceride values were different (P < 0.05) between treated and control sows (71.80 mg dl vs 65.04 mg dl; 42.30 mg dl vs 37.00 mg dl, and 59.40 mg dl vs 53.40 mg dl, respectively), indicating the action of the drug on protein and lipid metabolism. This experiment demonstrated that the use of ractopamine in pregnant sows did not affect the performance of the sows and the progeny until weaning. Additional key words: beta-adrenergic, blood parameters, gestation, lipid profile, swine.


Introduction
The growth of lightweight piglets is usually slower and less eff icient than that of heavier littermates.According to Wigmore and Stickland (1983), it is possible that slower growth may result from continuous competitive disadvantage, and not necessarily be caused by reduced numbers of secondary muscle fibers, when compared to heavier littermates.
It is known that the uterine environment may affect antenatal development of secondary muscle f ibers mainly due to the influence of nutritional and hormonal factors, able to stimulate increased fiber formation, thus affecting post-natal growth (Dwyer et al., 1993).These factors may affect not only the number of fibers, but birth weight and growth rate of animals as well (Handel and Stickland, 1987;Dwyer and Stickland, 1991).
Low glucose or amino acid uptakes by the fetoplacental unit resulting from nutritional def iciencies will promote increased fetal catabolism (Simmons et al., 1978;Battaglia and Meschia, 1978, cited by Gluckman,
1986), and reduce the endocrine stimulus for cell replication.In addition, the development of the placenta is also affected (Pilistine et al., 1984, cited by Gluckman, 1986).Maternal glucose crossing the placenta is the primary nutrient for fetal production.Thus, glucose is considered to be an important fetal growth-regulating factor (Bassett et al., 1990).In addition, high blood sugar levels promote the release of fetal IGF (Insulinlike Growth Factor) that has a direct effect on myoblast proliferation and differentiation.
From this, it can be concluded that fetal development could be influenced, and consequently, birth weight and post-natal growth could also be changed (Hegarty and Allen, 1978).There is a positive correlation between antenatal and post-natal development (Campbell and Dunkin, 1982).
During the stage when muscle f ibers undergo hyperplasia, the number of membrane beta-adrenergic receptors is increased (Parent et al., 1980;Schonberg et al., 1980).Thus, the use of a beta-adrenergic agonist (ractopamine) during this stage could optimize fetal muscle f iber replication through adenosine cyclic monophosphate (cAMP) modulation.In turn, development of the piglets could be improved during the post-natal life stages.
Administration of the beta-adrenergic agonist cimaterol to rats has resulted in increased functional activity and size of mammary gland cells (Choi et al., 1992), suggesting that the use of ractopamine in pregnant sows could improve milk production, allowing for a better nutrition of the progeny (Kim et al., 1994).Kim et al. (1994) treated sows with salbutamol (beta-adrenergic agonist) during three different stages of pregnancy and did not see improvements in birth weights.However, when the authors quantified muscle f ibers, the results favored the treated groups, suggesting that the number of muscle f ibers is not directly related to birth weight.
The goal of this trial was to evaluate the use of ractopamine in pregnant sows and to assess possible effects on reproductive measures, on the performance of the litter up to weaning and on some blood parameters.

Material and Methods
The trial was conducted at the gestation and farrowing units of a commercial 450-sow farm located in Rolândia, Parana State, Brazil.
Forty hybrid (Large White × Landrace) 3-4-parity pregnant sows were used.During pregnancy, the breeders were housed individually.After farrowing, the piglets were identified to allow follow-up according to their mothers' treatments.Piglets were maintained with the sows up to weaning (at 21 days of age).
The trial was started at artificial insemination of the sows.The semen used for insemination was obtained from hybrid boars with the same genetic background.
During gestation, routine management was maintained, and the sows were fed 1.8 kg of feed per day up to 80 days of pregnancy.From day 80 on, the sows were fed on average 2.8 kg of feed per day until farrowing.Pregnancy and pre-lactation feeds for all the four treatment groups were formulated according to the NRC (1998) (Table 1).
During pregnancy, blood samples were collected from two groups of 5 sows at 20, 40, 60, 80, and 100 days.Five sows belonged to the group receiving ractopamine from 25 to 80 days of pregnancy, and the other 5 sows belonged to the control group (without ractopamine).Blood tests were conducted at the Clinical Pathology Laboratory of the Londrina State University and in the Pathology Laboratory of the North of Parana.
From farrowing to weaning, sows were fed lactation feed ad libitum, formulated according to the NRC guidelines (1998).
The following measures were used to assess the reproductive performance of the sows and litter performance: total number of piglets born, number of piglets born alive, number of stillborns, litter weight at farrowing, number of weaned piglets and weaning weights.Blood collected from the sows was tested for the following parameters: total lipids (TL), total cholesterol (TC), low density lipids (LDL), high density lipids (HDL), triglycerides (TG), blood glucose (BG), blood urea nitrogen (BUN), creatinine (CR), total serum protein level (TP), hemoglobin (HB), hematocrit (HM), leukocyte count (LC), lymphocyte count (LF), neutrophil count (NC), monocyte count (MC), rod count (RC), and eosinophil count (EC).
For reproductive and litter performance measures, the experimental design was completely randomized, with 4 treatments and 10 replicates per treatment.
For blood parameters, the experimental design was completely randomized using a 2 × 5 factorial arrangement of treatments (2 treatments and 5 blood collection periods), with 5 replicates, each sow representing a treatment repetition.
Variance analysis and Tukey's test were used in the GLM procedure as outlined by SAS (1999) to evaluate the results obtained in the trial.Blood parameters were tested by regression analysis and Student's t Test according to the sample collection schedules.

Results
Table 2 shows the results related to the total number of piglets born, piglets born alive and weights at birth and at weaning.No differences were detected among treatments (P > 0.05).
Table 3 shows the results obtained for blood counts.Total cholesterol (TC), HDL and triglycerides (TG) were significantly different (P < 0.05) among treatments.There were no significant differences seen for the other measures (P > 0.05).
Table 4 shows the results of blood cell counts: hemoglobin (HB), hematocrit (HM), leukocyte (LC), lymphocyte (LF), neutrophil (NC), monocyte (MC), rod (RC) and eosinophil (EC) counts.There were no significant differences (P > 0.05) among treatments.It can, therefore, be concluded that the drug had no harmful effects on any of the blood parameters evaluated.
When blood parameters were analyzed by sampling period for both treatments, it was noted that total lipids showed no response to regression analysis in ractopamine-treated animals, but in untreated controls (Fig. 1) there was a linear effect (Y = 160.02+ 0.689X; R 2 = 0.70; P < 0.01).
Low density lipids (LDL) were positive for regression analysis in both treatments (Fig. 2), with a cubic effect in ractopamine-treated sows (Y = 59.6451There was no signif icant difference between treatments (P > 0.05).
BUN showed a positive response to regression analysis for both treatments (Fig. 5).For ractopamine-treated sows, the equation is Y = 50.395-1.48241X + 0.0139571X 2 (R 2 = 0.80; P < 0.01), and for the untreated group, Y = 51.6705-1.64148X + 0.0164076X 2 (R 2 = 0.91; P < 0.01).Although no interaction was observed between the treatments and days, according to the Student's t test only the means at 100 days were different (P < 0.05) between the control and the test group.

Discussion
Ractopamine did not affect piglet performance up to weaning or the reproductive performance of the treated sows.These results agree with those obtained by Kim et al. (1994), who used salbutamol, a betaadrenergic agonist in pregnant sows and did not see any effect on birth and weaning weights in piglets produced by treated sows compared to the controls.
Although birth weights were improved by ractopamine, this does not necessarily mean that the number of muscle fibers remained unchanged.According to Handel and Stickland (1988), birth weight is not a good indicator of total number of muscle fibers.In pigs with a high number of muscle fibers, these fibers are of smaller diameter than in animals with fewer fibers (Dwyer et al., 1993).Higher numbers of muscle fibers only became evident when pigs reached 70 days old or weighed 25 kg, compared to animals with a lower number of fibers (Dwyer et al., 1993).Thus, growth rate up to 25 kg of bodyweight is independent of the number of fibers.
If we analyze only birth and weaning weights, the absence of significant differences shows that when sows are treated in periods other than the final third of pregnancy, there is no effect on piglet growth.Based on weaning weights, it can be hypothesized that the treatments had no effect on milk production, in contrast to the hypothesis of Kim et al. (1994), and findings by  ) by sampling day, for ractopamine-treated (25 to 80 days of pregnancy) and untreated sows.Choi et al. (1992), who worked with the beta-adrenergic drug cimaterol and did not see improvements in the activity and diameter of mammary gland cells in rats.Total cholesterol and triglyceride levels were increased in ractopamine-treated sows, probably because of the lipolytic effect of the drug.This also resulted in increased HDL levels, since these molecules are responsible for the transport of cholesterol from the adipose tissue to the liver (Lehninger et al., 1993).
Creatinine is a product of muscle contraction, and its synthesis is increased in more active animals.The results obtained in this trial did not reveal significant differences (P > 0.05) among treatments.This indicates that beta-adrenergic drugs have a negligible action on muscle contraction, even when the drug is from the same family as adrenaline and noradrenaline (Marsden and Meadows, 1970;Bülbring, 1976, cited by Ingram andDauncey, 1986).
The serum lipid data showed that ractopaminetreated sows presented different levels of compounds related to lipid metabolism.This difference was caused by the action of the drug on the lipid metabolism, through the stimulation of the adenyl cyclase system that promotes cAMP production, increasing the activation of kinases which are responsible for the phosphorylation and modification of the activities of several enzymes, modulating metabolic processes such as muscular contraction, lipolysis and glycogenolysis.
Although BUN levels were similar for both treatments up to 60 days of pregnancy, a difference was noted at 80 days of pregnancy when the treated group was compared with the controls indicating a lower protein catabolism during the stage of secondary fiber hyperplasia.This occurrence could improve muscular development.
The total protein values were very close for both groups, probably because the test method used measures total serum protein levels, regardless of the source and use of the protein.
According to the results obtained in this trial, it can be concluded that the 20 ppm dose of ractopamine had no effect on reproduction, independently of the treatment period.As for the biochemical parameters, some were changed as a result of the action of the drug on lipid and protein metabolism.
In conclusion, the use of ractopamine at 20 ppm during the pregnancy stages studied did not affect the number of piglets born or the birth or weaning weights.
The lipid profile of ractopamine-treated pregnant sows was changed, with elevation of total cholesterol, triglyceride and HDL values, when compared to the control group (71.80 mg dl -1 vs 65.04 mg dl -1 ; 42.30 mg dl -1 vs 37.00 mg dl -1 , and 59.40 mg dl -1 vs 53.40 mg dl -1 , respectively).Immune cells or blood values were not affected in ractopamine-treated pregnant sows.

Table 1 .
Percentage and calculated composition of the experimental feeds fed during pregnancy (0 to 80 days of pregnancy), pre-lactation (81 days of pregnancy to farrowing) and lactation (from farrowing to weaning) 4As-fed basis.