ORIGINAL

Performance and plasma urea nitrogen of immunocastrated males pigs of medium genetic potential

Rendimiento y nitrógeno de urea en plasma de cerdos machos inmunocastrados de potencial genético medio

Fabiana R Caldara,¹* Ph.D, Rita KS Santos, ¹ M.Sc, Luan S Santos,¹ B.Sc, Luciana Foppa,¹ B.Sc, Irenilza A Nääs,¹ Ph.D, Rodrigo G Garcia,¹ Ph.D, Simone P Machado,¹ B.Sc.

¹Universidade Federal da Grande Dourados (UFGD), Faculdade de Ciências Agrárias (FCA), Zip Code 79823-350, Dourados, MS, Brazil.

*Correspondence: fabianacaldara@ufgd.edu.br

Received: June 2014; Accepted: January 2015.

ABSTRACT

Objective. A study was carried out to evaluate the performance and the plasma urea nitrogen (PUN) of male pigs of medium genetic potential for lean meat deposition in carcass, which underwent immunocastration. Materials and methods. Forty-five seventy-days old Large White x Landrace crossbred were used. The pigs were distributed in a randomized design in three treatments: castrated males, females and immunocastrated males. Each treatment group was replicated three times with five pigs per replicate. The trial period was of 70 days, divided into phases of growing (70 to 110 days old) and finishing (111 to 140 days old). The pigs were weighed four times: at the beginning of the trial, at the first immunocastration vaccine dose (80 days old), at the second immunocastration vaccine dose (110 days old) and just before slaughter (140 days old). Blood samples were taken on the same day that the animals were weighed. Results. Between 80 and 110 days old, there was an increase in PUN value, only for castrated males and females. No differences were found in weight gain between the studied groups within the periods. Immunocastrated males had lower feed intake than females and these had a lower feed intake than castrated males. To 110 days old, immunocastrated animals showed feed conversion ratio similar to females and better than castrated males. However, after the second dose of the vaccine, feed conversion was similar between groups. Conclusions. The benefits of immunocastration are prominent in animals with low to medium genetic potential.

Key words: Castration, feed conversion, feed intake, immunocastration, swine production, weight gain (Source: USDA).

RESUMEN

Objetivo. Se realizó un estudio para evaluar el rendimiento y la concentración de urea en plasma (PUN) de los cerdos machos de medio potencial genético de carne magra en la canal sometidos a la inmunocastración. Materiales y métodos. Se utilizaron 45 cerdos de 70 días de edad Landrace x Large White. Los animales se distribuyeron en un diseño completamente al azar con tres tratamientos: machos castrados, hembras y machos inmunocastrados. Cada tratamiento consistió en tres repeticiones, con cinco animales por réplica. El período experimental fue de 70 días, divididos en las etapas de crecimiento (70 a 110 días de edad) y terminación (111 a 140 días de edad). Los cerdos fueron pesados cuatro veces: al inicio del experimento, en la primera dosis de vacuna de inmunocastración (80 días de edad), en la segunda dosis de la vacuna de inmunocastración (110 días de edad) y antes de el sacrificio (140 días de edad). Las muestras de sangre se recogieron en el mismo día en que se pesaron los animales. Resultados. Entre 80 y 110 días de edad, hubo un aumento en la cantidad de PUN, sólo para machos castrados y hembras. No hubo diferencias en la ganancia de peso entre los grupos en ninguno de los períodos estudiados. Machos inmunocastrados tuvieron menor consumo de alimento que las hembras y éstas mostraron un menor consumo que los machos castrados. En 110 días de edad, los animales inmunocastrados mostraron la conversión de alimento similar a las hembras y mejor que los machos castrados. Sin embargo, después de la segunda dosis de la vacuna, la conversión alimenticia fue similar entre los grupos. Conclusiones. Los beneficios de inmunocastración son prominentes en animales con bajo a médio potencial genético.

INTRODUCTION

Surgical castration of young male pigs is a common practice in swine production worldwide. However, castrated male pigs have feed conversion efficiency and nitrogen retention impaired and they present lower lean: fat ratio than boars, which makes production significantly more expensive. The boars have the capability of high protein retention caused by the anti catabolic effect of gonadal steroids. The gonadal steroids influence the balance between protein synthesis and breakdown in favor of a high protein deposition (1). The anti catabolic effect of androgens, and thus the improved N-retention, is partly explained by the fact that androgens antagonize glucocorticoids and their catabolic functions (2).

Surgical castration without anesthesia has become an animal welfare issue and has been banned in many countries (3,4). However, anesthesia may promote acute pain during castration and does not eliminate stress and discomfort due handling the animals before surgery and it will not prevent the chronic post-castration pain (5,6). Although these factors produce significant importance to its progressive elimination in swine production, problems associated with boar taint, still are successfully solved by the adoption of the surgical castration. The odor is associated with sexual maturity and swine male hormones production, making the meat of uncastrated pigs unsuitable for human consumption (7).

It is clear that alternatives to the surgical castration of pigs need to be found. They must have practical application, be economically viable, do not present adverse impacts to the productive performance of the animals and meet consumer requirements and principles of welfare animal. The immunocastration is a procedure, which can replace surgical castration of male pigs, as it has proved effective in reducing the concentration of the hormones responsible for the boar taint (8). It also allows the animals to have longer satisfactory performance and carcass characteristics than those of non-castrated males; generating positive productive impact on the pig production (9).

Many studies support the effectiveness of the immunocastration, which is used in animals of high genetic potential (pigs of commercial lines genetically improved, with potential for lean meat deposition in carcass greater than 56%)(9-12), with benefits that are not automatically extended to pigs with lower performance.

The research aimed to evaluate the effects of immunocastration on performance parameters and plasma urea levels of medium genetic potential pigs.

MATERIAL AND METHODS

Study site and animals. A study was carried out at the Swine Experimental Sector, at the Agrarian Sciences College, Universidade Federal da Grande Dourados (Federal University of Grande Dourados), MS, Brazil, using 45 crossbreed of Landrace and Large White genetic strains pigs. The animals were 70 days old, with an average weight of 25.2 ± 2.8 kg, being 15 females and 30 males. All pigs were submitted at the same rearing conditions, in open sided pens with semi-automated feeders and nipple drinkers, concrete floor and a herd density of 0.8 m²/ animal.

Treatments and experimental design. The animals were distributed in a fully randomized experimental design with three treatments, and three replications with 15 pigs per treatment. The treatments were T1 (females), T2 (surgically castrated males), and T3 (immune-castrated males).

The pigs in the castrated group underwent the orchiectomy procedure on the seventh day of life. The group of immunocastrated animals were subjected to two doses of Vivax®, which is a vaccine based on a synthetic analogue of GnRH coupled to a large carrier protein. It was applied subcutaneous in two dosages: the first at 60 days before slaughter (80 days old), and the second at 30 days before slaughter (110 days old).

Nutritional management and experimental period. The trial period lasted 70 days, divided into two phases: growing (from 70 to 110 days) and finishing (from 111 to 140 days). The experimental diets were based on corn and soybean meal and were formulated using the nutritional requirements according to Rostagno et al (13), for entire males during growth and for females in the finishing phase. These recommendations were adopted to ensure that both phases in all categories evaluated would be assisted in their nutritional requirements, thus opting for formulating rations based on the most demanding category in each phase. In the finishing phase were used the dietary recommendations for females, since the animals immunocastrated group after receiving the second dose of vaccine, have lower requirements for entire males. The diets and water were provided ad libitum throughout the trial (Table 1).

Evaluation parameters. The animals of the all experimental treatments were weighed four times, at the beginning of the trial, at the first immunocastration vaccine dose, at the second immunocastration vaccine dose, and at the day to the slaughter. The diets provided and feed remainder were weighed weekly to evaluate the performance, which was measured as the daily weight gain, daily feed intake and feed conversation rate at each stage.

Blood samples were taken in heparinized tubes, by the vein puncture on the same day of animal weighing. Before collection, piglets were fasted from 18:00 h to 07:00 h in the following day. From 07:00 h to 08:00 h, the animals were fed ad libitum and returned to fast from 08:00 h until 13:00 h, when it was started the blood sampling. The blood was centrifuged at 3000 rpm for 15 minutes to get the plasma, which was transferred to Eppendorf tubes (± 1.5 ml) and stored in a freezer (-18°C). The concentration of plasma urea nitrogen (PUN) was obtained using the enzymatic method (commercial kit).

Statistical analysis. The results were analyzed using the SAS 9.2 software (14). ANOVA was applied to mean values using the general linear model (GLM). The means were compared by Tukey test considering a 5% level of significance.

Ethical considerations. This investigation was conducted according to the guidelines established by the Ethical Committee on the Animal Use in Experimentation of the Universidade Federal da Grande Dourados (Brazil), under Protocol No031/2013, in accordance with the ethical principles for animal experimentation, animal care and use.

RESULTS

No differences were found (p>0.05) for Plasma Urea Nitrogen (PUN) in the first two samplings (at the beginning of the trial and just before immunocastrated animals receive the first dose of vaccine) amongst the three animal groups.

However, for females and castrated males there was an increase in PUN after the second sampling. This might indicate a reduction in the efficiency of protein utilization from this stage, while, for immunocastrated males there was an increase in PUN which occurred only after the third sampling, after immunocastration vaccine second shot. This may indicate advantage in the utilization of dietary protein by this animal category in this period, between the first and second dose of vaccine (Table 2).

No difference (p>0.05) was found in PUN results in 4th sampling between groups. This might indicate that the effect of vaccine second dose, in which immunocastrated animals begin to behave physiologically as castrated animal, may lead to the ability of retaining nitrogen and protein deposition in muscle similar to boars.

No difference (p>0.05) was found in average daily weight gain between immunocastrated males and other groups in all evaluated periods. Castrated males and females differed only in period 2 (80 to 110 days old), (Table 3).

Immunocastrated males showed lower feed intake than females and these, on the other hand, presented lower intake than castrated males in the first and second periods. In the third period, immunocastrated animals present feed intake similar to females, and lower than it was in the castrated group.

In the first and second periods, the immunocastrated males present feed conversion similar to females, and better than it was in the castrated group. After the second dose of the vaccine (period 3), the feed conversion was similar between treatments.

DISCUSSION

The reduction of PUN concentration reflects the superior nitrogen use efficiency and can be used to estimate the quantity and quality of dietary protein (15) and its increase may indicate inefficient use of amino acids (16).

Since the diets were formulated to comply with the boars' requirements for growing pigs and for females in the finishing phase (13), the greatest potential for utilization of amino acids dietary by immunocastrated males, after receiving the second dose of vaccine, becomes clear. This difference translates their increased nutritional requirement, since increased PUN values for castrated and females in the first phase indicate that these animals were not able to maintain nitrogen in the same proportion that immunocastrated animals.

The maximization of amino acids efficient utilization has considerable importance for swine producer because the amino acids supply is one of the most relevant items on the final cost of feed. The concentration of urea nitrogen in plasma can be used to evaluate the quality of protein consumed and may be used as an indicator of maximum amino acids utilization (16). In this way, concentration of PUN is particularly useful in comparing the protein utilization effective for different swine's groups (females and castrated males immunocastrated males).

Disagreeing from the present study other researchers have demonstrated positive effects on daily weight gain and immunocastrated males showed superior performance about 8.3% and 32% (8,17) respectively compared to castrated males. The superior performance of immunocastrated males in relation to castrated males, in the delayed finishing phase, can be considered an indicative of nutrient requirements for these different groups. Both studies used animals with superior genetic potential while in the present study the animals were from medium genetic potential. These results suggest that the benefits of immunocastration may not be extended in the same proportion to the low genetic potential animals for both weight gain and lean meat deposition in the carcass.

Comparing the effects on the pigs' performance, Santos et al (17) found that immunocastrated swine showed better feed-conversion than castrated males. Immunocastrated animals were more effective in the nutrients use than barrows, even after the second immunization dose, similar to the response observed by other authors (12). The authors refer these results to the temporary existence of residual effect of endogenous anabolic hormones in immunocastrated pigs.

Castrated male pigs have higher feed consumption than the entire males (18), whose response has been related to low testosterone concentration in these animals (8). Furthermore, it has been observed an increase in daily amount of feed ingested by immunocastrated males when compared to castrated animals after the second dose of immunocastration vaccine (19). This fact may be related to the sharp decline in testosterone levels in immunocastrated pigs. However, this response was not observed in the present study, agreeing with the result obtained by Jaros et al (20).

In a study involving males undergoing to the immunocastration, the reserachers found that at the time of the second dose of immunogenic vaccine, 85% of treated males had a serum testosterone level above 2 nM. Two weeks after the second vaccination, only 6% of the animals had testosterone concentrations above 2 nM, which did not differ from castrated males. This may explain the results of the present study, in which immunocastrated animals showed similar performance than females and higher than castrated males in the period before the second dose of vaccine, becoming physiologically as a castrated animal after the second immunization (8).

Researchers (10) compared the growth performance and carcass characteristics of castrated males, immunocastrated males and boars. The authors found for immunocastrated animals that the feed intake and feed conversion values are similar to the reported for boars, but lower than those found in castrated males. This may indicate that there is better efficiency in nutrients utilization and higher daily weight gain in boars than in castrated males, found especially during the late finishing phase.

Immunocastrated males presented lower plasma urea nitrogen concentrations in relation to females and castrated males, before to the second dose of the vaccine. The best utilization of dietary protein resulted in a performance benefits, with a reduction in the feed intake and the feed conversion, even for animals of low to medium genetic potential.

Acknowledgments

FUNDECT - Fundação de Apoio ao Desenvolvimento do Ensino, Ciência e Tecnologia do Estado de Mato Grosso do Sul, for the financial support to conduct the research.

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