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Revista mexicana de ciencias pecuarias
versión On-line ISSN 2448-6698versión impresa ISSN 2007-1124
Rev. mex. de cienc. pecuarias vol.7 no.4 Mérida oct./dic. 2016
Articles
Morphometry of native pigs in rural areas of Mexico
a Instituto Nacional de Investigaciones Forestales, Agrícolas y Pecuarias (INIFAP). Campo Experimental Santiago Ixcuintla. Km. 6 Entronque Carret. Internacional México-Nogales. Santiago Ixcuintla, Nayarit C.P. 63300.
b Centro Nacional de Investigación Disciplinaria en Fisiología y Mejoramiento Animal, INIFAP.
c Campo Experimental Chetumal; CIRSE, INIFAP.
d Sitio Experimental Aldama, CIRNE, INIFAP.
e Campo Experimental Valle de México, CIRCE, INIFAP.
f Facultad de Estudios Superiores Cuautitlán; UNAM.
g Campo Experimental La Laguna, CIRNOC, INIFAP.
h Campo Experimental La Posta, CIRGOC, INIFAP. México.
Data from 241 interviews collected in 2013 was analyzed to characterize populations of pigs (Mexican Hairless Pig (MH), Cuino Pig (CU) and Crossbred Pig (UD)). Variables were body weight (BW), head length (HL), body length (BL), thoracic perimeter (CG), height at withers (HW), croup width (RW), number of nipples (TC), dense or sparse hair (HD), presence or absence of tusks (TU), short or long snout (ST), upright or floppy ears (ER), calm or restless temperament (TM), proportionality index (PI), body index (BI) and relative weight index (RWI). Analyses were carried out with GLM and GENMOD of SAS. Models included state and population. Population was significant (P<0.05) for BW, BL, CG, HW, RW, TU, TM, PI, BI and RWI. Coefficients of variation (VC) showed the minor and major values for BW (18.8 %) and CG (27.8 %). VC were 13.0, 14.6 and 45.8 % for PI, BI and RWI. Least squares means for MH, CU and UD were: 48.06±6.17a, 35.93±3.04b and 61.11±7.42a kg (BW); 77.81±3.65ab, 69.56±2.02a and 88.52±4.93b cm (BL); 80.55±3.98ab, 71.72±2.20a and 93.23±5.37b cm (CG); 56.88±2.45ab, 51.26±1.36a and 60.32±3.31b cm (HW); 57±4a, 71±19b and 62±34a % (HD); 68±31ab, 70±14a and 61±27b% (TU); 65±30 a, 56±12b and 62±3a% (TM). The MH and UD populations were similar in morphometry and different from the CU population. The CU population showed lower weight, smaller size and calmer temperament. The characterization of these populations is important for designing strategies for their conservation and efficient use.
Key words: Morphometry; Creoles; Native pigs
Para caracterizar a las poblaciones del cerdo Pelón Mexicano (PPM), cerdo Cuino (PCU) y cerdos cruzados (PCI) se analizó información de 241 entrevistas realizadas durante 2013. Las variables analizadas fueron: peso corporal (Peco), longitud de cabeza (Loca), longitud del cuerpo (Locu), circunferencia del pecho (Circu), altura a la cruz (Acruz), ancho de pelvis (Anpe), número de pezones (Nupe), pelo denso o escaso (Cape), presencia o ausencia de colmillos (Colm), hocico corto o largo (Hoc), orejas erguidas o no erguidas (Posio), temperamento tranquilo o inquieto (Tem), índice de proporcionalidad (IP), índice corporal (IC) e índice de peso relativo (IPR). Los datos se analizaron con GLM y GENMOD del SAS. Los modelos estadísticos incluyeron Estado y Población. Población influyó (P<0.05) Peco, Locu, Circu, Acruz, Cape, Colm, Tem IP, IC e IPR. Los coeficientes de variación (CV) mostraron a Peco y Anpe como las características con menor y mayor variación (18.8 y 27.8 %). Para IP, IC e IPR los CV fueron 13.0, 14.6 y 45.8 %. Las medias de cuadrados mínimos para PPM, PCU y PCI fueron 48.06±6.17a, 35.93±3.04b y 61.11±7.42a kg (Peco); 77.81±3.65ab, 69.56±2.02a y 88.52±4.93 b cm (Locu); 80.55±3.98ab, 71.72±2.20a y 93.23±5.37b cm (Circu); 56.88±2.45ab, 51.26±1.36a y 60.32±3.31b cm (Acruz); 57±4a, 71±19 b y 62±34a% (Cape); 68±31 ab, 70±14a y 61±27b% (Colm); 65±30a, 56±12b y 62±3a% (Tem). PPM y PCI fueron similares en morfometría pero diferentes de PCU. La población PCU mostró menor peso, menor talla y temperamento más inquieto. Caracterizar a estas poblaciones es importante para diseñar estrategias para su conservación y uso eficiente.
Palabras clave: Morfometría; Cerdos criollos; Traspatio
Introduction
Rural, or backyard, pig farming in Mexico involves pigs raised in low-input management systems which take advantage of the rusticity and low nutritional requirements typical of these pig populations. In rural communities in Mexico, pig diets consist largely of roots, tubers, fruit, agricultural byproducts and kitchen waste1,2. Growing pigs is important for rural families because it provides animal protein and extra income.
Local rural pig populations can also function as reservoirs of genetic variation that can generate new alleles with potential applications in commercial pigs3. It is therefore important to phenotypically and genetically characterize these populations. Morphometric characterization is a vital first step towards efficient use of genetic resources. Studies have been done of morphometric variables in backyard pigs focusing on traits associated with growth and reproductive behavior in pigs in different production systems3,4,5.
The present study objective was the qualitative and quantitative morphometric characterization of backyard pig populations located in rural communities of Mexico.
Material and methods
In 2013, 241 surveys were applied to backyard pig owners in rural communities in 18 states in Mexico: Chihuahua, Coahuila, Durango and Zacatecas (arid and semiarid regions, n= 45); Colima, Guerrero, Nayarit and Oaxaca (dry tropical region, n= 71); Campeche, Chiapas, Quintana Roo, Tabasco, Veracruz and Yucatan (humid tropical region, n= 88); and Mexico, Hidalgo, Jalisco and Querétaro (temperate region, n= 37).
Sample size was calculated using the formula recommended by the FAO6: n=(z/m) 2 p(1-p); where z is 1.64 for a 90% confidence level, m is the margin of error (0.05= ± 5 %), and p is the estimated value of the sample proportion that will answer the survey in the same way, in this case 0.45. Survey subject selection was done using the snowball sampling technique; backyard pig owners were identified, the data from the first subject was used to locate the following subject, and this process was repeated until the estimated sample size was attained7. On the same day the survey was applied to an owner, his/her pigs were weighed, measured and photographed. Each documented animal was assigned to one of three populations of pigs: Mexican hairless (MH, n= 65), Cuino (CU, n= 25) and Undefined cross (UD, n= 151).
Analyzed variables were body weight (BW); head length (HL), measured from the tip of the snout to the base of the head; body length (BL), measured from the base of the neck to the base of the tail; chest girth (CG), which is circumference measured at the thoracic level from the back; height at withers (HW), measured from ground surface to the withers; rump width (RW), measured as the distance between the iliac tuberosities; teat count (TC); dense or sparse hair (HD); presence or absence of tusks (TU); long or short snout (ST); upright or floppy ears (ER); and calm or restless temperament (TM). While body measurements were being taken, temperament was classified into one of two categories: moderately manageable or difficult to handle. Three zoometric indices were also calculated: proportionality index (PI) = (HW *100)/BL; body index (BI) = (BL *100)/HW; and relative weight index (RWI) = (BW *100)/HW.
Data was analyzed with the general least squares method using the GLM and GENMOD procedures in the SAS statistic package8. The GLM procedure was applied to the variables BW, HL, BL, CG, HW, CW, RW, TC, PI, BI and RWI under the assumption of a normal probability distribution. The GENMOD procedure was applied to the variables HD, TU, ST, ER and TM under the assumption of a binomial probability distribution. The variation coefficient (VC) was calculated for all variables using the formula: VC= (standard deviation ÷ mean) * 100. The least squares means (LSM) estimated with GENMOD were transformed as follows: e (LSM) / ((1+e)LSM)9. The final statistical models for all variables included the fixed effects of state (18 levels) and population (3 levels). Other fixed effects such as sex or age were not included due to lack of data.
The basic statistical model was:
where: µ= general mean; Ei= fixed effect of the i-th state (i=1, 2,…, 18); Pj= fixed effect of the j-th population (j=1, 2 and 3); eijklm= distributed residual effect NI(0, σ²e); or distributed B(n, p).
Results and discussion
Variation coefficients (VC), least squares means (LSM) and standard errors are shown in Table 1. The effect of State was significant (P<0.01) for all variables whereas population affected (P<0.05) BW, BL, CG, HW, RW, TU, TM, PI, BI and RWI.
Table 1 Least squares means (± standard error) and variation coefficients (VC) for morphometric variables in Mexican hairless (MH), Cuino (CU) and undefined cross (UD) pigs from rural areas in Mexico
BW= body weight (kg); HL= head length (cm); BL= body length (cm); CG= chest girth (cm); HW= height at withers (cm); RW= rump width (cm); TC= teat count; HD= hair density (%); TU= presence or absence of tusks (%); ST= long or short snout (%); ER= upright or floppy ears (%); TM= calm or restless temperament (%); PI= proportionality index= (HW *100)/BL; BI= body index = (BL *100)/HW; RWI= relative weight index = (BW *100)/HW.
abc Different letter superscripts in the same row indicate difference (P<0.05).
Morphometric variability
Based on the estimated VC values, BW exhibited the least variation (18.8 %) and CG the most (27.8 %). Other variables had intermediate VC values, such as HL (24.9 %), CG (23.5 %), BL (23.3 %), TC (22.8 %) and HW (21.2 %). Other studies have reported estimated VC values lower than those observed here. In a study of morphometry in native Cuino pigs in Nayarit, Mexico, the VC values were 7.56 % for TC, 8.46 % for CG and 11.79 % for BL3. A study done in Venezuela found VC values of 7.62 % for HW, 9.26 % for RW, 9.78 % for CG, and 10.9 % for HL10. In a zoometric characterization of native pigs done in Columbia, estimated VC values were 10.36 % for HW, 11.84 % for CG and 12.76 % for RW11. Values reported for the Pampa Rocha breed, from Uruguay, agree with the previous values: 5 % for HW; 6 % for BL; 10 % for HL; 11 % for RW; and 19 % for live weight12. Another study done with the same breed found VC values of 5.90 % for HW in males and 6.92 % in females, 11.90 % for RW in males and 11.06 % in females; and 8.88 % for live weight in females and 25.36 % in males13. In contrast, VC values for native pigs in Guatemala have been reported to be lower in males than in females: 11.09 vs 15.06 % for CG; 15.35 vs 16.72 % for RW; 16.29 vs 19.16 % for HL; and 17.68 vs 23.74 % for live weight14.
The VC values in the present study exhibited greater morphological variability than other native pig populations in Latin America3,10-14. This variability can be attributed to differences in the management systems and environments in which the subpopulations are grown as well as genetic diversity within subpopulations.
Among the three zoometric indices calculated in the present study, the smallest data dispersion was in the PI (VC= 13.0 %), suggesting the presence of a homogeneous breed pattern in the evaluated populations. In contrast, the VC values for the RWI (45.8 %) and BI (14.6 %) suggest that data comes from populations with heterogeneous production focuses. These results support the use of zoometric indices as useful tools in breed and functional evaluations15. Similar PI (12 %) and BI (10 %) values have been reported in a morphostructural study of a local pig population in Corrientes Province, Argentina16. Lower VC values (7.04 % for PI; 7.74 % for BI) were estimated for a native pig population in Venezuela10. Similar VC values for the BI were reported for male (7.89 %) and female (8.04 %) pigs in Guatemala, while the corresponding PI values were of 12.72 % in females and 22.39 % in males14. Much higher values (44.87 to 87.09 %) have been reported for the compactness index in a morphometric evaluation comparing local pig populations in different municipalities of Brazil17.
Quantitative variables
The LSM for BW, BL, CG and HW variables in Table 1 show that, in general, morphometry was similar between the MH and UD populations, which differed from the CU population. In addition, the CU population had lower weight and size than the MH and UD populations.
Average index values similar to those of the MH and CU populations have been reported for native pigs in indigenous communities in the state of Chiapas, Mexico (52.63 ± 4.81 cm for HW; 46.57 ± 13.35 kg for live weight; and 86.74 ± 10.61 for CG)2. Similar values have also been reported for native pigs in low input production systems in Venezuela (59.51 ± 4.71 cm for HW; 17.07 ± 1.57 cm for RW; 84.85 ± 8.30 cm for CG)10, and Colombia (56.41 ±6.0 cm for HW; 17.29 ± 2.21 cm for RW; 85.66 ± 10.14 cm for CG)11. For the same traits, lower values were reported for native pigs grown in rural communities in Guatemala (47 ± 5.8 for HW; 15 ± 2.5 for RW; 65 ± 7.2 cm for CG; and 45.52 kg for live weight)14.
In contrast to the present average values for the MH and CU populations, higher values have been reported for other native pig populations. Mexican hairless pig populations in the state of Nayarit, Mexico, had clearly higher values in confinement (68.34 ± 1.39 for HW; 102.53 ± 1.57 for CG; and 82.10 ± 3.01 for BL) and grazing systems (68.14 ± 1.84 for HW; 102.66 ± 2.08 for CG; and 79.52 ± 4.0 for BL)18. Live weight was also higher (57.42 kg) in these MH populations in intensive weight gain systems at 175 d of age19. Similarly to those studies above zoometric data for local Pampa Rocha pig populations have been also generated in Uruguay (72.7 ± 3.55, 74.97 ± 5.18 and 82.33 ± 4.85 cm for HW; 27.2 ± 2.89, 26.97 ± 2.98 and 25.66 ± 3.05 cm for RW; 103.68 ± 6.69, 102.02 ± 6.95 and 99 ± 9.16 cm for BL; and 137 ± 26.2, 148.6 ± 37.69 and 173.66 ± 15.41 for live weight)12,13. Body weight higher than the observed in the present study for the MH and CU populations have been estimated for local pigs sampled from farms in Brazil (live weight = 54.40 kg)17, and native pigs from rural areas in Argentina (live weight = 60.47 ± 10 kg)16. However, in the latter study averages similar to those for the present MH population were reported for HW (56.09 ± 3.49 cm), BL (75.82 ± 4.96 cm), and RW (17.26 ± 1.54 cm). Some morphometric values reported for Cuino native pigs in Nayarit were lower than those observed in the present CU population (HW= 47.60 ± 4.14 cm; BL= 62.25 ± 7.69 cm) while others were higher (CG= 87.28 ± 7.39 cm; live weight= 43.84 ± 10.55 kg)3.
Qualitative variables
The LSM for HD (71 ± 19 %), TU (70 ± 14 %) and TM (56 ± 12 %) indicate that the CU population had greater hair density, more tusk frequency and more animals with a restless temperament. Hair density and temperament have been evaluated in different native pig populations. For example, a study of native pigs in Chocó department, Colombia, found that 85.29 % of the sampled population had hair11, and in a phaneroptical characterization of native pigs in rural communities in Venezuela 63.24 % of the sample had abundant hair14. All the native pigs sampled in one study in rural areas of Argentina were found to have hair16. In a study of native pigs in indigenous communities in Chiapas State, Mexico, the animals were found to have large, thick bristles concentrated on the upper portion of the neck and around the withers2. In contrast to the present results, a morphometric study of native pigs in Nayarit, Mexico, reported that the sampled Cuino pigs exhibited a calmer temperament than the more aggressive Mexican Hairless pigs18. A more aggressive temperament has been reported for pigs sampled at different farms in northeast Brazil17.
Conclusions and implications
Overall, the present morphometric results indicate greater variability in the three evaluated populations than other native pig populations in Latin America. The observed morphometric variability can be attributed to differences in the management systems and environments in which the three populations were grown, as well as genetic diversity among them. Morphometrically, the MH and UD populations were similar while both differed from the CU population. The CU population exhibited higher hair density, lower weight and size, and a more restless temperament when compared to the MH and UD populations. It is important to characterize the backyard pig populations to design strategies that contribute to the conservation and efficient use of these genetic resources.
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Received: February 12, 2016; Accepted: March 01, 2016
Este es un artículo publicado en acceso abierto bajo una licencia Creative Commons
