Growth performance and meat quality of Large White and local pigs reared in the tropics

Growth performance and meat quality of Large White and local pigs reared in the tropics

E Depres, M Naves, Françoise Tamisier, A Xande and Dominique Rinaldo with the technical collaboration of P Marival

INRA Centre de Recherches Agronomiques Antilles-Guyane. Station de Recherches Zootechniques. BP 1232-97184 Pointe-à-Pitre Cedex (Guadeloupe - French West Indies).

The aim of this study was to compare Large White (LW) and local "Creole" pigs (CR), intensively reared in a tropical environment, in terms of growth performance and meat quality. The experiment involved a total of 30 LW and 30 CR pigs which were slaughtered at 4, 5 and 6 months of age. CR animals exhibited a 34% lower daily weight gain (P<0.001) and a fatter carcass than LW. The increase in back fat + leaf fat percentage was significant in CR pigs at age of 5 months whereas in LW animals it was noticeable only at 6 months of age (interaction genotype x age at slaughter: P<0.001). Muscle pH values determined at 45 minutes and 24 hours post mortem were higher in the indigenous pig than in the purebred LW animal (P<0.01). Drip loss was significantly lower in CR pigs than in the LW ones (P<0.001). A taste panel judged the meat of local pigs of better sensory quality than that of LW animals. CR meat was found to be more tasty (P<0.05), more juicy (P<0.01) and more tender (P<0.001). Local pigs are considered to be of little importance for commercial pig production due to their fatness. However, meat quality of CR pigs was superior to that of LW animals, as the former exhibited a higher ultimate pH value, lower drip loss and better sensory qualities.

L'objectif de cette étude était de comparer, en milieu tropical, les performances de croissance et la qualité de la viande du génotype local, le porc Créole (CR), et d'une race importée, le Large White (LW), en fonction de l'âge à l'abattage. Soixante animaux ont été répartis en six lots selon le type génétique (CR vs LW) et l'age d'abattage (4, 5 et 6 mois). Les CR se sont distingués des LW par un gain de poids journalier inférieur de 34% (P<0.001) et par une carcasse significativement plus grasse (P<0.001). L' augmentation du pourcentage bardière + panne avec l'age des animaux était notable dès 5 mois chez le CR et à partir de 6 mois seulement chez le LW (interaction génotype x age d'abattage: P<0.001). Les pH mesurés 45 mn et 24 h post-mortem sur le Long Dorsal et l'Adducteur étaient plus élevés chez le CR que ceux déterminés pour le LW (P<0.001). Sur l'Adducteur, le temps d'imbibition était plus élevé de 9.4 unités (P<0.001) et le pourcentage de pertes au ressuage plus faible de 4.4 points (P<0.001) chez le CR que chez le LW. L'analyse sensorielle a révélé un goût plus intense (P<0.05) et surtout, une jutosité secondaire (P<0.01) et une tendreté (P<0.001) plus grande de la viande chez les animaux locaux comparés aux porcs LW. L'adiposité coporelle excessive du porc CR limite donc son utilisation en élevage semi-intensif. En revanche, du point de vue de la qualité de la viande, le porc indigène se révèle supérieur au LW avec, notamment, une vitesse et une amplitude de chute du ph post-mortem plus faible, une capacité de rétention d'eau plus élevée et de meilleures qualités organoleptiques.

The local pig (CR), from the Caribbean, constitutes an heterogeneous population coming from different successive crossbreeds of animals from Iberian, French and American breeds. This population is to be found mainly in small numbers at household level (less than five pigs per household) and represents 36% of the pigs in Guadeloupe. The trading of these animals is done informally.

Studies have been made by INRA, Guadeloupe in order to compare local pigs (CR) with Large White, an improved race imported in 1965. This work showed that in semi-intensive conditions the CR is inferior to Large White both in growth performance and reproduction (Canope and Raynaud 1981; Canope and Raynaud 1982) and gave prominence to the limits of using the local CR pig in a semi- intensive production system (Despois and al 1991).

The carcass quality of CR pigs has not been studied yet the meat of these animals is particularly appreciated by the people of Guadeloupe. The organoleptic criteria of fresh meat such as tenderness, juiciness and taste should be taken into account since 78% the meat eaten in Guadeloupe comes from pork.

A study was made at the Animal Research Station with the aim of comparing, under tropical conditions, the growth performance and the meat quality of Large White and CR pigs managed in a semi- intensive production system. The aim of this article is to show the results obtained and to suggest new ways of demonstrating the value of local pig genotypes in the Caribbean region.

30 castrated males and 30 females from the INRA herd (INRA, Duclos, Guadeloupe: 16° Latitude North and 61° Longitude) were allocated to 10 groups each of 6 animals according to their sex in a 2 x 3 factorial design including 2 genotypes (Large White or CR) and 3 ages of slaughter (4, 5, and 6 months).

At the beginning, the pigs were 78.0"5.9 days old. They were reared in groups in a covered half-open-sided shed with an outside yard. They were fed ad libitum with a commercial cereal-based feed providing 13.8 MJ of digestible energy and 160 g of crude protein per kg. The animals were slaughtered in the experimental abattoir of the Animal Research Station of INRA in standardized conditions of minimum stress. The measurements on meat quality were made on 2 white muscles: the Longissimus Dorsi and the Adductor. In these two muscles the pH was determined 45 minutes (initial pH, pH 1) and 24 hours (last pH, pH 24) post-mortem. The saturating time was measured 24 hours after slaughterer. The water retention capacity was estimated as the drip loss measured on a sample of adductor muscle weighing about 100 g. The content of "haemolytic pigments" in the longissimus dorsi muscle was measured on fresh tissue.

After measuring the drip loss, three joints of pork were taken from the longissimus dorsi between the 7th dorsal vertebra and the last lumbar vertebra and were frozen at -20 °C until the sensory analysis. The joints were thawed out and allowed to mature for 24 hours in a cold room at 4 °C. Then they were roasted at 75°C, cut in slices similar in thickness and size, and offered to tasters at ambient temperature.

The tasting room was made of eight isolated posts corresponding to the AFNORV 09105 norm (a standard established in France). A panel of eight trained people was selected in order to determine the effect of the genotype on the organoleptic quality of the meat. The panel members were asked to identify the organoleptic qualities of the meat according to 5 criteria: smell, taste, tenderness, primary juice and secondary juice. The panel gave a mark to each sample for each of these criteria and a global mark according to a scale going from O to 10 continuous and non-structured.

Analysis of variance was performed using the General Linear Model of the Statistical Analysis Systems Institute package (SAS 1987). The data concerning the growth performances were evaluated using an analysis of covariance according to a linear model with fixed effects; the sensory data from the taste panel were analyzed using an analysis of variance.

The growth performances of the animals are shown in table 1. At the beginning of the experiment, at the same age the Large White and the CR pigs weighed 32.4"1.7 and 22.2"1.8 kg (P< 0.001), respectively. During the course of the experiment the daily weight gain of CR pigs was lower than the Large White (P< 0,001): average of 402"33 g and 610"31 g, respectively. The result was that, at the same age, the weights at slaughter were significantly lower for CR pigs than for the imported genotype (P< 0,001).

The carcass yield was 81.4"0.6% for the Large White and 79.4"0.6 % for the CR (P< 0.001) (Table 2). The relative weights of the carcass cuts, apart from the shoulder, also varied with the genotype (P< 0.001) (Table 2).

Table 1: Effects of genotype and age of slaughter on the growth performances (n=10)

	Slaughter age (months)
	4	5	6	RSD

Liveweight (kg)
Start
Large white	30.8a	33.4a	33.1a
Creole	22.3b	24.3b	20.0b	5.2
End
Large white	59.3c	69.5b	92.9a
Creole	34.0e	48.3d	62.3c	8.0
Daily gain (g)
Large white	664a	575b	590ab
Creole	327d	397c	482c	90

abc: means within the two lines (genotypes) line with the same superscript do not differ (P<0.05)
RSD: Residual standard deviation

Table 2: Effects of the genetic type and the age at slaughter on the carcass yield and the weights of the cuts (n = 10).

	Slaughtering age (months)
	4	5	6	RSD

Carcass yield
Large White	79.2c	81.6b	83.5a
Creole	76.1d	79.2c	83.1ab	0.02
Shoulder (%)
Large White	12.7ab	11.8bc	10.9c
Creole	13.5a	10.8c	11.6bc	1.2
Anat Chest (%)
Large White	10.5a	9.9b	10.2a
Creole	8.7c	9.1c	9.7abc	1.0
Back fat + Leaf Fat (%)
Large White	12.8bc	11.2c	14.5b
Creole	12.4bc	18.1a	18.4a	3.1
Ham + Loin (%)
Large White	49.7ab	51.6a	48.1bc
Creole	49.1ab	45.7c	45.7c	3.5

At the age of 4 months the genotype had no effect on the percentage of back fat + leaf fat (P>0.10). In contrast, for the animals slaughtered at 5 or 6 months-old, this percentage was significantly higher for the CR pigs than for the Large White (P<0.001). The increase in the percentage of back fat + leaf fat with the age of the animals was significant from the age of five months for the CR and only from the age of six months for the Large White (interaction genotype x age at slaughter: P < 0.001). Similarly, at the age of 4 months the percentage of ham + loin was independent of the genotype (P>0.10) but when the pigs were slaughtered at the age of 5 or 6 months this percentage was lower for the CR pigs than for the Large White (P<0.01) (interaction between genotype and age at slaughter for the percentage of ham + loin [P < 0.01]). This percentage decreased noticeably as from the age of 5 months for the CR pigs and from 6 months for the Large White.

Table 3: Effect of the genotype and age at slaughter on the parameters of meat quality (n = 10)

	Slaughter age (months)
	4	5	6	RSD

pH 45 min Adductor
Large White	6.05c	6.11b	6.31ab
Creole	6.50a	6.37a	6.29ab	0.20
pH 45 min Long Dorsi
Large White	6.50ab	6.28c	6.26c
Creole	6.64a	6.40b	6.55ab	0.19
pH 24 hr Adductor
Large White	5.91b	5.64c	5.77bc
Creole	6.10a	5.92b	5.99ab	0.17
pH 24 hr Long Dorsi
Large White	6.05b	5.75c	5.84c
Creole	6.27a	6.00b	6.02b	0.15
Saturation time (10s)
Adductor
Large White	5.3b	1.8b	4.3b
Creole	13.8a	12.8a	13.1a	4.3
Long Dorsi
Lare White	5.9c	1.8c	1.7c
Creole	15.9a	10.7b	13.6ab	5.2
Drip loss (%)
Adductor
Large White	6.85bc	8.55c	5.04c
Creole	2.39a	2.20a	2.50a	0.12
Haemolytic pigments (mg/g)
Long Dorsi
Large White	2.27a	2.43a	2.68a
Creole	1.38b	1.69b	2.18a	1.06

Concerning meat quality there was no effect of sex on the different criteria considered (P>0.10). Table 3 shows that the genotype affected all the parameters of meat quality. For example, the pH after one hour in the Adductor was 6.16"0.07 for the Large White and 6.3"0.08 for the CR pig (P<0.001). The corresponding values for the Longissimus Dorsi muscle were 6.35"0.06 and 6.53"0.07 (P<0.01), respectively.

Similarly the pH at 24 hr was lower for the Large White than for the CR pig (P<0.001). For the two muscles the saturation time was lower for the imported genotype than for the local pig (P<0.001). Furthermore, the Longissimus Dorsi muscle of the Large White pig was significantly richer in haemolytic pigments than the Creole.

Table 4: Effects of genotype and age at slaughter on the criteria of sensory quality (n = 48).

	Slaughter age (months
	4	5	6	RSD

Smell
Large White	6.7ab	7.1a	6.3b
Creole	6.3b	6.4b	6.9ab	1.4
Taste
Large White	5.0c	5.6bc	6.0b
Creole	6.2b	5.6a	6.7a	1.7
Juiciness Primary
Large White	4.5a	3.0b	5.1a
Creole	4.9a	3.3b	4.9a	1.9
Juiciness Secondary
Large White	5.1c	4.7c	5.4b
Creole	6.3a	5.3b	6.1a	1.8
Tenderness
Large White	4.1c	4.6c	4.9c
Creole	7.4a	6.1b	7.1ab	2.1
Index of quality
Large White	4.4c	4.3c	5.4b
Creole	6.3a	5.0bc	5.8a	1.9

The taste panel preferred the meat of the CR pigs at all slaughter ages (Table 4). The global score for quality was: 5.8?0.4 for the local genotype and 4.7?0.3 for the Large White (P<0.001). Taste, secondary juiciness and tenderness were also scored higher for the CR pigs than for the Large White (P<0.001). On the contrary, smell and primary juiciness appeared to be independent of the genotype (P>0.10).

The pH values after 45 min and after 24 hours post mortem for the Large White were higher than those registered on pigs of the same genotype in a temperate country (Gandemer et al 1990; Castaing 1991). In contrast, they are close to the values obtained in an air-conditioned room at a temperature of 28 ?C (Lefaucheur et al 1989), which corresponds to the average temperature in Guadeloupe. This implies that the tropical climate influences the evolution of the pH after slaughter.

In our conditions, the higher values of pH for the local Creole pig at 45 minutes and at 24 hr indicate a lower rate of decline and higher absolute values than for the Large White. The pH values for the CR pig are noticeably superior to those estimated for a large variety of genotypes such as Pietrain and Hampshire (Gueblez et al 1990), Large White (Castaing 1991) and the crosses with Chinese breeds (Gandemer et al 1990). The values obtained for the saturation time and the percentage of drip loss for the Large White imply a capacity for water retention of the muscle totally inferior to that registered for the same genotype in a temperate country (Gandemer et al 1990; Castaing 1991). The higher saturation time and the lower drip loss for the CR pig, compared with the Large White would imply a better capacity of water retention of the muscle for the local genotype, linked to the higher pH values. These higher pH values and higher capacity for water retention for the CR pig are elements in its favour as regards the technological yield of cooked ham.

Contrary to the findings of Gandemer et al (1990), who compared the Large White to Gascon-Chinese cross, we have shown an effect of genotype on the content of haemolytic pigments in the Longissimus Dorsi muscle with the Creole pig being less pigmented. These data show the superiority of the CR pig compared with the Large White in terms of the organoleptic quality of the fresh meat. This result is especially interesting as the meat of the Large White is generally considered to have a high rating for these criteria (Gandemer et al 1990). The CR pig distinguishes itself from the Large White for its taste and above all for its secondary juiciness and its tenderness.

In a study of another rustic breed, Touraille et al (1989) showed that the meat of Large White x Meishan crosses had a more intense flavour, was more juicy and tender than the meat of pure Large White.

Among the Chinese crosses it has been proved that the better juiciness is associated with, mainly, the richness in lipids of the muscle. The higher capacity for water retention and the longer saturation time were poorly correlated with juiciness (Gandemer et al 1990). The differences in tenderness between genotypes were attributed also to the lipid content of the muscle, as the content of collagen hardly varied (Touraille 1990).

It is necessary to complete our study by measuring the content of lipids within the muscles and their composition in fatty acids as these criteria are highly linked to the results of the sensory analysis (Girard et al 1986).

However, following the example of what has been observed for meat from Chinese crosses (Touraille 1990) the visible presentation of pieces rich in intermuscular fat could result in refusal by the consumer. This might limit the use of the Creole breeds in the form of fresh meat.

This study has given prominence to the better technological and organoleptic qualities of meat from local Creole pigs compared to the Large White meat in semi-intensive management using a commercial concentrate feed. The conditions of housing and feeding in Guadeloupe vary widely. According to Gandemer et al (1990), who compared animals in an intensive system to those reared in covered pens with access to a yard and receiving beet root and concentrates, the conditions of accommodation have no noticeable influence on the technological and organoleptic qualities of the meat. On the contrary, it is well known that composition of the feed affects the organoleptic qualities of the meat (Girard et al 1986).

Our data confirm the earlier results of Unshelm et al (1972) and the more recent reports concerning the meat quality of the Chinese cross (Touraille et al 1989; Touraille 1990), according to which the meat coming from rustic genotypes or at least, those with low potential of muscle growth, have better organoleptic qualities than breeds selected for leanness. Furthermore, we have shown the superiority of the local pig compared with the imported genotype as concerns the criteria of technological quality of the meat. It is true that the use of the Creole pig is limited to semi-intensive systems, owing to the high proportion of fat in the body. Therefore, as in Corsica (Molenat and Casabianca 1979), the evaluation of local pig breeds should be based on the parameters of technological and organoleptic qualities of the meat, reared in an extensive system. The superior meat quality could be identified by means of a label.

Further research is needed especially to estimate the effects of the quantity and the nature of the food given in extensive conditions on the quality of the meat from the Creole pigs.

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