Agris category code: L02, Q01
FEEDING STRATEGIES FOR LOCAL BREEDS IN VIEW OF PRODUCT QUALITY
Carolina PUGLIESE 1 2, Francesco SIRTORI Oreste FRANCI 1
ABSTRACT
The effect of quantitative-qualitative modulation of diet on quality of meat and cured product in pig local breeds is reviewed, focusing on the effect on intramuscular fat (IMF) which is the most important of the meat traits. IMF does not develop the last among fat depots, so high level of feeding in advanced age favours subcutaneous fat deposition, whose commercial destination is often problematic also for the local pig. The compensatory growth, as consequence of re-alimentation after feeding restriction, attains better to local breeds than to conventional ones, because of the longer rearing period and the exploitation of natural resources in sylvo-pastoral system. This practice in Cinta Senese produces meat with higher cooking loss, fatter, less tender, darker and redder and subcutaneous fat richer in MUFA and PUFA n-3. However, the compensatory effect seems to depend also to the age when fattening starts. Knowledge on protein requirements in the local breeds is less available but researches on Iberian and Cinta Senese pig highlighted that only very low dietary protein content (below 9%) produced significant effect on overall fatness and on some meat traits. On other hand, that protein content is usual in the diet of sylvo-pastoral feeding system, based on grass and acorn without any aminoacidic integration.
Key words: local pig / feed restriction / dietary proteins / intramuscular fat / meat quality
Invited lecture COBISS: 1.06
1 introduction
Strategies for feeding pig have a great importance in the determination of chemical, physical and sensorial characteristics of meat (fatty depots included) and of processed products. The literature refers largely to conventional and improved breeds but, from those general rules, it is possible to obtain indication which, mutatis mutandis, can also be useful for the management of local breeds, even if these genotypes are to be reared according to the systems more congenial in form of compliance of the specification required by the marks of origin. The recent review of Lebret (2008) examined extensively the link between feeding/rearing system and the quality of carcass and meat in pigs, with particular emphasis to the conventional breeds. The feeding strategies can be categorised according the following points: 1) feeding
restriction; 2) feeding restriction and re-alimentation (and, consequently, compensatory growth); 3) dietary level of protein (or lysine): energy ratio. The analytical, physical and sensorial traits, considered to define the quality of pig products, are largely influenced by the fat components, both by that portion indissolubly linked to meat (IMF) and by the subcutaneous and intermuscular depots, which, although mechanically separable from the muscle, ultimately participate directly to the cured products as a whole piece (i.e. ham) or as sausages (i.e. salami). So, the quantitatively and qualitatively variation of fat, largely dependent to the diet, is to be considered primarily in the relationship between feeding strategy and products quality. However, even the muscular component, participates in the definition of quality parameters through the relations between stromatic and fibrillar proteins, the proportion of the various types of muscle
1	DiSPAA, Animal Science Section. University of Firenze, Via delle Cascine, 5. 50144 Italy
2	Corresponding author, e-mail: carolina.pugliese@unifi.it
fibers and the process of post-mortem acidification (pH fall). The latter is perhaps the main factor affecting water holding capacity (WHC) and the tenderness of the meat. The influence of feeding on the muscular component is well recognised in the review of Andersen et al. (2005), where particular emphasis to muscle protein turnover and energy level in conventional pig is made. The present review is focused on influence of feeding strategy on adipose depots, as main responsible of the characteristics of the products of local pig of the Mediterranean area.
2 fat depots
IMF represents the inseparable component of the meat and its proportion is generally associated with the improved sensory traits of meat (Fernandez et al., 1999; Wood et al., 2004) to the point that Wood et al. (1986) stated that particularly low IMF content may not assure desirable organoleptic properties. Moreover, IMF plays a major role in the quality of dry-cured meat products, as Iberian ham, since it strongly influences the technological feasibility and the sensory quality of the final products (Lopez-Bote, 1998). IMF content is higher in local pigs than in the "improved" ones, as reviewed by Pugliese and Sirtori (2012) and as found in some direct comparisons between the two genotypes (Franci et al., 2005; La-broue et al., 2000; Serra et al., 1998). The fat content in Longissimus muscle of local pigs is generally higher than 3% but can exceed also 20% in Iberian pig that exhibited the highest variability for this trait. Moreover, studying the relationships among various fat depots, Franci et al. (2001) pointed out that IMF was only partially linked to overall fatness and this relative independence was mainly due to breed differences. This finding was confirmed by Wood et al. (2004) which indicated: low IMF and subcutaneous fat (SF) content in Large White, high percentage of both fats in Berkshire, low SF and high IMF in Duroc, high SF and low IMF in Tamworth. Also in some Mediterranean local pigs there are differences between IMF and carcass fat content (Table 1), but the comparison
should be conducted in the same experiment to achieve scientific evidence. However it seems important to report the findings of Wood et al. (2004) that the composition of the IMF are influenced not by the IMF content but by the overall body fatness which definitively controls the fatty acid profile. In this context, the allometric growth of the various fat depots is to be examined. According to Lee and Kauffman (1974), IMF develops later than the other fat depots and then it is more sensitive to the environmental and nutritive manipulation during the fattening. Anyway this finding was relative to very light pig. Results concerning a wide weight range, inclusive of high weights usual in the pig production of the Mediterranean area (Table 2), highlight that IMF is late developing tissue, but not the latest among the fat depots because this record is mainly attributable to subcutaneous/intermuscular fat. This pattern implies that nutritional manipulation performed in the late fattening in order to increase the IMF deposition and, consequently, to improve the meat quality and characterize the cured product, involves in a considerable increase of the subcutaneous depot, whose commercial destination is often problematic.
3 feed restriction
Studies on the improved pig breeds demonstrated that feed restriction, in comparison to ad libitum feeding, particularly during the growing-fattening period, reduces the growth rate and, consequently, leads to leaner carcasses (Quiniou et al., 1995; Lebret et al., 2001). This is due to the fact that the relative growth rate of adipose tissue increases with the age, whereas the protein deposition remains rather constant and priority; hance, the fat deposition appears more sensitive to a reduction of energy intake during the fattening period. Lebret et al. (2001) demonstrated that a restriction of 25% in feeding allowance decreases the growth rate for 27% and reduces the overall carcass fatness and the IFM deposition in Longissimus. This confirms previous research (i.e. Quiniou et al., 1995; Candek-Potokar et al., 1998), where
Table 1: Comparison of fat content in carcass and in Longissimus muscle of some local breeds
Breed	Body weight (kg)	Age (days)	Total fat cuts (%)	IMF (%)	Author
Casertana	200	494	39.5	4.7	Fortina et al., 2005
Mora Romagnola	193	514	44.7	6.1	Fortina et al., 2005
Nero Siciliano	102	448	39.4	3.3	Pugliese et al., 2004
Cinta Senese	136	312	37.1	3.2	Franci et al., 2005
Cinta Senese	154	430	33.5	6.0	Sirtori et al., 2011
Iberian	152	482	~56*	~10*	Mayoral et al., 1999
* Adaptation of original data 70 Acta agriculturae Slovenica, Supplement 4 - 2013
Table 2: Allometric coefficients (b ± se) of fat depots
Author	Franci et al. (2001)	De Pedro-Sanz (1987)	Geri et al. (1984)
Breed	conventional	Iberian pig	conventional
Live weight range (kg)	124-183	50-175	20-200
Part of reference	carcass	Ham	total carcass fat
Subcutaneous fat	1.34 ± 0.08	1.70 ± 0.03	1.06 ± 0.01
Intermuscular fat	1.47 ± 0.14	1.41 ± 0.06	0.68 ± 0.04
IMF	1.26 ± 0.22	1.04 ± 0.04	0.81 ± 0.03
the feeding restriction did not affect the meat quality (pH, reflectance, drip loss). On the contrary, Blanchard et al. (1999) found that a restriction of 0.8% of ad libitum diet produced less tender and juicier meat and Bee et al. (2006) stated that feeding restriction had detrimental impact on meat quality, with lower water holding capacity and tenderness. These general principles can be applied also on the local pig breeds, characterised by low protein deposition and high body fatness. Actually, in these breeds, the feeding system is extremely variable and produces different weight gain, as demonstrated by Crovetti et al. (2012) on Cinta Senese which, according to the different systems, reached the slaughter weight of 150 kg at ages from 12 until 24 months. Unfortunately, in the extensive conditions, the reduction of growth rate is consequence both of feeding allowance restriction and of use of natural resources, as pasture on grass; so, it is impossible to evaluate the true effect of feeding restriction on the quality of the products. On other hand, on the Italian local breeds there is no experimental trial on this topic but it is possible to extrapolate some indications comparing different studies where weight gain is the discriminating factor. Hence, comparing the findings of Franci et al. (2005) and Pugliese et al. (2003), emerged that in Cinta Senese the 15% decrease in growing rate determines a lower percentages of fat cuts and IMF and also lower WHC. Similar tendency can be achieved reprocessing data of Sirtori et al. (2011) on Cinta Senese reared indoors and outdoors.
4 feed restriction and re-alimentation
This topic has been well reviewed by Lebret (2008) in relation to the conventional breeds. This feeding strategy is applied to encourage the compensatory growth, an accelerated the rate of weight gain due to ad libitum feeding subsequent to a period of limited food supplied. Compensatory growth was firstly defined by McMeekan (1940) and, thereafter extensively studied by many authors. Normally this strategy allows to localise the high
energy supply when the pig is older, because of the limited growth in the previous phase, and the biological rhythm should favour the fat deposition, both in the subcutaneous and muscular depot. According to Kristensen at al. (2004), the compensatory growth should improve meat tenderness, as it can favour the muscle protein turnover. On the contrary, Lebret et al. (2007) and Heyer and Lebret (2007) found that 28 or 34 days of re-feeding period had no positive effect on the IMF content of Longissimus and on meat eating quality. Similar results were achieved on light pigs (up to six months of age) by other authors with analogous experimental design (Skiba, 2010; Oksb-jerg et al., 2002; Wiecek et al., 2011).
In conclusion, increase of the IMF level and improvement of meat quality might depend from the onset and duration of the restriction and re-alimentation period, the rate of reduction of growth during the restriction and from the age at the re-feeding. However, the positive effect of compensatory growth on the increase of IMF seems to be difficult to achieve in the conventional pig breeds and in the intensive pig production where the increase of age or weight at slaughter is to be avoid. On the contrary, the compensatory growth is well suitable in the rearing scheme of the local pig in the Mediterranean regions where natural feeding resources are widely used in a sylvo-pastoral system and where pigs are slaughtered at high weight and/or age with the aim to enhance the quality of processed products. The best example of such feeding strategy is the one used in the rearing of Iberian pig (Lopez-Bote, 1998). Also recently, other local breeds of the Mediterranean area have been studied in relation to the extensive system, as Alentejano in Portugal (Neves et al., 2007; Tirapicos Nunes, 2007); Corsican pig in France (Secondi et al., 2007); Nero Siciliano and Cinta Senese in Italy (Pugliese et al., 2004 and 2005). Normally, the extensive system, particularly linked to the availability of natural resources, per se determined the feeding restriction and re-alimentation but in some rearing systems, as the one of Iberian pig (Lopez-Bote, 1998), the feeding restriction during the growth is deliberately practiced to exalt the weight gain during the final period of Montanera. The shape of the growth curve in
Figure 1: Trend of growth in Cinta Senese pig according to rearing system (Acciaioli et al., 2002)
free-range system, in comparison with that of the intensive system, is well represented in Fig. 1, relative to Cinta Senese pig. The consequence of this pattern on carcass and meat composition is reported in Table 3. Free-range pigs had more IMF, but also higher fat cuts percentage, and they produced meat with higher cooking loss, less tender, darker and redder. Subcutaneous fat was richer in MUFA and PUFA, including the PUFA n-3. It is difficult to attribute all these characteristics exclusively to the compensatory growth, given the differences in the diet composition. However, the study of Mayoral et al. (1999) on Iberian pig, during the traditional management system with fattening on acorns and pasture, highlighted that, following a growth pattern analogous to that shown for Cinta Senese in Fig. 1, IMF of Longissimus increased up to 10%, water loss decreased continuously, total col-
Table 3: Performances of Cinta Senese pig according to rearing system, as in Fig. 1 (Pugliese et al., 2005)
	Indoor	Pasture
Slaughter weight (kg)	136.2a	127.7b
Age (days)	312a	510b
Total fat cuts (%)	36.7a	41.0b
IMF (%)	3.3a	4.0b
Cooking loss (%)	26.6a	30.3b
Shear force on cooked meat (N)	105a	151b
L*	50.13a	45.78b
a*	11.77a	14.95b
In subcutaneous fat (% of FAs)		
MUFA	53.3a	55.08b
PUFA n-3	0.39a	1.02b
PUFA n-6	10.05a	12.30b
a, b; P < 0.05
lagen did not vary but insoluble collagen increased from 7 to 77% of total collagen. Unfortunately, the carcass fat increased markedly during the last 80 days reaching the value of 56% of the carcass weight. The effect of Montanera pasture on fat quality characteristics of Iberian pig was less pronounced in pigs starting the fattening with 8 months than in pigs starting with 12 an 14 months (Daza et al., 2007a), whereas a severe reduction of the feeding level before the fattening in Montanera did not produced compensatory growth and resulted in only a small improvement in fatty acid profile of SF (Daza et al., 2008). Other works in Iberian pigs reared in intensive system, allows better understanding of the effects of the compensatory growth on meat and fat traits avoiding confusion with other factors such as the different diet composition present in the abovementioned researches. Daza et al. (2007b) found that the re-alimentation on ad libitum level, following feed restriction, did not modify the back-fat thickness and the IMF content but increased the oleic content in the subcutaneous fat (about 2%) whereas Serrano et al. (2009) found the same results for carcass traits and IMF content but higher content of oleic acid in back-fat of pigs feed continuously ad libitum.
5 protein level and quality
The protein requirements of the improved pig breeds have been widely studied (see review of Whitte-more et al., 2001) also in terms of the growth and feeding efficiency (Campbell et al., 1984; Hansen and Lewis, 1993). But only a limited number of studies have addressed the effect of the dietary protein or lysine levels on the carcass composition and, in particular, on the meat quality. A summary of the studies on conventional breeds (Lebret, 2008) reports, that unbalanced diets (with insufficient ratio of protein or lysine to energy contents) in-
creased IMF content and improved tenderness and juiciness of meat. The knowledge on protein requirements in the local breeds is less available and, in particular, studies that define the composition of ideal protein ratio at different stages of growth are few. Only on Iberian pig a wide research has been conducted to study the effects of different dietary levels of ideal protein on protein and energy retention (Barea et al., 2007; Nieto et al., 2012) and on carcass characteristics (Nieto et al., 2003; Barea et al., 2006). In detail, Barea et al. (2006) observed that a diet with 6.2% of protein (0.42% of Lys) produced at 100 kg of live weight a higher percentage of dissectible fat in the ham and shoulder compared with other three diets with 8.4 (0.57), 10.6 (0.72), 12.8 (0.87) % of protein (Lys), which behaved in similar manner. Unfortunately, information on specific influence on meat and cured products quality is not available.
Similar results on overall body fatness have been found in Cinta Senese by Sirtori et al. (2013) that also shows the influence of dietary protein content on meat quality (Table 4). It emerged that the diet at 8% of protein is well distinguishable from the others as it resulted in greater fatness of the carcass and in meat with higher IMF, cooking loss, lightness and redness. It is noticeable that the three other diets, at higher protein content, had the same behaviour, confirming the picture found also for the in vita performance (Sirtori et al., 2010). This result demonstrates the low protein requirements of this breed and justifies the use of a diet at 10% of protein, without any aminoacidic integration. On other hand, the integration of amino acids into the diet is prohibited by the rules of an organic system or of the "Cinta Senese" PDO label, to which many breeders of Cinta Senese adhere. Finally, it is evident that, the lowest protein contents tested in the researches of Barea et al. (2006) and Sirtori
et al. (2013), are difficult to implement in a conventional pig productive system as they are lower than protein content of cereals, but are usual in the diet of sylvo-pastoral feeding system. In fact, Rodriguez-Estevez et al. (2009) demonstrated that Iberian pig, reared in the Dehesa, intakes daily about 3.6 kg of acorn endocarp and 0.4 kg of grass (as dry matter) with a dietary protein content of 6.5% (on dry matter basis). So the results on meat quality obtained indoors with the diet at a lower protein content, can be realistic in animal reared in free-range on natural pasture.
6 conclusion
This review limits its examination to some aspects of the feeding strategy related to quantitative and qualitative modulation of the diet, focusing on changes in the IMF that is considered the main responsible for the quality of meat and cured products. It turns out that researches on the developmental pattern of fat deposits for many local breeds in the Mediterranean would be useful, since it is not appropriate to generalize, given the evident differences in fat partitioning among genotypes. In fact the local breeds are slaughtered at high weights and ages and have better chances to feel the effects of compensatory growth linked to dietary restrictions for energy and/or protein. However, this tool must be properly calibrated to avoid excessive development of fat deposits of problematic commercial value. This principle must be kept in mind also in consideration of the fact that for many of these breeds the niche market of products requires the respect of breeding systems which ensure also the image of naturalness and healthiness, in the respect of specific
Table 4: Effect of dietary protein content on	traits of Longissimus l. muscle in Cinta Senese pig (Sirtori			et al., 2013)	
	Protein content of diet (%)				
	8	10	13	16	rsd
Dietary Lysine (%)	0.21	0.37	0.57	0.79	
Total fat cuts (%)	37.16a	32.92b	33.95b	33.30b	1.98
Cooking loss (%)	20.90a	16.26b	16.51b	18.32	4.64
WB shear force on cooked meat (kg)	9.70	10.32	10.93	9.60	2.18
IMF (%)	6.58a	4.18b	3.78b	4.07b	1.24
Protein (%)	21.36a	22.78b	23.52b	23.23b	1.17
Colour parameters					
- L*	48.47a	45.75b	44.85b	45.38b	2.62
- a*	11.33	10.55	11.00	10.94	1.46
- b*	3.59a	2.90b	2.52b	2.74b	0.79
b Within row, means assigned with different letter differ significantly (P < 0.05)
regulations that prevent integration with synthetic substances.
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