RESEARCH ARTICLE

Performance, carcass characteristics, economic margin and meat quality in young Tudanca bulls fed on two levels of grass silage and concentrate

Emma Serrano

Gobierno de Cantabria. D.G. Desarrollo Rural. Centro de Investigación y Formación Agrarias (CIFA), C/Héroes Dos de Mayo, 27, 39600 Muriedas (Cantabria), Spain.

M. José Humada

Gobierno de Cantabria. D.G. Desarrollo Rural. Centro de Investigación y Formación Agrarias (CIFA), C/Héroes Dos de Mayo, 27, 39600 Muriedas (Cantabria), Spain.

Irma Caro

Universidad de León, Dept. Higiene y Tecnología de los Alimentos. Campus Vegazana s/n, 24007 León, Spain.

Ibán Vázquez

Gobierno de Cantabria. D.G. Desarrollo Rural. Centro de Investigación y Formación Agrarias (CIFA), C/Héroes Dos de Mayo, 27, 39600 Muriedas (Cantabria), Spain.

Ana M. Olaizola

Universidad de Zaragoza, Instituto Agroalimentario de Aragón-IA2 (Universidad de Zaragoza-CITA), Dept. Ciencias Agrarias y del Medio Natural. C/ Miguel Servet 177- 50013 Zaragoza, Spain.

Helena Resano

Universidad de Zaragoza, Instituto Agroalimentario de Aragón-IA2 (Universidad de Zaragoza-CITA), Dept. Ciencias Agrarias y del Medio Natural. C/ Miguel Servet 177- 50013 Zaragoza, Spain.

Sergio Soto

Universidad Autónoma del Estado de Hidalgo, Instituto de Ciencias Agropecuarias. Ave. Universidad s/n km 1. 43600 Tulancingo (Hidalgo), Mexico.

Javier Mateo

Universidad de León, Dept. Higiene y Tecnología de los Alimentos. Campus Vegazana s/n, 24007 León, Spain.

 

Abstract

This study investigates the effect on performance, carcass and meat characteristics of increasing the forage level in the diet of fattening Tudanca young bulls using silage as the forage source as compared with a conventional ad libitum straw plus concentrate diet. Twenty two Tudanca young bulls were assigned to three different finishing diets: ad libitum grass silage plus ad libitum concentrate (GS-AC), ad libitum grass silage plus concentrate limited to a half of the intake of the ad libitum group (GS-LC), ad libitum barley straw plus ad libitum concentrate (Str-AC) and then slaughtered at around 11 months of age. GS-LC diet resulted in relation to GS-AC and Str-AC diets in lower (p≤0.05) average daily weight gain (750 vs 1,059 and 991 g/animal/day, respectively), lower (p≤0.05) carcass weight (133 vs 159 and 152 kg, respectively) and carcasses with slightly lower conformation scores. Although GS-LC diet allowed for a lower dependence on concentrate (372 vs 657 and 729 kg/animal, respectively), economic margin was similar for the two GS groups (-63.1 and -64.1 vs -91.8 €/head). The polyunsaturated/saturated fatty acid ratio was the lowest (p≤0.05) in GS-AC meat (the group showing the highest IMF levels) and the ratio n-6/n-3 was the highest (p≤0.05) in Str-AC meat. GS-LC meat showed higher collagen content and Str-AC meat presented higher cohesiveness, springiness and chewiness values. Results suggested that the substitution of straw by grass silage and the restriction of the concentrate level could be recommended for finishing young Tudanca bulls in indoors systems.

Additional keywords: rustic breed; beef; fat deposition; concentrate level; production efficiency; fatty acid; texture.

Abbreviations used: ADWG (average daily weight gain); BBU (bovine bulk unit); DM (dry matter); FAME (fatty acid methyl ester); GS-AC (ad libitum grass silage plus ad libitum concentrate diet); GS-LC (ad libitum grass silage plus limited concentrate diet); IMF (intramuscular fat); MUFA (monounsaturated fatty acids); PDI (protein truly digestible in the small intestine); PUFA (polyunsaturated fatty acids); SFA (saturated fatty acids); Str-AC (ad libitum barley straw plus ad libitum concentrate diet); TBARS (thiobarbituric acid reactive substances); UFL (Unités Fourragères Lait, or net energy for maintenance and gain expressed in milk feed units).

Authors' contributions: Conceived and designed the experiments: ES and MJH. Performed the experiments: ES, MJH, IC, SS, JM. Wrote the paper: ES, MJH, JM, IC, IV, AMO, HR. All authors analysed and interpreted the data, read and approved the final manuscript.

Citation: Serrano, E.; Humada, M. J.; Caro, I.; Vázquez, I.; Olaizola, A. M.; Resano, H.; Soto, S.; Mateo, J. (2018). Performance, carcass characteristics, economic margin and meat quality in young Tudanca bulls fed on two levels of grass silage and concentrate. Spanish Journal of Agricultural Research, Volume 16, Issue 3, e0609. https://doi.org/10.5424/sjar/2018163-13027

Received: 12 Feb 2018. Accepted: 01 Aug 2018.

Copyright © 2017 INIA. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International (CC-by 4.0) License.

Funding: Comunidad Autónoma of Cantabria, Spain; INIA (RTA2012-00084-C03-00 project); E. Serrano postdoctoral contract (DOC-INIA-CCAA 2008).

Competing interests: The authors have declared that no competing interests exist.

Correspondence should be addressed to Emma Serrano: emmaserrano@cifacantabria.org


 

CONTENTS

Abstract

Introduction

Material and methods

Results

Discussion

Acknowledgments

References

IntroductionTop

The Tudanca breed is an endangered breed (BOE, 2008) from Cantabria, Northern Spain, used for meat production, with a population of 11,148 breeding cows in 2015 (ICANE, 2017). Tudanca calves are usually sold at weaning (around 6 months of age) to units specialized in intensive fattening, located in other Spanish regions (Humada et al., 2013). A traditional type of Tudanca production was based on young animals, slaughtered at approximately 10 months of age and suckled until slaughter, which, depending on the season and the availability of feeding resources, were raised grazing with their dams or receiving hay and small quantities of concentrate indoors. A number of Tudanca calves are still reared on local farms but most of the produced young Tudanca bulls are weaned at 4-6 months of age and finished with cereal straw and concentrate ad libitum until 10-11 months of age (Vázquez et al., 2016).

The Tudanca is a rustic breed with low carcass yield and conformation scores and high capability of fat deposition, as much in the carcass as in the not carcass (Humada et al., 2013). This fact leads to a reduction in the profitability of intensive finishing of Tudanca bulls on the one hand, while on the other hand, makes it possible to obtain acceptable results (e.g. enough intramuscular fat deposition) with forage based rations (Humada et al., 2013).

In recent years there has been an increase in consumer demand for beef from cattle production systems not exhibiting negative effects on animal welfare and physiology (Bernués et al., 2003; Maria, 2006) and contributing to improve the nutritional quality of beef, i.e., a healthier fatty acid composition (Kallas et al., 2014). In this context, increasing the forage/concentrate ratio of finishing diets to an appropriate level could be an interesting approach to meeting those consumer demands. Moreover, some ruminant meat quality labels, i.e., organic beef (EC, 2007) establish a limit on the proportion of concentrates in ruminant rations during the finishing period.

Unlike dairy breeds, currently in Spain there are still relatively high censuses of beef cows of native breeds with rusticity characteristics similar to those in the Tudanca (MAPAMA, 2017a). Notwithstanding, the market penetration of differentiated beef produced with these native rustic breeds is still low. Despite fresh beef in Europe has been traditionally sold unbranded; a niche of market for differentiated beef has been detected within the literature (Resano & Sanjuán, 2017). In this sense, a more successful marketing policy may be achieved by developing quality labels based on a local breed and the use of natural resources by extensive or semiextensive systems (Bernués et al., 2003; Olaizola et al., 2012). Nevertheless, the availability of grazing surfaces and pasture characteristics of many farms make it difficult to set up grazing systems. Besides, there are periods of the year in which meteorological conditions make it necessary to stable animals, so alternative indoor systems should be considered.

Any alternative to reducing concentrate level in fattening rations implies replacing low quality forages (such as straw) with high quality ones. In the conditions of Cantabrian Cornice regions, the forage conservation system that yields higher quality forages is silage, and the most widespread silage method in beef farms is round bales, in spite of its higher cost (Martínez-Fernández et al., 2014). The effects of the forage/concentrate ratio on carcass performance and carcass quality have been the subject of research. Some studies have found that increasing the levels of forage resulted in lighter carcasses with lower fat content and a more yellow fat colour (Sami et al., 2004; Cerdeño et al., 2006). In contrast, other studies report that increases in forage level exerts no or only slight effects on carcass characteristics (Blanco et al., 2010; Daza et al., 2014). However, different confounding factors, such as breed, age, plane of nutrition or forage type, make it difficult to compare between studies.

It is known that the amount of forage vs concentrate in diet can affect beef quality, i.e. intramuscular fat content, lipid composition, fat colour or sensory scores (Muir et al., 1998; Resconi et al., 2010; Humada et al., 2012; Van Elswyk & McNeill, 2014). Several quality traits seemed to be hardly affected, i.e., meat colour (Priolo et al., 2001) or instrumental texture characteristics (Nuernberg et al., 2005). The effects of high forage diets on beef quality depend on the forage vs concentrate ratio, so partial replacement of concentrate by forage would have less effect than a total replacement (Moloney & Drennan, 2013).

Taking into account all these considerations, the aim of this work was to evaluate the effect on growth, carcass characteristics, economic performance and meat quality of feeding young Tudanca bulls with finishing diets including two rates of silage versus the more conventional feeding system consisting of barley straw plus ad libitum concentrate.

Material and methodsTop

Animal management, diet composition and feed sample collection

This study was conducted at the experimental farm “Finca Aranda” of the Cantabria Government (latitude: 43º23’15”N, longitude: 04º11’32”W; 84 m above sea level). The climate of this area is Atlantic with about 1,206 mm of annual rainfall and a 13.2 ºC mean temperature (mean values of 30 years).

Twenty two Tudanca young bulls (average birth date February 28) were used. Calves were raised on pasture with their mothers until weaning at 5 months of age. Then the animals were blocked according to age and live weight at weaning, allocated at random in three feedlot pens (age at weaning 150±20.1 days, p=0.997; live weight at weaning 129±23 kg, p=0.861) and fed on ad libitum hay and 1 kg/animal/day of commercial growing concentrate for 15 days. After this adaptation period, lots were assigned to three different diets: ad libitum grass silage plus ad libitum commercial concentrate (GS-AC), ad libitum grass silage plus commercial concentrate limited to a half of the intake of the ad libitum group (GS-LC), ad libitum barley straw plus ad libitum commercial concentrate (Str-AC), until slaughter at around 11 months of age (323±16.3 days of age). All animals were individually weighed each 7 days at 9:00 a.m. before feed distribution and on the day before slaughter. Average daily weight gain (ADWG) was calculated by linear regression.

Silage was made in round bales. The grass used was 2nd year spring Lolium perenne growths obtained from two parcels cut at 16 April (1st batch) and 6 May (2nd batch) wilted to a dry matter (DM) content of approximately 30% and chopped to 12 cm length. Grass silage and straw were offered ad libitum (adjusted to allow a 10% refusal) once a day and group intakes were controlled 3 days a week. Concentrate was offered in a collective calf feeder to GS-AC and Str-AC groups, and group intake was calculated once a week. Half of the daily amount of concentrate ingested by GS-AC the previous week was offered daily to GS-LC and there were no refusals. Water and mineral blocks were always available to animals.

Feed samples (grass silage: 3 samples per bale; commercial concentrate and barley straw: 1 sample per feed) were analyzed to determine DM, crude protein, ether extract, ash (AOAC, 1990), crude fibre (Van Soest, 1982), acid detergent fibre (Goering & Van Soest, 1970) and neutral detergent fibre (Van Soest et al., 1991). Net energy content (UFL/kg DM) of all feeds and bulk units (BBU/kg DM) of forages were calculated using the equations proposed by INRA (2007) (Table 1). Furthermore, fatty acid contents of straw, grass silage and concentrate were analysed in duplicate following the procedure described below for meat samples (Table 1).

Table 1. Percentage of dry matter, chemical composition, net energy content and fatty acids content (expressed as percentage) of feeds and forage ingestibility.

Slaughter procedures and carcass characteristics

Animals were divided in two slaughter batches, January 14 (4 GS-AC, 4 GS-LC and 4 Str-AC) and January 21 (3 GS-AC, 3 GS-LC and 4 Str-AC) according to age. The experimental period lasted 143±3.6 days. Slaughter took place in a commercial slaughterhouse located 35 km from the farm. The lairage period in the slaughterhouse lasted for 12 hours. The slaughter procedures comply with the Council Regulation (EC) No 1099/2009 (EC, 2009).

After slaughter, the perirenal fat and the hot carcass weight were obtained. Afterward, carcasses were split in two halves and then conformation and fatness carcass scores were determined according the European Union beef carcase classification grid (EC, 2006) with each score subdivided into high (+), medium (=) and low (-). This conformation scale ranged from 18 [(S+, very good) to 1 (P-, very poor)] and the fatness scale from 15 (5+, very high) to 1 (1-, very low). Carcass yield was calculated as the relation between hot carcass weight and slaughter weight. Right carcasses were weighed and stored immediately in a refrigeration room set to 1-2 ºC until 7 hours post-mortem and then in a refrigeration room set to 2-4 ºC following the routine refrigeration procedure used in the slaughterhouse. The left half-carcasses were assigned at random to two refrigeration procedures: room temperature or wrapping. In the room temperature treatment, carcasses were kept at room temperature (between 10 and 13 ºC) until 7 hours post-slaughter and then in a refrigeration room set to 2-4º C. In the wrapping treatment, carcasses were protected with a cotton cover and placed in the same refrigeration rooms as right ones.

At 24 hours post-mortem colorimetric variables of the CIE L*a*b* uniform colour space (CIE, 1976) were measured in triplicate on the loin subcutaneous fat area of right carcasses using a portable colorimeter Minolta CR-400 (D65 iluminant, 2º observer angle, 8 mm aperture size).

Meat sampling, sample preparation and analyses

Selected quality analyses were carried out at different anatomical locations and post-mortem time in order to assess the effect of diet on meat quality (Table 2).

Table 2. Experimental plan showing the analysis carried out, the muscles used and the post-mortem time elapsed before analysis.

At 24 hours post-slaughter, the pH of Longissimus lumborum muscle of left and right carcasses was measured in duplicate, between the 4th and 5th lumbar vertebrae (pHmeter Crison 507, Hach Lange Spain, L’Hospitalet de Llobregat, Spain). The loin portions from the limit between the 5th and 6th rib to the end of the loin were then removed from right and left carcasses, and a sample of Rectus abdominis muscle (750 g approximately; right side) was taken at the back area of the thin flank and stored at 4ºC. The loin section corresponding to the left 6th rib was used to determine tissue composition by dissection (Carballo et al., 2005). A steak from the right Longissimus thoracis muscle was obtained from the 6th rib, minced and used to determine moisture, fat, protein and ash.

At 48 h post-slaughter another two 2 cm-thick steaks were cut at the level of the right side 8-11th rib. One steak was immediately used to determine colour and water holding capacity as drip loss and, and the other was frozen at -32 ºC until being tested for collagen content. Moreover, a 3 cm-thick steak was obtained from the left-side Longissimus thoracis muscle at the level of the 7-10th rib at 48 h post-slaughter. Steaks were then vacuum-packed and maintained at 4 ºC for 7 days (until 9 days post-slaughter) for ageing. Afterwards these steaks were frozen at -32 ºC until being used for cooking losses and texture profile analysis.

The Rectus abdominis samples, at 48 h post-slaugh­ter were divided into two subsamples. One subsample was minced and used to determine fatty acid profile. The other half of the samples were stored for 7 days (until 9 days post-mortem) in hermetic trays at 4 ºC and then used for the determination of lipid oxidation.

Meat proximate composition and lipid composition

Proximate composition was carried out according to ISO, 1973 (Determination of total fat content; Standard R-1443); ISO, 1978 (Determination of nitrogen content; Standard R-937); ISO, 1997 (Determination of moisture content; Standard R-1442); ISO, 1998 (Determination of total ash; Standard R-936). Fatty acid composition was analysed in the intramuscular fat (IMF) from Rectus abdominis muscle as described in Domínguez et al. (2015). Fatty acid results were expressed as g/100g of the total fatty acids identified.

Technological meat quality traits

Total and heat-insoluble collagen were analysed according to AOAC (1999). For texture profile analysis of cooked meat, the corresponding meat steaks were thawed at 4 ºC for 24 h, weighed, placed into hermetic bags and cooked in a water bath at 80 ºC until a core temperature of 70 °C was reached. After cooling the cooked steaks under a running tap, the steaks were weighed again. Cooking losses were calculated as weight differences expressed in percentage on initial weight basis. Afterwards, the cooked steaks were wrapped in aluminium foil and held overnight at 4 ?C. Subsequently, after tempering the samples for 1 h at room temperature (20 ºC), five 1 cm3 cubes were cut with one of the axes being parallel to muscle fibre orientation. Instrumental texture profile analysis (TPA; Bourne, 1978) was performed with a texture analyser TA.XT2i and software Texture Expert, v1.20 (Stable Micro Systems, Godalming, Surrey, UK) with a 25 kg load cell and a 5 cm diameter cylindrical probe set to run at 1 mm/s. Cubes were compressed twice (80% of the thickness of the sample; parallel to fibre direction) with a 5-s elapse between the two compression cycles. Mean values for hardness, springiness, and cohesiveness were obtained from the force–time curves. Chewiness was calculated as the product of hardness multiplied by cohesiveness and springiness.

Regarding drip loss and colour, the steaks used for the determinations were placed on polystyrene trays immediately after being sliced, then wrapped with an oxygen permeable film and allowed to bloom for 1 h at 4 ºC. Next, the steaks were taken from the trays and colour parameters (lightness (L*), redness (a*) and yellowness (b*)) were registered on 3 homogenous zones of the steak surface using a Minolta CR-400 colorimeter (C illuminant, 2º standard observer angle and 8 mm aperture size, SCI mode). Thereafter, chroma (C*) and hue angle (Hº) values were calculated as C*a,b=[(a*)2 + (b*)2]0,5 and Hºa,b=arctan (b*/a*). Then, steaks were halved and the two slices (weighting approximately 100 g) were stored at 4º C for 24 h and drip loss was assessed according to Honikel (1998). Lipid oxidation in freshly meat samples was measured by the thiobarbituric acid reactive substances (TBARS) method (Nam & Ahn, 2003). Results were expressed as mg of malonaldehyde per kg of meat.

Economic analysis

The costs and incomes associated to each strategy of production were calculated to compare them in economic terms. Data on both input and output prices was based on the reference year 2014. The costs considered were: feeding (grass silage, straw, hay, vitamin-mineral supplements and concentrate); health and hygiene products and services (veterinarian products and services, cleaning and maintenance of feedlot pens); machinery [costs derived from the use of a tractor 1 hour per week, estimated from Márquez (2007) and considering the evolution of the consumer price index between 2005 and 2014 recorded in INE (2016)]; transport to slaughterhouse and slaughter cost (calculated considering the average value of prices of the three slaughterhouses operating in Cantabria in 2014 and the average value of prices of two livestock transport companies); interests of the working capital (opportunity cost calculated considering a legal interest rate of the money set at 4%; BOE, 2013). Grass silage cost was 0.034 €/kg of fresh matter and it includes grass purchase, grass mown and round bales elaboration. Straw and hay costs were calculated using the average price of barley straw and hay in the main cooperatives of Cantabria (0.072 €/kg and 0.11 €/kg of fresh matter, respectively) and include transport to the farm. Concentrate cost was calculated considering the average price of growing and finishing concentrate (0.399 and 0.366 €/kg of fresh matter, respectively). Total income achieved per animal at slaughter was calculated as carcass selling income (considering the selling price of 4.2 €/kg of carcass recorded in Vázquez et al. (2016) for Tudanca young bulls) plus coupled payment for calf fattening according to new CAP 2014-2020 (32.7 €/head; FEGA, 2017). The economic margin was calculated as the total income minus the above mentioned costs and minus the opportunity cost of a weaned calf (the market value of a 5 months old weaned Tudanca calf, 200 €/head) and the cost of family labour. Family labour was estimated as 2 h/day and the value of 1 hour of work was fixed at 4.95 €/h (MAPAMA, 2017b). In order to compare the economic margin under different scenarios a sensitivity analysis was carried out taking into account an increase of 25% in concentrate prices and a rise by 24% of carcass selling price up to the price suggested by local farmers as the price to overcome the threshold of profitability (5.2 €/kg of carcass; Vázquez et al., 2016).

Statistical analysis

Data for performance and carcass characteristics were compared by means of analysis of covariance considering diet as a fixed effect and weight at weaning as a covariate. The covariate was removed from the statistical model when p > 0.05. Fat colour variables were compared by means of analysis of variance considering diet as the variation factor. Meat quality variables were statistically compared using a model including diet as a fixed factor and slaughter batch as a random factor. Values of 24 h pH, cooking losses and texture profile, determined in samples from left carcasses, were compared, in a first step, using a model including diet and refrigeration procedure (room temperature or wrapping) as fixed factors. Then, as refrigeration procedure effect was not statistically significant for any considered variable, data were analyzed, in a second step, considering diet as fixed factor and slaughter batch as random factor. When p was lower than 0.05 for the fixed factor, Bonferroni’s test was used to separate treatment means. The above-mentioned analyses were carried out using the statistical package SPSS 17.0 (IBM Corp., Armonk, NY).

ResultsTop

Figure 1 shows the weekly evolution of average daily forage and concentrate intakes per animal. Daily grass silage intakes were on average 1.48 and 2.26 kg DM/animal for the GS-AC and GS-LC groups, respectively (total intakes of 215 and 329 kg DM/animal, respectively). Daily barley straw intake was on average 0.52 kg DM/animal for the Str-AC group (total intake of 77 kg DM/animal). Daily concentrate intakes were on average 4.56, 2.58 and 5.02 kg DM/animal/day for the GS-AC, GS-LC and Str-AC groups, respectively (total intakes of 657, 372 and 729 kg DM/animal). Figure 2 shows the evolution of UFL and PDI intakes from forage and concentrate expressed as total intake. Average total net energy intakes were 5.62, 4.25 and 5.19 UFL/animal/day for the GS-AC, GS-LC and Str-AC groups, respectively. Average total daily PDI intakes were 583, 411 and 562 g/animal for GS-AC, GS-LC and Str-AC groups, respectively.

Figure 1. Evolution of voluntary intake in the three experimental groups (GS-AC= ad libitum grass silage plus ad libitum concentrate diet; GS-LC= ad libitum grass silage plus limited concentrate diet; Str-AC=barley straw plus ad libitum concentrate diet).

Figure 2. Evolution of net UFL (Unités Fourragères Lait: net energy for maintenance and gain expressed in milk feed units) and PDI (protein truly digestible in the small intestine) intake in the three experimental groups. GS-AC= ad libitum grass silage plus ad libitum concentrate diet; GS-LC= ad libitum grass silage plus limited concentrate diet; Str-AC= barley straw plus ad libitum concentrate diet.

The forage/concentrate ratios (on a DM basis) calculated for the three experimental diets, GS-AC, GS-LC and Str-AC, were respectively 25/75, 47/53 and 9/91. The concentrate substitution effect obtained by comparing forage and concentrate intake of GS-AC and GS-LC groups was 0.4 (a reduction of 0.4 kg de DM of forage intake per kg DM concentrate intake). The higher grass silage intake of GS-LC group was not enough to compensate the limitation in concentrate intake and it implied that total UFL and PDI intakes of GS-LC animals were lower than those of GS-AC animals (-1.37 UFL/animal/day and -172 g PDI g/animal/day). The GS-AC lot also showed higher values of UFL and PDI intake than the Str-AC lot, although differences were smaller (+0.43 UFL/animal/day and +21 PDI g/animal/day).

ADWG was significantly (p=0.001) affected by diet (Table 3). Significant differences (p=0.05) were observed between the three diets. GS-AC animals presented the highest values; Str-AC animals presented intermediate values and GS-LC the lowest ones. Differences in ADWG implied significant differences (p=0.05) in live weight at slaughter and hot carcass weight only between the two ad libitum concentrate groups (GS-AC and Str-AC) and the group with limited concentrate intake (GS-LC).

Table 3. Effect of diet 1(GS-AC, GS-LC and Str-AC) on animal performance and carcass characteristics.

No significant differences (p > 0.05) were observed between the experimental groups in carcass yield and fatness score (Table 3); however, a significant effect of diet on conformation score (p=0.006) was observed. Conformation values for the GS-AC group were significantly higher than those of GS-LC group (p = 0.05), and the Str-AC group presented intermediate values with no significant differences to the other two groups (p > 0.05).

A significant effect of diet on the weight of perirenal fat was observed (p = 0.001). GS-AC animals presented higher values (p = 0.05) than the other two groups, with these groups not differing from each other. Diet had not significant effect on % of total dissectionable fat of 6th rib-loin section, but a significant effect (p=0.031) on the percentage of intermuscular dissectionable fat was observed when intermuscular and subcutaneous fat were considered separately. The GS-AC group presented higher (p=0.05) values than the Str-AC group, whilst the GS-LC group presented intermediate values not statistically different (p>0.05) to the other two groups.

Diet significantly affected subcutaneous fat a* and b* colour values (p = 0.001). GS-LC animals presented higher values (p = 0.05) than the other two groups, which showed similar values (p > 0.05).

Table 4 shows feed energy and concentrate efficiency utilisation in the three experimental groups. The highest value of UFL/kg of live weight gain corresponded to the animals from the GS-LC group, indicating a lower efficiency of net energy utilization. However, if energy and feed utilisation are expressed per kg of carcass, the lowest average values of UFL and kg DM concentrate/kg carcass corresponded to the GS-LC group (5.09 UFL and 2.99 kg DM concentrate/kg carcass). These average values increased by 0.38 UFL and 1.31 kg DM concentrate per kg carcass for the GS-AC group and by 0.20 UFL and 1.94 kg DM concentrate for the Str-AC group.

Table 4. Feed energy and concentrate efficiency in the three experimental 1groups.

Meat proximate composition and lipid composition

Proximate composition of R. abdominis and L. thoracis muscles (Table 5) showed some differences attributable to diet. Moisture was lower in the GS-AC meat whereas, in turn, intramuscular fat content of R. abdominis tended to be higher. Fatty acid profile of intramuscular fat of R. abdominis muscle was also significantly affected by diet (Table 5). The most relevant finding regarding the sums of saturated, monounsaturated and polyunsaturated fatty acids (SFA, MUFA and PUFA, respectively) percentages was a higher PUFA content in Str-AC meat. Furthermore, this treatment resulted in the highest n-6 (mainly C18:2n-6) fatty acid percentage followed by the GS-LC and then the GS-AC, while GS-LC meat showed the highest percentages of n-3 (mainly C18:3n-3). Therefore, Str-AC treatment resulted in the highest n-6/n-3 ratio, followed by the GS-AC and then GS-LC group (p ≤ 0.05).

Table 5. Effect of 1diet on meat quality.

Technological meat quality traits

No differences were found between diets for pH and water losses (Table 5). However, diet affected collagen content, which was higher in GS-LC meat, followed by GS-AC and finally Str-AC, with significant differences (p<0.05) between the former and the latter. However, the percentage of collagen per total protein did not show differences between treatments, although GS-LC meat showed again the highest mean value. As regards to texture profile, hardness was not affected by diet; however, cohesiveness, springiness and chewiness were affected. Str-AC meat showed the highest values, with significant differences being found for the three characteristics as compared to GS-LC, and for cohesiveness as compared to GS-AC and GS-LC. No differences were found in the meat texture between the groups of bulls fed on silage (GS-LC vs GS-AC). Str-AC meat was thus the most different group in texture.

The effect of the diets on meat colour (Table 5) was only observed for hue. Hue was significantly lower in Str-AC meat than in GS-LC meat, with GS-AC meat being in an intermediate position. Finally, lipid oxidation of the meat was not affected by diet.

Economic margin

The estimated economic margin from the three strategies presented negative values (Table 6). The estimated economic margin was similar for the GS-AC and GS-LC diets (-63.1 and -64.1 €/head, respectively). The higher feeding cost showed by the GS-AC group as compared to the GS-LC one was compensated with a higher carcass selling income in GS-AC with regard to GS-LC due to a higher carcass weight. The average value of economic margin of the Str-AC group was the lowest (-91.8 €/head), which is mainly a result of the relatively high feeding costs.

Table 6. Economic performance (€/head) for the three strategies of 1production.

DiscussionTop

The GS-LC animals presented the highest average value for UFL/kg of live weight gain and thus the lowest efficiency of energy utilisation. This agrees with the study by Blanco et al. (2011), who found lower energy utilization efficiency for a fattening diet based on lucerne supplemented with a restricted amount of barley with regards to an ad libitum concentrate diet in young Parda bulls. However, Serrano et al. (2007) observed no significant effect due to concentrate level (ad libitum vs the half of ad libitum) or forage type (hay or grass) in diet on the energy utilisation efficiency shown by young Salers bulls slaughtered at 10 months of age. On the contrary, Humada et al. (2013) obtained higher values of UFL/kg of live weight gain for intensive finished young Tudanca bulls (fed on concentrate and cereal straw) as compared to semi-extensive reared ones. The discrepancies could be related, at least partially, to differences in forage/concentrate ratios and in fat deposition between studies. In the study by Humada et al. (2013), the forage/concentrate ratio in the diet of the semi-extensive reared bulls was higher than that found in present study for the GS-LC group (64:36 vs 47:53, respectively) and carcass fat deposition was lower (total dissectionable fat of the 6th rib 7% in Humada et al. (2013) vs 14% in present work).

Differences in energy and protein intake between the feeding groups of this experiment were detected. These differences, in turn, would be responsible for the significant differences found in the growth rates. The slowest growth rate was shown by the animals from the group fed on high forage and restricted concentrate diet, which showed the lowest efficiency of energy utilisation. In the study by Serrano et al. (2007) growth rates were also lower in half-ad libitum-concentrate fed bulls than in ad libitum-concentrate fed bulls. However, the difference found in that study for ADWG was lower than that found between the GS-AC and GS-LC groups (100 vs 260 g/animal/day).

Other works have also compared performance results of young bulls finished on straw and ad libitum concentrate or on a high quality forage and limited concentrate diet, in grazing systems (Blanco et al., 2011; Humada et al., 2013; Daza et al., 2014) or in stall systems (Cerdeño et al., 2006). Cerdeño et al. (2006) reported a significantly higher ADWG (increases of 600 g/animal/day) when Parda × Limousin young bulls (8 months old) were finished for 60 days on straw plus ad libitum concentrate than when the bulls were finished on lucerne hay and restricted concentrate diet. Blanco et al. (2011) and Daza et al. (2014) did not observe differences in ADWG in Parda and Avileña young bulls, respectively, finished on grazed grass plus a limited quantity of concentrate or with straw and ad libitum concentrate. Humada et al. (2013) found in a 220-280 day post-weaning period higher ADWG (around 180 g/day/animal) in young Tudanca bulls fed on straw and ad libitum concentrate than in those reared under a semi-extensive system (grass and restricted concentrate feeding). The ADWG found for the straw plus ad libitum concentrate bulls was similar to that found for the Str-AC animals in this study. However, when considering only the last 120 days of the finishing period, Humada et al. (2013) found a higher ADWG for the bulls reared under the semi-extensive system. In order to explain this apparent contradiction, the authors suggested that the growth rate depended not only on the levels of protein and energy in the ration but also upon a mix of animal physiological factors interrelated with those levels, e.g. compensatory growth or differences in fat deposition associated to age and growth rate. The higher ADWG of GS-AC animals with respect to Str-AC ones should be due to the higher energy and protein intakes of the former.

It is worth taking into account that the grass silage used in this experiment should be considered as a medium quality forage (INRA, 2007). It would have been expected that the use of higher-quality silage would have enabled an increase in forage and nutrient intakes in GS-LC cattle and thus an improvement in growth performance. The feeding value of grass silage can vary dramatically depending on several factors such as harvest season, botanical composition, growth, wilting, etc. (Martínez-Fernández et al., 2014). Keady et al. (2008) observed that when high-feed value grass silage was offered to finishing steers, increasing concentrate level was not associated with an increase in metabolizable energy intake. They also observed that concentrate level showed greater effects on growth performance and carcass quality when animals were offered low-quality silage, than when they were offered high-quality silage. Increasing forage quality would be necessary too to meet limitations in the proportion of concentrates in the ration as that of the Standard Organic (minimum forage to concentrate ratio of 60:40 in DM basis; EC, 2007).

In this study it was found that feeding the animals with a relatively high level of forage (silage) and a restricted level of concentrate showed some negative effects on carcass conformation and perirenal fat amount – no other fatness characteristic was affected – as compared to feeding with the ad libitum concentrate diets. However, these effects would be expected to have a low impact on the commercial value of the young Tudanca bull carcasses. This is because the differences in conformation appeared to be slight, taking into account that following the European Union beef carcass classification grid (EC, 2006) the conformation score turned out to be the same for the carcasses from the three experimental groups (= P, poor conformation; EC (2006)), and the amount of perirenal fat is not used for carcass classification purposes. Furthermore, conformation and fatness of GS-LC carcasses might be improved by increasing the slaughter live weight of animals until reaching the weight of the animals fed on concentrate ad libitum or by decreasing the level of concentrate restriction. Moreover, when comparing the bulls fed on silage with those fed on straw (both using concentrate ad libitum; GS-AC vs Str-AC) no effect on carcass conformation was evidenced. However, with regard to fatness, perirenal fat amount and intermuscular dissected fat percentage were higher in the animals fed silage. This difference could be related with the higher ADWG in these animals, which could have resulted in higher fat deposition.

In studies comparing the carcass characteristics of young bulls fed on ad libitum concentrate vs restricted concentrate diets where bulls were slaughtered at a fixed live weight (Blanco et al., 2010; 2011; Daza et al., 2014) no differences in carcass weight, conformation and fatness were observed between diets. On the other hand, when bulls were slaughtered at a fixed age, as in the present study (Cerdeño et al., 2006; Serrano et al., 2007; Humada et al., 2013) some significant differences were found between diets. Serrano et al. (2007), in agreement with our results, observed lower carcass weight (p<0.05) in animals receiving a restricted quantity of concentrate than in ad libitum concentrate fed animals and no significant effects of concentrate level on dressing percentage and carcass fatness score; however, unlike our results, they found no significant effect of concentrate level on carcass conformation. Cerdeño et al. (2006), in contrast, reported lower carcass fatness score and percentages of dissected fat from the 6th rib loin section for the carcasses of young bulls fed with a restricted concentrate diet regarding those from straw plus ad libitum concentrate fed bulls, and did not report differences in carcass conformation score. In agreement with this study, Humada et al. (2013) observed no differences in carcass conformation and fatness score between carcasses of Tudanca young bulls finished in a grazing system supplemented with restricted concentrate and those finished in a stall system fed on straw and ad libitum concentrate. However, and also in agreement with the present results, in spite of the lack of differences in carcass fatness score, the amount of perirenal fat was significantly higher in carcasses from the ad libitum concentrate fed animals. These authors attributed this increase to both a higher energy level of their diet and a more precocious development of perirenal fat than that of other fat depots, i.e., intramuscular or subcutaneous fat. Discrepancies between studies on the effect of the concentrate restriction on young bull carcass fatness could be at least partially explained by animal breed- or age-related variability (Piedrafita et al., 2003; Humada et al., 2013).

Muscle pH values for all treatments were in the normal range and no differences were observed between diets. With regard to meat colour, the high forage (GS-LC) experimental diet resulted in a subcutaneous fat with a more yellow and red colour (higher a* and b*, respectively). These results can be attributed to differences in the levels of ß-carotene in fat between the feeding treatments (Cerdeño et al., 2006; Blanco et al., 2010, 2011). This compound is the predominant carotenoid pigment in bovine fat and its colour is orange so it contributes to fat redness and yellowness (Yang et al., 1992). Although carotenoids are partially destroyed as a consequence of forage conservation processes, ensiled forages presented a relatively high content of these compounds compared to straw and concentrates (Chauveau-Duriot et al., 2005; Serrano et al., 2006).

GS-AC showed a tendency to higher IMF content, this result agrees with the higher intermuscular fat content of the 6th rib and perirenal fat weight of this treatment. These effects would be associated with the higher ADWG in these animals resulting in a higher growth rate of fat depots. Perirenal and intermuscular fat depots have earlier development than intramuscular fat (Vernon, 1986; Arana et al., 1998).

In the literature, the effect of forage type and concentrate level in the diet of young bulls on the IMF content is not consistent across studies. Cerdeño et al. (2006), Serrano et al. (2007) and Daza et al. (2014) observed no significant effect due to concentrate level or forage type. However, Blanco et al. (2010) and Humada et al. (2013) observed differences in the IMF content of meat. Differences among the studies might explained by for a range of confounding factors such as breed, age, forage quality, length of the finishing period or physical activity (Micol et al., 1993).

The effect of the dietary treatments on the fatty acid profile could be attributed to two interrelated factors, i.e., fatty acid content in the diet and IMF content in meat. On the one hand, the corresponding intake of grass silage, rich in n-3 fatty acids, and concentrate, rich in n-6, by the young bulls from the different experimental feeding groups (Table 1), would be mainly responsible for the highest n-3 proportion (and lowest n-6/n-3 ratio) in the GS-LC meat and the highest n-6 proportion (and n-6/n-3 ratio) in the Str-AC meat, GS-AC meat being at an intermediate position with regards to that ratio. On the other hand, it is well known that higher contents of IMF in meat involve higher neutral lipids and lower phospholipid rates, and, in turn, higher SFA and lower PUFA proportions (Wood et al., 2008); this effect would mainly account for the lower PUFA/SFA in GS-AC meat (showing the highest IMF content; p=0.056). A healthy dietary fat source should contain a high proportion of PUFA compared with SFA and a high proportion of n-3 fatty acids within the PUFA (Simopoulos, 2002). According to this statement, the fat of GS-LC meat should be the most valuable, because it shows the highest PUFA/SFA ratio (together with Str-AC meat) and the lowest n-6/n-3. On the other hand, the disadvantage of GS-AC meat would be its comparatively low PUFA/SFA ratio and that of Str-AC meat its high n-6/n-3 ratio.

The higher amount of collagen in GS-LC meat (Table 5) could be explained at least partially by a lower growth rate at slaughter of GS-LC animals, due to lower concentrate intake. However, as collagen solubility (soluble collagen to total collagen) was not affected by diet, the reported positive effect of growth rate on collagen solubility (Miller & Cross, 1987; Muir et al., 1998) was not observed in the present study, which could be justified by the young age of bulls at slaughter.

The results of the texture profile analysis regarding hardness were in partial agreement with Moloney & Drennan (2013), who did not find effect of grass silage vs concentrate based diets on this characteristic, although in that study hardness was assessed as the shear force value. The lack of effect of total collagen content on collagen solubility and hardness could be attributed to high collagen solubility and relatively small variation in collagen content, due to the young and similar age of animals at slaughter (Gerrard et al., 1987; Purslow, 2005).

With regard to colour, the present results confirm the statement of Moloney & Drennan (2013), that there seems to be a lack of effect (or hardly any) due to grass silage-based rations being supplemented with concentrates, as compared to concentrate plus straw-based rations on meat colour (as well as other meat quality traits such as pH and sensory characteristics). TBARS levels were under the threshold of 2 mg of malondialdehyde per kilogram of meat, considered as the acceptable oxidation level of raw beef (Campo et al., 2006).

The economic margin calculated in this study presented negative values for the three strategies of production. Moreover, if family labour costs are not considered for calculations, only silage using strategies (GS-AC and GS-LC) would reach positive net profits. However, an increase of 24% of carcass selling price from the market value to 5.2 €/kg of carcass (price suggested by the local farmers as the price to overcome a threshold of profitability) would lead to positive net profits in the three groups.

The higher amount of concentrate consumed by the Str-AC animals considerably reduced the economic margin of this group with regard to the other two groups, which presented similar profitability. Under the assumption of an economic context with increased concentrate prices (sensitivity analysis), which could be especially relevant considering its current trend subject to strong volatility, the GS-AC and Str-AC would be the most affected feeding strategies. On the other hand, in a context with increased carcass prices, the economic margin of the GS-AC group would be increased to values higher than that estimated for the GS-LC group (Table 6). In agreement, Blanco et al. (2011) and Humada et al. (2013) also reported greater profitability from the rearing of young bulls finished on pasture and restricted concentrate allowance as compared to feeding alternatives using concentrate ad libitum. They also pointed out a higher robustness of low concentrate systems in a situation of high concentrate prices.

The higher forage (GS-LC) finishing diet as compared with the ad libitum concentrate finishing diets (GS-AC and Str-AC) has resulted in animals showing lower ADWG; moreover, GS-LC-carcasses tended to have slightly lower conformation. On the other hand, high-forage feeding has demonstrated a relatively high profitability and lower dependence on concentrate. When ad libitum concentrate diets were compared, the carcass characteristics obtained from the animals fed on the GS-AC and Str-AC diets were very similar; however, the GS-AC diet resulted in higher ADWG and a greater economic margin. Decreasing the concentrate levels has had an effect on fatty acid profile attributable to both a decrease of intramuscular fat deposition and a dietary change in the fatty acid profile, i.e., higher levels of n-3 fatty acids. This has resulted in a tendency for the ad libitum grass-silage and restricted concentrate diet to produce the most favourable fatty acid composition. The study confirms that in indoor feeding systems, technological meat quality traits, such as texture, colour and lipid oxidative stability of raw meat, are not negatively affected by the inclusion of silage as forage source with regard to straw and the reduction in concentrate level. The results suggest that both substitution of straw by grass silage and restriction of the concentrate level in the finishing diets could be recommended for finishing young Tudanca bulls and for the establishing of Tudanca beef quality labelling schemes. In order to generate further recommendations regarding more appropriate high-forage finishing diets, further studies are recommended using additional concentrate levels to those of this study and higher quality grass silage; the latter because increasing forage quality could be essential to increase forage consumption and nutrients intake when using restricted concentrate diets. Those further studies should consider the effect of diet on sensory characteristics of meat and the effect of live weight at slaughter as an additional experimental factor on both, carcass quality and economic performance.

AcknowledgmentsTop

The authors thank César Cimadevilla, the personnel at the Finca Aranda, Carlos Murga, Patricia Manrique, Sara Jiménez and Irene Velasco, the Laboratorio Agrícola del CIFA, the Cooperativa Agrocantabria, GESCANORSA staff and the Official Veterinarian staff for their assistance.


ReferencesTop

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