Effect of gender on growth performance, carcass traits and meat quality of calves of Avileña-Negra Ibérica breed

The objective of this experiment was to study the effect of gender on growth performance and carcass and meat quality of calves of Avileña-Negra Ibérica breed. Sixteen calves, eight males and eight females, were used. The calves were fattened under intensive conditions, housed in confinement and fed with the same feed and cereal straw from 230.7 to 478.3 kg. The males grew more than the females (1.390 vs 0.932 kg day –1 respectively). Carcass weight, carcass length, leg length, leg perimeter, carcass and leg compactness, legs, fore-quarters and loins weights and fore-quarters percentage regarding carcass weight were higher ( p < 0.05) in males than in females. The gender had not significant influence on CIE a* , b* , chroma and hue variables but CIE L* value was significantly ( p < 0.05) lower in males than in females. The a* value decreased and b* and hue values increased with ageing time. The subcutaneous backfat from the females had significantly ( p < 0.05) higher C14:0, C16:0, C16:1, C18:1 n-9, Σ MUFA and lower C10:0, C18:0, C18:2 n-6, C18:3 n-3, C20:0, C20:3 n-9, C20:4 n-6, C22:5 n-3, Σ n-6, Σ n-3 and Σ PUFA proportions than that from males. It is concluded that the gender has influence on growth performance, carcass traits and fatty acid compo sition of subcutaneous backfat; gender does not have effect on instrumental colour variables; and meat colour can reach acceptable values for consumers until four days after slaughter.


Introduction
The Avileña-Negra Ibérica breed is a local breed raised under extensive conditions in the Southwest area of Spain. The most frequent product type is the grazing calf weaned at approximately six months old and live weight around 200-230 kg (Daza, 1998). After weaning calves are generally fattened in confinement and fed with cereal straw and concentrates until they reach around 13-14 months of age with 500 kg of live weight (550 kg the males and 450 kg the females). The calves growth performances and carcass and meat quality obtained during the fattening period depend on factors such as genetic type, gender, initial and slaughter weight, feeding, environment and housing conditions and sanitary status (Daza, 1999). Although there are some experiments that have studied the productive traits and carcass and meat quality of calves of Avileña-Negra Ibérica breed (Sánchez Belda, 1983;Vassallo et al., 1989;Albertí et al., 1997;García & Cruz-Sagredo, 1999), to our knowledge there is not still enough information on the influence of the different variation factors on the performance traits, carcass characteristics and meat quality and, specially, on the fat quality of calves of this breed. Therefore, the objective of the present experiment was to study the effect of gender on growth performance, carcass quality, muscle and fat colour and fatty acid profile of backfat of calves of Avileña-Negra Ibérica breed.

Material and methods
Sixteen calves, eight males and eight females, of Avileña-Negra Ibérica breed from Agricultural Research Center "El Dehesón del Encinar (39º 55' 9" N, 5º 10' 40" O) (Junta de Comunidades de Castilla-La Mancha, Oropesa Toledo, Spain) were used. The calves were weaned at around seven months of age and 230.7 ± 8.6 kg of weight. After weaning, males and females were separated and grouped in independent pens (6.0 m 2 animal -1 ) from an indoor housing. The calves were approximately weighed every 30 days. The duration of the fattening period was of 210 and 218 days for the males and females, respectively. During this phase, all animals were fed with the same feed, which composition is presented in Table 1. During all the fattening period feed, cereal straw and water were given ad libitum.
The data obtained for performance were studied by means of covariance analysis that considered the gender as fixed effect and the calves' initial weight as covariate.
The carcass characteristics were studied by means of variance analysis (gender as fixed effect), although a covariance analysis that consider the slaughter weight as covariate was also carried out. The muscle colour was studied by means of variance analysis that included the gender and ageing time as fixed effects, while to study fat colour only the gender was considered as variation factor. The fatty acid composition of subcutaneous backfat was studied by means of variance analysis that included the gender as fixed effect and carcass weight and fatness degree as covariates. The covariates were considered significant when p < 0.05, removing them from statistical models when p > 0.05. In addition, simple and multiple regression and correlation analyses were carried out in order to estimate the relationships between the carcass joints weight and other carcass characteristics, and the instrumental colour variables and the ageing time. All analysis were carried out by means of the statistical package SAS (1999).

Results and discussion
The performance results are shown in Table 2. In accordance with Sánchez Belda (1983Belda ( , 1984 in the current experiment the average daily gain during the experimental period was higher in males than in females (1.39 vs. 0.93 kg). The calves initial weight had significant (p < 0.05) effect on slaughter weight but did not affect to the average daily gain. The slaughter weight increased 0.58 kg per each kilogram of initial weight increase.
It is interesting to note that, at the beginning of the fattening period (0-13 days), the average daily gains of males and females were very low. This was due to that calves consumed small quantities of feed and straw during this first phase of fattening period because of the weaning stress (Neumann, 1989). Also, it is of interest to note that at the end of the fattening period (from the day 136 to the slaughter) males, as well as females, reduced the average daily gain, which agrees with the results found by Sánchez-Arjona (2001) in Morucha breed calves. This is because as the calves weight increased the feed conversion efficiency impaired due to  (Neumann, 1989;Albertí, 1998). During the total fattening period males consumed 1,510 and 205 kg of feed and straw per animal respectively, whereas the female's consumption was 1,060 and 149 kg. The slaughter weights of the males and females were 529.0 and 427.5 kg respectively. Therefore, the feed conversion efficiency was 5.17 and 5.21 kg kg -1 for males and females respectively. Alberti et al. (1997) found a feed conversion efficiency of 4.9 kg kg -1 for males of Avileña breed that were fattened between 252.6 and 451.5 kg. The feed conversion efficiency was higher in our experiment because the slaughter weight of the males was greater than those data reported by Albertí et al. (1997).
The results of variance analysis (without the slaughter weight as covariate) for carcass traits by gender and the slaughter weight effect as covariate on carcass characteristic are presented in Table 3. The carcass characteristics values found in the current study are in agreement with those found by García & Cruz-Sagredo (1999) in Avileña breed calves. Carcass weight, carcass length, leg length, leg perimeter, carcass and leg compactness, legs, fore-quarters and loins weights and fore-quarters percentage regarding carcass weight were higher (p < 0.05) in males than in females. Also Sueiro (1994) detected less carcass length in females of Rubia Gallega breed. Moreover, the males tended (p < 0.10) to have a leg width and flank weight higher than the females. Nevertheless, legs and flank percentages regarding carcass weight values were significantly (p < 0.05) higher in females than in males, and the females tended (p < 0.10) to show conformation values higher than the males. No significant (p > 0.05) differences were observed between males and females for the variables carcass yield, thorax depth, leg width, leg length -1 ratio, loins percentage regarding carcass weight and fatness degree. The slaughter weight as covariate (Table 3) had a significant (p < 0.05) effect on the most of the carcass characteristics studied. However, no significant (p > 0.05) effect on the variables carcass yield, leg width and leg width × leg lenght -1 ratio was observed, which agrees with data reported by Panea et al. (1999) in Pirenaica breed calves. The slaughter weight had not significant influence (p > 0.05) on the legs, fore-quarters, loins and flank percentages respect to carcass weight.
In order to quantify the relationships between the weight of carcass major joints and the independent variables carcass weight (CW) and other easily measurable carcass characteristics, simple and multiple regression equations were calculated (Table 4). The relationships between the legs, fore-quarters and loins weights and CW adjusted to linear functions, whereas the relationship between flank weight adjusted to an inverse function of type y = a + bx -1 . CW accounted for 95, 94, 96 and 66% of the variations in legs, fore-quarter, loins and flank weight respectively. Nevertheless, the addition to the regression equation that related flank weight with carcass weight of the independent variable conformation (C) increased the determination coefficient (R 2 ) from 0.66 to 0.76. It means that the variables CW and C, jointly, accounted for 76% of the variation in flank weight. However CW only accounted for 31, 28, 7 and 11% of the variations in legs, fore-quarters, loins and flank percentages regarding carcass weight respectively, while only C accounted for 25% of the variation in flank percentage and CW and C, jointly, accounted for 56% of the variation in fore-quarters percentage. The effects of gender and ageing time on muscle instrumental colour are shown in Table 5. It is considered that the males have less bright and more pigmented meat than the females due to their higher physical activity and mioglobine content (Lawrie, 1977). In this experiment the gender had not significant influence on CIE a*, b* chroma and hue variables of muscle colour, but L* value was significantly (p < 0.05) lower in males than in females. Monserrat et al. (2001), in calves of Rubia Gallega breed finished in confinement under intensive conditions, did not find effect of gender on muscle colour. The ageing time had significant effect on muscle colour. The a* value observed eight days after slaughter was lower than those found one day after slaughter and three days later, while b* value found one day after slaughter was lower than those observed three and seven days afterwards. Carballo et al. (2001) and Onega et al. (2001) observed an increase of b* value with the ageing time, but the a* value not varied. The gender had not effect on chroma and hue values, which agrees with the data from Monserrat et al. (2001). The hue value increased with the ageing time, which is related with meat Table 4. Relationships between the weight (kg) and percentage of the carcass major joints and the carcass weight (CW in kg) and carcass conformation (C)  To clarify results Pearson correlation coefficients were calculated between colour variables and ageing time ( Table 6). The correlation coefficients for L* and chroma and ageing time were not significant (p > 0.05), but the coefficient between a* and ageing time was negative and significant (p < 0.05), whereas correlation coefficients for b* and hue and ageing time were positive and significant (p < 0.05).
The gender had not significant effect on subcutaneous backfat L* and b* values (data no presented), but the males had higher (p < 0.05) a* value than the females (8.29 vs. 6.44, SEM = 0.58), which is not in concordance with data from Monserrat et al. (2001).
The higher values of the desaturation indexes C18:1/C18:0 and Σ MUFA/Σ SFA observed in the subcutaneous fat from females suggests that the delta-9desaturase enzyme activity was higher in females than in males. However, high Σ SFA/Σ PUFA and Σ n-6/Σ n-3 ratios in beef fat have been considered harmful for  health (Moloney et al., 2001). In the current study the Σ SFA/Σ PUFA ratio was higher in females than in males, although occurred the contrary effect for the Σ n-6/Σ n-3 ratio. Since in the current experiment C18:1 n-9 and Σ MUFA proportions were higher in females than in males while Σ n-6/Σ n-3 ratio was lower, subcutaneous fat from females would be healthier than that from males. Wood & Enser (1997) also reported that these variables would be good indicators of fat quality.
In the present experiment the carcass weight and fatness degree had not significant (p > 0.05) influence on fatty acids proportions of subcutaneous backfat. However, some studies have considered that an increase in beef fat led to an increase in Σ MUFA and decrease in Σ PUFA (Moreno et al., 2006), although according to Prior et al. (1983) the manipulation of sex hormone status of living cattle influenced lipid metabolism in the adipose tissue, and sex differences in the fatty acid composition are known to be associated with hormonal changes and their possible effect on enzymatic systems.
It is concluded that the gender has influence on growth performance, carcass traits and fatty acid composition of subcutaneous backfat of Avileña-Negra Ibérica calves fattened under intensive conditions; gender does not have effect on instrumental colour variables; and meat colour can reach acceptable values for consumers until four days after slaughter.