Sex and slaughter weight on carcass traits and non-carcass components of horses

ABSTRACT: The study evaluated the effect of sex and slaughter weight on carcass traits and non-carcass components of 1,489 horses (739 geldings and 750 females, classified into eight groups according to their weight). Data were analyzed under a completely randomized design. Geldings had a higher (P < 0.05) hot carcass yield (HCY) and cold carcass yield (CCY) than females; however, fat yellowness values (b*) were greater (P < 0.05) in females. Slaughter weight (SW) affected the carcass characteristics. Hot carcass weight (HCW), cold carcass weight (CCW), HCY, and CCY increased (P < 0.05) in accordance with slaughter weight, while cool loss percentage (CL%) was lower (P < 0.05) in horses weighing more than 300 kg. In addition, the non-carcass components decreased (P < 0.05) as the weight of the horses increased. In conclusion, sex and body weight are factors to consider in the production of equine meat since they affect carcass characteristics and non-carcass components.


INTRODUCTION
Horsemeat is classified as meat of excellent quality (TATEO, 2008;LORENZO et al., 2010;STANCIU, 2015).However, the consumption of pork, chicken and beef is higher than that of horsemeat (GILL, 2005;LOMBARDI-BOCCIA et al., 2005).Per capita horsemeat consumption is difficult to estimate; however, BELAUNZARAN et al. (2015) have reported a world average of 0.10 kg.Moreover, LORENZO & CARBALLO (2015) mentioned that part of the horsemeat consumed worldwide comes from horses that ended their productive life.
Horses have advantages over other meat-producing species, due to their high carcass yields (60 to 70%) composed principally by the muscle (70%) but low in fat (10%) and bone (20%) (SARRIÉS & BERIAIN, 2005;LANZA et al., 2009).Previous research reports described that sex, age, breed, and production system affect carcass traits and meat quality (JUÁREZ et al., 2009;FRANCO et al., 2011, CITTADINI et al., 2021).However, there are few research reports on the factors that affect carcass and meat characteristics of horses slaughtered in America.Thus, this study evaluated effects of sex and slaughter weight on carcass traits and non-carcass components of horses.

MATERIALS AND METHODS
Protocols for care and animal handling were carried out following the official Mexican standards: Ciência Rural, v.53, n.4, 2023.

Animals
A sample of 1,489 Quarter Horses and their crosses owned by the packing plant "Empacadora de Carnes Fresnillo S.A. de C.V." located in Zacatecas, México was used.Daily visits were made for 4 weeks to the slaughterhouse until the sample was completed.Horses were classified according to their sex in gelding (739) or female (750).Slaughter weight (SW) was measured before slaughter using an electronic scale (model PG, Torrey, México), and they were classified into eight groups according to SW: 150 to 200 kg, 201 to 250 kg, 251 to 300 kg, 301 to 350 kg, 351 to 400 kg, 401 to 450 kg, 451 to 500, and > 500 kg.

Slaughter and carcass data collection
The slaughter procedures were performed following the Mexican Official Standard NOM-033-SAG/ZOO-2014.After slaughter, non-carcass components (Head, skin, heart, lungs, stomach, caecum, spleen, liver, small intestine, and large intestine) and hot carcass weight (HCW) were obtained.Internal organs were individually removed and weighed.The organ mass was expressed as a percentage of empty slaughter weight (BW).To obtain cold carcass weight (CCW) and dressing percentage, carcasses were stored for 24 h at 4 °C and 98% of relative humidity.Cooling loss (CL) was calculated from the difference between HCW and CCW, and expressed as percentage.
Color determination (L * , a * , b * ) in fat (subcutaneous and abdominal) and muscle (semitendinosus) was carried out 45 minutes post-mortem directly on the carcass using a portable spectrophotometer (CR-400, Konica Minolta Sensing Inc., Japan).

Statistical analyses
A normality test of the data was performed with UNIVARIATE procedure of the SAS University Edition software (SAS Institute, Cary, NC, USA).Data were analyzed as a completely randomized design using the GLM procedure.The model included the sex and slaughter weight as fixed effects.A multiple comparison was made whit option MEANS Tukey in SAS.Main effects significance was declared at P < 0.05.Results were presented as least square means ± SEM.

RESULTS
Sex effects on carcass characteristics are shown in table 1.It was observed that sex affected (P < 0.05) the HCY and CCY, being higher in geldings.The HCW, CCW and CL were unaffected (P > 0.05) by sex.Regarding the semitendinosus muscle color, the L * value was not affected (P > 0.05), but the a * value was higher (P < 0.05) in geldings than in females.However, the b * value was higher (P < 0.05) in females.Regarding abdominal and subcutaneous fat color, the L * and a * values were not affected (P > 0.05), but the b * value was higher (P < 0.05) in females than in geldings.Concerning body components, geldings had a higher (P < 0.05) head percentage than females; however, other body components were unaffected (P > 0.05).
SW affected (P < 0.05) HCW and CCW.Similar behavior was observed in HCy and CCy, observing that horses weighing more than 400 kg had higher dressing (P < 0.05) concerning those of lower weight (Table 2).The SW in horses also affected CL%, observing that in horses weighing more than 300 kg, CL% is lower (P < 0.05) with respect to those of lower weight.Additionally, the percentage of non-carcass components decreased as the SW increases (P < 0.05).Color parameters in the semitendinosus muscle (L * , a * , and b * values) were unaffected by SW (P > 0.05).However, color fat was affected by SW, in abdominal fat L * was less in horses over 450 kg, the opposite was observed in a * , where it is higher in horses over 300 kg (P < 0.05).In subcutaneous fat, it was observed that b * increase as the SW increases (P < 0.05).
Regarding the sex of the animals, it has been described that it influences carcass characteristics (JUÁREZ et al., 2009).Different authors conclude that the sex effect on carcass characteristics is related to the fat in the carcass (HORCADA et al., 1998;DÍAZ et al., 2003).For their part, SARRIÉS & BERIAIN (2005) reported a CCW of 270 kg in males, which is higher when compared to the averages observed in females and males in this study.
In this sense, NIVIA et al. ( 2014) reported greater weight and performance of the carcass in males.Similarly, HERNÁNDEZ et al. (2018) conducted a study in donkeys in which they observed greater CCW and CCY in geldings than in females.However, different investigations mentioned that the sex in horses does not have a significant effect on growth, weight, and carcass performance (MARTIN- ROSSET & DULPHy, 1987;FURTADO et al., 2011).
At this point, it should be noted that the differences between the animals evaluated in this study and those evaluated in European countries    are mainly due to the different breeds to which they belong, as well as the age and production system (TATEO et al., 2008;FRANCO et al., 2011).In horses, the effect of age and production system on carcass characteristics has been previously described (SARRIÉS & BERIAIN, 2006) in their study, they observed that carcass yield was higher in 24-monthold males and females compared to 16-month-olds, which are superior to the yields in horses observed in our investigation.In relation to the above, LORENZO et al. (2014) observed that carcass weight and dressing percentage were lower in horses from extensive production systems, compared to horses from semi-extensive and supplemented semiextensive systems.Likewise, a relationship between the breed, age and the type of feeding in horses      finished with different diets is documented (RUIZ et al., 2017, CITTADINI et al., 2021).Being its final weight and the characteristics of the carcass superior regarding the horses slaughtered in Mexico.
There is little scientific information describing the performance of non-carcass components in horses.However, results in this study showed that there is an effect of SW on the performance of the non-carcass component.In this regard, differences in visceral mass have been described in pigs slaughtered at different SW (SANTOS-RICALDE et al. 2011).Likewise, other authors reported that SW affected red viscera such as the heart, liver, lungs, and kidneys; and body components such as the head, skin and legs are also affected (PÉREZ-MELÉNDEZ et al., 2007).Conversely, our results showed that equine sex did not affect non-carcass components, except head.
Meat color is an important characteristic in fresh meat (MANCINI & HUNT, 2005), and genetics, age, sex, feed system, and slaughter method are factors that could affect meat color (PRIOLO et al., 2002;RIPOLL et al., 2012).For their part, SARRIÉS & BERIAIN (2006) observed differences in meat color between female and male horses of 16 and 24 months of age, respectively.Reporting similar values for L * , a * and b * to those reported in this study.However, in younger foals, DOMINGUEZ et al. (2015) did not observe differences in the color of longissimus dorsi in foals slaughtered at 8 and 11 months of age.
Myoglobin content in meat is related to luminosity and red coloration and influenced by the production system and feeding (POLIDORI et al., 2015).In addition, intramuscular fat content and water in muscle were related to meat color (LORENZO et al., 2015).In relation to the above, in lambs, it has been described that heavy and old animals showed differences in color, related to a greater amount of intramuscular fat than light and young animals, even when they received the same diet (OKEUDO & MOSS, 2007).

CONCLUSION
Data from this study indicated that geldings have a heavier and higher-yielding carcass and a lower yellowness color in abdominal and subcutaneous fat than females.
SW affected the carcass characteristics and the percentage of non-carcass components.As body weight increased, carcass weight and dressing also increased.Horses weighing more than 400 kg presented a higher carcass yield.The opposite happened with the non-carcass components, since the proportion of these had to increase the slaughter weight.

Table 1 -
Effect of sex on carcass traits and non-carcass components in equines.

Table 2 -
Effect of slaughter weight on carcass traits and non-carcass components in equines.