Meat-type buffaloes: age at slaughter by survival analysis

Edison Julián Ramírez Toro, Jaime Alberto Mesa R*, Divier Antonio Agudelo Gomez*, Diana Maria Bolivar Vergara** and Mario Fernando Cerón-Muñoz

Genetics, Animal Breeding and Modeling Research Group (GaMMA) at the School of Agricultural Sciences and Institute of Biology,
University of Antioquia. Carrera 75 No. 65-87 Medellín, Colombia
edjurato@gmail.com  ;   mceronm@hotmail.es
* School of Administrative and Agricultural Sciences at the Lasallian University Corporation.
Carrera 51 118 sur 57 Caldas - Antioquia - Colombia
** School of Agricultural Sciences at the National University of Colombia, Medellín.
Calle 59A No 63-20 Medellín - Colombia

 Abstract

Meat quality is influenced by various factors such as breed, gender, age, body weight (BW) and fatness, among others. Both BW and fatness are commonly used for the evaluation of carcasses, thus influencing its market value.. This study aimed to determine the slaughtering probability for a group of male buffaloes after reaching either a pre-determined (ideal) slaughtering weight (PBW) equivalent to 420 kg, or rump fat thickness (RFT) of 6mm. Body weights and ultrasound fat measurements of 123 castrated male buffaloes were used. Survivability values were estimated by the nonparametric Kaplan Mayer test.

At 24 months of age, 8% and 7% of the animals had reached PBW and RTF, respectively. At 27 months of age, 62% of the animals reached the ideal weight for slaughter. The last animal reached the PBW at 34 months of age.

Keywords: Beef cattle, carcass quality, growth

Resumen

La calidad de la carne está influenciada por diferentes factores, tales como raza, sexo, edad, peso vivo (PV) y el grado de engrasamiento (acabado) del animal, entre otros. El PV y el acabado, por ser tenidas en cuenta en el momento de la evaluación de la canal, influencian su valor comercial.. El presente trabajo tuvo como objetivo identificar la probabilidad de salida de un grupo de búfalos machos por haber alcanzado un peso vivo predeterminado para sacrificio (PPV) de 420 kg, o un espesor de grasa de cadera (EGC) de 6 mm. Se utilizó información de pesos y ultrasonido de 123 búfalos machos castrados. Los valores de supervivencia fueron estimados mediante la  prueba no paramétrica de Kaplan Mayer.

A los 24 meses de edad el 8% y 7% de los animales habían alcanzado el PPV y el EGC. A los 27 meses de edad el 62% de los animales alcanzaron el peso ideal de sacrificio. El último animal alcanzó el peso ideal a los 34 meses.

Palabras claves:  Calidad de canal, crecimiento, ganado de carne,

Introduction

Meat quality is influenced by various factors, such as age, gender, breed, body weight (BW) and fatness, among others. Age at slaughter has an impact on carcass traits (Depetris 2000). In fact, growth precocity is directly related to meat quality (Huerta 2002). It is known that buffalo is a fast growing animal, able to reach slaughter weight in just 24 months under grazing conditions, and even faster (18 months) under confinement (Mattos et al 1990). On the other hand, fatness also influences carcass quality because it partly determines its commercial value (Briskey and Bray 1964). In fact, fat is the single most important quality criterion for carcass evaluation. Fat content affects meat tenderness during the cooling process. Carcasses having less fat will cool faster, which can cause a hardening of the muscle fibers, ending up in less tender meat (Avilez 2006). Therefore, it is important to keep in mind these characteristics, since they are factors in product acceptance by the final consumer (Jorge et al 2006).

The most commonly used criterion to determine the best time to sell animals for slaughter in Colombia is BW (Apple 1999). The degree of fatness is less used for this purpose (Velasquez and Alvarez 2004). As a tool for finding the best slaughtering time, farmers should use statistical methods that allow them to obtain the probability for an animal to reach ideal traits at different ages, and the survival analysis is a good statistical alternative. Survival models are used in livestock production to determine the probability of survival to a specified age.

The aim of this study was to determine the probability of slaughtering a group of buffaloes as they reach a pre-defined slaughter weight or rump fat thickness (RFT), using survival models.

Materials and Methods

Weight measurements and ultrasound data of 123 castrated male buffaloes (Bubalus bubalis sp.) was used for the survival analysis. The animals were raised at El Teatro farm, located in Buena Vista, Colombia (8.07 degrees, -75.4 minutes of longitude from Greenwich), an area classified as tropical moist forest (altitude 80 m. over sea level, and 28 ºC temperature). Animals were grazing on Brachiaria humidicola and native pastures.

Weightings and ultrasound images were taken every 3 months. Rump fat thickness (RFT) measurements were obtained with an ultrasound equipment (Akila-Pro, Esaote, Holanda), equipped with a 3.5-MHz, 18cm transducer (Figure 1). Each image was taken between the ischial and iliac tuberosities, from the tip of the hip towards its caudal region. Subsequently the images were measured using Eview software (Pie Medical 1996).

Apple (1999) suggested that body weight can be used to determine the time of sale for slaughter. We established 420 kg BW as the determinant weight for sale. Considering that RFT affects beef carcass quality (Gallo et al 1999), we used it as the other end point. It is known that carcasses should have a thin layer of fat to protect it at the time of cooling, but an excess of fat is not desired. The recommended fat cover should be from 5 to 8 mm thick (Smith 2002).

Figure 1. Researchers taking the ultrasound image to determine the fat thickness at the hip of castrated male buffaloes in northern Colombia.

Statistical analysis

The survival function describes the risk of change of state in different periods of time, and represents a sequence of conditional probabilities: f(t) = P (probability for an animal to reach 420 kg in time t, giving that it had not reached it in t‐1 (Ayala 2004).

The probability function is given by:

where T is a discrete non-negative random variable, representing the life of an animal, and can be 0 ≤ t₀ ≤ t₁ ≤ t₂ ≤ t_i.. Survival function is defined as:

and represents the probability for T being greater or equal to a t value. The risk function defining the probability for an individual to reach the event in t_j, given it had not reached it before, is defd

Where d_j represents the number of individuals that registered the event of interest at time j, and n_j represents the total number of elements present at time j. 

In this study, there were censored data corresponding to animals that failed to reach the characteristic of interest at the end of the measurements, or have left the farm before the end of the study without achieving any of the two events.

The R statistical software (version 2.11.1) with Survival and MASS libraries for R (R Development Core Team 2007) was used for the analysis of the information.

Results and Discussion

At 24 months of age, 8% and 7% of the animals had reached the BW and the RFT, respectively. This is in disagreement with Mattos et al (1990), who reported 24 months of age to reach slaughter weight for buffaloes grazing in Brazil, which suggests Colombian buffaloes reach slaughter weight at an older age. At 26 months of age 25% of the animals reached the BW and the RFT (Table 1 and Figure 2). The censored data were 44 and 37 for BW and RTF, respectively.

A greater number of animals reached the end points at 27 months of age: 62% reached BW and 65% reached RFT (Table 1 and Figure 3). This is the age at which most animals, under grazing conditions, reach slaughter weight in Colombia. In a study by Angulo et al (2005) researchers found that crossbreed buffalo, under grazing conditions can reach slaughter weight at a young age in Colombia, which results in better carcass scores. This benefits consumers, who buy a better quality product, and producers, who obtain a greater economic benefit from the sale of their animals.

According to this, the evaluated animals would be classified as “four stars” under the Colombian cattle carcass classification system (Gómez and Palacios 1995), considering they have the age, the RFT, and the BW within the ranks for this grade. This is consistent with Mattos et al (1990) who state that buffalo is a fast growing species that reaches slaughter weight at an early age.

According to our results, it took a maximum of 34 and 36 months for the animals to reach BW and RFT (6mm), respectively (Table 1 and Figure 2). According to Smith (2002), this is the appropriate fat coverage of the carcass to avoid losing quality. Fat coverage exceeding 10 mm is considered to be in excess. According to Berg et al (1976) fatty animals have slower muscle growth, reflected in lower feed efficiency, which means higher feed costs, and leads to fatty carcasses that get a lower rating. Colombian buffalo farmers should take this into account, and consider 36 months as the maximum age to slaughter their animals.

Body weight	Rump fat thickness
Figure 2. The probability for buffaloes in northern Colombia to reach slaughter weight or 6 mm rump fat thickness.

 Until about 23 months of age none of the animals had reached the BW or RFT. Similarly, there was a rapid decline between 23 to 30 months, a period where most of the animals reached the BW or RFT. A stabilization of the curve can be noticed from 30 to 36 months of age, because only two individuals reached the BW and the RTF in this period.

Conclusions

• Buffalo are precocious animals, they can reach slaughter weight at 27 months of age, with 6 mm fat thickness.

• Of all the animals in this study, 92% received the highest carcass grade for bovines in Colombia, after considering their age, weight and fat thickness.

Acknowledgements

This paper is derived from the research project "Genetic evaluations of meat-type buffalo in Colombia", funded by the Colombian Ministry of Agriculture and Rural Development, the Colombian National Livestock Fund, the Colombian Association of Buffalo Breeders, the Lasallian University Corporation, and the University of Antioquia. The first author was financed by an agreement between the University of Antioquia and San Martin University Foundation. The authors are very grateful to El Teatro farm for having provided the information for this study.

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Received 4 January 2011; Accepted 1 March 2011; Published 1 April 2011

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