The effects of docking on growth traits, carcass characteristics and blood biochemical parameters of Sanjabi fat-tailed lambs

Asian - Australasian Journal of Animal Sciences, June, 2009 by E. Nooriyan Sarvar, M.M. Moeini, M. Poyanmehr, E. Mikaeli

INTRODUCTION

Fat-tail removal (docking) of lambs is an important management practice in commercial sheep production (Snyman et al., 2002; Cloete et al., 2004). The results of many investigations have shown that docking decreases metabolizable energy (ME) requirement due to lower fat deposition, has a positive impact on reproductive performance and produces more uniform and blocky lambs in appearance (Wohlt et al., 1982; Shelton 1990; Snayman, 2002). Lambs are cleaner and less prone to infection and external parasites (Wohlt et al., 1982). Therefore, it is beneficial in improving daily live weight gain, fattening trait and carcass characteristics for consumers (Bingoal et al., 2006). The fat deposited in the body or tail is laid down at a much higher cost in terms of feed energy than lean meat.

Dressed lamb carcasses have a neater appearance and thus receive higher market prices (Gokdal et al., 2003). Also, consumers in many instances show an increasing preference for lean meat (Emam Jom-e Kashan et al., 2005).

Approximately 64% of the sheep population in Iran consists of fat-tailed breeds. The fat tailed sheep are characterized by adaptation to harsh environments i.e. extreme temperatures and poor feeding conditions (Emam Jom-e Kashan et al., 2005). The Sanjabi is a dual-purpose (mutton and wool) native breed which has a high growth rate with good meat quality. Since this breed is classified as a long fat-tail family, propagation of docking may lead to good economical benefits for the sheep husbandry in this region. Changes in consumer preferences favoring leaner meat, the growing awareness of the danger of high fat diets, as well as the availability of alternative cheaper and healthier fat sources have resulted in a reduced demand for sheep with a fat-tail. The objective of this study was to evaluate the effects of docking on growth traits, fattening performance, carcass characteristics and some biochemical parameters of fat-tailed Sanjabi male lambs. This investigation is the first report on the effect of docking on economic traits and blood biochemical parameters of Sanjabi sheep.

MATERIALS AND METHODS

This experiment was conducted in a large commercial Sanjabi herd located at Kermanshah province in the west of Iran. A total of 24 fat-tail Sanjabi single-born male lambs were used in this study. The lambs were born in June 2007 and immediately were randomly divided into two groups. One group (n = 12) were docked at two days of age with rubber-rings using an elastrator. The second group (n = 12) were left intact. The lambs were allowed to stay with their dams for 3 months until weaning. All lambs were moved to rustic rangelands after the weaning period for 40 days. Lamb weights were recorded weekly and normal inoculation, drenching and tick control programs were also followed during the experiment. Then, all lambs were placed on a fattening diet for 60 days. The lambs were housed in two groups and fed with concentrate and forage (Table 1) for the duration of the fattening period. At the beginning and end of the fattening period, live weights of all lambs were recorded. The following growth traits were recorded: initial weight, final weight, total weight gain and average daily gain (ADG) in the pre-weaning and fattening periods.

Carcass traits

Four docked lambs and four intact ones were slaughtered immediately after the fattening period. Lambs were killed by exsanguination using conventional humane procedures. The body was divided into individual components which were then weighed separately as internal organs (liver, heart, lungs and trachea, kidneys, testes and spleen), head (disarticulated at the occipito-atlantoid articulation), feet (disarticulated at the tarso-metatarsal and the carpo-metacarpal articulations), and carcass. Visceral fat (separable fat in the body cavity) was separated at the time of harvest and weighed. The kidney fat was also physically separated from both sides and weighed. All carcasses were weighed hot (approximately 1 h. after harvest) and then chilled (-4[degrees]C) for approximately 24 h. After chilling, the carcasses were weighed again and then longitudinally halved with a band saw. Records of carcass components included carcass measurements (cm) (Chest dept, Leg dept, Chest width, shoulder width, rump width, leg width, leg length, carcass length), Carcass weight (kg) and dressing percentage (%) i.e.; Slaughter weight, cold carcass weight (CCW), offal items (head, 4 feet, skin, heart, lung, liver, testes, kidney, spleen, kidney and pelvic fat, internal fat and tail weights). The cold carcass was split along the backbone according to the procedure of Colomer-Rocher et al. (1987). The left half of the carcass was separated into five anatomically defined cuts (Fernands et al., 2008).

Chemical analysis

The whole soft tissue (fat and lean meat) of the left side of the carcass was ground and passed twice through a plate with a 4 mm orifice. After fine grinding of the small, frozen pieces and thorough homogenization, representative samples were taken for determination of moisture, dry matter (DM), crude protein, ash and lipid contents using AOAC (1990) procedures.