Effects of testicular status and feeding diets containing date palm by-product on the sensory attributes of Omani lamb meat

Abstract

The effects of testicular status and diet on the tenderness and flavour intensity of Omani lamb meat were evaluated. Thirty male lambs were divided into three testicular status treatments shortly after birth, entire, castrated or induced to cryptorchidism. The animals were fed a maize and soya bean meal based diet, isocalorically supplemented with either palm fronds or Rhodesgrass hay. The animals were slaughtered at an average age of 161 days and weight of 27.6 kg. Sensory evaluation of meat for tenderness and intensity of flavour were undertaken using descriptive analysis with unstructured scales. Meat from New Zealand lambs was also evaluated for comparison. Meat from castrated lambs tended to be more tender than meat from either entire or cryptorchid lambs. This effect was related to the significantly lower daily weight gains, lower carcass weight and lower intermuscular fat content of castrated lambs. The effect of induced cryptorchidism or inclusion of date frond was not significant on tenderness, nor flavour of the lamb meat. Meat from New Zealand lambs was significantly more tender, but similar in flavour compared to Omani lambs.

Introduction

Consumers have identified tenderness and flavour as the most important factors regarding lamb meat quality, preferring tender as opposed to tough (Lawrie, 1991), and mild flavoured as opposed to strong flavoured lamb (Melton, 1991). These sensory attributes depend on factors that may include diet and management practices. Management practices examined in the present study are male fertility control.

Unlike temperate areas, desert climates do not have abundant grazing land for ruminants. Sources of roughage, like Rhodesgrass, must be grown under irrigation, at considerable cost. Alternate sources of roughage would be economically desirable. In Oman, some 14,000 tonnes dry weight of palm frond prunings are produced from approximately eight million date palm trees each year (Myhara et al., 1999), most of which are disposed of by burning. Palm frond, used in experimental diets, were shown to be inferior to Rhodesgrass hay as a source of roughage, but were economically viable given the latter’s high cost of production (Mahgoub et al., 1998). The effect of feeding palm frond upon the lamb meat quality had not been evaluated.

Lamb meat tenderness, in general, is not significantly affected by diet. Fahmy et al. (1992) found that diet did not significantly affect meat tenderness from lambs slaughtered at ages ranging from 198 to 243 days.

Lawrie (1991) reported that post-mortem handling conditions such as chilling rate have a profound effect upon the ultimate pH of meat. Generally, the closer the ultimate pH is to the isoelectric point of the meat proteins, the less tender the resultant meat becomes.The significance of diet on lamb meat flavour has not been determined with certainty. Cramer et al. (1967), Park and Thomas (1973) and Field et al. (1983), found feed source to significantly affect the flavour of lamb meat, however, Paul et al. (1964) and Ford and Park (1980) failed to show significant dietary effects. Certainly dietary factors could quite possibly affect meat flavour, especially so as the animals age.

Raising entire males can introduce management problems related to breeding programs, so castration is a common means of fertility control that could Mahgoub et al. (1998) found that castration of male Omani lambs resulted in lower daily growth rates, carcass weights and intermuscular fat content. Induced cryptorchidism, an alternative to castration, controls fertility (Chesworth et al., 1996) but does not significantly decrease growth rate, average slaughter weight or intermuscular fat content (Mahgoub et al., 1998).

In the present study, a trained sensory panel assessed the tenderness and flavour intensity of entire, cryptorchid or castrated Omani lambs fed either Rhodesgrass or palm frond.