Allometric coefficients for carcass and non-carcass components in a local meat-type sheep breed

Abstract

The aim of the research was to assess the type of development of carcass and non-carcass components and tissue partitioning in the Cornigliese sheep breed. The study involved 164 animals (104 females, 60 males) from one flock. The selection of those animals accounted for ages and weights differences. Fasted body weight (BW) was recorded before slaughtering. Four BW-classes were identified by means of percentiles distribution: 0–25th percentile, 15.90–50.70kg BW; 25th–50th percentile, 50.71–63.22kg BW; 50th–75th percentile, 63.23–75.50kg BW; 75th–100th percentile, 75.51–111.15kg BW. After slaughter, the carcasses were weighed, measured (carcass length, croup width, chest width, chest depth, thigh length) and sectioned (shoulder, neck, thigh, ribs, loin, and lean and fat trimmings). A samplecut from 1st to 4th thoracic vertebra was then separated into its tissue components (lean meat, fat, bone). Non-carcass components (skin+fleece, head, liver, heart, lungs+trachea) were weighed. The data were analyzed using a GLM procedure accounting for the following fixed effects: sex, BW-class, year of birth and the interaction between sex*BW-class and the covariate: day of slaughter. The relative growth of carcass and non-carcass components on BW was calculated by applying the nonlinear allometric function (y=axb). We found high coefficients of variation (CVs) (from 39% to 77%) for the weight of carcass components and low CVs (from 8% to 22%) for carcass measures. Non-carcass parameters showed intermediate values of CVs (from 30% to 42%). Body weight-class had a significant effect (P<0.05) on all parameters, except on lean/fat ratio and lean percentage of the sample cut. Significant mean differences between genders were observed in the lean/fat ratio. In particular, in the lowest BW-class, females scored higher than males, whereas, in the highest BW-class, we observed the opposite trend (P<0.05). Carcass, loin, lean and fat trimmings grew faster than BW, regardless of the sex. In contrast, as far as the neck is concerned, significant differences between females and males were observed (P<0.05). Among carcass measures, a late maturing rate was recorded for croup width (b=0.5042) and, in this case, females tended to be earlier than males (P<0.10). Among non-carcass parameters, only head and skin+fleece weights showed differences between sex groups, with males showing a later development than females (P<0.05). Tissues (lean, fat, bone) in the sample cut developed with different speed: the earliest tissue was bone (b=−0.3191), followed by lean (b=0.0768) and finallyby fat (b=0.8394). Bone development was significantly (P<0.05) sex related, with males showing a later growth than females. Sex differences in the sample cut composition were also associated to lean/fat, (lean+fat)/bone and lean/bone ratios. This study has shown the potential use of the Cornigliese sheep as a commercial breed for meat production, although significant interaction between sex and body weight was observed. For this reason, it is recommended to implement a breeding strategy to reduce the incidence of extreme fattening females and the high incidence of non-carcass component in males when they reach high BWs.