The size of fat tail does not have an effect on growth performance and carcass characteristics in Lori-Bakhtiari lambs

This study compared the growth performance and carcass characteristics of Lori-Bakhtiari lambs with three types of fat tail. Thirty lambs were divided into three groups according to the size of their fat tail: big (BF), medium (MF), and small (SF) fat tail. The weaned lambs were finished over 100 days, and their average daily gain (ADG) and feed intake (FI) were measured, and the feed conversion ratio (FCR) was calculated accordingly. At the end of experiment, all lambs were slaughtered and the fat surrounding their intestines and abdomen as visceral fat (VF) and their kidneys and pelvic fat (KPF) as internal fat were weighed. The hot carcasses were weighed and the fat tails were cut and weighed for each carcass. Finally, the subcutaneous fats (SCF) related to the left side of the carcasses were dissected and weighed. ADG, FI, and FCR were not affected by the size of the fat tail. Final body weights of BF, MF, and SF were 59.0 +/- 0.71, 58.7 +/- 0.68, and 59.8 +/- 0.70 kg, respectively (P > 0.05). The weight of the fat tail was 8.7 +/- 0.29, 7.6 +/- 0.28, and 6.3 +/- 0.28 kg for BF, MF, and SF lambs, respectively (P < 0.0001). An inverse relationship was found between the weight of the fat tail and other fat components of the carcass. The weight of the SCF differed among the lambs (P < 0.05), and was 3566 +/- 387.7, 4395 +/- 372.1, and 4743 +/- 383.4 g in BF, MF, and SF lambs, respectively. Additionally, the KPF weight was 179 +/- 54.8, 268 +/- 52.6, 415 +/- 54.2 g for BF, MF, and SF lambs, respectively (P < 0.05). Lambs with SF had the heaviest VF followed by MF and BF (1086 +/- 96.0, 629 +/- 93.2, and 418 +/- 97.1 g, respectively; P < 0 .0003). Total carcass fat and total body fat were similar among the lambs, while the carcass weight without fat tail (CWFT) and carcass weight without fat tail and SCF (NCW) were greater in SF lambs than in MF and BF lambs (P < 0.05). It can be concluded that the lambs with SFs are not superior to those with BFs in terms of FI, weight gain, or FCR, but lambs with SF reached the desired body condition score for slaughtering sooner than those with BF, which in turn prevents the storage of more fat in the other fat depots, especially VF, and reduces the length of the finishing period, thus reducing the production costs.