Impact of Particle Length of Alfalfa Hay in the Diet of Growing Lambs on Performance, Digestion and Carcass Characteristics

Thirty-six Najdi ram lambs, weighing an average of 24 kg and circa 3 months old, were utilized in this trial to evaluate the effects of various alfalfa hay particle lengths in the diet on growth performance, digestion coefficients, nitrogen retention and carcass characteristics. Lambs were randomly allotted to three dietary treatments: 9.5 and 14 mm diets, where alfalfa hay was processed to 9.5 and 14 mm particle lengths, respectively, mixed with 3 parts of concentrate and pelleted as a total mixed ration (TMR), and long hay diet, where one part of loose alfalfa hay (17.8${\pm}$2.4 cm) was offered in combination with 3 parts of only-concentrate pellet. All dietary treatments were homogeneous in their ingredient composition. All lambs were slaughtered after a 14-week feeding trial. Although the results showed no significant effect of hay particle length on DMI, TDN and DCP, lambs fed the 9.5 mm pelleted diet had higher (p<0.05) final body weight, ADG, gain efficiency and nitrogen retention than lambs fed the 14 mm and long hay diets. Altering the particle length of alfalfa hay in diets did not affect the digestibility of DM or CP, whereas digestibilities of ADF and NDF were 3.7% and 5.4% higher (p<0.05), respectively, for the long hay diet versus the 9.5 mm pelleted diet. Hot carcass weight, percentage of separable lean from the $9-11^{th}$ rib joint, and percentages of protein and EE in the separable lean increased (p<0.05) as the particle length of alfalfa hay in the diet decreased. Under the conditions of this study, the reduction of particle length in the TMR played an important role in enhancing performance without altering DM consumption, and this may lead to more efficient productivity of lamb fattening compared with longer chopping lengths.