Effects of a partial or total mixed ration silage based on sugar beet tops on the rumen and blood variables, performance, and carcass quality of fattening lambs

Silage made from sugar beet tops (SBT) has the potential to provide a large amount of fermentable energy in the rumen. A dry total mixed ration (TMR) was compared with a partially or fully ensiled mixed ration based on SBT, on ruminal and blood variables, estimated microbial protein synthesis (EMPS), nutrient digestibility, productive performance, carcass quality, and antioxidant status in fattening lambs. In vitro methane release from the tested diets was also evaluated. Thirty-nine Ghezel male lambs (31.5 ± 1.1 kg body weight) were fed for 88 days in a completely randomized design (13 lambs per ration), including a 14-day adaptation period to the experimental protocol. Sugar beet tops were incorporated into 2 silage products differing in fiber content: 1) a high-fiber silage mixture based on SBT and fibrous byproducts (HFS) for subsequent blending with dry concentrates for a TMR at feeding, or 2) a low-fiber ensiled TMR based on a blend of SBT, fibrous byproducts, and concentrate ingredients (TLF). Three isonitrogenous and isoenergetic diets were formulated: 1) a dry TMR without SBT (control), 2) a partially ensiled ration consisting of HFS blended with dry concentrate (PHF), and 3) the fully ensiled TMR consisting only of TLF. The animals were fed ad libitum daily at 8:00 a.m. and 4:00 p.m., with 5% orts allowed, and clean water was always available. Compared to the control, feeding PHF or TLF improved rumen total short-chain fatty acids (P = 0.01), propionate (P = 0.02), butyrate (P = 0.02), and EMPS (P < 0.01), but decreased acetate and total protozoa number (P < 0.01). Apparent digestibility (P < 0.01), feed efficiency (P < 0.01), and total unsaturated fatty acids in the carcass (P = 0. 01) increased and dry matter intake (P < 0.01), feeding costs (P < 0.01), and carcass total saturated fatty acids (P < 0.01) decreased in the animals fed PHF or TLF, compared to the control. Feeding animals with PHF or TLF resulted in increased antioxidant capacity of blood and carcass compared to animals receiving a control diet (P < 0.05). In vitro estimated methane production in PHF and TLF fed lambs showed a significant decrease (P < 0.01), but cellulolytic bacteria increased (P = 0.049), compared to the control group. Under the current experimental conditions, replacing dry TMR with the totally ensiled mixed ration based on SBT did not affect the productive performance, so it is recommended to feed fattening Ghezel lambs.