Brassicas used as cover crops (CC) also have the potential to provide high-quality forage as part of a lamb rearing system. We compared growth, carcass traits, and meat quality in lambs finished on two brassica-based CC pasture treatments or two grain feeding systems in 2019 and 2020. Lambs (n=60; Dorset x Polypay; 3 pens/pastures, 5 lambs each) were randomly assigned to four treatments: 1) GRN ⁰́₃ 6 wk on grain; 2) BRO - 8 wk grazing pure brassica CC; 3) MIX ⁰́₃ 8 wk grazing a mixture of brassica and other CC species; and 4) BKG - 4 wk background grazing of pure brassica followed by 4 wk on grain. Cover crops were planted in late summer after winter wheat harvest and grazing began after 4 Mg DM/ha of CC was available. Pre-grazing CC biomass did not differ; however, botanical composition did, reflected as less fiber (ADF and NDF), DM and CP in BRO and BKG compared to MIX (P < 0.001). Lambs fed grain (361 g/d GRN and 308 g/d BKG) grew faster (P < 0.001) than those on CC (204 g/d BRO and 186 g/d MIX). Gain per hectare did not vary by CC but declined over time (218 kg/ha on d 14-28 to 137 kg/ha on d 43-56; P < 0.01). Plasma NEFA concentration was elevated in CC compared to when lambs ate grain (P < 0.001), and plasma PUN was depressed in lambs on pure brassica CC compared to other treatments (P < 0.01). Carcass characteristics and IMF (3.9 ⁰́₃ 4.2%) were not affected by CC treatment but lambs finished on CC were leaner (backfat 0.7 cm versus 1.0 cm; P <0.05) and smaller (hot carcass weight 28 kg versus 30 kg; P <0.01) than grain-fed lambs. In a sensory evaluation of loin chops, all treatments were rated acceptable, but consumers preferred BRO over other treatments for flavor and juiciness (P < 0.05). We conclude that brassica CC rearing systems can produce lambs of acceptable carcass and superior meat quality. Further work is needed to assess the economics of these rearing options and the basis for the depression of PUN when grazing forage with high brassica content.
Read
