Ewe metabolic performance and lamb carcass traits in pasture and concentrate-based production systems in Churra Tensina breed

Thirty-eight adult ewes rearing single male lambs were randomly allocated to two adjacent paddocks (n = 19) grazing permanent Pyrenean pastures in spring (0.57 ha/paddock). Treatments were: indoor (IND) in which ewes grazed during 8 h a day (08:00 to 16:00 h) without their lambs and thereafter remained indoors with them, receiving a supplement of 0.5 kg of barley meal/day. Lambs were fed concentrate ad libitum and they were weaned at 53 days old; grazing (GR), ewes and lambs were continuously grazing, no concentrate was available to them and lambs were unweaned. Both management strategies showed a similar pattern of live-weight and BCS during spring grazing, except at day 49 post-lambing, when body reserves of GR ewes were greater than their IND counterparts (P < 0.05). Milk production of GR ewes was greater on days 13 and 27 of lactation (P < 0.05). Milk composition was not affected by the management system (P > 0.05) and fat and protein content increased with advancing lactation (P < 0.001). Milk fatty acid composition was different across treatments during the first month of lactation, with greater contents of short and medium chain and lower long chain fatty acids in GR treatment (P < 0.05). The stage of lactation had no effect on plasma TRIG, urea and BHB (P > 0.05). Ewes from GR treatment presented greater TRIG and urea, and lower concentrations of BHB than IND (P < 0.01). Concentration of NEFA were greater in IND ewes on days 13 and 27 post-partum (P < 0.05), but not on day 41 of lactation. The subjective carcass classification showed that GR treatment presented a slightly inferior conformation score (O+ versus R−) and fatness degree (slight versus average–slight fat cover) to IND (P < 0.01). No differences were detected in redness and yellowness of muscle (P > 0.05), whereas IND lambs presented greater lightness values (P < 0.05). Lightness and redness of subcutaneous lumbar fat were not affected by treatment (P > 0.05). However, yellowness was greater in GR lambs (P < 0.001). It is concluded that neither productive nor metabolic performance was impaired in continuous grazing ewes in spite of their greater milk and protein production observed during the first month of lactation. Dietary supplementation of rationed grazing ewes was not sufficient to avoid mobilising their body reserves in early lactation. Carcass classification from grazing lambs was slightly penalised in comparison with indoor lambs, but differences were poorly appreciated in meat and fat colour.