Grass Finishing Systems for Lambs

There is strong interest in sustainably produced meat. Grass-fed lamb could fulfill this market by reducing off-farm inputs. The objective was to examine the effect of grass-finishing or minimal supplementation on performance of lambs in the southeastern US. Katahdin lambs born in October 2013 and 2014 and February 2014 were weaned in January 2014/2015 and May 2014, respectively. Lambs were blocked by gender (fall; winter included only ram lambs) and randomly assigned to receive no (NON) or grain co-product supplement (SUP; 15% CP) at 0.5% of BW/d. Lambs were rotationally grazed on predominantly grass. Body weight, fecal egg counts (FEC), packed cell volume (PCV), and body condition score (2014 fall-born lambs only) were determined every 14 d. Winter lambs were removed from the study after 56 d due to poor performance. Live carcass composition was estimated by ultrasound on d 70 of study and when lambs reached light market weight. Data were analyzed by repeated measures in a mixed model. In the 2013 fall-born lambs, average daily gain (ADG) was greater for SUP than NON rams (184 ± 4.9 \u3e 149 ± 5.5 g/d; P = 0.007), but did not differ among ewes (118 vs. 113 ± 5.2 g/d, respectively). The ADG of winter lambs was greater for SUP than NON (44 \u3e 11 ± 9.5 g/d; P = 0.02). The ADG did not differ among treatments in 2014 fall lambs. The FEC tended to be lower in SUP than NON (P \u3c 0.06) in fall 2013 lambs, but PCV was not different. The FEC of winter-born lambs and 2014 fall lambs was similar between treatments, but PCV was increased in SUP compared with NON lambs (27.0 \u3e 25.5 ± 0.4%; P = 0.015; 29.0 \u3e 27.8 ± 0.3%, P = 0.019). Modest supplementation can lead to greater gains and improved tolerance to gastrointestinal parasites for fall-born ram lambs when forage quality is limiting, and high quality forage can result in good weight gain without supplementation in these lambs. Winter or spring-born lambs may not be suitable for a grass-finished system in the southeastern US under these conditions