| 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 > 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 > 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 < 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 > 25.5 +/- 0.4%; P = 0.015; 29.0 > 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. |
