THE EFFECTS OF SHEARING AND RALGRO IMPLANTS ON FEEDLOT PERFORMANCE OF LAMBS DURING THE SUMMER

Abstract

To evaluate the effects of shearing and Ralgro® implants on the performance of fast-gaining feedlot lambs during the summer, 84 group-fed crossbred wether lambs (34.8 ± 1.8 kg) were shorn on day 0 of the feeding period (ES), shorn 3 wk later (LS), or left unshorn (NS), and either implanted with 12 mg Ralgro on day 0 (R) or not implanted (C). Lambs were blocked by initial weight. Heavy and light pens of lambs were shipped to market when the average weight within a pen was 52 kg after 40 and 55 d, respectively. Between days 0 and 40, mean average daily gain (ADG) of all lambs was 384 g and feed conversion was 4.38 kg dry matter kg−1 gain. During the first 40 d of the feeding period, shearing did not affect ADG (P > 0.05), but ES lambs had higher feed intake and poorer feed conversion than NS lambs (P < 0.05). Performance of the LS lambs was similar to the NS lambs prior to shearing, and similar to the ES lambs after shearing. A delay period between implantation and growth response was observed. Ralgro did not affect ADG between days 0 and 21 (P > 0.05) but improved ADG by 14.2% between days 21 and 40 (P < 0.01), giving an overall growth improvement of 6.5% between days 0 and 40 (P < 0.06). Ralgro had no effect on ADG after day 40. There were no interactions between the effects of shearing and Ralgro implantation on ADG (P > 0.05). Key words: Lambs, shearing, Ralgro, feedlot, summer