Lack of straw during finishing affects individual and social lamb behavior

The aim of this study was to analyze the effect of straw bedding on individual and social behavior in lambs. Four groups of 6 lambs of the Rasa Aragonesa breed (n = 24; 17.2 ± 0.2 kg live weight and approximately 60 days old) were formed and fattened for 28 days, in an experimental design that included 2 treatments and 2 replicates. One treatment was given cereal straw either to eat or to lie on, whereas the other treatment had no straw. All groups were housed in 5.6 m² feedlot pens (ad libitum commercial concentrate and water). The lambs in each pen were recorded using a digital video camera (08:00-20:00 hours) for 28 days to measure lying, standing, walking, feeding, and drinking behavior as well as the use of space (scan sampling every 10 minutes). Stereotypies, social interactions, and productive performance parameters were observed by continuous sampling on days 1, 7, 14, 21, and 28 of fattening. There were no significant differences in terms of productive performance. In general, the frequency of standing, walking, and eating concentrate was higher in lambs without straw (P ≤ 0.001). As expected, lambs spent more time standing in the straw box when this substrate was available (P ≤ 0.001). Aggressive interactions decreased after 2 weeks in both treatments, but just lambs without straw kept low levels until the end of the trial (P ≤ 0.05). Affiliative interactions increased in both groups throughout the experiment, indicating greater group cohesion. Stereotypic behaviors were more frequent in lambs with no straw on all observation days (P ≤ 0.05). The absence of cereal straw was a source of stress for the lambs, which affected their behavior during fattening. Providing straw can be a practical way to increase environmental enrichment aimed at improving welfare.