Early experience with food diversity influences stress responses and subsequent open field behavior in sheep

VILLALBA, J.J.; CATANESE, F.; DISTEL, R.A.

Mar del PLata

Congreso; 34º Congreso Argentino de Producción Animal- 1st Joint Meeting ASAS-AAPA; 2011

Asociación Argentina de Producción Animal

This study determined (1) whether early experiences by sheep to monotonous or diverse diets influence plasmatic profiles of cortisol, a hormone involved in stress responses by mammals, and (2) if those experiences influence the link between the open field test (OFT) and stress induced hyperthermia (SIH) – and the readiness to eat new foods. Twenty, 2-mo-old lambs were randomly assigned to two treatments (10 lambs/ treatment). Lambs in one treatment (Diversity) received in successive periods of exposure, during 45 days, all possible 4-way choice combinations of two feeds high in energy and two feeds high in protein from an array of six feeds: three high in energy (beet pulp, oat grain, and a mix of grape pomace: milo [40:60] and three high in protein (soybean meal, alfalfa pellets, and corn gluten meal). Lambs in the treatment Monotony received a monotonous balanced ration containing all six feeds used in Diversity throughout the study. Immediately after exposure, lambs were offered a choice of the aforementioned six feeds (Diversity) or the monotonous diet (Monotony). Animals were then bled 1, 2, and 3 h post-feeding and subjected to an Adrenocorticotropic hormone (ACTH) challenge test. After washout periods that lasted for two months, when all lambs were fed the same diets, we assessed reluctance to eat novel flavored foods (onion-, coconut- and cinnamon-flavored wheat bran; each food offered for 20 min. in two consecutive days) in a new environment, open field behavior, and SIH in both groups. Data was analyzed using a split-plot design with lambs (random factor) nested within treatment (fixed factor). Day was the repeated measure in the analysis. Lambs in Monotony showed greater concentrations of plasma cortisol 1 h post feeding than lambs in the Diversity group (87.7 vs. 59.6 ± 8.2 ng/ml, respectively, mean ± 1 s.e.m., p=0.04). Lambs in Diversity consumed more onion-flavored wheat bran than lambs in Monotony (4.71 vs. 2.95 ± 0.71 g/kg LW, respectively, mean ± 1 s.e.m., p=0.05), and also showed a greater cumulative consumption (sum of all flavored foods) on day 2 than lambs in Monotony (group x day, p=0.01; 17.5 vs. 13.6 ± 0.6 g/kg LW, respectively, mean ± 1 s.e.m., p<0.05). During OFT lambs in Diversity tended to show a lower increase in rectal temperature (0.60 vs. 0.87 ± 0.06 ºC, respectively, means ± 1 s.e.m., p=0.07) and to manifest lower ambulation (number of lines crossed of a grid on the floor) (157.3 vs. 208.1 ± 31.9, respectively, means ± 1 s.e.m., p=0.11) than lambs in Monotony. Our results suggest that exposure to diverse foods in early life is less stressful than exposure to monotonous rations, as measured by plasma cortisol concentrations after food ingestion. Moreover, lower stress signs were seen during the OFT in the Diversity group when compared to the Monotony group long after exposure was finished. Reluctance to ingest new foods in a new environment may be also influenced by early exposure to diverse or monotonous feeds.