This study was carried out to investigate central nervous system pathways which may be involved in the depression of food intake exhibited by parasitised lambs. Ten lambs with intake depression (c.20%; p<0.05); as a result of chronic infection with 4000 T.colubriformis larvae/day together with 10 non-infected animals were used in a factorially designed experiment. The factors were a 24 h fast or no fasting followed by; saline solution (control), or 0.6 mg/kg brotizolam (blocks satiety signals at the ventromedial hypothalamus), or 0.125 mg/kg of naloxone (an opioid antagonist), all in a 2 ml volume given i.v. immediately prior to feeding. Trickle infection depressed mean daily intake by 20% (p<0.05), likewise short term intake was depressed by infection (p<0.05). Fasting stimulated both short term and daily intake by approximately 100% (p<0.001) and 12% (p<0.05) respectively. Naloxone depressed cumulative intake for up to 2 h (p<0.01 - p<0.001) while brotizolam stimulated intake at both 60 and 120 minutes (p<0.001). These results show that opioid signals stimulate food intake in lambs and that fasting will overcome the effects of parasitism on appetite in the short term. A lack of opioid signals may be a factor in parasite induced food intake depression.
Proceedings of the New Zealand Society of Animal Production, Volume 51, , 323-326, 1991
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