Effect on performance of weanling alpacas following treatments against gastro-intestinal parasites.

Nematodes and coccidia are common parasites of alpacas (Vicugna pacos), and important causes of disease in this increasingly popular livestock species. Endoparasitic infestation is thought to increase at times of natural or imposed stress, and antiparasitic treatments are often administered, although to date there is little evidence regarding their effect. Thirty-one alpaca juvenilles (cria) were divided into four groups at weaning, and received either no treatment as a control (C), fenbendazole anthelmintic (FB), toltrazuril coccidiostat (T), or both treatments (FBT). Body weights and faecal egg/oocyst counts were recorded weekly for six weeks following treatment. Although the prophylactic treatments decreased faecal egg/oocyst counts of the target organisms in the short term, there was no significant difference in egg/oocyst output over the course of the trial from animals given wormer, coccidiostat or both treatments. The group receiving anthelmintic only showed a significant reduction in live weight gain (LWG), with no significant difference in LWG between the other groups. At the conclusion of the trial, 'wormed only' alpacas weighed 3.3% less than at weaning, losing an average 1.3 kg over six weeks, whereas average LWG in the control group was 2.5 kg. Antiparasitics transiently reduced egg/oocyst output but results suggest that further investigation is required on the action of anthelmintics administered to alpaca cria at weaning and their effect on animal health and welfare.

Avian retinal oil droplets: dietary manipulation of colour vision?

Avian vision is highly developed, with bird retinas containing rod and double-cone photoreceptors, plus four classes of single cones subserving tetrachromatic colour vision. Cones contain an oil droplet, rich in carotenoid pigments (except VS/ultraviolet-sensitive cones), that acts as a filter, substantially modifying light detected by the photoreceptor. Using dietary manipulations, we tested the effects of carotenoid availability on oil droplet absorbance properties in two species: Platycercus elegans and Taeniopygia guttata. Using microspectrophotometry, we determined whether manipulations affected oil droplet carotenoid concentration and whether changes would alter colour discrimination ability. In both species, increases in carotenoid concentration were found in carotenoid-supplemented birds, but only in the double cones. Magnitudes of effects of manipulations were often dependent on retinal location. The study provides, to our knowledge, the first experimental evidence of dietary intake over a short time period affecting carotenoid concentration of retinal oil droplets. Moreover, the allocation of carotenoids to the retina by both species is such that the change potentially preserves the spectral tuning of colour vision. Our study generates new insights into retinal regulation of carotenoid concentration of oil droplets, an area about which very little is known, with implications for our understanding of trade-offs in carotenoid allocation in birds.