ABSTRACT:Cattle Egrets have a worldwide distribution, feed in proximity to cattle and other domestic animals, and often nest in large colonies in urban woodlots. Over a 3-yr period, nestlings from five Cattle Egret colonies from Central Texas, USA, were surveyed for salmonellosis. Prevalence of infection ranged from 29% to 95%. Seventeen Salmonella enterica subsp. enterica serotypes were isolated, of which the 4,5,12:i-monophasic serotype predominated in cultures of both the digestive tract and pooled spleen and liver. Of 11 4,5,12:i-monophasic isolates phage typed, eight were determinate type 193. The 4,5,12:i-monophasic isolates were susceptible to all antibiotics tested and were highly invasive in the day-old chick infection model. Microscopic lesions were found in the livers of Cattle Egrets with systemic infections with the 4,5,12:imonophasic serotype, suggesting that infections with this serotype may often be fatal. Twenty-nine serotypes were identified in 179 S. enterica subsp. enterica isolates from horses admitted to the Texas A&M University Veterinary Teaching Hospital in 2 yr following the Cattle Egret study. The 4,5,12:i-monophasic serotype was not isolated from horses, but 12 serotypes were isolated from both horses and Cattle Egrets. The temporal distribution of the horse cases suggested that Cattle Egrets and horses may be exposed to similar sources of Salmonella, but provided no evidence of transmission between these two species. Similar conclusions were drawn when Cattle Egret isolates were compared to isolates from feedlot and dairy cattle from Texas and surrounding states. Given that the Cattle Egret 4,5,12:i-monophasic serotype was highly invasive and other isolates of this serotype have been associated with food poisoning, it is likely that Cattle Egret colonies pose a health risk to humans living near them.

Naturally occurring secondary nutritional hyperparathyroidism is described in the nestlings of two colonies of cattle egrets (Bubulcus ibis) from Central Texas (Bryan and San Antonio, Texas, USA). Nestlings from a third colony (Waco, Texas, USA) were collected in a subsequent year for comparison. Birds from the first two colonies consistently had severe osteopenia and associated curving deformities and folding fractures of their long bones. These birds also had reduced bone ash, increased osteoclasia, a marked decrease in osteoblast activity, variable lengthening and shortening of the hypertrophic zone of the epiphyseal cartilage, decreased and disorganized formation of new bone, and a marked hypertrophy and hyperplasia of the parathyroid glands as compared to birds collected from the third colony. Fibrous osteodystrophy was found in all of the birds from San Antonio and Bryan. Evidence of moderate to severe calcium deficiency was also identified in 33% of the cattle egrets collected from Waco. Gut contents of affected chicks contained predominately grasshoppers and crickets; vertebrate prey items were absent from the Bryan birds. Grasshoppers and crickets collected from fields frequented by the adult egrets in 1994 had 0.12-0.28% calcium and 0.76-0.81% phosphorus. Pooled grasshoppers and crickets collected during a subsequent wet early spring averaged 0.24% calcium and 0.65% phosphorus. Although the phosphorus content of the insect prey was adequate for growth, calcium was approximately one-third the minimum calcium requirement needed for growth for other species of birds. It was postulated that cattle egrets breeding in Central Texas have expanded their range into habitat that contains less vertebrate prey, and as a result, many nestling egrets are being fed diets that contain suboptimal calcium. Therefore, in years where vertebrate prey is scarce and forage for insect prey is reduced in calcium, nestling egrets are at risk for developing secondary nutritional hyperparathyroidism.

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