Hormonal Responses to High and Low Planes of Nutrition in Weanling Thoroughbreds

Abstract

Growth-related skeletal diseases in young horses have been associated with high planes of nutrition, although the mechanisms underlying such an association have not been determined. It is likely that nutrition-induced effects on growth rate or growth quality involve the endocrine system. Hormonal and metabolic responses to the ingestion of meals containing either 80% (diet A) or 160% (diet B) of National Research Council energy and protein recommendations were examined in eight Thoroughbred weanling horses after 3 wk of dietary adaptation. After 24 h fasts, prefeeding serum concentrations of thyroxine (T4) and insulin and plasma concentrations of glucose, total protein, total triglycerides, creatinine, Ca and P were similar regardless of which diet the horses had been consuming. Serum cortisol concentrations were higher (P less than .05) in horses when fasted from diet B. Thyroxine, insulin and glucose concentrations increased during ingestion of both meals. During the first hour after ingestion of diet A, T4 concentrations increased to about 150% of fasting concentrations, whereas after diet B, T4 concentrations decreased to about 85% of fasting concentrations. Concentrations of T4 were not different from fasting concentrations 4 h after the ingestion of both diets. Glucose concentrations increased during the first hour postprandially, from about 105 mg/dl to about 165 mg/dl. However, glucose decreased more rapidly after ingestion of diet B. Serum insulin concentrations increased more rapidly after ingestion of diet B. Cortisol concentrations decreased after both meals, and the concentrations of the other metabolites measured were not affected by diet level or by meal consumption.(ABSTRACT TRUNCATED AT 250 WORDS)

Thyroid hormones correlate with field metabolic rate in ponies,Equus ferus caballus

“…However, the restrictive feeding of the TG animals in our study did not seem to influence the T 4 and T 3 concentrations, even though the FMR of restrictively fed animals was reduced compared with that of CG animals. Similar results have been found for food-restricted steers (Ellenberger et al, 1989) and horses (Glade et al, 1984;Sticker et al, 1995a,b). Normally, T 4 is converted to T 3 and rT 3 (an inactive metabolite of T 3 ) in equal parts.…”

The Relationship Between Glycemic Response and the Incidence of OCD in Thoroughbred Weanlings: A Field Study

“…7 In foals, hyperinsulinemia may affect chondrocyte maturation, leading to altered matrix metabolism and faulty mineralization, or altered cartilage growth by influencing other hormones such as thyroxine. 1,8 Within each farm, there was no significant difference in glycemic response between horses that had lesions and normal individuals. Therefore, using this type of glycemic response test in older weanlings to identify individuals that may be predisposed to OCD does not look promising.…”

“…1,2 More specifically, foals that experience an exaggerated and sustained increase in circulating glucose or insulin in response to a carbohydrate (grain) meal may be predisposed to development of osteochondrosis. In vitro studies with fetal and foal chondrocytes suggest that the role of insulin in growth cartilage may be to promote chondrocyte survival or to suppress differentiation and that hyperinsulinemia may be a contributory factor to equine osteochondrosis.…”

Protein, amino acid and energy requirements of weanling foals and yearlings

“…On the other hand, Thompson et al, (1988) found no detrimental effcets on growth or bone development due to high energy (159% /VRC-1978) (97.5 MJ DE) or protein (275% /VBC-1978) intakes, although there was a decrease in mineral deposition into bone. The accelerated growth causing skeletal abnormalities is largely due to high intake of carbohydrates, which in turn causes hormonal changes stimulating a rapid growth of cartilage, resulting in improper cadilage maturation (Glade et al 1984). Consequently, reducing the grain intake has been repofted to be associated with fewer signs of skeletal abnormalities.…”