Enhancement of cellular and humoral immunity in young broilers by the dietary supplementation of beta-hydroxy-beta-methylbutyrate

As a dietary supplement, beta-Hydroxy-beta-Methylbutyrate (HMB), a cataboli te of leucine, has been shown to reduce broiler mortality. In a series of e xperiments, male broilers (Experiments 1 and 2, n = 576) were grown for 21 days on diets that contained HMB at 0, 0.01. 0.05, and 0.10% of diet. In Ex periment 3 (n = 240), chicks were fed diets containing 0, 0.05, 0.075, and 0.10% HMB. HMB dietary supplementation did not significantly affect broiler weight gain in any experiment. However, a trend toward increased mean broi ler weight gain per bird was observed in Experiments 1 and 3 when HMB was c onsumed at 0.10% of the diet. Mean feed to gain ratio was not affected by t he inclusion of HMB in broiler diets. In Experiment 3, HMB supplemented die ts did not affect bursa of Fabricius, thymus, and spleen weights at 21 days of age. Cutaneous basophilic hypersensitivity response against pokeweed mi togen was higher (P less than or equal to 0.05) at 48 and 72 hours post-inj ection in chicks on 0.05% dietary HMB (Experiment 1). In Experiment 2, this increase occurred 24 hours post-injection in chicks fed HMB at 0.01% of th e diet. On the contrary, the T-cell mediated response against PHA-P mitogen was comparable between all dietary treatments in multiple experiments. Mac rophage function profiles were determined at 21 days of age.: All chicks in experiments 1 and 2 on HMB supplemented diets showed an increase in the re cruitment of Sephadex-G50(R)-elicited abdominal exudate cells (AEC). A 2-fo ld increase in AEC numbers occurred at the 0.10% HMB level (Experiment 1, P less than or equal to 0.05). Although HMB supplementation did not signific antly affect the phagocytic potential of the abdominal macrophages, nitrite levels in the macrophage culture supernatants were higher in 0.01% and 0.0 5% treatment groups as compared to the controls (Experiment 2, P less than or equal to 0.04; Experiment 3, P less than or equal to 0.05). HMB suppleme ntation did not alter the bird's ability to clear Escherichiacoli or Salmon ella arizona from the bloodstream. Beginning 7 days post-hatch, chicks were injected i.v. with a 7% sheep red blood cells suspension. Serum samples we re collected to determine the primary and secondary antibody response. Chic ks receiving the 0.1% HMB diet in Experiments 1 and 2 exhibited increased I gG and total anti-sheep red blood cell (SRBC) antibody levels during the pr imary response. During the secondary response, birds consuming the 0.10% HM B diet had elevated IgM levels as well as increased total anti-SRBC levels over the controls in Experiments 1 and 3. These studies show that HMB suppl ementation improves several immunological functions in young broilers, and such improvement may result in decreased mortality.