Immunoresponsiveness of fast-growing chickens as influenced by feeding regimen

Influence of body weight restriction in a body-weight-selected line of turkeys on response to challenge with Pasteurella multocida

Previous research has shown that a line (F) of turkeys selected long-term for increased 16-wk BW was more susceptible to challenge with washed Pasteurella multocida (PM) than a randombred control line (RBC2), the base population of the F line. Published research indicated that the mortality of the F line following challenge with PM was similar to that of two commercial sire lines. The purpose of the present study was to determine the influence of reducing BW of the F line to that of the RBC2 line by nutrient restriction on resistance to PM. Four challenge trials were conducted over a 2-yr period. The BW of a group of F line birds was restricted to that of the RBC2 line by limiting access to feed from 1 to 6 wk of age. The F line restricted birds and full-fed RBC2 and F line birds were challenged with a field isolate of washed PM (1.2x10(7) organisms/bird of capsular serogroup A and somatic serotype 3, 4) at 6 wk of age. Birds were checked twice daily for 14 d. Resistance to PM was measured by days to death of those that died and percentage mortality. The BW of the restricted group of the F line did not differ from full-fed RBC2 birds for males or females. In males, the restricted F line birds had similar mortality (48.0%) to the full-fed RBC2 line birds (44.3%), and the mortalities in both groups were significantly lower than that observed for the full-fed F line birds (81.3%) following challenge with PM. The mortality following challenge in females did not differ significantly among groups, even though mortality of the full-fed F line birds (64.1%) and restricted F line birds (63.3%) was more than 9% higher than that (54.2%) observed for the full-fed RBC2 line birds. Days to death was not a sensitive indicator of resistance to PM, as no differences among the three groups of birds were observed for either sex.

Effect of feed withdrawal or challenge with Pasteurella multocida on growth, blood metabolites, circulating growth hormone, and insulin-like growth factor-I concentrations in eight-week-old turkeys

The daily effects of feed withdrawal or a bacterial disease (Pasteurella multocida; PM) challenge was studied in a slow-growing line of turkeys. The following groups (n = 6 birds/group) were sampled for up to 13 d: untreated control (CON), 4-d feed withdrawal followed by refeeding (FAST), a group that succumbed within the first 2 to 3 d after PM challenge (E-DEAD), a group that succumbed 8 to 9 d after PM challenge (L-DEAD), a group that survived the PM challenge (SUR), and a group treated with both PM challenge and 4-d feed withdrawal followed by refeeding (FAST/CHAL). Daily feed intake and BW gains were markedly reduced in the E-DEAD and L-DEAD groups immediately and 3 d after PM challenge, respectively. Feed intake and BW gain between CON and SUR groups of turkeys were not different throughout the trial. The turkeys in the FAST group followed the expected feed withdrawal and refeeding patterns for feed intake and BW loss or gain. The FAST/CHAL turkeys consumed the minimal amount of feed to maintain BW after refeeding. Plasma uric acid sharply increased 1 d prior to death in both E-DEAD and L-DEAD groups of turkeys. Plasma uric acid also increased each consecutive day during fasting in the FAST and FAST/CHAL groups of turkeys. Plasma growth hormone was measured in only the CON and FAST groups and increased from about 40 to 85 ng/mL in the FAST group during fasting but returned to control levels within 1 d of refeeding. Circulating plasma insulin-like growth factor-I (IGF-I) decreased from about 17 to 5 ng/mL in the PM-challenged (E-DEAD, L-DEAD, and FAST/CHAL groups) and FAST groups. The concentration of IGF-I returned to prefeed withdrawal levels within 3 d of refeeding the FAST group of turkeys. It was concluded that 1) turkey poults that were not susceptible to the PM challenge generally maintained physiological functions at control bird levels, 2) susceptible turkey poults generally exhibited depressed feed intake and BW gains, and 3) poults challenged with both feed withdrawal and PM treatment responded differently than poults challenged with either feed withdrawal or challenge with PM. The depletion of energy intake and mobilization of energy stores in susceptible poults might have contributed to the rate at which PM caused the poults to die.

Stunting syndrome in broilers: effect of stunting syndrome inoculum obtained from stunting syndrome affected broilers, on broilers, leghorns and turkey poults

Responses to stunting syndrome (SS) infective material obtained from affected broilers and administered per os were monitored for 3 wk in a fast-growing commercial broiler population, in slow-growing Leghorn chicks, and in turkey poults. At 2 and 3 wk, the size of the gastrointestinal tract (GIT) segments, the pH of the GIT contents, and the activities of digestive enzymes in the intestinal contents and of disaccharidases on the jejunum mucosae were determined. Inoculation affected the genetic stocks differently. In broiler chicks, growth and feed utilization were markedly reduced. In contrast, inoculation of Leghorns was accompanied by improved feed intake and growth rate. Performance of poults was affected only slightly, albeit significantly. The effect of inoculation on the pH of crop and intestinal contents in Leghorn chicks was opposite to that found in broiler chicks, i.e., a significant increase in the crop and small intestinal pH in the former vs a significant decrease in inoculated broilers. Although inoculation of the broiler chicks did not affect the pH in the proventriculus, in Leghorn chicks it was reduced by 25%. In poults, inoculation did not significantly affect GIT contents pH. The GIT segments were markedly enlarged in broiler chicks, whereas in Leghorn chicks the opposite trend was observed; namely, intestinal segment weights were significantly reduced. In poults, inoculation caused a reduction in the intestinal segments and gizzard weight at 3 wk. During this same period, the liver and pancreas relative weights were dramatically increased in broiler chicks. A higher relative heart weight at 2 wk was observed in broilers and poults; this trend persisted to Week 3 in poults but not in broiler chicks. In broiler chicks, a nonsignificant reduction was observed for all enzymes assayed at 3 wk and for chymotrypsin at 2 wk. In Leghorn chicks, inoculation was accompanied by a marked and significant increase in the activity of chymotrypsin during both periods. In poults, inoculation caused a marked increase in the activities of amylase during Week 2 and 3, and trypsin at 3 wk. Maltase and saccharase activities in the jejunum of broiler chicks were slightly depressed a t 2 and 3 wk, the depression being significant at 2 wk for maltase and at 3 wk for saccharase. In the Leghorn chicks, inoculation caused a twofold increase in the activities of both enzymes. As in Leghorns, inoculation of poults with SS infective material caused a marked increase in the activities of the disaccharidases. The different responses to SS inoculation in the different genetic stocks are discussed.

Feeding regimen by sire family interactions on growth, immunocompetence, and disease resistance in chickens

Progeny from matings of 12 sires from a White Plymouth Rock line selected for high juvenile BW and 96 dams from a White Leghorn line selected for low antibody production to SRBC were reared under alternate-day (AD) or ad libitum (AL) feeding regimens. Within a feeding regimen males were heavier than females, and within a sex, chicks fed AL were heavier than those fed AD. Feeding regimen by sire family interactions were significant for BW at 21 d of age for both male and female progeny. The interaction was due to differences among sires in the magnitude of the AD: AL relationship. Product moment correlation coefficients between feeding regimens for male and female progeny of sire families for 21-d BW were essentially zero, which was consistent with the sire family by feeding regimen interactions observed at this age. At 41 d of age, relative to BW, weights of empty esophagus plus crop and of crop contents were greater for AD than AL chicks. There were differences among sire families for crop content and breast weights relative to BW. Lesion scores to Escherichia coli challenge were lower and antibody titers to SRBC antigen were higher in AD than in AL chicks. Sire families differed in antibody titers to SRBC antigen. Feeding regimen by sire family interactions were significant for percentage change in BW 144 h after E. coli challenge and lesion scores were greater for AL than AD chicks.