Immunoresponsiveness of fast-growing chickens as influenced by feeding regimen

1. Immunoresponsiveness and disease resistance were measured in broiler males maintained on ad libitum feeding throughout or on alternate-day feeding. Alternate-day restrictions were started 1 and 2 d after hatch so that on any one day there were chicks fed and fasted. 2. Severity of response to E. coli challenge as measured by lesion scores, and mortality was greater for chicks fed ad libitum than those fed on alternate days. For chicks fed on alternate days, lesion scores were lower for those without access to feed for the 24-h period immediately after challenge. 3. Spleen weights, the indicator of response to marble spleen disease virus challenge, were higher for chicks fed ad libitum than those fed on alternate days. 4. Antibody response to sheep red blood cell antigen was not affected by feeding regimen. 5. Ratios of heterophils to lymphocytes were higher for chicks given access to feed for the previous 24-h period than for those fasted during the previous 24-h or those that had been fed ad libitum. 6. Results of this experiment suggest that for alternate-day feeding programs, vaccination be administered on the day that chicks are not fed.

Effect of early nutrient restriction on broiler chickens. 2. Performance and digestive enzyme activities

An experiment was conducted to determine the effect of two early nutrient restriction programs on performance, selected characteristics of the gastrointestinal tract (GIT), and activities of digestive enzymes of broiler chickens. Three hundred and sixty male broiler (Ross x Ross) chicks kept in floor pens were assigned to three groups. The control group (C) was given ad libitum access to feed from 1 to 48 d of age. Another group was restricted from 11 to 14 d (R4) of age to an energy intake of .74 x BW.67 kcal ME/d, and a third group was restricted from 7 to 14 d (R7) of age to an energy intake of 1.5 x BW.67 kcal ME/d. Then, both restricted groups were given ad libitum access to feed through 48 d. Body weight and feed intake were determined weekly and selected carcass characteristics were measured at 48 d of age. Broilers also were sampled at 7, 14, 21, and 42 d of age to obtain data on components of the GIT (proventriculus, gizzard, pancreas, and small intestine) and activities of selected digestive enzymes. Feed-restricted groups were lighter in body weight (P < .01) at 14 and 48 d of age than the C group but were superior in overall feed efficiency. No treatment effects were observed for percentage yields of breast meat and abdominal fat pad. Absolute weights of GIT components were significantly reduced at 14 d of age by feed restriction. However, GIT components increased in weight more quickly after refeeding than did the whole body. Restricted groups had reduced (P < .01) specific activities of jejunal alkaline phosphatase and pancreatic trypsin, amylase, and lipase as compared with the C group at 14 d of age but not at 21 and 42 d of age. Relative activities for jejunal maltase and sucrase were greater (P < .01) at 21 d of age in the R4 and R7 groups than in the C group. The present data show that feed restriction results in transient changes in organs and activities of digestive enzymes, suggesting a functional adaptation to feed restriction.

Growth of broiler chickens in response to feed restriction regimens to reduce ascites

A trial was conducted to investigate the impact of early feed restriction on ascites induced by cold temperatures and the subsequent effect on the whole body and breast muscle growth of broilers. Two feed restriction regimens were tested, consisting of limiting daily feed intake of the birds to 75% of the ME required for normal growth from either 4 to 11 d or from 7 to 14 d. At 21 d, half of the birds were moved to a cold house (17.8 C) to induce ascites. Five birds from each pen were killed for the breast muscle growth, Pectoralis major and Pectoralis minor, and heart and abdominal fat pad weights at 4, 7, 11, 14, 21, 35, and 49 d of the experiment. Birds in the cold house were heavier and had better feed conversion than birds in the control house at 49 d of age. This could be attributed to the high ambient temperatures (27 to 33 C) in the control house. The ad libitum birds had a significantly greater percentage of P. major than the feed-restricted birds. Exposure to cold temperatures caused significantly higher percentage of ascites from 21 to 49 d. Cold temperatures also increased the percentage of total heart and the right ventricle weight relative to total heart weight ratio at 35 and 49 d of age, suggesting that the surviving birds were more likely to develop ascites. Although catch-up growth was observed, the final body weight of feed-restricted birds was not the same as ad libitum birds. Early feed restriction reduced the incidence of ascites, but at the cost of breast muscle growth.

Effect of early nutrient restriction on broiler chickens. 1. Performance and development of the gastrointestinal tract

An experiment was conducted to determine the effects of early nutrient restriction on performance and development of the gastrointestinal tract of broiler chickens. Four hundred male broiler (Ross x Ross) chicks raised in floor pens were assigned to two treatment groups. One group was given ad libitum access to feed from 1 to 48 d of age. The second group was feed restricted from 7 to 14 d of age to an energy intake of 1.5 x BW.67 kcal ME/d and then given ad libitum access to feed from 14 to 48 d. Body weight and feed intake were determined weekly. At 49 d of age, birds were processed for carcass yield, abdominal fat pad measurement, and body composition analysis. Broilers were also sampled at 7, 14, 21, and 41 d of age for proventriculus, gizzard, small intestine (duodenum, jejunum, and ileum), pancreas, and liver weights and for intestinal length measurements. Total DNA, protein:DNA, and RNA:DNA ratios of livers and jejuna were determined as indexes of changes in cell size and number. Feed-restricted broilers failed to catch up to the Control birds in BW at 48 d of age but were superior (P < .01) in overall feed efficiency. No treatment effects were observed on breast meat yields or abdominal fat. Moreover, percentage carcass fat, crude protein, ash, and dry matter were not affected by restricted feeding. Body weight and weights of gastrointestinal organs were reduced (P < .01) by feed restriction at 14 d of age. Restricted feeding, however, did not decrease the relative weights of organs, except for liver. Feed restriction also resulted in a reduction (P < .01) of liver cell number and size and a decrease in jejunum cell number. All organs recovered normal weight on refeeding, and all cellular constituent ratios (e.g., RNA:DNA, RNA:protein, and protein:DNA) returned to normal by 41 d of age. Absolute and relative weights of supply organs (e.g., proventriculus, gizzard, small intestine, liver, and pancreas) were less affected by feed restriction and responded more quickly to refeeding than the whole body.

Effect of early feed restriction and realimentation on heat production and changes in sizes of digestive organs of male broilers

Two experiments were conducted with broilers to determine the effect of early feed restriction and realimentation on metabolic heat production and changes in sizes of digestive organs. An indirect open circuit calorimeter was used. Treatments were a full-fed control (FF) and a feed-restricted group (FR). Feed during the restriction period (6 to 12 d) for the FR birds was limited to 50% of voluntary feed intake of the FF birds. This was followed by realimentation period when all birds were provided feed for ad libitum consumption. The purpose of Experiment 1 was to measure basal metabolic rate (BMR), and Experiment 2 was designed to measure 36-h fasting metabolic rate (FMR), in both cases during time of restriction and realimentation. At the end of the 36-h unfed period, birds were killed and their digestive organs excised, blotted, and weighed. The FR birds showed significantly (P < .01) lower BMR compared with the FF birds during the restriction period. This lower BMR did not carry over into the refeeding period, when there was no difference between the two treatments. Thirty-six-hour FMR, like the BMR was also lower for FR compared with FF birds, but only during the period of restriction. Weights of digestive organs (expressed as a percentage of BW) during restriction were generally heavier for FR compared with FF birds. Measurements of organ weights taken during realimentation show significantly (P < .05) heavier liver and pancreas for FR compared with FF birds. Results of these experiments suggest that lower MR of "restricted-refed" birds does not play a role in the ability of the birds to show improved feed efficiency and growth compensation. Greater feed intake relative to BW and its associated digestive adaptations seem to be contributing factors to any growth compensation.