Western
Meeting of Poultry
Clinicians and Pathologists
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Clinicians and Pathologists
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Growth Performance of Broiler Chicks after Severe Early Feed Restriction D.K. Onderka and J.A. Hanson Poultry Section Animal Health Laboratories Alberta Department of Agriculture
Introduction Poor growing broilers (runting) resulting in uneven flocks are of concern to broiler producers as they cause management problems with feed and water line adjustments. In the processing plant, they contribute to downgrading, cause extra handling on the automated size specific cut-up lines or are condemned as emaciated because of their small relative size. Reasons for poor growth performance in broilers may be congenital runting, infectious stunting syndrome (Bracewell and Randall, 1984), bacterial infection (Tian and Baracos, 1989) or feed restriction (Washburn and Bondari, 1978). In most cases submitted to the diagnostic laboratory, infectious causes cannot be detected. This suggests that early feed restriction from inadequate accessibility to feeder space may possibly be the underlying cause. Field Problem A flock having a significant percentage of poorly growing broilers was the focus of a recent investigation. Some chicks had only 25% of the expected body weight at 20 days of age. During subsequent free choice feeding to 56 days, there was some compensatory growth, but at the end, these chicks reached only 67% of the roaster market weight. At the broiler market age of 42 days, they had reached only 57% of the expected weight. Examination of specimens from this flock during the first two weeks showed no evidence of infectious disease. At necropsy, all birds were normal. Published experiments in compensatory growth of broilers (Auckland and Morris, 1971; Wasburn and Bondari, 1978) used low protein diets or limited feed restriction as the basis for body weight reduction and investigated different time frames than we had in our case scenario. The present experiment was to establish if early severe feed restriction could be the underlying cause for a growth pattern similar to the field case. Experimental Design Thirty-five, one-day-old male Hubbard
broilers were floor brooded at 92oF for seven days under infrared
heat bulbs with feed and water available ad libitum. They were kept at a density
of 1 bird/sq ft. throughout the experiment. During the first week they were on a
24-hour light cycle and then on 18L: 6D for the remainder. A commercial broiler
starter ration was fed for two weeks followed by a grower ration. At 22 days of age, the feed restricted birds had an average body weight of 254 grams (STD+36.3) or 44.6% of the control birds (793+43.1 gm). One bird in the control group died at 16 days of age with acute death syndrome. One bird from each group was killed on day 22 in order to compare body condition and relative fat deposits. All other birds survived to the end of the experiment with some developing moderate tibial dyschondroplasia. The resulting leg weakness had no effect on the ability to feed competitively. Comparison of body condition showed the feed restricted bird to have similar fat deposits in relation to organ size and similarly developed pectoral musculature except for the absolute size. In fact, without control and knowledge of age, it was difficult to identify the feed restricted bird. When restricted birds were initially allowed free choice feed, there was a large jump in feed consumption. Over the next 8 days, this equaled that of the controls, but then remained below (Fig. 1). This resulted in a feed conversion of 1.93 to 43 days of age (broiler) as compared to 2.40 for the control group. When calculated for 57 days (roasters) the feed conversion was 2.07 for the restricted and 2.77 for control birds (Fig. 2). When feed conversion was compared at similar average body weights, it was almost identical to 1800 grams, but then the feed restricted bird showed a better feed conversion to 3,000 grams of body weight (Fig. 3). Weight gain after commencement of full feeding shows a steep compensatory growth rate for the next 7 days with considerable slowing of compensatory growth for the remainder of the growth cycle. As a result, at 43 days the average weight of the restricted group approached 80% of the of the control group. They continued to compensate until they averaged 91% at 57 days (Fig 4). The two experimental groups were fairly homogeneous in weight as shown by the relatively small standard deviations, but from 50 days onward the difference between feed restricted and control birds overlapped by the standard deviation in individual weights (Fig. 5). Discussion Stunted growth in broiler from feed restriction results in smaller body size with proportionate amount of body fat. This is distinct from birds with Runting and Stunting Syndrome, which is characterized by poor, juvenile feathering, little or no body fat, pale shanks, often times diarrhea and in some outbreaks pancreatic fibrosis (Bracewell and Randall, 1984; Riddell and Derow, 1985). Compensatory growth after feed restriction is an interesting metabolic phenomenon, which is being exploited to reduce fast growth rate associated problems such as ascites and leg weakness (Robinson et al, 1992). If it is done in a measure way, there is virtually no effect on the body weight at broiler market age. However, when feed restriction is severe, compensatory growth is not sufficient to catch up to market weights. In our experiment, weight reduction by 56% did not allow weight recovery at broiler age, but did come close at roaster age. In order not to inflict undue stress on the birds, a weight reduction by 75% as was seen in the field case was not targeted. Nevertheless, by extrapolation one can seen that these birds would have correspondingly lower weights at broiler age the more sever the initial feed restriction is. It is therefore plausible that the field case, in the absence of other contributing causes, may have been the result of insufficient access to feed. The question of whether or not it is worthwhile to keep the resulting runts in the hope for sufficient compensatory growth was also answered and found not to be of benefit to the producer. This study confirms work done with broilers in Israel by Plavnik and Hurwitz (1983) that birds in a compensatory growth mode have a significantly better feed conversion particularly when body weights exceed 1500 grams. This might be economically exploited by modest feed restriction during the second week of life. We thank Lillydale Cooperative, Edmonton for donation of the birds and United Feeds, Edmonton for donating the necessary feed. The technical assistance of Blair Headrick was appreciated. |
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