Featherless broilers perform better in heat

Featherless broilers perform better in heat

*Dr. William A. Dudley-Cash is a poultry and fish nutritionist and has his own consulting firm in Kamuela, Hawaii. To expedite answers to questions concerning this column, please direct inquiries to Feedstuffs, Bottom Line of Nutrition, 7900 International Dr., Suite 650, Bloomington, Minn. 55425, or email [email protected]

TREMENDOUS progress has been made in increasing broiler growth rates and meat yields. Broiler growth rates are driven by higher rates of feed intake and metabolism, and the result is elevated internal (metabolic) heat production.

Hot environmental conditions interfere with the dissipation of internally produced heat. Broilers adjust to hot conditions by reducing feed intake, and the result is a reduced growth rate and lower final bodyweight.

Feathers provide an insulating cover, which reduces the dissipation of internally produced heat. Modern commercial strains of broilers require low ambient temperatures to fully express their genetic potential for rapid growth. Featherless broilers presumably would perform better than feathered broilers in hot environmental temperatures.

Abbott and Asmundson (1957) reported a recessive mutation, called scaleless, that blocks feather formation in homozygous sc/sc chickens. The mutant gene was recently found to be fibroblast growth factor-20.

This spontaneous mutation was found in the New Hampshire breed, which has a substantially reduced growth rate compared with commercial broilers.

In the late 1970s, experimental featherless broilers were derived from a cross between the scaleless mutant and commercial broilers of that time. Under hot conditions, the growth rate and carcass composition of these featherless birds were superior to those of their feathered counterparts. However, these effects were small, because the growth rate of the birds in that study was very low. Based on these results, practical use of featherless broilers was not considered an option.

Y. Hadad et al. (2014) recently reported on the results of a study with featherless broilers from a new experimental population of featherless broilers that was initiated at the Hebrew University Faculty of Agriculture in 2002. Males from the original New Hampshire scaleless line (sc/sc) were mated with females from contemporary high-growth rate broiler stocks (+/+). The +/sc male progeny were repeatedly backcrossed to females from contemporary broiler stocks.

After one cycle of backcross, the featherless birds were markedly superior to their fully feathered and naked-neck siblings under hot conditions. After two additional cycles of backcross, the mean growth rate and bodyweight of the featherless broilers and their feathered siblings were further elevated but were still considerably lower than those of contemporary commercial broilers under normal (comfortable) ambient conditions.

However, under hot conditions in both studies, only the featherless broilers maintained normal body temperature, and consequently, their mean growth rates and final bodyweights were not depressed by heat, in contrast to the growth rates and final bodyweights of their feathered siblings and the contemporary commercial broilers.

Hadad et al. hypothesized that: (1) a lack of feathers contributes to higher breast muscle yields and better meat quality, particularly when broilers are reared under hot conditions, and (2) these differences are due, at least in part, to higher cardiovascular capacity.

The study reported in this paper consisted of two similar experiments. The birds used in both experiments were the progeny of intermating among sc/sc sires and +/sc dams. Thus, the progeny of each dam segregated into one-half featherless (homozygous sc/sc) and one-half normally feathered (heterozygous +/sc).

All birds from both genotypes/phenotypes shared the same average genetic background. The featherless parents of the birds in both trials were the progeny of four backcross cycles to fast-growing contemporary broiler stocks. Contemporary fast-growing commercial broilers were included in each experiment as an industry reference.

After hatch, male and female chicks from all groups were brooded intermingled on deep litter and were fed a commercial diet ad libitum. The brooding temperature started at 35 degrees C for the first three days after hatch, followed by a gradual reduction to 32 degrees C on day 11. On day 21, the broilers were assigned to two environmental temperatures: control at 26 degrees C (78.8 degrees F) and hot at 32 degrees C (89.6 degrees F). Relative humidity was about 70%.

In experiment 1, 60 random birds from each group — featherless, feathered and commercial — were divided equally between the two treatments and randomly assigned to individual cages.

At the end of the experiment on day 44, body temperature was measured by inserting a digital thermometer into the cloaca. The birds were individually weighed after 10 hours of feed withdrawal, killed (according to the rules of kosher slaughtering), plucked and eviscerated.

The carcasses of all birds, including the featherless birds, were free of downgrades. The carcasses were stored at 4 degrees C for 24 hours, after which breast muscles (pectoralis major and pectoralis minor) were removed from each carcass (by a single operator) and weighed. The sex of each bird was confirmed by the presence of ovaries or testicles, and the heart was removed and weighed.

The meat quality of the breast muscles was evaluated for color and drip loss. Color was measured using a Minolta spectrocolorimeter. To measure drip loss, the breast meat of each bird was packed in an individual plastic bag and stored for 48 hours at 4 degrees C. After storage, the deboned meat muscle was wiped of all excess fluids and weighed. The drip loss was calculated from the difference in meat weight before and after the 48-hour storage.

Experiment 2 was designed and conducted very much like experiment 1, with birds processed on days 47 and 54 of the experiment. In addition, blood was collected from selected birds on the day before processing (day 46 and day 53) for the measurement of blood hematocrit.

The results of experiment 1 are shown in the Table. For the control temperature treatment (26 degrees C), the commercial broilers were significantly heavier than the other two groups at the end of the experiment. The feathered birds, at 2,117 g, weighed 14% less than the commercial broilers at 2,446 g. The featherless broilers weighed about the same as their sibling-mate feathered broilers.

The results for the hot temperature treatment (32 degrees C) were much different. The featherless broilers, at 2,160 g, were significantly heavier than both their feathered siblings and the commercial broilers, at 1,828 g and 1,959 g, respectively. At the hot temperature, the feathered birds weighed 14% less than the weight they had achieved at the control temperature. The commercial broilers were affected even more by the hot temperature, with a decrease of 20% in weight from their performance in the control temperature environment. In contrast, the featherless broilers grew just as well in the hot temperature environment as in the control temperature environment (2,160 g versus 2,101 g).

Breast meat weight was pretty much a reflection of the bodyweight results. At the control temperature, the commercial broilers had the heaviest breast meat weight, although it was not significantly heavier than the breast meat weight of the featherless broilers. At the hot temperature, the breast meat weight of the commercial broilers was severely depressed and was significantly less than the breast meat weight of the featherless broilers.

Breast meat yield as a percent of bodyweight was significantly larger for the featherless broilers than the commercial broilers at both temperatures. Drip loss of the breast muscle yielded mixed results. At the control temperature, the percent drip loss was the same for the featherless and commercial broilers (3.87%). At the hot temperature, the drip loss for the featherless birds was significantly less than the drip loss for the commercial broilers (4.00% versus 6.08%).

The body temperature of the featherless birds was significantly less than both the feathered birds and the commercial birds at both environmental temperatures. Furthermore, while the body temperature numerically increased for both the feathered birds and the commercial birds when they were raised in the hot environment, the body temperature of the featherless birds was actually numerically lower in the hot environment.

The featherless birds had outstanding performance for heart weight and heart weight as a percent of bodyweight at both environmental temperatures. At the control temperature, the heart as a percent of total bodyweight was 0.63% for the featherless birds but was only 0.44% for the commercial birds. In the hot environment, the heart as a percent of bodyweight was 0.52% for the featherless birds versus 0.40% for the commercial birds.

The results for experiment 2 were very similar to the results for experiment 1. Hematocrit levels were measured in experiment 2. The mean hematocrit level of the featherless broilers was significantly higher than of the feathered sibling-mates, approximately 36% versus 31% and 30% versus 27% for the control and hot treatments, respectively. The commercial broilers had hematocrit values of about 28%.

The researchers concluded that featherless broilers performed better than feathered broilers — including commercial broilers — in hot environments. Bodyweight and breast meat weight, yield and quality were all better for the featherless broilers in the hot environment.

The researchers proposed that the higher meat yield and better meat quality of the featherless broilers could be attributed to their larger hearts and higher hematocrit levels, which result in a superior cardiovascular capacity to supply oxygen to the muscles.

In addition, nutrients directed to the feathers in feathered broilers are probably mobilized toward muscle growth and, consequently, increased meat production in the featherless birds.

 

The Bottom Line

New varieties of featherless broilers may be economically superior to feathered commercial broilers in geographic areas where the environmental temperature tends to be "hot." Perhaps at locations that often reach 90 degrees F and above, featherless broilers are a practical option.

 

Reference

Hadad, Y., O. Halevy and A. Cahaner. 2014. Featherless and feathered broilers under control versus hot conditions. 1. Breast meat yield and quality. Poult. Sci. 93:1067-1075.

 

Results, experiment 1

 

-Control, 26 degrees C (78.8 degrees F)-

-Hot, 32 degrees C (89.6 degrees F)-

Trial 1, to 44 days of age

Featherless

Feathered

Commercial

Featherless

Feathered

Commercial

Number

20

16

16

20

16

16

Slaughter bodyweight, g

2,101b

2,117b

2,446a

2,160x

1,828y

1,959y

Breast meat, g

405a

355b

429a

388x

259z

321y

Breast meat, % of bodyweight

19.3a

15.8c

17.5b

18.0x

14.2z

16.3y

Drip loss, %

3.87b

5.02a

3.87b

4.00y

6.82x

6.08x

Body temperature, degrees C

40.8b

41.2a

41.2a

40.4y

42.1x

41.9x

Heart, g

13.34a

9.82b

10.89b

11.33x

7.03y

7.85y

Heart, % of bodyweight

0.63a

0.46b

0.44b

0.52x

0.38y

0.40y

a,b,cGroup means compared within 26 degrees C treatment; those means with different superscripts are significantly different (P < 0.05).

x,yGroup means compared within 32 degrees C treatment; those means with different superscripts are significantly different (P < 0.05).

 

Volume:86 Issue:22

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