Two experiments were conducted to evaluate dietary and environmental factors involved in skin tensile strength of commercial broilers. In Experiment 1 the effect of added dietary fat (4 or 7%), environmental temperature (25 or 20.5 C after 21 d), and anticoccidial drug (halofuginone or salinomycin fed continuously) were examined factorially using male and female chicks. Skin tensile strength was measured at 21, 35, and 40 d of age. Thickness of the dermal layers was measured from skin taken at Day 35. In Experiment 2, the effect of added dietary fat (0 or 7%), environmental temperature (25 or 18.5 C after 21 d), and anticoccidial drug (halofuginone or salinomycin) were examined factorially using female chicks. Skin strength and collagen content of the skin were measured at 21, 38, and 42 d of age. Skin tensile strength increased with age in both experiments, but female skin strength was subject to periodic decline. Males had significantly strong skin than females. Levels of added fat or environmental temperature did not affect skin strength in either experiment. Continuous feeding of halofuginone significantly (P < .0001) decreased skin strength compared with that of birds fed salinomycin in both experiments. Halofuginone reduced skin strength in females more than males (25 and 9%, respectively). Dermis thickness was correspondingly reduced in the birds consuming halofuginone. In Experiment 2, soluble collagen contents were reduced at all ages in birds consuming halofuginone; insoluble collagen was significantly decreased at 21 d of age. Birds with weakened skin exhibited increased incidence of skin tears during slaughter in a commercial processing plant (P < or = .0043). These results suggest that halofuginone interferes with collagen synthesis, causing decreased collagen formation and reduced skin strength. Neither added dietary fat nor ambient temperature were involved.

A FTER more than 35 years of investi->• gation, there is considerable disagreement in the literature as to the levels of calcium and phosphorus required for optimum performance of growing chickens. A review of the more pertinent literature by Lillie et al. (1964) indicates that the range of discordant values is being narrowed to some extent and that the calcium level recommended by the National Research Council is higher than that which many investigators found to be adequate for optimum growth. The majority of the recent investigations (Formica et al., 1961(Formica et al., , 1962Vanderpopuliere, 1961; Waldroup et al. 1962a, b;Simco and Stephenson, 1961;Lillie et al., 1964) have been aimed at refinement of the requirement of the growing chick in the light of current nutritional knowledge. Such was the motive for the experiment reported herein. EXPERIMENTAL A 5X4X2 factorial arrangement was employed in the design of the experiment. The three-factor design included five levels of total phosphorus (0.50, 0.55,0.60, 0.65, 0.70%), four levels of calcium (0,50, 0.60, 0.70, 0.80%) and two sexes (males and females reared separately). Sixty-four hundred sexed day-old VantressX Arbor Acres chicks were randomly distributed within sex into 20 groups of males and 20 groups of females. The 40 groups of 160 birds each were placed in individual floor

No abstract

Continuous feeding of the anticoccidial halofuginone to broilers is associated with reduced skin tensile strength and increased skin tearing during processing. The possible mitigating effect of shuttle administration of halofuginone and salinomycin to female broilers was evaluated. Halofuginone or salinomycin were included in the starter and grower diets in all four possible combinations, with anticoccidial omitted from the finisher diets. Starter, grower, and finisher diets were fed to broilers through 3, 6, and 7 wk of age, respectively. Skin strength of pullets fed a diet based on milo and corn (NW) vs a diet based on corn was also compared in a factorial arrangement. Two further treatments were also included: 1) halofuginone-only NW diet supplemented with 2,500 ppm ascorbic acid from 0 to 7 wk; and 2) NW diet reared on wire floor without anticoccidial treatment. Skin tensile strength was determined at 3, 6, and 7 wk of age. Dietary composition had no effect upon skin strength or BW of broilers. Addition of ascorbic acid to the diet containing halofuginone anticoccidial did not improve skin strength. Continuous feeding of halofuginone reduced skin strength whereas withholding anticoccidial and continuous feeding of salinomycin resulted in high skin strength. When halofuginone was used in shuttle feeding programs with salinomycin, there were no differences in skin strength at 7 wk of age compared to birds that were continuously treated with salinomycin. These results suggest halofuginone may be used in a shuttle program either during the starter or grower phase without adverse affect on skin tensile strength at slaughter.

Two experiments were conducted to determine whether supplemental levels of L-proline in the diets of broiler chickens would mitigate the skin weakening effect caused by continuous feeding of the anticoccidial halofuginone. In Experiment 1, tensile strength and collagen levels in thigh apteria skin were determined at 21 and 42 d of age in male broilers fed 0, .5, and 1% L-proline with either halofuginone (3 mg/kg) or salinomycin (61 mg/kg). In Experiment 2, the same measurements were made on female broilers receiving diets containing halofuginone and supplemented with 0, .5, or 1% L-proline, 1% L-proline through 21 d of age, or 1% L-glutamic acid through 21 d of age, or a diet containing high L-proline feedstuffs (corn gluten meal and ring dried blood meal). In Experiment 1, dermis thickness of thigh apteria was measured in the males at Day 21. Skin strength was increased in male and female broilers fed halofuginone with addition of .5 and 1% L-proline, respectively, at 21 and 42 d of age. Continuous incorporation of synthetic L-proline into diets was shown to improve skin strength in females, whereas diets formulated to contain high levels of L-proline from feedstuffs, 21-d feeding of L-proline, or L-glutamic acid did not increase skin strength.