M. Y. Shim

The effects of growth rate on leg morphology and tibia breaking strength, mineral density, mineral content, and bone ash in broilers

Fast-growing broilers are especially susceptible to bone abnormalities, causing major problems for broiler producers. The cortical bones of fast-growing broilers are highly porous, which may lead to leg deformities. Leg problems were investigated in 6-wk-old Arkansas randombred broilers. Body weight was measured at hatch and at 6 wk. There were 8 different settings of approximately 450 eggs each. Two subpopulations, slow-growing (SG; bottom quarter, n=511) and fast-growing (FG; top quarter, n=545), were created from a randombred population based on their growth rate from hatch until 6 wk of age. At 6 wk of age, the broilers were processed and chilled at 4°C overnight before deboning. Shank (78.27±8.06 g), drum stick (190.92±16.91 g), and thigh weights (233.88±22.66 g) of FG broilers were higher than those of SG broilers (54.39±6.86, 135.39±15.45, and 168.50±21.13 g, respectivly; P<0.001). Tibia weights (15.36±2.28 g) of FG broilers were also greater than those of SG broilers (11.23±1.81 g; P<0.001). Shank length (81.50±4.71 g) and tibia length (104.34±4.45 mm) of FG broilers were longer than those of SG broilers (71.88±4.66 and 95.98±4.85 mm, respectively; P<0.001). Shank diameter (11.59±1.60 mm) and tibia diameter (8.20±0.62 mm) of FG broilers were wider than those of SG broilers (9.45±1.74, 6.82±0.58 mm, respectively; P<0.001). Tibia breaking strength (28.42±6.37 kg) of FG broilers was higher than those of SG broiler tibia (21.81±5.89 kg; P<0.001). Tibia density and bone mineral content (0.13±0.01 g/cm2 and 1.29±0.23 g, respectively) of FG broilers were higher than those of SG broiler tibia (0.11±0.01 g/cm2 and 0.79±0.1 g; P<0.001). Tibia percentage of ash content (39.76±2.81) of FG broilers was lower than that of SG broilers (39.99±2.67; P=0.173). Fast-growing broiler bones were longer, wider, heavier, stronger, more dense, and contained more ash than SG ones. After all parameters were calculated per unit of final BW at 6 wk, tibia density and bone ash percentage of FG broilers were lower than those of SG broilers.

Evaluation of corn distillers dried grains with solubles as an alternative ingredient for broilers

The effects of graded levels of corn distillers dried grains with solubles (DDGS) were investigated as a partial replacement for sources of protein, energy, and other nutrients for broilers when the digestible amino acid balance was maintained. Zero, 8, 16, and 24% DDGS were incorporated into isonutritive diets at the expense of corn, soybean meal, and dl-Met. Poultry oil, l-Lys, and l-Thr additions increased with increasing levels of DDGS. Diets were each fed to 36 Cobb 500 straight-run broilers in 6 floor pens in 2 experiments. In experiment 1, broilers fed ≥8% DDGS showed increased BW gain compared with those fed the control diet during the 0- to 18-d starter period (P = 0.0164) but were almost identical in BW at 42 d (P = 0.9395). The only difference at 42 d was in the carcass fat composition of female broilers: percentage of fat pad decreased with increasing DDGS level (P = 0.0133). Corn DDGS reduced the pellet durability index. However, the pellet durability index was not related to growth or feed utilization. In experiment 2 at 42 d, broilers fed all levels of DDGS showed increased BW gain compared with those fed the control diet. Broilers may perform well when fed properly balanced feeds containing up to 24% DDGS despite reduced pellet quality.

Phytate and other nutrient components of feed ingredients for poultry

Samples of feed ingredients were collected from poultry feed mills in the United States and Canada: corn (133), soybean meal (114), corn distillers dried grains with solubles (DDGS; 89), bakery by-product meal (95), wheat (22), wheat middlings (31), canola meal (21), and wheat shorts (15). The samples were assayed by standard wet chemical techniques for CP, fat, neutral detergent fiber (NDF), acid detergent fiber, calcium, phosphorus, phytate phosphorus, and ash. There was considerable variation found in most of the ingredient components. Forty-two of the 64 CV were above 10.0%. The calcium contents of the ingredients were the most variable, followed by the fat contents. The CP contents were the least variable. There were some fairly consistent relationships observed across samples; in general, acid detergent fiber and NDF were positively correlated, as were ash and mineral levels. Crude protein and fiber levels were positively related, except for wheat shorts, but the relationships were not strong. Phytate P was found to be positively related to ash and total P, as expected, except for corn DDGS. The fat content of corn was found to be negatively related to the NDF content. Significant (P < 0.004) linear regressions were found between phytate P and total P for corn, soybean meal, bakery by-product meal, wheat, wheat middlings, and wheat shorts. The average nonphytate P content of the ingredients was 49.8%, ranging from 38.8% for wheat middlings to 73.2% for DDGS. The phytate P content of wheat and wheat by-products could be predicted from their proximate compositions, with coefficients of determination in excess of 0.740. Predictions for the other ingredients were not as good.

The effects of broiler chicken growth rate on valgus, varus, and tibial dyschondroplasia

An experiment was conducted to test the hypothesis that the growth rate of broilers influences their susceptibilities to bone abnormalities, causing major leg problems. Leg angulations, described in the twisted legs syndrome as valgus and bilateral or unilateral varus, were investigated in 2 subpopulations of mixed-sex Arkansas randombred broilers. Valgus angulation was classified as mild (tibia-metatarsus angle between 10 and 25°), intermediate (25-45°), or severe (> 45°). Body weight was measured at hatch and weekly until 6 wk of age. There were 8 different settings of approximately 450 eggs each. Two subpopulations, slow growing (bottom quarter, n = 581) and fast growing (top quarter, n = 585), were created from a randombred population based on their growth rate from hatch until 6 wk of age. At 6 wk of age, tibial dyschondroplasia incidences were determined by making a longitudinal cut across the right tibia. The tibial dyschondroplasia bone lesion is characterized by an abnormal white, opaque, unmineralized, and unvascularized mass of cartilage occurring in the proximal end of the tibia. It was scored from 1 (mild) to 3 (severe) depending on the cartilage plug abnormality size. Mean lesion scores of left and right valgus and tibial dyschondroplasia (0.40, 0.38, and 0.06) of fast-growing broilers were higher than those (0.26, 0.28, and 0.02) of slow-growing broilers (P = 0.0002, 0.0037, and 0.0269), respectively. Growth rate was negatively associated with the twisted legs syndrome and a bone abnormality (tibial dyschondroplasia) in this randombred population.

Effects of incubation temperature on the bone development of broilers

Manipulating the development of the leg bone by making simple changes to incubation temperature could help reduce the incidence of abnormalities. This study tested the hypothesis that increasing or decreasing the temperature of chick incubation by 1°C for 3 d during ED 4 to 7 affects hatchability, growth, and leg abnormalities of Cobb 500 broilers fed 3 diets: a diet that induced tibial dyschondroplasia, a Ca-deficient diet that induced rickets, and a P-deficient diet that induced rickets. In experiment 1, eggs hatched earlier, and more eggs hatched, at 38.5°C (92.77%) compared with at 37.5°C (86.22%). Body weight was lower in chicks incubated at the higher temperature compared with those incubated at the lower temperature (44.66 vs. 42.92 g). In experiment 2, egg setting times were +17 h for 36.5°C eggs and -10 h for 38.5°C compared with standard setting at 37.5°C (508 h). Hatchability of fertile eggs (92.92%) was highest at 37.5°C and decreased at 36.5°C (89.82%) and 38.5°C (81.55%). Body weight was lower (48.98 g) at 36.5°C than at 37.5°C (49.57 g) and at 38.5°C (50.56 g). Experiment 3 separated effects of incubation temperature and incubation time and was conducted with control and Ca-deficient diets. No main effects or interactions between incubation temperature or time and bone abnormalities were detected. It is important to note that eggs hatched at different times in this study. A difference as little as 1°C for 3 d during ED 4 to 7 affected hatching time and weight.

Strain and sex effects on growth performance and carcass traits of contemporary commercial broiler crosses

In total, 3,840 sexed birds from 6 commercial cross broiler strains (4 male and 3 female) were raised and processed to analyze the effect of strain and sex on growth performance and carcass traits. Chicks from M1 × F1, M2 × F1, M3 × F1, M4 × F1, M3 × F2, and M4 × F3 crosses were sexed. Fifty female and 40 male chicks were randomly allocated to 24 floor pens (119 × 300 cm) covered with pine shavings in each of 4 rooms. The FCR was adjusted for the weight of dead birds (AFCR). Four birds/pen were processed at 7 wk of age. Carcasses were deboned after 2 h of chilling (n = 32 birds per treatment). There were significant strain by sex interactions for BW gain from 0 to 21 and 0 to 48 d. Strain differences in growth rate and mortality increased with age. The cross with the fastest growth rate also had the highest mortality. Because of differences in mortality and carcass yields, birds with the fastest growth (0-48 d) did not produce the most salable meat. Both the heaviest live BW per bird at 48 d (3.45 kg) and highest mortality (13.40%) were observed with the M4 × F3 cross. However, the heaviest live BW per 1,000 chicks placed was from the M3 × F2 cross (3,107 kg). The highest chilled carcass yield was from the M3 × F2 cross (76.05% of live BW) as was the highest meat yield (2,364 kg per 1,000 chicks placed) and highest pectoralis meat yield (805 kg per 1,000 chicks placed). The M3 × F2 cross produced the most total white meat (1,058 kg per 1,000 chicks placed), but interestingly the slowest-growing strain (M1 × F1) produced more white meat (breast + tenders + wings) than did the fastest-growing M4 × F3 strain (980 kg vs. 1,002 kg per 1,000 chicks placed). These results demonstrate the complexity of choosing between commercial strain crosses. The most profitable choice will be dependent on whether whole birds or parts are marketed and the relative values of the parts.

Effects of balanced dietary protein levels on egg production and egg quality parameters of individual commercial layers

The effects of a series of balanced dietary protein levels on egg production and egg quality parameters of laying hens from 18 through 74 wk of age were investigated. One hundred forty-four pullets (Bovans) were randomly assigned to individual cages with separate feeders including 3 different protein level series of isocaloric diets. Diets were separated into 4 phases of 18-22, 23-32, 33-44, and 45-74 wk of age. The high protein (H) series contained 21.62, 19.05, 16.32, and 16.05% CP, respectively. Medium protein (M) and low protein (L) series were 2 and 4% lower in balanced dietary protein. The results clearly demonstrated that the balanced dietary protein level was a limiting factor for BW, ADFI, egg weight, hen day egg production (HDEP), and feed per kilogram of eggs. Feeding with the L series resulted in lower ADFI and HDEP (90.33% peak production) and more feed per kilogram of eggs compared with the H or M series (HDEP; 93.23 and 95.68% peak production, monthly basis). Egg weight responded in a linear manner to balanced dietary protein level (58.78, 55.94, and 52.73 g for H, M, and L, respectively). Feed intake of all hens, but especially those in the L series, increased considerably after wk 54 when the temperature of the house decreased due to winter conditions. Thus, hens fed the L series seemed particularly dependent on house temperature to maintain BW, ADFI, and HDEP. For egg quality parameters, percent yolk, Haugh units, and egg specific gravity were similar regardless of diets. Haugh units were found to be greatly affected by the variation of housing temperature (P = 0.025). Maximum performance cannot always be expected to lead to maximum profits. Contrary to the idea of a daily amino acid requirement for maximum performance, these results may be used to determine profit-maximizing levels of balanced dietary protein based on the cost of protein and returns from different possible protein levels that may be fed.

The Effect of Breeder Age and Egg Storage Time on Phosphorus Utilization by Broiler Progeny Fed a Phosphorus Deficiency Diet with 1α-OH Vitamin D3

Two experiments were conducted to determine that variation in broiler P utilization is due to breeder age and egg storage time. Experiment 1 was conducted with chicks hatched from eggs laid by Ross x Ross 308 breeders (27 vs. 61 wk old) and stored for 0 or 10 d. The age of breeders had significant effects (P < 0.05) on 0 to 16 d chick growth (379 +/- 18 vs. 308 +/- 19 for 27- and 61-wk-old breeders, respectively). The longer egg storage time of chicks from older breeders resulted in higher P rickets scores and incidence, but longer egg storage time of chicks from younger breeders resulted in lower P rickets score and incidence (significant interaction, P = 0.0455). The longer egg storage time of chicks from older breeders resulted in lower bone ash (%), and the longer egg storage time of chicks from younger breeders resulted in higher bone ash (%). Experiment 2 was conducted with chicks hatched from eggs laid by Ross x Ross 308 breeders (26 vs. 60 wk old) and stored for 0 or 10 d. The diets were P deficient and with or without 5 microg/g of 1alpha-OH cholecalciferol (1alpha-OH vitamin D(3)). Breeder age had significant effects (P = 0.0003) on 0 to 16 d chick growth (272 +/- 7 vs. 339 +/- 8 for 26- and 60-wk-old breeders, respectively) and chick mortality (P = 0.0134). The P rickets score increased with breeder age (P = 0.0186) and egg storage time (P = 0.1057). The factors influencing the incidence of P rickets in broilers should include breeder age and egg storage time as well as genetics and dietary levels of Ca, P, and vitamin D activity of the P-deficient diets.

Effect of feeding low-oil distillers dried grains with solubles on the performance of broilers

Manufacturers of distillers dried grains with solubles (DDGS) are changing practices to extract corn oil from DDGS in the process of ethanol production. The resulting product is called low-oil DDGS (LO-DDGS) and may be included in broiler diets. Two LO-DDGS and one unextracted DDGS were used in a broiler performance trial to determine maximum levels of inclusion without detrimental effects. Corn- and soybean meal-based mash diets were used with different DDGS samples included at 10 or 20%. Six hundred thirty Cobb 500 male by-product chicks were randomly assigned to 6 replicate pens containing 15 chicks each and fed diets from 0 to 18 d of age. There was a significant interaction between source and level on BW at d 11 and 18 when 10 and 20% of LO-DDGS was included compared with the control group. There was also a significant effect of source and level interaction on BW at d 18 (P < 0.05). Feed efficiency from d 0 to 18 was improved when 10% LO-DDGS was used compared with 20% inclusion. Abdominal fat pad weights were higher when LO-DDGS samples were included at 10 or 20% compared with the control group. There was a significant effect of DDGS source and level on fat pad weights (P < 0.05). Producers may achieve an increase in performance when including 10% LO-DDGS in broiler diets. Up to 20% inclusion levels may have no detrimental effects on performance parameters compared with a standard corn-soybean diet.

Broiler performance, hatching egg, and age relationships of progeny from standard and dwarf broiler dams

The relationship of egg and chick weights to the performance of broiler chickens from two 42-wk-old flocks (standard and dwarf dams) having male parents from the same genetic stock was investigated in this study. Fertility (91.7 vs. 94.7%) and hatchability (95.2 vs. 96.3%) were not significantly (P > 0.10) different for eggs from standard and dwarf dams, respectively. Egg weight contributed significantly to the variation in BW [BW = β(0) + β(i) (egg weight) + β(i) (dam) + β(i) (sex)]. Body weight as a function of chick weight was not significant. However, chick weight was significant when included in a model with egg weight, suggesting that significant differences in BW at 50 d could be attributed to both egg and chick weights. The negative coefficient for chick weight indicated that between the 2 broilers of the same egg weight, the one with the greater chick weight would have the smaller 50-d BW. Chick weight was a linear function of egg weight. Similarly, the effect of egg or chick weight on broiler BW at 35 or 50 d was best represented by a single linear function. Dam genotype did not contribute significantly to variation in 50-d BW after variation attributable to egg weight was removed from the model. Differences in BW attributable to egg weight increased with broiler age. The coefficients of egg weight and chick weight showed that the differences in BW per gram of egg were 1.43, 3.06, 6.24, and 7.61 g and those per gram of chick were 1.87, 3.99, 8.14, and 9.93 g, respectively, at 7, 21, 35, and 50 d. Body weight increased by 0.1563 times egg weight (and 0.2092 times chick weight) with each additional day of age for both sexes and genotypes. Clearly, both egg and chick weights are important for modeling or predicting market-age broiler BW and economic returns. The relatively small relationship between BW and egg weight demonstrates that genetic selection over the past 3 decades has decreased the influence of egg weight on broiler growth. The present dwarf broiler breeder dams may produce progeny comparable in performance with standard dams.