Effect of eggshell temperature throughout incubation on broiler ...

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vented or reduced by providing a growing broiler em- bryo or hatchling with optimal circumstances for leg bone and muscle development. Leg bone weights at ...
PHYSIOLOGY, ENDOCRINOLOGY, AND REPRODUCTION Effect of eggshell temperature throughout incubation on broiler hatchling leg bone development C. W. van der Pol,*†1 I. A. M. van Roovert-Reijrink,* C. M. Maatjens,*† I. van den Anker,† B. Kemp,† and H. van den Brand† *HatchTech B.V., PO Box 256, 3900 AG Veenendaal, the Netherlands; and †Adaptation Physiology Group, Wageningen University, PO Box 338, 6700 AH Wageningen, the Netherlands ABSTRACT Leg problems in broiler chickens may partly be prevented by providing optimal circumstances for skeletal development during incubation. one of the factors demonstrated to affect bone development is eggshell temperature (EST), which provides a reliable reflection of embryo temperature. The present experiment aimed to investigate the effect of EST on development and asymmetry of the femur, tibia, and metatarsus in broiler chicken hatchlings. Eggs were incubated from d 0 until hatch at 1 of 4 EST: low (36.9°C), normal (37.8°C), high (38.6°C), and very high (39.4°C). At hatch, chick quality was determined in terms of chick length, yolk-free body mass, navel score, and organ weights. Tibia, femur, and metatarsus were weighed, their length and width (mediolateral diameter) and depth (craniocaudal diameter) at the middle

of the shaft were measured, and their ash content was determined. Relative asymmetry of the leg bones was determined from their relative dimensions. Hatchability, chick quality, and organ development were lower for very high EST compared with all other treatments. Very high EST resulted in lowest tibia and metatarsus lengths (−3.1 to −8.4%) compared with all other treatments, and lower metatarsus weight (−9.1%) and femur length (−4.9%) compared with high EST. Relative asymmetry and ash content did not differ among treatments and no relation between EST and bone parameters was found. To conclude, very high EST resulted in lower bone development, hatchability, and chick quality. Few differences in bone development and chick quality were found between low, normal, and high EST.

Key words: incubation, eggshell temperature, bone development 2014 Poultry Science 93:2878–2883 http://dx.doi.org/10.3382/ps.2014-04210

INTRODUCTION At slaughter age, leg problems (pathologies that result in impaired walking ability), such as tibial dyschondroplasia, rickets, and femoral head necrosis, are highly prevalent in broiler chickens (reviewed by Dinev, 2012). These leg problems constitute a welfare problem and result in economic losses. Poor skeletal leg health in later life may be related to suboptimal leg bone development (defined here as bone weight, dimensions, and ash content) during incubation (Yalçin et al., 2007; oviedo-Rondón et al., 2008, 2009a). It has therefore been suggested that leg problems can partly be prevented or reduced by providing a growing broiler embryo or hatchling with optimal circumstances for leg bone and muscle development.

©2014 Poultry Science Association Inc. Received May 27, 2014. Accepted July 14, 2014. 1 Corresponding author: [email protected]

Leg bone weights at hatch have been found to decrease at high (39.6°C) and low (36.9°C) incubator temperature when applied between embryonic d (E) 10 and E18 (Yalçin et al., 2007), or at high (38.9°C) eggshell temperature (EST) applied between E18 and E21 (oviedo-Rondón et al., 2009b) compared with control (37.0 to 37.8°C throughout). However, oviedo-Rondón et al. (2008) found higher femur weights at 36.0 and 39.0°C than at 37.0 and 38.0°C incubator temperature when applied from E17 till hatch. They furthermore found higher tibia length at 38.0°C than at 36.0 or 39.0°C incubator temperature (oviedo-Rondón et al., 2008), although others (Yalçin and Siegel, 2003; Hammond et al., 2007) found that leg bone lengths increased at temperatures deviating from the control. Leg bone lengths have been shown to increase at high and low incubator temperatures when these were applied between E4 and E7 (Hammond et al., 2007) or between E0 and E8, at E14, or between E10 and E18 (Yalçin and Siegel, 2003) compared with control (37.5°C throughout). It is clear that incubation temperature can alter bone development, but results are ambiguous. Possibly, this

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is due to differences in the embryo temperature used. Because of differences in heat production or level of heat loss, embryo temperatures may vary greatly from incubator temperatures at different stages of incubation (Lourens et al., 2011), and this could explain the discrepancies in the literature. Most previous studies on bone development did not measure embryo temperature or EST, but incubator temperature. To preserve the embryo, EST is measured as a reflection of embryo temperature. It has been shown that an EST of 37.5 to 38.0°C throughout incubation leads to highest yolk-free body mass (YFBM) and hatchability (Lourens et al., 2005, 2007; Molenaar et al., 2010, 2011a). Whether this holds for bone development as well is not known. The aim of the present experiment is to investigate the effect of a constant low (36.9°C), normal (37.8°C), high (38.6°C), and very high (39.4°C) EST, applied from set until hatch, on the development of the femur, tibia, and metatarsus of a broiler chicken hatchling. Furthermore, the effect of EST on embryonic mortality, hatchability, and chick quality (chick length, YFBM, navel score, and organ development) will be investigated.

MATERIALS AND METHODS The experimental protocol was approved by the Institutional Animal Care and Use Committee of Wageningen University, Wageningen, the Netherlands.

Experimental Setup Storage and incubation of eggs took place at a commercial hatchery (Lagerwey, Lunteren, the Netherlands). Ross 308 hatching eggs (n = 223) from a parent stock aged 44 wk with an average egg weight of 65.0 g ± 3.6 were stored on setter trays for 2 d at 18°C. Number of eggs set was based on expected hatchability, and calculated to result in 37 hatchlings per treatment. Eggs were incubated from d 0 of incubation (E0) until hatch at 1 of 4 EST: low (36.9°C; n = 62), normal (37.8°C; n = 46), high (38.6°C; n = 53), and very high (39.4°C; n = 62). Each treatment was incubated in a HT-4,800 setter and hatcher (HatchTech B.V., Veenendaal, the Netherlands) with a capacity of 4,800 eggs. Eggs were equally divided within the incubator on 24 trays to maintain constant EST. The EST was measured by 4 temperature sensors per treatment (NTC Thermistors: type DC 95; Thermometrics, Somerset, UK) attached to the equator of 4 individual eggs using tape and heat conducting paste (Dow Corning 340 Heat Sink Compound, Dow Corning GmbH, Wiesbaden, Germany). Eggs were warmed from 18.0°C storage temperature to their treatment EST in a time window of 10 h. Incubator temperature was adjusted automatically to maintain the treatment EST. Eggs were turned to an angle of 45° and then turned hourly by 90°. The RH was maintained between 45 and 60%,

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and CO2 concentration was maintained between 0.25 and 0.35% throughout incubation. At E18.5, eggs were transferred to hatcher baskets and placed in the hatcher. In the hatcher, eggshell sensors were attached to the eggs to determine EST. Incubator temperature was adjusted to maintain the treatment EST. At E19.5, the incubator temperature was fixed at the incubator temperature that corresponded with the treatment EST at that moment, and the EST was allowed to increase during the hatching process. The EST were thus maintained at contrasting levels until hatch. A difference in incubation time was expected for the various EST. Eggs were therefore allowed to hatch until E23.5. However, all viable eggs in normal, high, and very high EST had hatched by E21.5 and incubation was terminated at this point. All viable eggs in low EST had hatched by E22.5.

Measurements On E0 (day of set), each egg was numbered individually and weighed. Eggs were candled at E18.5. Clear eggs at E18.5 and unhatched eggs at E21.5 (for normal, high, and very high EST) or E22.5 (for low EST) were opened to determine infertility or stage of embryonic mortality per week (Lourens et al., 2005). From E19.5 onward, hatched chicks (n = 133) were pulled every 12 h. Chicks were weighed, their length was recorded from the tip of the beak to the tip of the middle toe, excluding the nail (Molenaar et al., 2010), and navel condition was scored as 1 (a clean and closed navel), 2 (a black button or gap of 2 mm; Molenaar et al., 2010). Residual yolk was removed and weighed after cervical dislocation. Yolk-free body was frozen at −20°C. The YFBM was calculated as BW minus yolk weight. After thawing at room temperature for 12 h, heart, liver, stomach (gizzard and proventriculus), and intestines were weighed. Both legs of each chick (n = 133) were removed at the hip joint and boiled in water for 5 min to allow easy removal of soft tissue. Tibia, femur, and metatarsus were cleaned of soft tissue and cartilage and weighed in grams to 4 decimals. Using a digital caliper (Skandia, Ridderkerk, the Netherlands), their length and the width (mediolateral diameter) and depth (craniocaudal diameter) at the middle of the shaft were measured twice in millimeters to 2 decimals. Relative asymmetry was calculated with the following formula (Møller et al., 1999): RA = {|R − L|/[(R + L)/2]} × 100, in which RA = relative asymmetry of the left and right bone (%), R = length, depth, or width of the right bone (mm), L = length, depth, or width of the left bone (mm), and |R – L| = absolute difference between R and L.

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Tibia, femur, and metatarsus of the left leg (n = 133) were dried and ashed by the Animal Health Centre, Deventer, the Netherlands. Each bone was placed in a porcelain container and weighed to the nearest 0.1 mg. Bones were placed in a 550°C oven for 4 h and then placed in an desiccator for cooling. After cooling, bone ash was weighed to the nearest 0.1 mg. Ash content was calculated as a percentage of fresh bone weight.

Statistical Analysis The overall model used for all data was Yi = µ + Temperaturei + εi,

[1]

where Yi = the dependent variable, µ is the overall mean, Temperaturei = EST (i = low, normal, high, or very high), and εi = the residual error term. Hatch time, YFBM, chick length, organ weights, relative asymmetry, and bone ash content were analyzed using the GLM procedure. Tibia, femur, and metatarsus weight, length, width, and depth were analyzed using the Mixed procedure with an auto-regressive covariance structure with side (left or right) as the repeated factor. Navel score, fertility, embryonic mortality, and hatch of fertile were analyzed using the Logistics procedure. All data were analyzed in SAS (SAS Institute Inc., Cary, NC). Individual eggs or chicks were considered the experimental unit. Model assumptions were verified by examination of the distributions of the means and residuals. Chick length data were sinus transformed to obtain normality. Relative asymmetry of tibia length was logtransformed to obtain normality. Relative asymmetry of metatarsus length, width, and depth, and femur width and depth were square root transformed to obtain normality.

For bone dimensions (weight, length, depth, and width) and organ weights (stomach, liver, heart, and intestines), YFBM was added to model 1 as a covariable. To verify if the relation between EST and bone dimensions was linear or quadratic, EST was added as a fixed factor instead of a continuous factor in model 1. Least squares means were compared using Bonferroni adjustments for multiple comparisons. Data are presented as least squares means ± SEM. In the case of data transformation, least squares means and SEM are presented untransformed and P-values are presented as those of the transformed data. In all cases, differences were considered significant at P ≤ 0.05.

RESULTS Bone Parameters Metatarsus weight was higher for high EST than for very high EST (+0.012 g; P = 0.044; Table 1). Femur (P = 0.06) and tibia (P = 0.15) weights were not different among treatments. Femur length was higher for high EST than for low EST (+0.628 mm) and very high EST (+0.977 mm; P = 0.001). Tibia length was lower for very high EST than for low EST (−1.428 mm), normal EST (−1.768 mm), and high EST (−2.270 mm; P < 0.001). Metatarsus length was higher for high EST than for low EST (+0.748 mm) and very high EST (+1.344 mm) and it was higher for normal EST than for very high EST (+1.207 mm; P < 0.001). Femur (P = 0.06), tibia (P = 0.14), and metatarsus (P = 0.46) depth did not differ among treatments. Tibia width was higher for very high EST than for normal EST (+0.117 mm) and high EST (+0.086 mm; P < 0.001). Femur (P = 0.18) and metatarsus (P = 0.08) width did not differ among treatments. No linear or quadratic relation was found between EST and bone dimensions (P ≥ 0.06).

Table 1. Femur, tibia, and metatarsus weight, length, depth, and width of chicks incubated at a low (36.9°C), normal (37.8°C), high (38.6°C), or very high (39.4°C) eggshell temperature (EST) from set until hatch Weight (g)

Depth1 (mm)

Length (mm)

Width2 (mm)

EST

n

Femur

Tibia

Metatarsus

Femur

Tibia

Metatarsus

Femur

Tibia

Metatarsus

Femur

Tibia

Metatarsus

Low Normal High Very high SEM P-value3  Linear  Quadratic  Overall  YFBM4

35 38 38 22            

0.129 0.121 0.128 0.126 0.003   0.99 0.98 0.06