J. Anim Sci. 2006. 84:2942-2949. doi:10.2527/jas.2006-255
© 2006 American Society of Animal Science
ANIMAL GROWTH, PHYSIOLOGY, AND REPRODUCTION |
Enhanced skeletal growth of sheep heterozygous for an inactivated fibroblast growth factor receptor 31
L. B. Smith,
M. R. Dally,
R. D. Sainz,
K. L. Rodrigue and
A. M. Oberbauer2
Department of Animal Science, University of California, Davis 95616-8251
 |
Abstract
|
|---|
Normal fibroblast growth factor receptor 3 (FGFR3) acts as a negative bone growth regulator by restricting chondrocyte proliferation and endochondral bone elongation. In sheep, a heritable mutation that inactivates FGFR3 produces skeletal overgrowth when homozygous, this condition is commonly referred to as spider lamb syndrome (SLS). We hypothesized that sheep heterozygous for the inactivated FGFR3 mutation (FGFR3SLS/+) would exhibit enhanced long bone growth and greater frame size; additionally, the isolated effects of increased bone growth would translate into greater BW and larger LM area relative to normal lambs at harvest. The current study investigated bone length and LM area of FGFR3SLS/+ sheep at maturity and during growth. At maturity, FGFR3SLS/+ ewes exhibited a larger frame size and longer bones than normal FGFR3+/+ ewes (P < 0.05). Similarly, FGFR3SLS/+ lambs had greater frame sizes than normal FGFR3+/+ lambs, as indicated by increased metacarpal III length and height at withers (P < 0.05). The FGFR3SLS/+ lambs took longer than the normal FGFR3+/+ lambs to reach the 60-kg common BW harvest end point (P < 0.05). The FGFR3SLS/+ lambs showed no difference in BW, ADG, or LM area at any age compared with normal FGFR3+/+ lambs (P > 0.2). A similar LM area produced in the context of a greater frame size and skeletal length produces a greater muscle volume, thereby potentially increasing meat yield. The results of this study suggest that FGFR3SLS/+ animals exhibit a relaxation of the normal inhibition of chondrocyte proliferation, resulting in an increase in the overall frame size. The sheep industry could utilize the naturally occurring genetic mutation in FGFR3 to potentially increase meat yields with enhanced skeletal growth as an alternative to exogenous growth promotants.
Key Words: inactivated fibroblast growth factor receptor 3 • longissimus muscle area • sheep • skeletal growth • spider lamb syndrome
|
INTRODUCTION
|
|---|
Chondrocyte proliferation at the epiphyseal growth plate regulates endochondral bone growth and is a major determinant in mature skeletal size (Kember, 1993
). The fibroblast growth factor receptor 3 (FGFR3) functions as a negative regulator of cell proliferation and differentiation in growth plate chondrocytes (Deng et al., 1996). Normally, FGFR3 is phosphorylated upon ligand binding and inhibits chondrocyte proliferation through signal transducer and activator of transcription (STAT)-mediated induction of cell cycle inhibitors (Xiao et al., 2004). A loss-of-function mutation in the FGFR3 was identified as causing spider lamb syndrome (SLS) in sheep (Beever et al., 2006). Lambs homozygous for the SLS allele (FGFR3SLS/SLS) have bone deformities; in contrast, heterozygous lambs (FGFR3SLS/+) appear normal, though perhaps through relaxed inhibition of chondrocyte proliferation at the growth plate, are physically larger than normal lambs.
Greater mature BW and frame size are correlated with accelerated ADG, increased muscle accretion, and decreased fat deposition during active growth (Owens et al., 1995). However, because of the complex mechanisms involved in skeletal development it is difficult to establish if a greater mature frame size is solely responsible for these characteristics or if these features are simply correlated with enhanced systemic factors (Oberbauer et al., 1989). The FGFR3SLS/+ genotype provides a model to study the effects of a single factor accelerating linear bone growth on overall body composition.
We hypothesized that FGFR3SLS/+ sheep will exhibit enhanced long bone growth and greater frame sizes at all ages, which translates to greater BW and a larger LM area. To test this hypothesis, mature FGFR3+/+ and FGFR3SLS/+ ewes were contrasted for body composition variables, and FGFR3+/+ or FGFR3SLS/+ lambs were evaluated for growth characteristics from weaning to a 60 kg of BW harvest end point.
|
MATERIALS AND METHODS
|
|---|
Animals
The experimental protocols for this study were approved by the University of California, Davis Institutional Animal Use and Care Committee.
Mature Ewe Groups.
Eighteen mature Suffolk and Suffolk-cross ewes (range 2 to 6 yr of age) were randomly selected based on breed and age and were genotyped for the presence of the FGFR3 mutation using a commercially available test (Livestock Molecular Research and Development Inc., Monticello, IL). The ewes were from a single commercial flock with a common genetic background. Body measurements of ewes (n = 9) homozygous for the normal, fully functional FGFR3 allele (FGFR3+/+) were compared with measurements from ewes (n = 9) heterozygous for the mutant, loss of function FGFR3 allele (FGFR3SLS/+). Body weight was recorded, and skeletal dimensions were measured to the nearest 0.1 cm. Height measurements were taken at the scapula; long bone length and midpoint circumference were observed at the metacarpal III (MCIII; the large metacarpal bone) of the right front leg. In a separate analysis, the effect of purebred Suffolk vs. Suffolk cross was evaluated, and no significant effect of breed was detected for any of the body measurements (P = 0.55).
Longissimus muscle area and fat thickness were determined by ultrasound after shearing. Ultrasound images were collected on each animal between the 12th and 13th ribs and over the rump using an Aloka 500V (Corometrics Medical Systems, Wallingford, CT) with a 17-cm, 3.5-MHz transducer. Images were analyzed for LM area, depth of gluteus medius, and subcutaneous fat thickness over the rib (backfat) and rump (rump fat) using Scion software (Scion Corp., Frederick, MD; Sainz and Vernazza Paganini, 2004).
Lamb Growth Trial.
Two purebred American Suffolk rams from a similar genetic background were genotyped as FGFR3SLS/+ by Genmark labs (Madison, WI). Polypay ewes of a similar genetic background (n = 37) that were determined homozygous normal (FGFR3+/+) through Genmark lab testing were estrus-synchronized (Oberbauer et al., 1995). These ewes were bred using laparoscopic AI (Cushwa et al., 1992) to minimize the duration of the lambing period to create a more uniform cohort of lambs for the growth trial.
The ewes were bred to the 2 FGFR3SLS/+ rams by the laparoscopic introduction of fresh semen into the lumen of the uterus, as previously described (Cushwa et al., 1992; Oberbauer et al., 1995). Ewes bred through laparoscopic AI showed no incidence of infection during this study. Approximately 2 wk after laparoscopic AI, the SLS FGFR3SLS/+ rams were placed with the ewes for natural breeding of those ewes that failed to conceive by the laparoscopic AI procedure. Lambs were weighed at birth and processed with normal herd protocols. At approximately 14 d of age, the lambs were given selenium supplementation, vaccinated for Clostridium persfringens type C and D, tetanus, and ovine ecthyma, and were tail-docked and castrated (male lambs). Lambs were weaned at 63 d of age and given a booster vaccine for type C and D toxoid. At weaning, blood (2 mL) was collected from each lamb by jugular venipuncture for FGFR3 genotyping.
Before weaning, lambs had ad libitum access to a pelleted starter ration consisting of (as-fed basis) approximately 12% alfalfa, 30% rolled barley, 26% flaked corn, 20% soy meal, 8% molasses, 2% fat, and 2% of a mineral mix [specifically containing 0.5% ammonium sulfate, 1% white salt, 0.1% Deccox (Alpharma Corp., Fort Lee, NJ), 0.1% ammonium molybdate, and 0.4% Ameri-Blend commercial supplement (Ameri-Mills Corp., St. Joseph, MO)]. Starter ration was supplemented with a molasses-based mix as a top-dressing for palatability. The starter ration was 89.5% DM and had a nutrient profile of 16.6% CP, 4.6% crude fat, 3.3% lignin, 68.8% TDN, and 1.08 Mcal of NEg/kg.
After weaning, the lambs had ad libitum access to a growing ration typical of a feedlot (Tatum et al., 1998; Thomas et al., 2003) and consisting of (as-fed basis) approximately 68% alfalfa meal, 30% flaked corn, and 2% mineral mix (specifically containing 0.5% ammonium sulfate, 1% white salt, 0.1% Deccox, 0.1% ammonium molybdate, and 0.4% Ameri Blend commercial supplement). The grower ration was 89.5% DM and had a nutrient profile of 16% CP, 2.8% crude fat, 4.3% lignin, 60.9% TDN, and 0.86 Mcal of NEg/kg. Starter and grower rations were milled at University of California, Davis, 227 kg at a time in a commercial tub mixer.
Genotyping of Lambs.
Lambs were genotyped for the presence of a FGFR3 mutation by PCR-RFLP analysis as developed and patented by Cockett and Beever (2001). The PCR amplification was performed as described in Cockett et al. (1999) with the forward and reverse primers 5'-TCGACGTACCCTGGCATCCTCG-3'and 5'-TCAGCGCCCGGCCCTCGAGACT-3', respectively, used with permission of J. Beever (University of Illinois, Urbana, IL). Cycle conditions were also modified to 95°C for 5 min, 94°C for 30 s, 63°C for 45 s, and 72°C for 45 s, followed by 31 cycles of 94°C for 30 s, 63°C for 45 s, and 72°C for 45 s, and final incubations of 72°C for 5 min and 10°C for 5 min. This amplified a 147-bp portion of the ovine FGFR3 gene encoding the second tyrosine kinase domain (Cockett and Beever, 2001).
The primers have XhoI restriction sites incorporated, and when cleaved by XhoI produce a 132-bp fragment and a 15-bp fragment, which acts as an internal control (Figure 1; Cockett and Beever, 2001). The XhoI digestion was performed as described by Cockett and Beever (2001). If an animal had a nucleotide substitution representing the mutant FGFR3 allele, then a second XhoI restriction site within the 132-bp fragment was created and that fragment was further cleaved into a 112-bp fragment and a 20-bp fragment (Cockett and Beever, 2001). Thus, homozygous normal lambs were characterized by the presence of a 132-bp fragment, whereas heterozygotes exhibited a 132-bp fragment created from a normal allele, and a 112-bp fragment from the mutant FGFR3 allele (Cockett and Beever, 2001). The digestion products were run on 4% agarose gels with Gelstar fluoresent dye. Gel images were digitally captured on a ChemiImager model 4000 (Alpha Innotech, San Leandro, CA) to record the genotypes of the lambs.
View larger version (81K):
[in this window]
[in a new window]
|
Figure 1. Agarose gel depicting the presence of an SLS (spider lamb syndrome) allele [loss-of-function fibroblast growth factor receptor 3 (FGFR3) allele] from Xho I-cleaved PCR-RFLP products. The figure above represents distinct banding patterns for genotyping FGFR3SLS/+ lambs (Cockett and Beever, 2001). Lane 1 shows a 100-bp ladder. Lanes 2 and 3 depict the FGFR3SLS/+ genotype as 2 bands representing 132- (top) and 112- (bottom) bp fragments. Lanes 4 and 5 depict a normal genotype (FGFR3+/+) as a single band representing a 132-bp fragment. Lane 6 represents a positive PCR control, showing a single band representing a 147-bp fragment undigested by the Xho I restriction enzyme. Lane 7 represents a negative PCR control with no DNA present.
|
|
Growth Measurements.
Forty-three lambs, 17 FGFR3SLS/+ (7 wethers and 10 ewes) and 26 normal FGFR3+/+ lambs (13 wethers and 13 ewes), were measured once every 2 wk beginning at 60 d of age and ending at 60 kg of BW. Measurements began at weaning and included BW, height at scapula, length and circumference of the MCIII, and ultrasonography of the LM area. All measurements were taken by the same individual.
For measuring height at the scapula, lambs were restrained at the head; wool at the shoulders was sheared to avoid wool influencing the height measurement. To ensure measurement accuracy, the measurement equipment was balanced and leveled before each animal height determination. After height measurements, the lamb was positioned on its rump for MCIII measurements of the front right leg. Any wool present between the knee and the fetlock joint on the MCIII was clipped. Length of the MCIII was from the distal end of the MCIII at the knee to the proximal end of the MCIII at the fetlock joint. Circumference of the MCIII was measured at the proximal-distal midpoint of the MCIII.
In the current study, a 7% mortality rate and a 37% morbidity rate of rectal prolapse was observed. Previous studies of the incidence of rectal prolapse in lambs finished on high concentrate diets suggest that docked tail length (Thomas et al., 2003) may have been a major contributing factor to the incidence of rectal prolapse. Frequency of rectal prolapse was not associated with genotype or sex. Rectal prolapse and corrective treatment temporarily decreased the observed BW and MCIII circumference postincidence, presumably due to dehydration, a clinical symptom associated with prolapse. Postincidence compensatory rates of gain in lambs that experienced a loss of BW due to morbidity balanced the negative gains observed as a result of prolapse. All animals that were treated for a rectal prolapse were placed in a separate, neighboring pen in the same feeding facility for a 2-wk recovery period and then were integrated back into the growth trial. Measurements taken during this 2-wk recovery period were not included in the final growth data. After 147 d of age, all lambs were weighed after a 12-h period with food and water withheld to minimize the probability of inducing rectal prolapse.
An Aloka ultrasound monitor unit (model SSD-500) and an Aloka 5-Mhz ultrasound probe/transducer (model UST-588U-5) were used to visualize LM images between the 12th and 13th ribs approximately 45 mm from and perpendicular to the dorsal midline, at which point light vegetable oil was applied as an acoustic couplant (Sainz and Vernazza Paganini, 2004). An 80 x 40-mm region of wool was shaved at the 12th and 13th ribs before each measurement to reduce attenuation of the ultrasound transmission signal by air present between wool fibers. A video output from the ultrasound monitor to a laptop computer captured the images digitally, and the images were analyzed for LM area with Image J version 1.3 image analysis software (Scion Corp., Frederick, MD), distributed in the public domain by the NIH (Sainz and Vernazza Paganini, 2004). At least 2 images of the LM were taken per animal at each scan, and these areas were averaged to yield the LM area of individual lambs. Similarly, Image J software analysis was also used to estimate backfat depth of these LM images.
Lambs were fed to a 60-kg BW end point and harvested in a USDA-inspected abattoir. Hot carcass weight was taken directly after processing the carcass. Carcass measurements of cold weight, quality grade, and yield grade were taken after a 24-h chill period. Assessment of quality grade and yield grade was performed by a USDA-certified grader. Immediately after the fabrication of carcasses for box processing, the LM area, and backfat of the rib sections were measured at the exposed cross-section between the 12th and 13th ribs.
Statistical Analysis
Mature ewe data were analyzed using ANOVA with genotype as the effect using the GLM procedure (SAS Inst. Inc., Cary, NC). Analysis of the data for repeated measures of growth variables in the lambs was performed using ANOVA in the MIXED procedure of SAS. The effects and interactions of fixed variables including genotype, sex, day of age, measurement number, and BW at weaning on random growth parameter variables, including LM area, backfat, BW, scapula height, and MCIII length and circumference, were included in the model. The animal within genotype, sex, and weaning BW class was used as a random effect to account for the auto-correlated observations of repeated measures on the same animal. Tests of hypotheses were evaluated within type III sums of squares computed with PROC MIXED. Additionally, the cross-class interaction of genotype with day of age was used to determine the effect of genotype on growth variables at various ages. Harvest data were analyzed using ANOVA, with genotype as the effect in the GLM procedure.
|
RESULTS
|
|---|
Mature Ewes
The BW was not different between FGFR3SLS/+ and normal FGFR3+/+ genotypes (P > 0.6, Table 1). Height at scapula and metacarpal length were greater in FGFR3SLS/+ ewes than normal FGFR3+/+ ewes (P < 0.05, Table 1), although the metacarpal circumference was unaffected by genotype. The LM area and gluteus medius depth were not influenced by genotype, although fat thickness over the rump was significantly diminished in the FGFR3SLS/+ ewes as compared with the FGFR3+/+ ewes (P < 0.05). Similar to rump fat, backfat thickness was less in the FGFR3SLS/+ ewes (P < 0.09).
View this table:
[in this window]
[in a new window]
|
Table 1. Growth variables1 for mature ewes heterozygous for the inactivating FGFR32 allele (SLS/+)3 and homozygous for the normal, wild type FGFR3 allele (+/+)4
|
|
Lambs
There was no difference due to genotype on BW at any age measured in the lambs (P > 0.3, Figure 2). The ADG (kg/d) of FGFR3SLS/+ lambs and normal FGFR3+/+ lambs was not different (P > 0.9) at 0.24 ± 0.01 and 0.25 ± 0.01, respectively. Additionally, ultrasound measurements of the LM area and width and depth between the 12th and 13th ribs indicated no difference between FGFR3SLS/+ lambs and normal FGFR3+/+ lambs at any age measured (P > 0.1, Figure 3) with mean areas of 12.14 cm2 ± 0.24 and 12.43 cm2 ± 0.20, respectively, at final ultrasound measurement (within 1 wk before harvest).
View larger version (10K):
[in this window]
[in a new window]
|
Figure 2. Body weights (kg ± SE) for 17 FGFR3SLS/+ lambs (square; SLS = spider lamb syndrome, FGFR3 = fibroblast growth factor receptor 3) and 26 normal FGFR3+/+ lambs (triangle) at each time point. Means did not differ at all ages measured (P > 0.2).
|
|
View larger version (10K):
[in this window]
[in a new window]
|
Figure 3. Loin eye area by ultrasound, cm2 ± SE for 17 FGFR3SLS/+ lambs (square; SLS = spider lamb syndrome, FGFR3 = fibroblast growth factor receptor 3) and 26 normal FGFR3+/+ lambs (triangle) at each time point. Means did not differ at all ages measured (P > 0.1).
|
|
A greater height at the shoulder and increased MCIII length was observed in FGFR3SLS/+ lambs relative to normal FGFR3+/+ lambs regardless of sex (P < 0.05, Figure 4). The increased height of FGFR3SLS/+ lambs was detectable at weaning and that height differential to normal FGFR3+/+ lambs was maintained throughout the study (Figure 5). This height difference was also reflected in greater MCIII lengths (P < 0.05) and a more rapid growth; the MCIII circumference was smaller in FGFR3SLS/+ lambs than in normal FGFR3+/+ lambs (P < 0.05, Figure 6).
View larger version (11K):
[in this window]
[in a new window]
|
Figure 4. Height at scapula, cm ± SE for 17 FGFR3SLS/+ lambs (square; SLS = spider lamb syndrome, FGFR3 = fibroblast growth factor receptor 3) and 26 normal FGFR3+/+ lambs (triangle) at each time point. Means differed at ages marked by an asterisk (*P <0.05).
|
|
View larger version (12K):
[in this window]
[in a new window]
|
Figure 5. Metacarpal III length, cm ± SE for 17 FGFR3SLS/+ lambs (square; SLS = spider lamb syndrome, FGFR3 = fibroblast growth factor receptor 3) and 26 normal FGFR3+/+ lambs (triangle) at each time point. Means differed at ages marked by an asterisk (*P <0.05).
|
|
View larger version (11K):
[in this window]
[in a new window]
|
Figure 6. Metacarpal III circumference, cm ± SE for 17 FGFR3SLS/+ lambs (square; SLS = spider lamb syndrome, FGFR3 = fibroblast growth factor receptor 3) and 26 normal FGFR3+/+ lambs (triangle) at each time point. Means differed at ages marked by an asterisk (*P <0.05).
|
|
The FGFR3SLS/+ lambs took on average 11 d longer than normal FGFR3+/+ lambs to reach the 60 kg slaughter BW (P <0.01). Analysis of carcass measurements showed no genotype difference in quality grade, yield grade, dressing percent or LM area, or width or depth between the 12th and 13th ribs. However, at harvest the mean backfat thickness of FGFR3SLS/+ lambs was greater than normal FGFR3+/+ lambs when compared at a common BW of approximately 60 kg (P <0.05, Table 2). In contrast, ultrasound analysis of age-matched measurements of backfat depth between the 12th and 13th ribs during the last 6 wk before harvest indicated no significant difference between genotypes (P > 0.9, Table 2). No sex x genotype interaction was detected, and there was no effect of sex on backfat thickness measured at harvest (P > 0.8) or through ultrasound analysis (P > 0.4, Table 3).
View this table:
[in this window]
[in a new window]
|
Table 2. Carcass quality variables1 for lambs heterozygous for the inactivating FGFR32 allele (SLS/+)3 and homozygous for the normal, wild type FGFR3 allele (+/+)4
|
|
|
DISCUSSION
|
|---|
The effect of the homozygous FGFR3SLS/SLS genotype on skeletal development has been well documented (Dedrickson, 1989; Oberbauer et al., 1995), and recently, Beever et al. (2006) reported that lambs with a heterozygous FGFR3SLS/+ genotype exhibited a greater canon bone length, demonstrating the skeletal-growth-enhancing effects of a single mutant FGFR3 allele. However, no studies have been published examining the effects of the heterozygous FGFR3SLS/+ genotype on body components associated with changes in frame size (i.e., muscle development). Endochondral bone growth is fundamentally dependent on extension and ossification at the growth plate (Hunziker and Schenk, 1989). Fibroblast growth factor receptor 3 acts as a negative bone growth regulator in the growth plate limiting chondrocyte proliferation and endochondral bone elongation (Ornitz and Marie, 2002). Evaluating the genetic mutations in FGFR3 has illustrated the critical function this growth factor plays in the process of endochondral bone growth (Ornitz and Marie, 2002). The FGFR3 gain-of-function mutations restrict growth plate activity resulting in dwarfism (Webster and Donoghue, 1996; 1997), whereas FGFR3 loss-of-function mutations (i.e., SLS) cause skeletal overgrowth (Beever et al., 2006).
The current study examined the FGFR3SLS/+ genotype in sheep to more accurately understand the physiological relationship of bone and muscle growth. Conclusions from the current study revealed a positive relationship between an FGFR3SLS/+ genotype and enhanced linear bone growth as hypothesized. The FGFR3SLS/+ lambs and mature ewes exhibited an increase in MCIII length presumably through increased proliferative activity of chondrocytes at the growth plate permitted by decreased FGFR3 activity. Additionally FGFR3SLS/+ lambs had a smaller MCIII circumference relative to normal FGFR3+/+ lambs. In a similar fashion, FGFR3–/ – mice exhibit thinner cortical bone because of increased proliferative activity at the growth plate (Valverde-Franco et al., 2004). Osteogenesis by the periosteum increases cortical width over time, yet if rate of bone elongation exceeds the time required for periosteal deposition to reinforce cortical bone thickness, then this is reflected in a decrease in diaphyseal circumference (Price et al., 1994). Of note, a decreased diaphyseal circumference reflects thinner cortical bone, which correlates with a decrease in mechanical strength (Nafei et al., 2000a,b). Comparison of MCIII circumference in mature FGFR3SLS/+ ewes with normal FGFR3+/+ ewes indicated no difference in mature diaphyseal circumference, suggesting that in time the cortical bone reinforces appropriately once bone elongation ceases.
Previous studies have indicated that animals exhibiting a larger mature frame size have a greater BW, improved efficiency of gain, decreased backfat and enhanced muscle development relative to normal framed animals (Nour and Thonney, 1987; Owens et al., 1995). The FGFR3SLS/+ lambs exhibiting a greater frame size than normal FGFR3+/+ lambs during active growth did not show an increased BW or ADG. The ADG was not different between FGFR3SLS/+ lambs and normal FGFR3+/+ lambs but was congruent with ADG reported in other industry feedlot environments on ad libitum, high-energy diets (Tatum et al., 1998). In contrast to the backfat observed in FGFR3SLS/+ mature ewes, the FGFR3SLS/+ lambs indicated a greater degree of backfat relative to normal FGFR3+/+ lambs at harvest. However, because it took FGFR3SLS/+ lambs an average of 11 d longer than normal FGFR3+/+ lambs to reach harvest BW, it is likely that the longer feeding time could account for the greater degree of accumulated backfat among the otherwise uniform group of lambs.
The current study demonstrated that mature FGFR3SLS/+ ewes and FGFR3SLS/+ lambs exhibited an increase in bone length and frame size relative to normal FGFR3+/+ lambs and mature ewes. Unexpectedly, FGFR3SLS/+ animals did not show an increase in LM area or BW in comparison with normal FGFR3+/+ animals. Although LM areas in FGFR3SLS/+ lambs and normal FGFR3+/+ lambs were not different, loin eye area measures only 2 of 3 muscle-volume dimensions. The FGFR3SLS/+ lambs were taller (Figure 4
) and had longer MCIII bones (Figure 5), indicating that they were larger framed. Larger-framed animals are longer than smaller-framed animals of the same BW, and they therefore have longer muscles (Siemens et al., 1990). Thus, the FGFR3SLS/+ lambs most likely had more muscle at the same LM area with potentially greater meat yield than the FGFR3+/+ lambs, supporting the hypothesis that increasing bone length results in an increase in muscle mass. Similarly, the results of Dolezal et al. (1993) indicate that in cattle, muscle:bone ratios do not differ among frame sizes, suggesting that a greater skeletal mass correlates with a greater amount of muscle. In addition, mature FGFR3SLS/+ ewes were leaner than FGFR3+/+ ewes, and proportion of muscle in the body (or retail product yield) is better reflected by differences in backfat than by LM area (Boggs and Merkel, 1990; Smith et al., 1992). Lambs harvested at 60 kg of BW did not show this difference, and in fact did not exhibit the increased growth rate expected of animals with greater frame size. This discrepancy may be due to the fact that the FGFRSLS/+ genotype is single point mutation, affecting only skeletal growth, whereas differences in frame size are due to a large number of loci affecting traits ranging from appetite to muscle fiber hyperplasia. For example, models that result in augmented GH or enhanced IGF affect a wide range of tissues in the body including bone, muscle, and fat (Oberbauer et al., 1992), thereby precluding the ability to study the isolated effects of increased bone growth on other body components. Alternatively, although no clinical signs of acidosis or feed-related illnesses were observed, feed intake may have been a limiting factor in lamb growth potential due to a low amount of fermentable fiber present in the feedlot ration. During growth the FGFR3SLS/+ lambs displayed only enhanced skeletal growth without the other growth traits that normally accompany a larger frame; however, the results of this study suggest that increased long bone growth will eventually result in greater muscularity and leanness.
|
Footnotes
|
|---|
1 This work was supported by California Agricultural Experiment Station Funds (CA-D*-ASC-5256-AH). L. B. Smith received financial assistance from the G. Kirk Swingle Scholarship. The authors thank Tom Famula for statistical guidance and Dana Van Liew of the University of California, Davis, Department of Animal Science Sheep Unit for assistance in the care and management of the animals. 
2 Corresponding author: amoberbauer{at}ucdavis.edu
Received for publication April 21, 2006.
Accepted for publication June 20, 2006.
|
LITERATURE CITED
|
|---|
Beever, J. E., M. A. Smit, S. N. Meyers, T. S. Hadfield, C. Bottema, J. Albretsen, and N. E. Cockett. 2006. A single-base change in the tyrosine kinase II domain of ovine FGFR3 causes hereditary chondrodysplasia in sheep. Anim. Genet. 37:66–71.[CrossRef][Medline]
Boggs, D., and R. Merkel. 1990. Live animal carcass evaluation and selection manual. Kendall/Hunt, Dubuque, IA.
Cockett, N. E., T. L. Shay, J. E. Beever, D. Nielsen, J. Albretsen, M. Georges, K. Peterson, A. Stephens, W. Vernon, O. Timofeevskaia, S. South, J. Mork, A. Maciulis, and T. D. Bunch. 1999. Localization of the locus causing spider lamb syndrome to the distal end of ovine chromosome 6. Mamm. Genome No. 10:35–38.[CrossRef][Medline]
Cockett, N., and J. Beever. 2001. Screening for the molecular defect causing spider lamb syndrome in sheep. United States Patent No. Patent No. 6,306,591 B1.
Cushwa, W. T., G. E. Bradford, G. H. Stabenfeldt, Y. M. Berger, and M. R. Dally. 1992. Ram influence on ovarian and sexual activity in anestrous ewes: Effects of isolation of ewes from rams before joining and date of ram introduction. J. Anim. Sci. 70:1195–1200.[Abstract]
Dedrickson, B. 1989. Spider lamb syndrome hereditary chondrodysplasia: A congenital skeletal defect in sheep. PhD. Diss., Kansas State Univ., Manhattan.
Deng, C., A. Wynshaw-Boris, F. Zhou, A. Kuo, and P. Leder. 1996. Fibroblast growth factor receptor 3 is a negative regulator of bone growth. Cell 84:911–921.[CrossRef][Medline]
Dolezal, H. G., J. D. Tatum, and F. L. Williams, Jr. 1993. Effects of feeder cattle frame size, muscle thickness, and age class on days fed, weight, and carcass composition. J. Anim. Sci. 71:2975–2985.[Abstract]
Hunziker, E., and R. Schenk. 1989. Physiological mechanisms adopted by chondrocytes in regulating longitudinal bone growth in rats. J. Physiol. 414:55–71.[Abstract/Free Full Text]
Kember, N. 1993. Cell kinetics and the control of bone growth. Acta Paediatr. Suppl. 82:61–65.[Medline]
Nafei, A., C. Danielsen, F. Linde, and I. Hvid. 2000a. Properties of growing trabecular ovine bone. Part I: Mechanical and physical properties. J. Bone Joint Surg. Br. 82:910–920.[CrossRef][Medline]
Nafei, A., C. Danielsen, F. Linde, and I. Hvid. 2000b. Properties of growing trabecular ovine bone. Part II: architectural and mechanical properties. J. Bone Joint Surg. Br. 82:921–927.[Medline]
Nour, A., and M. Thonney. 1987. Carcass, soft tissue and bone composition of early and late maturing steers fed two diets in two housing types and serially slaughter over a wide weight range. J. Agric. Sci. Cambridge 109:345–355.
Oberbauer, A., W. Currie, L. Krook, and M. Thonney. 1989. Endocrine and histologic correlates of the dynamics of the metacarpal growth plate in growing rams. J. Anim. Sci. 67:3124–3135.[Abstract/Free Full Text]
Oberbauer, A., T. Currier, C. Nancarrow, K. Ward, and J. Murray. 1992. Linear bone growth in OMTLA-OGH transgenic male mice. J. Physiol. 262:E936–E942.
Oberbauer, A., N. E. East, R. Pool, J. D. Rowe, and R. H. BonDurant. 1995. Developmental progression of the spider lamb syndrome. Small Rumin. Res. 18:179–184.
Ornitz, D. M., and P. J. Marie. 2002. FGF signaling pathways in endochondral and intramembranous bone development and human genetic disease. Genes Dev. 16:1446–1465.[Free Full Text]
Owens, F., D. Gill, D. Secrist, and S. Coleman. 1995. Review of some aspects of growth and development of feedlot cattle. J. Anim. Sci. 73:3152–3172.[Abstract]
Price, J., B. Oyajobi, and R. Russell. 1994. The cell biology of bone growth. Eur. J. Clin. Nutr. 48:S131–S149.
Sainz, R. D., and R. F. Vernazza Paganini. 2004. Effects of different grazing and feeding periods on performance and carcass traits of beef steers. J. Anim. Sci. 82:292–297.[Abstract/Free Full Text]
Siemens, A. L., R. J. Lipsey, H. B. Hedrick, F. L. Williams, Jr., S. W. Yokley, and M. G. Siemens. 1990. Comparison of market hog characteristics of pigs selected by feeder pig frame size or current USDA feeder pig grade standards. J. Anim. Sci. 68:2217–2221.[Abstract]
Smith, M., J. Oltjen, H. Dolezal, D. Gill, and B. Behrens. 1992. Evaluation of ultrasound for prediction of carcass fat thickness and longissimus muscle area in feedlot steers. J. Anim. Sci. 70:29–37.[Abstract]
Tatum, J. D., M. S. DeWalt, S. B. LeValley, J. W. Savell, and F. L. Williams. 1998. Relationship of feeder lamb frame size to feedlot gain and carcass yield and quality grades. J. Anim. Sci. 76:435–440.[Abstract/Free Full Text]
Thomas, D. L., D. F. Waldron, G. D. Lowe, D. G. Morrical, H. H. Meyer, R. A. High, Y. M. Berger, D. D. Clevenger, G. E. Fogle, R. G. Gottfredson, S. C. Loerch, K. E. McClure, T. D. Willingham, D. L. Zartman, and R. D. Zelinsky. 2003. Length of docked tail and the incidence of rectal prolapse in lambs. J. Anim. Sci. 81:2725–2732.[Abstract/Free Full Text]
Valverde-Franco, G., H. Liu, D. Davidson, S. Chai, H. Valderrama-Carvajal, D. Goltzman, D. M. Ornitz, and J. E. Henderson. 2004. Defective bone mineralization and osteopenia in young adult FGFR3–/ – mice. Hum. Mol. Genet. 13:271–284.[Abstract/Free Full Text]
Webster, M., and D. Donoghue. 1996. Constitutive activation of fibroblast growth factor receptor 3 by the transmembrane domain point mutation found in achondroplasia. EMBO. 15:520–527.[Medline]
Webster, M. K., and D. J. Donoghue. 1997. FGFR activation in skeletal disorders: Too much of a good thing. Trends Genet. 13:178–182.[CrossRef][Medline]
Xiao, L., T. Naganawa, E. Obugunde, G. Gronowicz, D. M. Ornitz, J. D. Coffin, and M. M. Hurley. 2004. STAT1 controls postnatal bone formation by regulating fibroblast growth factor signaling in osteoblasts. J. Biol. Chem. 279:27743–27752.[Abstract/Free Full Text]
Top
Abstract
INTRODUCTION
