Longitudinal development of equine forelimb conformation from birth to weaning in three different horse breeds.

There is limited published data on conformational changes in the forelimbs of growing foals. This study was designed to describe the changes in conformation of the carpus and distal forelimb from birth to weaning in foals of three different breeds. Evaluation of the conformation of the carpus, fetlock, pastern and foot was carried out in 134 Thoroughbreds, 162 French Trotters and 98 Selle Français (French Warmblood) within 1 month of age and then at approximately 2 month intervals until weaning at approximately 6 months of age. The prevalence of limb deviations decreased from birth to weaning. Angular limb deformities were the predominant conditions in the first month (63.6% of all observed limb deviations) and flexural limb deformities were the most common abnormalities at weaning. The most frequent congenital abnormalities were carpal valgus (42.1% of the foals), fetlock valgus (31.2%), over-at-the-knee (30.8%) and dropped fetlocks (13.0%), with French Trotters and Thoroughbred foals being more affected than Selle Français foals. During the study period, the carpal and fetlock conformation became less valgus. The predominant abnormalities at weaning were fetlock valgus (19.1%), club feet (13.0%) and fetlock varus (11.2%). These observations show that carpal, fetlock and foot conformations changed substantially from birth and weaning. There were significant conformational differences between the three breeds, especially in the first months of life. An understanding of the peculiarities of specific breeds may be useful for the evaluation of individual foal conformation.

Developmental basis of limb homology in lizards.

Shubin and Alberch (Evol Biol 1986;20:319-387) proposed a scheme of tetrapod limb development based on cartilage morphogenesis that provides the arguments to interpret the homologies of skeletal elements and sets the basis to explain limb specialization through later developmental modification. Morphogenetic evidence emerged from the study of some reptiles, but the availability of data for lizards is limited. Here, the study of adult skeletal variation in 41 lizard taxa and ontogeny in species of Liolaemus and Tupinambis attempts to fill in this gap and provides supporting evidence for the Shubin-Alberch scheme. Six questions are explored. Is there an intermedium in the carpus? Are there two centralia in the carpus? Is there homology among proximal tarsalia of reptiles? Does digit V belong to the digital arch? Is the pisiform an element of the autopodium plan? And should the ossification processes be similar to cartilage morphogenesis? We found the following answers. Some taxa exhibit an ossified element that could represent an intermedium. There is one centrale in the carpus. Development of proximal tarsalia seems to be equivalent with that observed among reptiles. Digit V could arise from the digital arch. Pisiform does not arise as part of the limb plan. And different patterns of ossification occur following a single and conservative cartilaginous configuration. Lizard limb development shows an early pattern common to other reptiles with clear primary axis and digital arch. The pattern then becomes lizard-specific with specialization involving some reduction in prechondrogenic elements.

Formation of the arthrodial membrane in the blue crab, Callinectes sapidus.

In this study the pattern of arthrodial membrane deposition in Callinectes sapidus was determined by histological and ultrastructural examination of tissues from the carpus joint of the cheliped collected during premolt, ecdysis, postmolt, and intermolt. Apolysis in the arthrodial membrane occurs at stage D(0) and is synchronous with apolysis of the calcified cuticle. Epicuticle formation begins at early stage D(1) and is completed in late stage D(1). Procuticle deposition starts at D(2) and continues until ecdysis. Numerous cytoplasmic extensions occur throughout the lamellae. Component fibers of the arthrodial membrane are intimately associated with dense plaques on the apical membrane of the underlying hypodermal cells, suggesting a site for fiber polymerization. Deposition of the arthrodial membrane continues after ecdysis, with most of the cuticle thickening occurring during stage C. When stained with PAS and counterstained with hematoxylin, a difference can be discerned between preecdysial and postecdysial procuticle of the arthrodial membrane, a distinction not made in previous studies. The boundary between the arthrodial membrane and calcified cuticle is thicker than either of the two layers and the layers overlap rather than butting up against one another. This pattern suggests that underlying hypodermal cells have to produce multiple types of cuticle over the molt cycle. A summary of the various molting patterns in C. sapidus suggests that the control of these diverse events may prove to be complex.

Influence of trotting and supplemental weight on metacarpal bone development.

The use of weight-training to alter bone strength has not been investigated in horses. Recognising that bone responds to loading, we studied the effect of carrying weight on bone development during training. Seventeen horses were divided into 3 groups: controls exercised counterclockwise in a free-flow exerciser; the weight group performed the same exercise carrying progressively increasing weight up to 45 kg and the weight supplement group also received a myo-anabolic supplement. Radiographic equivalence measure of bone mineral content of zones of the third metacarpi (MCIII) was determined on 4 occasions: baseline (Day 108), pre-conditioning following 108 days stall confinement (Day 0), mid-conditioning (Day 39) and end-conditioning (Day 78). Stall confinement resulted in loss of mineral in lateral and medial cortices of both MCIII. During conditioning, weight-carrying increased mineral deposition in lateral and medial cortices of MCIII of the left (inside) leg compared with controls. In the right leg, controls had lower mineral content of the lateral cortex at Day 39 than weight-carrying horses but no differences between treatments were recorded at Day 78. Markers of bone metabolism did not change from baseline to pre-conditioning, but increased from Day 0 to 39 and 78 for all groups. This study demonstrates the benefits to bone mineral deposition in the third metacarpi of carrying weight when trained at low speeds and re-emphasises the potential for bone loss when not given sufficient exercise.

Comparative analysis of weight gain, hand/wrist maturation, and dental emergence rates in chimpanzees aged 0-24 months from varying captive environments.

Variability during the first 2 years of growth and development is examined in captive chimpanzees. The mixed longitudinal study of 175 animals compares curves of weight, hand/wrist maturation, and dental emergence for groups within the sample which differ in sex, rearing circumstances (mother-reared versus hand-reared), and colony (Primate Foundation of Arizona, White Sands Research Center, and The University of Texas M.D. Anderson Cancer Center Department of Veterinary Sciences in Bastrop, Texas). Comparison of LOWESS fits of the curves, using a conservative jack-knife approach, reveals trends toward significant differences between colonies for weight (with 4 comparisons reaching significance) and between rearing groups for maturation (1 reaching significance). Results of a full versus reduced model approach show the same trends, for which significance is reached in a higher number of comparisons. The latter approach also indicates possible effects of sex and environmental differences on dental emergence rate. Difficulties with both approaches are discussed. It is concluded that the results are suggestive of significant sex and environmental effects on the variables monitored, justifying further analysis and continuation of the study. The study is significant in 1) providing norms specific to sex and rearing and colony environments with which individual colony animals may be compared in the assessment of their development and in 2) providing a standard, based upon data from a larger and more varied captive chimpanzee population than previously available, with which the dental emergence status and hand/wrist maturation of fossil apes and hominids may be compared.

Appearance of ossification centers of the lower arm, wrist, lower leg, and ankle in immature orangutans and chimpanzees with an assessment of the relationship of ossification to dental development.

This study examines the appearance of the secondary ossification centers in the lower arms, wrists, lower legs, and ankles of a cross-sectional sample of 20 infant orangutans and chimpanzees (15 of known age). The number of tarsal and carpal centers is analyzed relative to the degree of M1 development and the weight of individual animals. Variation in the appearance of these ossification centers is discussed relative to these variables and others. In addition, a sequence of appearance is established for the carpal and tarsal ossification centers in the orangutan and data is presented on the status of these centers in a fetal and newborn gorilla. Study results indicate that 1) there is variation in the number of secondary epiphyses present in animals of similar ages; 2) tarsal ossification is completed prior to carpal ossification in the orangutan; 3) there are indications of a relationship between weight and the number of ossification centers present in animals of similar age; and 4) there appears to be no evidence of specific relationships between carpal and tarsal development and M1 development.

A comparative study of neonatal skeletal development in Cebus and other primates.

Comparisons of hand/wrist radiographs of neonatal Cebus albifrons (n = 14) and Cebus apella (n = 4) with those of Saimiri sciureus boliviensis (n = 9) and Macaca mulatta (n = 63) reveal that the cebid monkeys show much less skeletal ossification at birth than macaques. Differences in gestation time alone cannot account for the differences in skeletal maturity at birth in the two groups of monkeys. The skeletal precocity of the newborn macaques indicates that their ossification either begins earlier in gestation or proceeds at a more rapid rate, or both. This, in turn, raises questions about the timing of organogenesis and gestational comparability in cebid and cercopithecid monkeys. The advanced state of ossification seen in macaques at birth is not typical of other groups of anthropoid primates, including Cebus, Saimiri, Pan and Homo, and may represent an ontogenetic specialization.