Comparative Morphology of European Elk and Cattle Pelves From the Perspective of Calving

Abstract

According to the anatomical literature, the osseous pelvis demarcates the pelvic cavity by the paired iliac, ischial, and pubic bones, as well as by the single sacral bone, as well as the first coccygeal vertebra. The findings of the present study show that, in addition to these bones, the elk and the EN cow have an interischial bone, which was previously described in the EHF breed. The latter plays a role in the attachment of muscles. In male animals it is necessary for the attachment of the penis. In female animals, this bone is involved in the fixation of the udder. The interischial bone is cartilaginous in young animals, but it ossifies with age and fuses together with the ischia. In the studied female animals the final ossification of the pelvic symphysis begins at the age of 5–6 years in the ischial symphysis and continues in the cranial part of the pubic symphysis. In all the studied pelves the space between the caudal branches of the pubes had not yet undergone ossification. Parts of the pelvis respond differently to sex hormones, and therefore the growth trajectories show sex- and species-related differences. Some structures of female pelves develop and ossify more quickly than others. Male animals develop longer although, for example, the cyclical nature of the lives of elk bulls slows down growth; however, in the case of favourable living conditions it enables them to grow larger. In the case of elks one cannot agree with the limit of the growth period determined on the basis of the jaw bones because the widening of the pelvic floor take place at the age of 6.5–7.5 years, and bulls experience additionally growth of the ilium and the sacral vertebrae. The shape of the pelvis in a female animal is conditioned mostly by lifestyle, fetal size, and the number of deliveries. Elk fetuses are small and the external measurements of the pelvis are rather narrow, which enables fast movement. The pelvic apertures are high and oval, and the width of the pelvic cavity is even throughout its length. The hip bones have a slanted position and the pelvic axis proceeds rather straight. The pelvic measurements and proportions largely complete their development by the first calving. It is possible to distinguish between the pelves of primiparous and pluriparous elks by the shape of the pubic symphysis, the pubic pecten, and the interischial bone, as well as the ossification of the tubers. Sexual dimorphism in adult elk pelves is more manifested in different configurations and in the case of the surface areas and transverse measurements of the pelvic apertures, which are considerably larger in female animals. The pelvic cavity of a bull is more longitudinal and tapers backwards. The pelves of adult elk bulls and cows can be distinguished by the shape of the pubic symphysis and the pubis, the size of the interischial bone, and the apophyses of its caudal branches. The pelvis of the EN cow shares some similarities with the pelvis of the medieval cow and the elk cow – it has small external measurements and is rather narrow. Suitability for calving is indicated by greater height of the pelvic apertures and an even diameter of the pelvic cavity, later ossification of the sacrum, and preserved mobility of the sacroiliac joint. Because in the EN cow the pelvic apertures quickly reach the possible full measurement, apparently earlier ossification of the pelvic symphysis does not pose a problem during calving. The sex-related difference in the pelvis is the largest in the pubic and ischial regions and becomes apparent with sexual maturity. The external absolute indicators of pelves of EHF bulls exceed those of cows; however, the latter are larger with regard to several internal measurements. More important age-related changes include replacement of cartilaginous tissue by osseous tissue in the acetabula up to ossification in the pelvic symphysis in an adult animal, order of ossification, fusion of the interischial bone with the hip bones. In the case of cows one should mention emergence of the cranial pubic tubercle, shifting of other pubic tubercles, and changes in the shape of the symphysial surfaces. The pelvic floor of medieval cows was similar to the pelvis of the elk cow as regards its gutter shape and caudodorsal widening, but the shape of the ischial tubers and the ilium were closer to the contemporary cow. Modern EHF cows have a large body and capacious digestive organs, which through abdominal muscles influence the strengthening of the prepubic tendon, the pubic pecten, and the symphysial crest. The pelvis is more adapted to carrying the udder and the internal organs; some new bony structures have emerged while mobility of limbs and suitability of the pelvis for calving have decreased. From the perspective of calving the pelvic apertures are too low, and a larger fetus may cause incompatibility between the fetus and the pelvis. For this reason, in cattle breeding and especially in the selection of bulls one has to take into account the height and evenness of the pelvic apertures of their mother and daughters, calving ability, and the birth mass of calves. The pelvis of the freely roaming elk has reached owing to natural selection and adaptation an optimum shape and position for living and procreation in its environment. The pelvis of the elk cow grants good mobility, support of the internal organs, udder attachment, and quick discharge during delivery. Humans have shaped the bovine pelvis by means of breeding and have caused a conflict between the different physiological functions of the pelvis. The specialized textbooks contain some statistical data about the bovine pelvis that need not be valid for modern animals because the breed and the time of measurements are unknown. The present study shows that the interischial bone occurs in addition to several ruminants; therefore, a proposal has to be made to include this term in the nomenclature of veterinary anatomy. At the same time it is necessary to check additionally whether this bone could exist in other animal species. Also, the nomenclature has to be supplemented with terms of the sub-parts by distinguishing between the cranial, lateral, and caudal tuberosities of the ischial tuber.

Väitekirja aluseks olev uurimus jätkab seni sigimisbioloogia ning veterinaaria alusteaduste ja populatsioonimeditsiini osakondades tehtud udara kandeaparaadi ja vaagna morfoloogiaalaseid töid. Artiklid annavad uut teavet euroopa põdra luulise vaagna kohta, kuid kirjeldavad ka EK lehmade ning EHF tõugu loomade vaagna iseärasusi. Uurimistööst lähtuvalt saab teha järgmisi järeldusi: • põtradel esineb samuti vaheistmikuluu, mis algselt on kõhreline ning vananedes luustub. See koosneb vaheistmikuluu-kehast, kraniaalsest ning paarilisest kaudaalsest harust; • täiskasvanud põdralehma ja -pulli vaagnat saab teineteisest eristada süleliiduse ja süleluude kraniaalse pinna kuju, vaheistmikuluu suuruse ja tema kaudaalsetel harudel asuvate apofüüside järgi; • esmas- ja korduvalt poeginud emaspõdra vaagnaid on võimalik üksteisest eristada süleliiduse, süleluukammi, köprude luustumise ulatuse ja vaheistmikuluu kuju järgi; • põtrade kasvuea piiri määramine alalõualuude pikenemise lõppemise alusel on ebatäpne, sest vaagna kasv jätkub Eestis elavatel loomadel ka hiljem; • luuliselt ühinevad vaagnas esmalt puusanapas puusaluude kehad ning seejärel istmikuköbrud istmikuluudega, omavahel ristluulülid ning puusa- ja ristluumised köbrud niudeluudega. Vaagnaliiduse luustumine algab kõigil uuritud loomadel istmikuliidusest ja kestab praktiliselt elu lõpuni, kusjuures luustumise ulatuse alusel on võimalik määrata isendi ligikaudset vanust; • sünnituseks on sobivamad põdra ja EK tõugu lehma vaagnad. Vaagnad asetsevad luipa ning nende konfiguratsioon areneb välja juba esimeseks sünnituseks. Vaagnaõõs on ühtlase diameetriga ja suhteliselt kõrge ning ristluu-niudeluu liiges on liikuv ka vanadel loomadel. Nii põdral kui EK tõugu lehmal on sarnaseid tunnuseid keskaegsete lehmade puusaluudega. EHF lehma vaagen paikneb valdavalt horisontaalselt ning selle suhteliselt väikesed vaagnaavad põhjustavad eriti oma madaluse tõttu loote-vaagna disproportsiooni; • EHF pullide vaagnat saab emaslooma vaagnast kindlalt eristada alates 1,5 eluaastast. Isasloomal areneb vaagen enam pikkusesse, vaagnapõhi on kitsas ning luud on jämedad. Luustumine ja kasv on võrreldes lehma vaagnaga kiirem. Vaheistmikuluu on pikk ning massiivsete apofüüsidega; • uurimistulemustele toetudes tuleks pöörduda rahvusvahelise veterinaar-anatoomia nomenklatuuri komitee poole, et lisada nomenklatuuri vaheistmikuluu nimetus ning täiendada istmikuluu jaotust, eristades istmikuköbrul kraniaalset, lateraalset ja kaudaalset köprust; • vaagnate suurimate soolahknevuste põhjuste selgitamiseks süle- ja istmikuregioonis tuleks edaspidi täiendavalt uurida suguhormoonide toimet neisse piirkondadesse ning luulise vaagna eri osade kasvamist.