Growth, Development and Composition of the Ovine Conceptus and Mammary Gland During Pregnancy

Litter-size-dependent intrauterine growth restriction in sheep

“…Furthermore, in a study in which average BWTs of singletons, twins, triplets and quadruplets were 5.4, 4.4, 3.6 and 3.1 kg, respectively, gestation lengths for ewes carrying twins, triplets and quadruplets were reduced by an average of 0.5, 1.0 and 1.5 days, respectively, compared with that for ewes carrying a single foetus (Gootwine and Rozov, 2006). Thus, only a minor part of the reduction in BWT of foetuses born in litters can be attributed to reduced gestation length, as foetal growth rate during the last part of the gestation is estimated to be 101 g/day for twins compared with 199 g/day for singletons (Rattray et al, 1974). The average increase in total litter weight for twins in sheep is about 1.6 times that for a single lamb (Freetly and Leymaster, 2004).…”

“…The average increase in total litter weight for twins in sheep is about 1.6 times that for a single lamb (Freetly and Leymaster, 2004). As illustrated in Figure 5, divergence in foetal weight gain as the number of foetuses increases can be detected before day 100 of gestation (Winters and Feuffel, 1936;Naaktgeboren and Stegeman, 1969;Rattray et al, 1974), when placental size is almost maximal but overall foetal mass is less than one-half that of a singleton foetus.…”

“…Placental weight may decrease slightly during the second half of gestation; however, the amount of DNA in the placentomes changes little during that period, suggesting that the reduction in placental weight is due Figure 4 Association between foetal weight at about 140 days of gestation and its daily growth rate in different experiments (FW Bazer, TE Spencer, WW Thatcher and DC Barron, unpublished results form study on Florida Native ewes; Rattray et al, 1974;Robinson et al, 1977;Sinclair et al, 1998;Corner et al, 2006;Gootwine and Rozov, 2006). mainly to structural modifications and/or the tissues' state of hydration, rather than changes in cell number (Ott et al, 1997;Reynolds et al, 2005a).…”

“…The reduction in BWT of individual lambs as litter size increases is closely associated with a reduction in total energy and total protein content in the lamb's body (Rattray et al, 1974). Lower foetal weights in pregnancies with twin lambs is associated with reduced weights of muscle and, for some muscles, differences were found between singleton and twin lambs in fiber number and crosssectional area (McCoard et al, 1997 and.…”

“…Litter-size-dependent IUGR is evident at about day 100 of pregnancy (Winters and Feuffel, 1936;Naaktgeboren and Stegeman, 1969;Rattray et al, 1974), when foetal size and growth rate are minimal, but placental size is maximal ( Figure 5). Interestingly, the conclusion that the foetal growth trajectory in twins is determined early in gestation can also be drawn from studies of women with multiple conceptuses (Alexander et al, 1995), in which foetal number was reduced early in pregnancy.…”