The effects of litter-size and maternal body weight on early postnatal growth in rat and mouse

The effects of litter size on maternal care, body weight and infant development of and rats were investigated at early growths of infants as aimed to set basic data for selection programes. The twelve mice (BALB/c) and the nine rats ( Spraque Dawley) at the age of fourteen weeks had been used in experiments.Dams and al suckling juveniles in litters housed together in cage systems until 3 weeks of age. All infant rats and mice born weighted individualy at fist day, 1, 2, 3, 4 and 5 weeks of ages. Each litter pubs were housed at same cage after dams were removed from cages. All animals were kept in a temparature (23 º) and humudity (50%) controlled room and the lights were on from 6 AM and 6 PM. The animals were fed a stock pellet diets. Both water and food were provided at libitum.Factors were evaluated for major effects and their interactions. While evaluating the datum a statictical model had been utilized and in this model, the litter-size had been dividen into 4 groups ( with 7, 8, 9 and 10 birth at once) in rats and into 4 groups ( with 8,8 and ten births at once) in mice. Dam?s body mass had been seperated into groups 169,171-175g, 190-207 g at rats and at the mice as 33-53 g,36-38 g, 39-41 g.In conclusion the effects of litter-size on growth and weight of newly borned infants were different in mice and rats.When the litter-size increased, the infant body weight and early postnatal growth in two species till the 5 week age decreased and while dam?s body mass indreased at end of the pregnancy the litter-size body weights at first day and during early growth peirod were increased. The effects of litter-size on body weights of newly borned and early infant growth changed by maternal body mass.Key words: Litter-size, Dam body mass, growth, mouse, rat