Protein restriction in early bovine gestation affects post-natal reproduction and production traits in progeny (Micke et al., 2011). This experiment evaluated the effects of dietary protein restriction during the peri-conception period and first trimester in yearling heifers on male fetal and postnatal growth and development; this period of dietary intervention being earlier than any previous bovine fetal programming studies.

 Three hundred and sixty primiparous twelve-month old Santa Gertrudis heifers were individually fed high (14% crude protein (CP)) or low (7% CP) diets for sixty days prior to conception. At 23 days post-conception (dpc), each high (HPERI) or low (LPERI) group was again split into high (HPOST) or low (LPOST) protein groups yielding four treatment groups in a 2x2 factorial design. From the end of the first trimester of gestation (98 dpc), the pregnant heifers were individually fed a 12% CP diet until parturition. Forty eight fetuses were excised at 98dpc. Sixty four heifers went on to calve. Fetal development from 36dpc until term was assessed via trans-rectal ultrasoundnography from 36dpc, fetal necropsy at 98dpc and live calf measures at term.

From birth the male progeny (n=39) were assessed monthly for scrotal circumference (SC), sperm motility (mass activity and percent progressively motile sperm) and laboratory assessment of percent morphologically normal sperm (PNS) as detailed by Fordyce et al., (2006).

Low protein in the periconception period affected the development of the fetus particularly in the male  (P <0.05), however, there was no effect of diet on the weight of testis, germ cell or sertoli cell number in the 98dpc fetus. At birth there was no difference in the weight of the male or female progeny.  From birth to puberty scrotal circumference was not statistically different between groups. Mass activity (1.0+0.1 vs. 0.5+0.1) and motility (30.9+4.3 vs. 14.4+3.4%) were all higher in ejaculates obtained from HPERI calves (P=0.05) compared to those calves whose dams received LPERI diet. PNS tended to be higher in ejaculates from HPERI calves (23.3+3.7 vs. 7.8+1.3%); P=0.09). There was no effect of POST diet on semen traits.

Protein under-nutrition during the period prior to the migration of the primordial germ cells to the gonadal ridge in the fetus, may have affected measures of semen traits however no effects upon germ cell or sertoli cell number could be determined at 98dpc. This period of maternal dietary intervention is earlier than any previous study on offspring reproduction reported in beef cattle to our knowledge. Later measures of reproductive development and metabolic function are currently being evaluated and may provide management information for producers to maximise progeny development and fertility.