PSIV-30 - Moderate maternal nutrient restriction in beef heifers reduces fetal crown-rump length at day 35 of gestation

Abstract: One-carbon metabolite (OCM) supplementation in beef cattle has shown to be a novel strategy that alters programming outcomes in tissues of the developing fetus. However, information regarding growth changes to the fetus during early gestation are limited. The objective of this study was to evaluate the effects of OCM supplementation in control-fed or nutrient-restricted pregnant heifers on fetal crown-rump length (CRL) during early gestation. We hypothesized that decreased nutrient availability in the maternal system would impact the growth of the fetus in utero and providing OCM supplementation would restore growth levels in a nutrient restricted environment. Angus crossbred heifers (n = 216; initial body weight [BW]: [365 ± 5.45 kg]) across three replicates underwent estrus synchronization and bred via artificial insemination (AI) using female-sexed semen from a single sire. At breeding (d 0), heifers were assigned to treatments in a 2 × 2 factorial design, which included two levels of daily gain; control (CON; +0.45 kg/day gain) or restricted (RES; −0.23 kg/day gain) and supplementation of OCM (+OCM; rumen protected choline [44.4 g/day] and methionine [7.4 g/day] in a ground corn carrier and weekly injections of 320 mg folate and 20 mg vitamin B12) or no supplementation (-OCM; corn carrier and saline injections). Heifers were weighed weekly and diets were adjusted on a dry matter basis of the total mixed ration to maintain targeted gain. Treatments were maintained through d 63 of gestation in pregnant heifers. Pregnancy diagnosis and fetal crown-rump length was determined via transrectal ultrasonography on d 35. A total of 103 heifers were confirmed pregnant (replicate 1, n = 37; replicate 2, n = 32; replicate 3, n = 34). Data were analyzed using the MIXED procedures of SAS as a 2 × 2 factorial including the effects of two levels of gain, two levels of OCM treatment, replicate, and their two-way and three-way interactions. There were no three-way interactions between gain × treatment × replicate. However, there was a gain × treatment interaction (P ≤ 0.05), in which fetuses from RES heifers with and without OCM supplementation had reduced CRL compared with fetuses from CON heifers that did not receive OCM (14.15 ± 0.21 mm, 13.88 ± 0.21 mm, 14.84 ± 0.21 mm, respectively). Fetal CRL from OCM supplemented CON heifers was similar (P = 0.06) to all other treatments (14.27 ± 0.21 mm). In conclusion, fetuses from RES heifers exhibited a decreased crown-rump length, and one-carbon metabolite supplementation did not mitigate these effects.