Prenatal Exposure to Different Nitrogen Supplementation Strategies in Beef Cows Enhances Foetal Growth and Induces Transcriptional Adaptations in Offspring Skeletal Muscle

This study aimed to assess the effects of different nitrogen supplementation strategies during mid-gestation on postnatal performance, skeletal muscle gene expression and morphology and nutritional and metabolic parameters of beef offspring during both the cow-calf and backgrounding phases. Thirty Zebu cows (532 ± 11 kg of body weight [BW]) were used. The following treatments were randomly assigned to cows from 127 ± 17 to 227 ± 17 days of gestation: (1) Control (CON; n = 10): basal diet (corn silage + sugarcane bagasse) and a mineral supplement with urea (60 g/100 kg BW); (2) Rumen-degradable protein (RDP; n = 10): basal diet plus a commercial protein supplement (250 g/100 kg BW) and ground corn (44 g/100 kg BW); and (3) Rumen-undegradable protein (RUP; n = 10): basal diet plus protected soybean meal (3.5 g/kg BW) and a mineral supplement with urea (60 g/100 kg BW). After supplementation, cows were managed as a single group on pasture. Offspring were evaluated during the cow-calf phase, and in a 60-day feedlot backgrounding phase. At the end of the supplementation period (227 days of gestation), cows in the RUP treatment had greater BW compared to those in the CON and RDP treatments (p = 0.01). Near parturition (282 days of gestation), no differences in BW were observed among treatments (p = 0.28). Birth weight was greater in the RUP group compared to the CON and RDP groups (p = 0.04), with no differences between the CON and RDP. No effects of treatment were observed on offspring weaning weight, average daily gain, ultrasound carcass traits, nutrient intake, apparent total tract digestibility, ingestive behaviour or muscle fibre number and histomorphometry (p > 0.05). At 346 ± 31 days of age, RUP offspring exhibited increased expression of skeletal muscle genes, including ACACA, FASN, PPARG, CPT2, IGF1R and COL3A1 compared to the CON group (p ≤ 0.05). Additionally, RUP offspring showed greater expression of ACACA, FABP4, PPARA, SCD1, COL3A1 and IGFR1 compared to RDP offspring (p ≤ 0.04). In conclusion, maternal supplementation with rumen-protected protein during mid-gestation enhances foetal growth and induces beneficial transcriptional adaptations in skeletal muscle compared to non-protein or RDP supplementation strategies, without affecting postnatal growth performance.