Influence of Maternal Protein Restriction in Primiparous Heifers During Mid- And/Or Late Gestation on Dam Performance and Progeny Growth, Carcass Characteristics, and Gene Expression

Effect of nutrient status in gestating beef cows has been shown to impact dam performance and may affect developmental processes in the fetus that could influence offspring throughout their lives. One hundred eight Angus × Simmental heifers were utilized in a randomized complete block design with control (CON = slightly exceeding MP requirements) and restricted (R = approximately 80% of MP requirements) treatments applied during mid- and/or late gestation. Diets were formulated to be isocaloric and meet net energy requirements. Dam performance measures were collected at the beginning and end of each gestation period. In a mid-gestation treatment × time interaction, R heifers lost BW and LM area (P \u3c 0.05), and % IMF tended (P \u3c 0.10) to decrease compared to CON heifers. Heifers restricted in late gestation gained less BW and lost BCS and LM area compared to CON heifers (P \u3c 0.05). Dietary treatment did not affect milk production or subsequent reproductive performance (P \u3e 0.05). Progeny were evaluated for growth performance from birth through harvest. Gene expression in longissimus dorsi muscle was evaluated at birth and before harvest for a subset of calves. There were no differences due to maternal nutritional treatments for calf birth, weaning, feedlot entry, or harvest BW (P \u3e 0.10). There were no differences in DMI, ADG, or the majority of carcass characteristics (P \u3e 0.10); however, LM area was increased in progeny from dams restricted in late gestation (P = 0.04). This was not significant when adjusted using HCW as a covariate (P \u3e 0.10). Maternal MP restriction throughout mid- and late gestation (R-R) or in late gestation only (CON-R) down-regulated (P \u3c 0.05) genes involved in muscle tissue development compared to CON-CON progeny at birth. Prior to harvest, progeny restricted in late gestation only (CON-R) had decreased expression (P \u3c 0.05) of genes related to muscle development compared to progeny restricted in mid-gestation (R-CON) or throughout gestation (R-R). Despite differences in dam performance and gene expression of progeny, it appeared that offspring were able to recover from moderate MP restriction imposed during gestation