Maternal nutrition during gestation and early life events impact offspring development throughout life, in a phenomenon known as developmental programming. The Barker hypothesis explains that undernutrition during specific developmental periods in pregnancy can create a scenario of pre- and post-partum metabolic mismatch (Hales and Barker, 2001). Metabolic mismatch occurs when offspring of undernourished cows are ‘programed’ to expect limited nutritional resources pre-partum, but postnatally consume diets that meet or exceeded nutritional requirements, which can influence fat and muscle development (Godfrey et al., 2007). In late gestation, fetal growth exponentially increases (Prior and Laster, 1979), additionally, offspring muscle fibres are maturing at this time, and intramuscular adipocytes (which accumulate fat throughout life and leads to marbling) begin to form (Du et al., 2010). Therefore, dietary manipulations specifically during late gestation may have a lasting impact on offspring development and meat quality. Previous studies show that maternal crude protein supplementation in late gestation influences steer offspring performance in the feedlot and carcass quality (Stalker et al., 2007; Larson et al., 2009). However, minimal research has been conducted to assess how maternal metabolizable protein (MP) alone influences steer offspring throughout life. Hare et al. (2019) observed that feeding cows 133% MP requirements did not impact gene expression (insulin-like growth factors (IGFs), insulin receptor (INSR), myogenic differentiation (MYOD), myogenin (MYOG)) in muscle from heifer calves at weaning. However, further examination is required to determine how maternal MP level influences steers in the feedlot. Methionine is an essential amino acid and is involved in many metabolic pathways in the body (Jacometo et al., 2017) and supplementation of methionine in maternal diets can alter offspring gene expression (Jacometo et al., 2017; Zhang, 2018). However, the majority of research investigating the impact of methionine on offspring have only followed dairy (Batistel et al., 2017; Alharthi et al., 2018) and beef (Clements et al., 2017; Moriel et al., 2020) calves from birth until weaning at 8 weeks and 6 months of age, respectively. Therefore, research to determine how maternal methionine supplementation impacts offspring development past weaning is warranted. The main objectives of this study were to assess how maternal metabolizable protein concentration and rumen-protected methionine supplementation in late gestation impacts beef steer offspring development in the feedlot, and carcass quality. To gain further insight into potential mechanisms involved in offspring development, the expression of genes associated with growth, muscle development, and fat accumulation were assessed.
In a research-intensive study (Exp. 1), 138 Angus cross cows were randomly assigned to one of three protein treatments, 90, 100, or 110% of metabolizable protein (MP) requirements. Half of each group was received pellets containing nine g/d of rumen-protected methionine (RPM, Smartamine®M), or no additional pellets (NoRPM). These diets were formulated to be isocaloric through the addition of palm fat (cow performance data previously reported by Collins et al., 2019). In a second study (Exp. 2) to evaluate how maternal nutrition impacts offspring in an industry applied setting, 67 Angus cross cows received 0.75 kg/head/d of pellet supplying 12 g/d of rumen-protected methionine (MET, Smartamine®M), or a similar pellet without additional methionine (CON). Maternal diets for both studies were fed for the last eight weeks of gestation. After weaning, steer offspring (Exp. 1 n=55, Exp. 2 n=34) were managed as a group in the feedlot and fed common diets formulated to meet or exceed the requirements for growing and finishing beef steers (NASEM, 2016). Body weights were recorded every 14 days, blood samples were collected three days before slaughter, and carcasses were graded by a certified grader 24 hours after slaughter. Samples of neck muscle (Sternomandibularis muscle) were collected at slaughter for mRNA expression of genes associated with growth (IGFs, INSR and pyruvate kinase (PKM)) and the development of muscle (MYOD and MYOG) and fat (peroxisome proliferator activated receptor gamma (PPARG)) using real-time PCR (as described in Paradis et al., 2017; Hare et al., 2019). Data from the research-intensive and industry applied studies were analyzed separately using PROC GLIMMIX in SAS (University Edition, Version 9.4; SAS Institute Inc., Cary, NC) with maternal dietary treatments as the fixed effects, and steer and pen as the random effect.
Results and Discussion
Exp. 1: Steers from cows fed below or at MP requirements had higher (90%: 0.34 mmol/L, 100%: 0.39 mmol/L, 110%: 0.21 mmol/L; SEM = 0.041, P = 0.01) circulating non-esterified fatty acid (NEFA) concentrations, which may be indicative of increased fat mobilization (Webb et al., 1969). Steers from cows fed at 90% MP also had higher (90%: 15.5 mm, 100%: 14.7 mm, 110%: 11.8 mm; SEM = 1.11, P = 0.04) carcass grade fat. These results support metabolic mismatch theory, in which undernutrition during gestation followed by diets that meet requirements postnatally increases fat development (Hales and Barker, 2001; Godfrey et al., 2007). Steers from cows fed over MP requirements had increased expression of MYOG (90%: 0.72, 100%: 0.94, 110%: 1.00; SEM = 0.083, P = 0.02), which is involved in muscle development (Paradis et al., 2017). Maternal MP level did not influence any other genes associated with growth (P > 0.09), fat (P = 0.30), or muscle (P = 0.57) development. Maternal methionine supplementation reduced the expression of PKM (RPM: 0.81, NoRPM: 1.16; SEM = 0.092, P = 0.01) in steer offspring muscle.
Exp. 2: Pyruvate kinase expression in offspring from methionine supplemented cows in the industry applied study had a higher (MET: 1.98, CON: 1.35; SEM = 0.221, P = 0.05) expression of PKM and was opposite of the effect in Exp. 1. This difference could be due to maternal management practices, as cows from the industry applied study had ad libitum access to their feed and dams from Exp. 1 feed intake was controlled. Steer offspring from MET cows also had consistently heavier body weight (P ≤ 0.02); which may be reflective of increased PKM expression, which is associated with tissue growth (Hamelin et al., 2006) and muscle development (Lametsch et al., 2006). Additionally, steers from MET cows had increased (MET: 1.82, CON: 1.20; SEM = 0.190, P = 0.02) expression of MYOD which is also involved in muscle development (Paradis et al., 2017).
These studies show that maternal nutrition in late gestation influences beef steer offspring fat and muscle development. Feeding cows below MP requirements in late gestation, followed by diets that met requirements postnatally, influenced steer offspring fat development, which supports metabolic mismatch of the Barker hypothesis. Maternal nutrition in late gestation may prove to be a promising management opportunity to improve offspring development, carcass quality, and may lead to more AAA Canadian steaks.
We would like to thank the Elora Beef Research Centre, New Liskeard Agricultural Research Station, and University of Guelph Meat Lab staff, as well as all laboratory technicians for their assistance in this project. We would also like to thank the Natural Sciences and Engineering Research Council of Canada, Agriculture and Agri-Food Canada, and Beef Farmers of Ontario for their funding support.
Presented at the 2021 Animal Nutrition Conference of Canada. For information on the next edition, click here.