**1. Introduction**

Recent advances in fetal programming research indicate that altering maternal nutrition during the fetal stage can result in altered offspring productivity measures, including growth, feed intake, feed efficiency, muscle development, and meat quality [1]. Within the first two months of conception in the ruminant, development of adipocytes (fat tissue) and fibroblasts (connective tissue) occur along with development of skeletal muscle cells, all of which are primarily derived from mesenchymal stem cells [2].

Development of intramuscular fat, or marbling, is of great economic importance to the U.S. beef industry. Adipogenesis is initiated around the fourth month of gestation, partially overlapping with the second wave of myogenesis [2]. This stage of development represents an opportunity for maternal nutrition to positively or negatively affect stem cell differentiation [2]. Since the number of mesenchymal stem cells decrease as cattle

**Citation:** Gubbels, E.R.; Block, J.J.; Salverson, R.R.; Harty, A.A.; Rusche, W.C.; Wright, C.L.; Cammack, K.M.; Smith, Z.K.; Grubbs, J.K.; Underwood, K.R.; et al. Influence of Maternal Carbohydrate Source (Concentrate-Based vs. Forage-Based) on Growth Performance, Carcass Characteristics, and Meat Quality of Progeny. *Foods* **2021**, *10*, 2056. https://doi.org/10.3390/ foods10092056

Academic Editors: Benjamin W. B. Holman and Eric Nanthan Ponnampalam

Received: 29 June 2021 Accepted: 27 August 2021 Published: 31 August 2021

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**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

mature, strategies to increase marbling during early life could be advantageous to improving meat quality. After 250 days of age, marbling is primarily enhanced only through the growth of preexisting adipocytes and nutritional influences have little impact on adipocyte development [3]. Further, different regulatory processes control fatty acid synthesis in intramuscular and subcutaneous adipose tissue, indicating that it may be possible to increase marbling without proportional increases in backfat that could negatively impact yield grades [4]. Thus, the fetal stage may be of key importance to programming carcass quality.

Volatile fatty acids (VFA) are the main products of the digestion of feed by bacteria in the rumen, provide a majority of the energy required by ruminants, and serve as substrates for synthesis of glucose and fat [5,6]. Major VFA produced by rumen microorganisms include acetate, propionate, and butyrate [6]. Various dietary carbohydrates ferment in the rumen to yield differing proportions of specific short- and long-chain fatty acids. Forage-based diets result in VFA composition of approximately 65 to 70% acetate, 15 to 25% propionate, and 5 to 10% butyrate in cattle [7]. Grain-based diets high in readily fermentable carbohydrate (starch) reduce acetate by 10 to 15% and increase propionate by 20 to 25% [7]. Propionate is the only VFA that contributes directly to the net synthesis of glucose, which is a major energy substrate utilized by uterine and placental tissues for fetal growth [5]. Although ruminal VFA production in gestating cows was not determined in the present study, it is plausible that diets based on nonstructural carbohydrates (starch), found in concentrate-based diets, rather than structural carbohydrates (fiber), found in forage-based diets, could influence fetal development and subsequent composition of the developing calf by way of altered VFA production profiles.

From a production perspective, management decisions made in response to drought, availability of feedstuffs, or cost of feedstuffs can alter the gestational environment, potentially leading to changes in fetal development. Previous literature has shown that providing first-calf heifers and mature cows with a high-energy diet 100 d prepartum increased body weight before parturition and calf birth weight [8]. In the study by Corah et al. [8] subsequent weaning weight was heavier for calves from cows consuming the high-energy diet. However, it has been reported feeding corn to dams in late pregnancy resulted in offspring with reduced marbling scores, a tendency towards reduced intramuscular fat percentage, and more carcasses grading United States Department of Agriculture (USDA) Select compared to offspring from hay-fed cows [9]. Because fetal adipocyte differentiation and growth is initiated during mid-gestation, it is possible that different responses would be observed if maternal dietary treatments had been implemented earlier. Based on these results, there may be differences in nutrient utilization and performance of offspring from cows fed forage or concentrate-based diets. We hypothesized that variations in the proportion of volatile fatty acids produced in the rumen of the gestating cow caused by differing dietary carbohydrate sources during mid- and late- gestation would differentially influence fetal development and offspring composition, leading to alterations in performance and meat quality of offspring. The objective of this study was to investigate the effects of maternal prepartum dietary carbohydrate source (forage- vs. concentrate-based) during mid- and late-gestation on growth performance, carcass characteristics, and meat quality of offspring.
