Steven A. Zinn

We hypothesized that maternal overfeeding and restricted feeding during gestation would alter the collagen content, muscle fiber cross-sectional area (CSA), and meat tenderness in offspring. Pregnant ewes were fed 100% (CON), 60% (RES), or 140% (OVER) of their requirements from day 30 of gestation until parturition. Male offspring were necropsied at 282 ± 1.8 days of age. Gene expression and CSA were quantified in the longissimus (LM) and semitendinosus (STN) muscles. The Warner–Bratzler shear force (WBSF) was quantified in LM. Data were analyzed by one-way ANOVA, with diet as a fixed effect. Differences were considered significant at p ≤ 0.05 or a tendency at p ≤ 0.10. Semitendinosus CSA was smaller in OVER and RES than CON rams (p = 0.02). Longissimus CSA was larger in RES than OVER and CON rams (p = 0.002). OVER LM had reduced WBSF compared with CON rams (p = 0.03). Myogenic genes bone morphogenic protein 1 (BMP1) and paired box 7 were greater in RES LM than OVER (p ≤ 0.02). Maternal diet altered the fibrogenic genes fibronectin 1 (p = 0.07), lysyl oxidase (p = 0.07), and collagen 1A1 (COL1A1; p = 0.08) in the LM and COL1A1, COL3A1, and BMP1 (p ≤ 0.09) in the STN. Poor maternal diet during gestation alters muscle and meat characteristics that may impact meat quality.

Mammals are a unique class of animals where the females have mammary glands to produce milk for the sustenance and maternal care of their offspring. The availability of milk allows a high survival rate of the offspring after birth which is crucial after the great maternal investment on offspring development during the intrauterine period. The synthesis, storage and delivery of milk to the offspring requires development of the mammary gland prepartum and the postpartum production of colostrum and milk. However, not all mammals have developed the same strategy to produce milk and nourish their offspring. This issue of Animal Frontiers “Mammalian milk: The elixir of life from maternal care to modern dairy production” focuses on mammary gland development, colostrum production, genetic selection, metabolism, and the evolution of milk production that have enhanced the modern dairy cow and the dairy industry ( Cole et al., 2023; Gross, 2023). The composition of milk differs considerably among species and is perfectly directed to the needs of the respective offspring. Therefore, this issue of Animal frontiers examines lactation in a variety of other species from mice ( Höflich et al., 2023) to marine mammals ( Avery and Zinn, 2023), from livestock [goats ( Castro et al., 2023), horses (Reed and Reiter, 2023), and swine ( Grahofer and Plush, 2023] to humans ( Neville, 2023) and dogs and cats ( Chastant, 2023).

The mechanisms by which fetal programming predisposes offspring to reduced β-cell function later in life are poorly understood. We hypothesized that maternal under- and over-nutrition during gestation would negatively affect offspring pancreas development and alter DNA methylation patterns. Pregnant ewes (n = 78) were fed 100, 60, or 140% of NRC requirements beginning at d 30.2 ± 0.2 of gestation. The fetuses are referred to as CON, RES, and OVER, respectively. Fetal pancreas tissue was collected at d 90 or 135 of gestation or within 24 h of birth. Tissue was preserved for histological (n = 8 to 9 offspring per treatment per time point) and DNA methylation analyses (n = 3 to 4 fetuses per treatment per sex). At d 135, OVER exhibited an increased islet size, reduced islet number, and greater insulin positive area compared with CON (p ≤ 0.03). An increased islet size was also observed at d 135 in RES (p ≤ 0.03) compared with CON. Cellular proliferation was reduced at birth in OVER vs. CON (p = 0.01). In the RES vs. CON females, 62% of the differentially methylated regions (DMRs) were hypomethylated (p ≤ 0.001). In the RES vs. CON males, 93% of the DMRs were hypermethylated (p ≤ 0.001). In OVER, 66 and 80% of the DMRs were hypermethylated in the female and male offspring compared with CON (p ≤ 0.001). In conclusion, changes to maternal diet during pregnancy affects the islet hypertrophy and cellular proliferation of the offspring at early post-natal time points. Additionally, changes in DNA methylation patterns appear to be in a diet-specific and sex-dependent manner.

Poor maternal nutrition can affect the growth and development of offspring, which may lead to negative consequences in adult life. We hypothesized that lambs born to poorly nourished ewes would have reduced growth rate and increased fat deposition, with corresponding changes in the somatotropic axis, and leptin, insulin and glucose concentrations. Ewes (n = 36; 12/treatment) were assigned 1 of 3 diets; 100% (CON), 60% (RES), or 140% (OVER) of NRC requirements for TDN at d 31 of gestation until parturition. One lamb per ewe (n = 35; 11 to 12 per treatment) was used; 18 lambs were euthanized at d 1, and 17 were fed the same diet for 3 mo and then euthanized. Lamb crown rump length (CRL), heart girth, BW, and BCS were measured, and blood samples were collected at d 1 and then at weekly intervals until euthanasia. Averaged from d 1 until 3 mo, lambs from OVER ewes were larger compared with lambs born to CON ewes (BW [16.97 vs. 15.44 kg ± 0.60; P = 0.09], ADG [0.23 vs. 0.21 ± 0.01 kg/d; P = 0.01], and CRL [68.9 vs. 66.1 ± 0.80 cm; P = 0.02]). On a BW basis, heart weight from lambs from RES (0.18 kg ± 0.03; P = 0.03) ewes was greater than that of CON lambs (0.15 kg ± 0.03). Backfat thickness was reduced in RES lambs (0.11 ± 0.06; P ≤ 0.04) compared with CON (0.20 ± 0.06) and OVER (0.26 ± 0.06) lambs. Concentrations of IGF-I at 3 mo and IGFBP-3 from weaning (d 56 of age) to 3 mo of age tended to be greater (P ≤ 0.06) in OVER lambs (334 ± 66 ng/mL and 175 ± 11 arbitrary units [AU], respectively) than CON lambs (149 ± 66 ng/mL and 140 ± 11 AU, respectively). At 3 mo, leptin was greater in OVER lambs compared with RES lambs (1.24 vs. 0.78 ± 0.13 ng/mL; P < 0.05). Over time, average insulin concentrations were greater in OVER and RES lambs than CON lambs (0.49 and 0.49 vs. 0.33 ± 0.05 ng/mL; P ≤ 0.02). However, concentrations of GH, IGFBP-2, glucose, triglycerides, and total cholesterol were not different (P > 0.10) between treatment groups. During in vivo glucose tolerance test, baseline insulin concentrations were 68% and 85% greater (P = 0.01), respectively, in RES and OVER lambs compared with CON lambs. Similarly, the glucose:insulin ratio was greater in RES and OVER lambs compared with CON lambs (P = 0.01). Thus, in this experiment, poor maternal nutrition during gestation influenced body size, organ growth, fat accumulation, and concentrations of IGF-I, IGFBP-3, leptin, and insulin of offspring during the first 3 mo of age.