Impacts of protein supplementation during late gestation of beef cows on maternal skeletal muscle and liver tissues metabolism.

Since nutritional requirements are increased at the end of gestation to meet the demands of the pregnant uterus, pregnant beef cows are susceptible to mobilization of body reserves (mainly fat and amino acids (AAs)) and to alter the metabolism of nutrients in the liver and muscle to support such demands. The objective of this study was to evaluate the effect of CP supplementation on maternal nutrient metabolism in the late gestation of beef cows grazing a low-quality pasture. Forty-three pregnant Nellore cows gestating male fetuses (average age = 6 years; average weight = 544 kg) at 193 ± 30 (mean ± SD) days (d) of gestation were divided into eight groups (experimental units, with four to five cows each). Treatments were (1) control (CON, n = 4): pasture-based (PB) diet without CP supplementation and (2) supplemented (SUP, n = 4): PB diet daily supplemented with 2 g/kg of BW of a 43.5% CP supplement. Liver and skeletal muscle biopsies were performed at 265 days of gestation and samples were collected for mRNA expression. On day 280 of gestation, blood samples were collected to assess plasma levels of AA. The CON-fed cows tended to have greater (P = 0.057) total circulating AA than SUP-fed cows. The circulating glycogenic AA was greater (P = 0.035) in CON than in SUP cows. CON cows was greater for histidine (P = 0.015), methionine (P = 0.007) and alanine (P = 0.036) than SUP cows. The CON- and SUP-fed showed no differences for gluconeogenesis, fatty acid transport and signaling axis markers in the liver. The mRNA expression of markers for skeletal muscle synthesis, p7056k (P = 0.060) and GSK3B (P = 0.096), tended to be greater in cows from CON than SUP group. No differences were found for mRNA expression of markers for skeletal muscle degradation. We conclude that CP supplementation to CP-restricted late-pregnant beef cows reduces the maternal tissue mobilization and changes the profile of plasma circulating AA and the mRNA expression of markers for the synthesis of skeletal muscle tissue.

Foetal development of skeletal muscle in bovines as a function of maternal nutrition, foetal sex and gestational age.

To determine the effects of maternal nutrition on modifications of foetal development of the skeletal muscle and possible increase in the potential of skeletal muscle growth in cattle, gestating cows were either fed 190% NRC recommendations (overnourished; ON) or 100% NRC recommendation (control; CO). Interaction between maternal nutrition (MN) and the foetal sex (FS) was also investigated. Foetuses were necropsied at four different time points throughout gestation (139, 199, 241 and 268 days of gestation) to assess the mRNA expression of myogenic, adipogenic and fibrogenic markers in skeletal muscle. Phenotypic indicators of the development of skeletal muscle fibres, intramuscular lipogenesis and collagen development were also evaluated. Modifications in mRNA expression of skeletal muscle of foetuses were observed in function of MN and FS despite the lack of effect of MN and FS on foetal weight at necropsy. Maternal ON increased the mRNA expression of the myogenic marker Cadherin-associated protein, beta 1 (CTNNB1) and adipogenic markers Peroxissome proliferator-activated receptor gamma (PPARG) and Zinc finger protein 423 (ZNF423) at midgestation. However, no differences on foetal skeletal muscle development were observed between treatments at late gestation indicating that a compensatory development may have occurred on CO foetuses making the effect of MN on skeletal muscle development not significant at late gestation. Moreover, our data have shown an evidence of sexual dimorphism during foetal stage with a greater skeletal muscle development in male than in female foetuses. In conclusion, providing a higher nutritional level to pregnant cows changes the trajectory of the development of skeletal muscle during midgestation, but apparently does not change the potential of post-natal growth of muscle mass of the offspring, as no differences in skeletal muscle development were observed in late gestation.

Intestinal development of bovine foetuses during gestation is affected by foetal sex and maternal nutrition.

We aimed to evaluate the effects of maternal nutrition (MN) and foetal sex on the intestinal development of bovine foetuses throughout different days of gestation (DG). Forty-four multiparous, dry Holstein × Gyr cows with average initial body weight of 480 ± 10 kg were fed the same diet of either restricted feeding at 1.15% of body weight (CO, n = 24) or fed ad libitum (overnourished, ON, n = 20). Six cows from CO group and five cows from ON group were slaughtered at 139, 199, 241 and 268 DG, and foetuses were necropsied to evaluate the intestinal development. The mass, length and density of foetal intestines were not affected by MN (p ≥ 0.260). An interaction between MN and DG was observed for the villi length of jejunum (p = 0.006) and ileum (p < 0.001). Villi length of jejunum and ileum was higher (p < 0.10) in foetuses from ON-fed cows than in foetuses from CO-fed cows at 139 DG. However, at 199 DG, the villi length of jejunum and ileum of foetuses from CO-fed cows was higher than in foetuses from ON-fed cows. Despite these differences, MN did not affect the villi length of jejunum and ileum at 268 DG (p > 0.10). Female foetuses had greater small intestine mass (p = 0.093), large intestine mass (p = 0.022), small intestine mass in proportion to body mass (p = 0.017) and large intestine mass in proportion to body mass (p < 0.001) than male foetuses. Female foetuses had also longer small intestine (p = 0.077) and greater small intestine density (p = 0.021) and villi length of jejunum (p = 0.001) and ileum (p = 0.010) than males. We conclude that MN affects the pathway for the development of foetal villi length throughout the gestation in bovine foetuses without changing the final villi length. Female foetuses had higher intestinal mass, density and villi length than males during the foetal phase in bovines.

Effects of day of gestation and feeding regimen in Holstein × Gyr cows: II. Maternal and fetal visceral organ mass.

This study investigated the influence of day of gestation (DG) and feeding regimens (FR) on maternal and fetal visceral organ mass in Holstein × Gyr cows. Forty-four pregnant multiparous Holstein × Gyr cows with an average initial body weight of 480±10.1 kg and an average initial age of 5±0.5 yr were allocated to 1 of 2 FR: ad libitum (AL; n=20) or maintenance level (ML; n=24). Maintenance level was considered to be 1.15% of body weight (dry matter basis) and met 100% of the energy requirements; AL provided 190% of the total net energy requirements. Cows were individually fed a corn silage and concentrate-based diet composed of 93% roughage and 7% concentrate (dry matter basis) as a total mixed ration twice daily. Pregnant cows were slaughtered at 4 DG: 139 (n=11), 199 (n=11), 241 (n=11), and 268 (n=11) d, which was followed by necropsy. Mass of heart, liver, and gastrointestinal tract was heavier in AL- than in ML-fed cows. Mammary gland mass was heavier in AL- than in ML-fed cows, and the heaviest mass was observed at 268 d of gestation. Feeding regimen did not influence fetal body weight in this study. The majority of the visceral organ masses were similar in fetuses from cows fed AL or ML. These data indicate that maternal feed restriction does not affect the development of most fetal organs or fetal development; however, some maternal organs are affected by the FR provided. Moreover, the negative effect on mammary gland mass caused by ML feeding will probably not affect the subsequent lactation because the crude protein concentration in the mammary gland increased with ML feeding. However, we suggest that the AL diet in pregnant dry cows should be provided with caution because the amount of fat in the mammary gland increased at 268 d of gestation.

Effects of day of gestation and feeding regimen in Holstein × Gyr cows: I. Apparent total-tract digestibility, nitrogen balance, and fat deposition.

This study investigated how feeding regimen (FR) alters apparent total-tract digestibility, performance, N balance, excretion of purine derivatives, and fat deposition in Holstein × Gyr cows at different days of gestation (DG). Forty-four pregnant multiparous Holstein × Gyr cows with an average initial body weight of 480±10.1 kg and an initial age of 5±0.5 yr old were allocated to 1 of 2 FR: ad libitum (AL; n=20) and maintenance level (ML; n=24). Maintenance level was considered to be 1.15% of body weight on a dry matter (DM) basis and met 100% of the energy requirements, whereas AL provided 190% of total net energy requirements. Data for hot and cold carcass dressing, fat deposition, average daily gain, empty body gain, and average daily gain without the gravid uterus were analyzed as a 4×2 factorial design. Intake, apparent total-tract digestibility, N balance, urinary concentration of urea, and purine derivatives data were analyzed as repeated measurements taken over the 28-d period (122, 150, 178, 206, 234, and 262 d of gestation). Cows were individually fed a corn silage-concentrate based diet composed of 93% roughage and 7% concentrate (DM basis) as a total mixed ration. Pregnant cows were slaughtered on 4 different DG: 139 (n=11), 199 (n=11), 241 (n=11), and 268 d (n=11). Overall, DM intake decreased as DG increased. This decrease observed in DM intake may be associated with the reduction in ruminal volume caused by the rapid increase in fetal size during late gestation. We observed an interaction for DM and organic matter apparent total-tract digestibility between FR and DG; at 150, 178, and 206 d of gestation, ML-fed cows had greater DM and organic matter apparent total-tract digestibility values than AL-fed cows. Rib fat thickness, mesentery, and kidney, pelvic, and heart fat were greater in AL-fed than in ML-fed cows at all DG, with the exception of rib fat thickness on d 139. Ad libitum-fed cows excreted more N in their feces and urine compared with ML-fed cows. Pregnant cows that were fed at maintenance had greater digestibility during some DG, excreted less N in feces and less N and urea in urine, and deposited less fat in the body. We therefore recommend ML (1.15% of body weight with 93% of roughage) as a FR for pregnant dry cows; however, during the last month of gestation, AL seems to be the most appropriate FR to avoid loss of body weight.

Effects of day of gestation and feeding regimen in Holstein × Gyr cows: III. Placental adaptations and placentome gene expression.

This study investigated the influence of day of gestation (DG) and feeding regimens (FR) on the expression of genes responsible for placenta development, nutrient transfer, and angiogenic factors in Holstein × Gyr cows. Forty pregnant multiparous Holstein × Gyr cows with an average initial body weight of 482±10.8kg and an initial age of 5±0.8 yr were allocated to 1 of 2 FR: ad libitum (AL; n=20) or maintenance level (ML; n=20). Maintenance level was considered to be 1.15% of body weight (dry matter basis) and met 100% of the net energy requirements and AL provided 190% of the total net energy requirements. Cows were slaughtered at 4 DG: 139, 199, 241, and 268d. After the cows were slaughtered, the placenta and uterus were separated and weighed. Caruncles and cotyledons were individually separated, counted, and weighed. Placenta expressed as kilograms and grams per kilogram of empty body weight (EBW) was heavier in ML- than in AL-fed cows at 268d of gestation. Placenta expressed as kilograms and grams per kilogram of EBW was the lightest at 139d of gestation, and the greatest mass was observed at 268d in ML-fed cows. However, in AL-fed cows, the heaviest placenta expressed as grams per kilogram of EBW was observed from 199d of gestation. Placentomes expressed as grams per kilogram of EBW were heavier in ML-fed cows during gestation, and the number of placentomes was greater in ML-fed cows at 268d of gestation. We observed that IGFR1 and IGFR2 were involved in placenta adaptations when ML was provided, as their expression in placentome cells was greater in ML-fed cows at 268d of gestation. The genes responsible for angiogenesis were also greater in ML-fed cows: VEGFA, GUCY1B3, HIFA, FGF2, and NOS3 were altered by FR and DG interaction and they were greater in ML-fed cows at 268d of gestation. In addition, VEGFB and ANGPT2 did not show interactions between FR and DG, but they were greater in ML-fed cows. Thus, we suggest that the placenta from an ML-fed cow develops adaptations to the reduced nutrient supply by altering its structure and gene expression, thereby developing mechanisms for potential increased nutrient transfer efficiency to the fetus.