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This study aimed to assess the impact of protein supplementation and its interaction with calf sex (CS) on the performance, metabolism and physiology of pregnant beef cows. Fifty‐two multiparous Zebu beef cows carrying female (n = 22) and male (n = 30) fetuses were used. Cows were individually housed from day 100 to 200 of gestation and randomly assigned to restricted (RES, n = 26) or supplemented (SUP, n = 26) groups. The RES cows were ad libitum fed a basal diet (corn silage + sugarcane bagasse + mineral mixture), achieving 5.5% crude protein (CP), while SUP cows received the same basal diet plus a protein supplement (40% CP, at 3.5 g/kg of body weight). All cows were fed the same diet during late gestation. Differences were declared at p < 0.05. No significant interaction between maternal nutrition and calf sex was found for maternal outcomes (p ≥ 0.34). The SUP treatment increased the total dry matter (DM) intake (p ≤ 0.01) by 32% and 19% at mid‐ and late‐gestation respectively. The total tract digestibility of all diet components was improved by SUP treatment at day 200 of gestation (p ≤ 0.02), as well as the ruminal microbial CP production (p ≤ 0.01). The SUP treatment increased (p ≤ 0.03) the cows' body score condition, ribeye area, the average daily gain (ADG) of pregnant components (PREG; i.e., weight accretion of cows caused by pregnancy) and the ADG of maternal tissues (i.e., weight accretion discounting the gain related to gestation) in the mid‐gestation. The SUP cows exhibited a lower maternal ADG (p < 0.01) compared to RES cows in late pregnancy. There was a 24% additional gain (p < 0.01) in the PREG components for SUP cows during late gestation, which in turn improved the calf birthweight (p = 0.05). The uterine arterial resistance and pulsatility indexes (p ≤ 0.01) at mid‐gestation were greater for RES cows. In conclusion, protein supplementation during mid‐gestation is an effective practice for improving maternal performance, growth of the gravid uterus and the offspring's birth weight. [ABSTRACT FROM AUTHOR]

Simple Summary: It is well known that intrauterine growth-restricted offspring present physiologic and metabolic modifications later in life. Therefore, understanding the impact of the maternal nutritional plane on feed intake patterns may lead to new feeding strategies to improve the feed efficiency and performance of beef cattle. In this study, we have evaluated the effect of maternal protein supplementation (PS) during mid-gestation and its interaction with the offspring's sex on the voluntary feed intake and nutrient use of the progeny. Our results show that PS during mid-gestation increases performance and improves the voluntary feed intake of the offspring. Prenatal PS induced favorable changes in the feeding behavior, in which CON offspring spent more time per day eating supplements and ruminating but spent fewer periods in idleness. Maternal protein restriction demonstrated positive effects on the ability to digest the nutrients of male calves. In summary, our data show that PS alters the gain potential, indirectly demonstrating an increase in their nutritional requirements. In contrast, protein restriction causes a compensatory mechanism on the offspring's nutrient useability in a sex-dependent manner, increasing the total tract digestibility of nutrients in response to a growth-restriction exposure during intrauterine development. This study aimed to assess the effects of maternal protein supplementation and offspring sex (OS) on the intake parameters of the offspring. Forty-three Tabapuã cows were randomly allocated in the following treatments: protein supplementation (PS) during days 100–200 of gestation (RES, 5.5% total crude protein (CP), n = 2, or CON, 10% total CP, n = 19) and OS (females, n = 20; males, n = 23). The offspring were evaluated during the cow–calf (0–210 days), backgrounding (255–320 days), growing 1 (321–381 days), and growing 2 (382–445 days) phases. The CON offspring tended to present higher dry matter intake (DMI) at weaning (p = 0.06). The CON males presented lower digestibility of major diet components in the growing 2 phase (p ≤ 0.02). The CON offspring spent 52% more time per day eating supplements at 100 days and 17% less time in idleness at 210 days. The CON males spent 15 min more per day ruminating than RES males in the feedlot phase (p = 0.01). We concluded that protein supplementation over gestation alters the offspring feed intake pattern as a whole, while protein restriction promotes compensatory responses on nutrient digestibility in males. [ABSTRACT FROM AUTHOR]