Production and physiology of pregnant beef cows supplemented with ruminally degradable or undegradable protein under low protein basal diets during mid-gestation

Abstract

Most of the breeding herd in Brazil is managed in extensive pasture systems, where the breeding season is planned in the spring and, therefore, the second half of gestation coincides with the dry season. Consequently, poor quality of forage can lead to a reduction in protein intake and restriction of nutrients to the dam. Thus, our objective was to evaluate the effect of protein supplementation via rumen degradable protein (RDP) based supplement or via rumen undegradable protein (RUP) based supplement, which one of the main amino acids is arginine, compared to a control treatment commonly used in practice, for pregnant cows feeding on a poor basal diet in the midgestation. Thirty Tabapuã beef cows with an average weight of 532 ± 11 kg and 6 ± 0.5 years were randomly assigned to three groups with different dietary treatments from 127 ± 17 days of gestation, lasting 100 days during this feeding period. All cows were fed a single basal diet composed of whole plant corn silage and sugarcane bagasse. Control treatment cows received a nitrogenous mineral supplement (CON; estimated 7.0% CP in the diet), while, cows supplemented with RDP supplement, received a protein commercial supplement (RDP; estimated 10.0% CP in the diet), or a rumen undegradable protein supplement (RUP; estimated 15.0% CP in the diet). Cows fed RUP had higher body weight at the end of the supplementation period (at day 227 of gestation) compared to RDP and CON cows (P ≤ 0.04). Cows fed with RDP or RUP lost 0.163 and 0.174 kg/day, respectively, while CON dams gained 0.360 kg/day during the prepartum period (P = 0.04). On the other hand, in the lactation phase (between days 55 to 200), cows fed RUP during mid-gestation had an average daily gain (ADG) of 0.159 kg/day, greater than the CON and RDP groups lost 0.060 and 0.078 kg/day, respectively (P < 0.01). When the total performance of the cows (from the beginning of the supplementation period until weaning, ~ a total production cycle) was evaluated, the dams fed with RUP were the only ones with positive values in the total ADG (0.047 kg/day), while the treatments CON and RDP lost weight (0.019 and 0.057 kg/day, respectively) (P = 0.05). The Rib eye area (REA) in RUP cows at the end of the supplementation period was ~15.6 and ~24.0 cm2 greater than RDP and CON cows, respectively (P < 0.01). The calf's body weight at birth tended to be higher when the dams were fed RUP compared to CON and RDP cows (P = 0.09). Cows in the CON group had higher pulsatility index (PI) at 217 days of gestation compared to RDP and RUP cows (P = 0.02). Therefore, supplementation with RUP during mid-gestation, reduces the mobilization of maternal body tissues, improving the performance of cows and consequently the calf's body weight at birth.