Effect of heat stress on ingestive, digestive, ruminal and physiological parameters of Nellore cattle feeding low- or high-energy diets

• Published in: Livestock science 2021-10, Vol.252, p.104676, Article 104676
• Main Authors: Meneses, Javier Andrés Moreno, de Sá, Olavo Augusto Arquimed Lopes, Coelho, Carlos Filipe, Pereira, Rodrigo Norberto, Batista, Erick Darlisson, Ladeira, Marcio Machado, Casagrande, Daniel Rume, Gionbelli, Mateus Pies
• Format: Article
• Language: English
• Subjects: Digestion rate; Pair-feeding; Physiology; Ruminal parameters; Water intake; Zebu cattle
• ISSN: 1871-1413; 1878-0490
• DOI: 10.1016/j.livsci.2021.104676

•Heat stress (HS) affected the ingestive behavior of Nellore heifers fed with tropical diets, leading to a 16% reduction in DMI and a 25% increase in water intake.•HS reduced energy intake in Nellore heifers fed low- and high-energy diets, respectively.•Ruminal and intestinal digestibilities of dry matter, organic matter and crude protein were affected by HS in Zebu heifers.•Nellore heifers under HS showed higher ruminal temperature values (0.26 Cᵒ), decrease of about 5 % in ruminal pH and showed 10 % less total VFA than those in thermoneutral conditions.•Body temperature indicated that the HS caused a significant strain in the animal thermal homeostatic mechanisms. This study aimed to verify the effects of heat stress and dietary energy level on dry matter intake (DMI), water intake, total and partial ruminal and intestinal digestibilities, ruminal characteristics, physiological and digestive behavioral parameters in beef cattle. Six ruminally cannulated Nellore heifers (280 ± 12 kg) were used in a 6 × 6 Latin square experiment with six treatments and six periods of 21 days. The treatments consisted of a 2 × 2 + 2 factorial arrangement, with two temperatures during the day (thermoneutrality, TN: 24°C; and heat stress, HS: 34°C), two dietary energy levels (low- or high-energy concentration) and two additional treatments of animals maintained in TN conditions but pair-fed with the heifers in HS (PFTN). The HS decreased DM intake by about 16% and increase water intake by 25.5% respectively (P ≤ 0.01). Heifers maintained in TN and fed high-energy diet showed 17.3 and 14.3% greater ruminal dry matter (DM) and organic matter (OM) digestibilities compared to their HS counterparts. The DM intake rate (ki, h−1) and digestion rates (kd, h−1) were affected by environment and dietary energy level (P ≤ 0.01), which heifers in HS having lower ki and kd. Heifers in HS presented lower pH and greater ruminal temperature values (P ≤ 0.01). When PFTN treatments were compared vs. HS, there was a significant effect of temperature on acetic acid. Heifers that underwent HS showed 14 % less acetic acid. The ocular temperature, body temperature, heart rate, and respiratory rate were greater in HS heifers (P ≤ 0.01) than in TN. Heifers with low energy level diets showed 33% greater values of rumination time (P = 0.05) when compared to high energy levels independent of the temperatures. We concluded that adaptive response to heat seems important factors responsible for the alterati