RESUMO
This research communication addresses the hypothesis that, during the summer in the subtropics, natural tree shade helps to improve milk functional characteristics such as stability and acidity. Sixteen Holstein lactating cows were enrolled. The study consisted of three periods (pre-stress, heat stress and post-stress) based on allocating grazing cows into two treatments (with and without access to shade during the Heat Stress period). Overall THI during the trial was (mean ± se) 76.0 ± 3.4. Access to shade prevented the heat stress-related decrease in milk stability both in the ethanol and in the coagulation time test, as well as maintained milk acidity within an acceptable range (14 to 18°D).
Assuntos
Criação de Animais Domésticos , Indústria de Laticínios , Meio Ambiente , Lactação/fisiologia , Leite/química , Árvores , Animais , Bovinos , Doenças dos Bovinos/prevenção & controle , Feminino , Transtornos de Estresse por Calor/prevenção & controle , Transtornos de Estresse por Calor/veterináriaRESUMO
The objective of this study was to explore the impact of thermal stress on hormonal level and antioxidant activity in goats during various phases of the estrous cycle in the Egyptian summer. Forty cycling does were allocated to two groups (20 animals each) divided by season (mild/hot). Daily meteorological, rectal temperature, and respiratory rate data were recorded in the two seasons. The estrous cycle of the goats was synchronized by two intramuscular injections of 5 mg of prostaglandin F2α (PGF2α) at 11-day intervals. Blood samples were collected every two days and the levels of total antioxidant, malondialdehyde, and ß-carotene were estimated. Total protein, albumin, cholesterol, triglycerides, progesterone, and thyroxine (T4) hormones were additionally measured in the serum of the collected samples. Under hot circumstances, both rectal temperature and respiratory rate increased considerably, with significant variation during the different stages of the estrous cycle. On the other hand, serum level of total protein, albumin, cholesterol, and triglycerides reduced significantly in animals in the hot environment, particularly during the luteal period of the estrous cycle (IV). During the Egyptian hot summer, the serum level of progesterone and T4 hormones declined in phases II and IV of the estrous cycle for progesterone and T4, respectively. Moreover, the serum content of all oxidative stress markers tested (total antioxidant, ß-carotene, and malondialdehyde) decreased considerably, especially in estrous cycle phase II in the hot environment. The Egyptian environmental conditions have detrimental effects on some antioxidant agents and some biochemical parameters throughout the estrous cycle of goats.(AU)