کد مقاله : GGR-002

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M. Hossein Yazdi, H. Amanlou, H.R.Mirzaei-Alamouti, M.T. Harkinezhad, A. Nabipour, E. Mahjoubi, N.Aghaziarati, G.R. Noori, L.H. Baumgard

Glucose appears to be a preferred systemic fuel during heat stress (HS) in a variety of species. Increasing the dietary grain contact can enhance the post-absorptive carbohydrate status, but providing excessive fermentable starch can cause rumen disorders and this is especially true during HS. Current study objectives were to evaluate the effects of a glycerol based supplemental product on growth and metabolic variables in Holstein bull calves during controlled HS. Before the star of the experiment, bull calves (n=14; 163.6 ± 30.1 kg body weight) were subjected to thermal neutral conditions [26.5± 3.4°C and a temperature – humidity index (THI) of 70.4 ± 2.8] for 7 d (period 1; P1). During this period, productive parameters as well as blood metabolites were measured and used as covariates for the subsequent HS period.

Following P1, a cyclical HS pattern was implemented for 21 d (P2) where daily ambient temperatures ranged from 29.1 to 39.7°C and the THL was ˃ 74 for 24h/d and ˃ 83 for at least 14 h/d. during P2, half of the HS calves (n=7) received a control diet (CON) and the other half received the control diet supplemented with a product (300 g/d) containing gluconeogenic precursors (GLU). Throughout each period respiration rate, rectal temperature and skin temperature at the shoulder and rump were recorded at 0600, 1100 and 1500 h daily. Blood samples were obtained prior and 4 h post the a.m. feeding during both periods. Although HS markedly reduced DMI (18%) and growth as expected, supplemental GLU did not affect body weight gain. Supplemental GLU decreased the shoulder temperature at 0600 and 1500 h (P˂ 0.01) , and decreased respiratory rate at 1500 h (P˂ 0.02). Feeding GLU did not affect blood urea nitrogen (BUN), glucose or nonesterified fatty acids (NEFA) concentrations, but increased circulating insulin prior to the a.m. feeding (P˂0.03) and this demonstrates that GLU was effective at enhancing the post- absorptive carbohydrate status. Our results suggest that feeding supplemental GLU improves some body temperature indices but did not enhance growth performance in Holstein bull calves during HS.