The effects of OmniGen-AF on serum metabolites, calcium concentrations and hormones of the adrenal axis during heat stress in lactating Holstein cows
The objective was to evaluate physiological, behavioral and hormonal changes in lactating cows supplemented with OmniGen-AF (Prince Agri Products, Inc.) subjected to heat stress. Thirty lactating Holstein cows from an Arizona were assigned to a control diet (CON, n=15h) or control diet plus OmniGen-AF (OG, n=15h). Cows within diet were balanced by DIM, milk production and parity (91 ± 5.9 DIM, 36.2 ± 2.5 kg/d, and 3.1 ± 1.4). The cows were fed OG at 56g/h/d for 52 days on the dairy, added to the TMR. On d 52, six cows were randomly selected from each of the diet groups, transported to the Agricultural Research Center (ARC), University of Arizona and housed in environmentally controlled modules (EM). Original diet assignments were continued. The OG was top-dressed 2x/d (28g/feeding) with molasses as the carrier and the CON cows received the molasses carrier 2x/d. Both were mixed into the top one-third of the TMR. In the EM, all cows were subjected to 7 days of thermal neutral (TN), 10 days of heat stress (HS), and 4 days of TN. Feed intake, milk production, and milk composition were measured daily. Rectal temperatures and respiration rates were recorded 3x /d (0600, 1400, and 1800 h). Blood samples were taken on days 7 (TN), 8 (HS), 10 (HS), 17 (HS) and 18 (TN) during the ARC phase and analyzed for selected blood metabolites, hormones and immune biomarkers. Serum cortisol levels were highest on d 8 for both the CON and OG fed cows however OG cows had significantly lower cortisol (P<0.05) on day 8 (CON= 0.8372 ug/dL; OG= 0.4838 ug/dL). No differences were detected at the other time points. Serum insulin and plasma glucose levels were not different between CON and OG cows. The OG cows maintained lower SCC compared to CON (P<0.01). Serum calcium were not different, however, serum NEFA (P=0.10) tended to be greater in OG cows throughout the 21 d ARC phase. Although serum cortisol were lower in OG cows, serum ACTH levels at each sampling point were higher (P<0.0001). Results suggest that feeding OG to lactating cows reduced many of the effects associated with HS by reducing cortisol. However, ACTH increased in OG cows suggesting that OG may alter adrenal response to ACTH. Additional research is needed to determine the cause of reduced serum cortisol and elevated serum ACTH in cows fed OG.
heat stress, lactating cows, OmniGen-AF