The effects of heat stress and dietary organic acid and pure botanical supplementation on growth and lactation in dairy cattle.

192 pagesHeat stress (HS) compromises the gastrointestinal barrier and leads to inflammation in non-ruminants. However, it is unclear whether exposure to environmental conditions that cause HS enhances gastrointestinal permeability with compromised growth and milk production in dairy cattle. Developing nutritional strategies to manage HS in cattle are of importance to the dairy industry. Dietary supplementation of organic acid and pure botanicals (OA/PB) has been shown to improve growth performance by enhancing gastrointestinal health in swine and poultry species. Because the role of dietary OA/PB supplementation in ruminants had not received prior attention, our objectives were to 1) evaluate the effects of HS and dietary OA/PB supplementation on growth in dairy calves, and 2) evaluate the effects of HS and dietary OA/PB supplementation on gastrointestinal permeability and milk production in mid-lactating dairy cows. For study 1, sixty-two weaned heifer and bull calves (62 ± 2 d; 91 ± 10.9 kg) were randomly assigned to one of five groups (n = 11 to 14/group): thermoneutral conditions (TN-Con), HS conditions (HS-Con), TN conditions and pair-fed to HS-Con (TN-PF), HS with low-dose OA/PB (75 mg/kg of body weight [BW]; HS-Low), or HS with high-dose OA/PB (150 mg/kg of BW; HS-High). After a 7-d acclimation period, calves were exposed to TN or HS for a period of 19 d. Blood samples were collected and growth performance was evaluated. We observed that HS-Con calves had reduced growth compared to TN-Con and TN-PF. Regarding dietary OA/PB supplementation, HS-Low partially restored dry matter intake (DMI) without modifying growth performance. Thus, we conclude that dietary OA/PB supplementation does not improve growth performance in heat-stressed calves. For study 2, forty-six multiparous lactating dairy cows (208 ± 4.65 d in milk; 3.0 ± 0.42 lactation; and 39.2 ± 0.26 kg of milk yield) were randomly assigned to one of four groups (n = 10 to 12/group): TN-Con, HS-Con, TN-PF, or HS supplemented with OA/PB (75 mg/kg of BW; HS-OAPB). Cows acclimated in TN for 7-d, and then exposed to HS or remained in TN for 14-d. Blood and milk samples were collected. Changes in milk production and gastrointestinal permeability were evaluated. We observed that HS-Con cows had reduced DMI, energy-corrected milk yield, and milk protein and lactose yields compared to TN-Con, TN-PF and HS-OAPB cows. Milk- and plasma-urea nitrogen were reduced in HS-OAPB compared to HS-Con cows. Gastrointestinal permeability was greater in HS-Con, relative to TN-Con or TN-PF. We conclude that HS increased gastrointestinal permeability and that OA/PB feeding partially restores lactation performance by increasing DMI and improving intestinal barrier, and thereby enhancing milk yield and nitrogen efficiency