Effects of heat stress and dietary zinc source on performance and mammary epithelial integrity of lactating dairy cows

Abstract

Dietary Zn and heat stress alter gut integrity in monogastric animals. However, effects of Zn on mammary epithelial integrity in heat-stressed lactating dairy cows have not been studied. Multiparous lactating Holstein cows (n = 72) were randomly assigned to 1 of 4 treatments with a 2 × 2 factorial arrangement to study the effects of environment and Zn source on performance and mammary epithelial integrity. Treatments included 2 environments [cooled (CL) or not cooled (NC)] and 2 Zn sources [75 mg/kg of supplemental Zn as Zn hydroxychloride (IOZ) or 35 mg/kg of Zn hydroxychloride + 40 mg/kg of Zn-Met complex (ZMC)]. The experiment was divided into baseline and environmental challenge phases of 84 d each. All cows were cooled during the baseline phase (temperature-humidity index = 72.5), whereas NC cows were not cooled during environmental challenge (temperature-humidity index = 77.7). Mammary biopsies were collected on d 7 and 56 relative to the onset of environmental challenge to analyze gene expression of claudin 1, 4, and 8, zonula occludens 1, 2, and 3, occludin, and E-cadherin and protein expression of occludin and E-cadherin. Deprivation of cooling increased respiration rate (64.8 vs. 73.9 breaths/min) and vaginal temperature (39.03 vs. 39.94°C) and decreased dry matter intake (26.7 vs. 21.6 kg/d). Energy-corrected milk yield decreased for NC cows relative to CL cows (24.5 vs. 34.1 kg/d). An interaction between environment and Zn source occurred for milk fat content as CL cows fed ZMC had lower milk fat percentage than other groups. Relative to CL cows, NC cows had lower concentrations of lactose (4.69 vs. 4.56%) and solids-not-fat (8.46 vs. 8.32%) but a higher concentration of milk urea nitrogen (9.07 vs. 11.02 mg/mL). Compared with IOZ, cows fed ZMC had lower plasma lactose concentration during baseline and tended to have lower plasma lactose concentration during environmental challenge. Plasma lactose concentration tended to increase at 3, 5, and 41 d after the onset of environmental challenge in NC cows relative to CL cows. Treatment had no effect on milk BSA concentration. Cows fed ZMC tended to have higher gene expression of E-cadherin relative to IOZ. Compared with CL, NC cows had increased gene expression of occludin and E-cadherin and tended to have increased claudin 1 and zonula occludens 1 and 2 gene expression in the mammary gland. Protein expression of occludin and E-cadherin was unchanged. In conclusion, removing active cooling impairs lactation performance and affects gene expression of proteins involved in the mammary epithelial barrier, and feeding a portion of dietary zinc as ZMC improves the integrity of the mammary epithelium.

Effects of dietary zinc source on the metabolic and immunological response to lipopolysaccharide in lactating Holstein dairy cows

“…Reduced milk SCC has been observed repeatedly with dietary Zn supplementation (Kellogg et al, 2004;Machado et al, 2013;Nayeri et al, 2014), and Weng et al (2018) recently observed reduced circulating lactose with Zn supplementation in heat-stressed cows. Zinc is required for normal epithelial barrier function and has been shown to improve integrity characteristics of mammary (Weng et al, 2018), lung (Bao and Knoell, 2006), and intestinal epithelial barriers (Sanz Fernandez et al, 2014;Pearce et al, 2015;Abuajamieh et al, 2016). Therefore, Zn appears to be a promising mitigation strategy for strengthening the integrity of multiple epithelial barriers, and it is of interest to evaluate whether dietary Zn can improve uterine epithelial integrity.…”

“…300 enzymes and plays a pivotal role in multiple systems (Prasad, 2012;Kambe et al, 2015). Furthermore, Zn improves epithelial integrity characteristics (mammary and intestinal; Sanz Weng et al, 2018) and immune function (cell adherence, clearance of E. coli, cytokine production; Kidd et al, 1994a;Finamore et al, 2008). Therefore, we hypothesized that supplemental complexed Zn would modify the inflammatory response to an intravenous LPS challenge and in turn alter the leukocyte energetic requirement.…”

Heat Stress Impacts Immune Status in Cows Across the Life Cycle

“…A study conducted in Kansas suggests that misters and fans reduce lactating cows' body temperature to a similar extent compared with soakers and fans (soakers operating cycle: 1 min on and 4 min off) (134). In a 3 months study conducted in southern Georgia, Weng et al (135) reported that the daily average vaginal temperature of lactating cows cooled by misters and fans over the feedline and stalls was 0.9 • C lower (39.0 vs. 39.9 • C, respectively) than those without cooling in a free stall barn.…”

Response of lactating dairy cows fed different supplemental zinc sources with and without evaporative cooling to intramammary lipopolysaccharide infusion: intake, milk yield and composition, and hematologic profile1

“…Cows used for the intramammary infusion of LPS reported here were part of an experiment reported by Weng et al (2018). Multiparous lactating Holstein cows (n = 72) were assigned to one of four treatments with a 2 × 2 factorial arrangement based on parity and days in milk.…”