Effects of heat stress abatement on systemic and mammary inflammation in lactating dairy cows

To examine the effects of evaporative cooling on systemic and mammary inflammation of lactating dairy cows, 30 multiparous Holstein cows (parity = 2.4, 156 d in milk) were randomly assigned to 1 of 2 treatments: cooling (CL) with fans and misters or not (NC). The experiment was divided into a 10-d baseline when all cows were cooled, followed by a 36-d environmental challenge when cooling was terminated for NC cows. The onset of environmental challenge was considered as d 1. Temperature-humidity index averaged 78.4 during the environmental challenge. Milk yield and dry matter intake (DMI) were recorded daily. Blood and milk samples were collected from a subset of cows (n = 9/treatment) on d -3, 1, 3, 7, 14, and 28 of the experiment to measure cortisol, interleukin 10 (IL10), tumor necrosis factor-α (TNF-α), haptoglobin, and lipopolysaccharide binding protein (LBP). Mammary biopsies were collected from a second subset of cows (n = 6/treatment) on d -9, 2, 10, and 36 to analyze gene expression of cytokines and haptoglobin. A subset of cows (n = 7/treatment) who were not subjected to mammary biopsy collection received a bolus of lipopolysaccharides (LPS) in the left rear quarter on d 30 of the experiment. Blood was sampled from cows and milk samples from the LPS-infused quarter were collected at -4, 0, 3, 6, 12, 24, 48, and 96 h relative to infusion, for analyses of inflammatory products. Deprivation of cooling decreased milk yield and DMI. Compared with CL cows, plasma cortisol concentration of NC cows was higher on d 1 but lower on d 28 of the experiment (cooling × time). Deprivation of cooling did not affect circulating TNF-α, IL10, haptoglobin, or LBP. Compared with CL cows, NC cows tended to have higher milk IL10 concentrations but did not show effects in TNF-α, haptoglobin, or LBP. No differences were observed in mammary tissue gene expression of TNF-α, IL10, and haptoglobin. Milk yield declined after LPS infusion but was not affected by treatment. Compared with CL cows, NC cows had greater milk somatic cell count following intramammary LPS infusion. Non-cooled cows had lower circulating TNF-α and IL10 concentrations and tended to have lower circulating haptoglobin concentrations than CL cows. Milk IL10 and TNF-⍺ concentrations were higher 3 h after LPS infusion for NC cows compared with CL cows. Additionally, NC cows tended to have higher milk haptoglobin concentration after LPS infusion than CL cows. In conclusion, deprivation of evaporative cooling had minimal effects on lactating cows' basal inflammatory status, but upregulated mammary inflammatory responses after intramammary LPS infusion.

Effects of evaporative cooling and dietary zinc source on heat shock responses and mammary gland development in lactating dairy cows during summer

The objective of this study was to examine the effects of evaporative cooling and dietary supplemental Zn source on heat shock responses and mammary gland development of lactating dairy cows during summer. Seventy-two multiparous lactating Holstein cows were randomly assigned to 1 of 4 treatments in a 2 × 2 factorial arrangement. Cows were either cooled (CL) or not cooled (NC) and fed diets supplemented with 75 mg of Zn/kg of dry matter (DM) from Zn hydroxychloride (IOZ) or 35 mg of Zn/kg of DM from Zn hydroxychloride plus 40 mg of Zn/kg of DM from Zn-Met complex (ZMC). The 168-d trial included a 12-wk baseline phase when all cows were cooled and fed respective dietary treatments, and a subsequent 12-wk environmental challenge phase when NC cows were deprived of evaporative cooling. Plasma was collected from a subset of cows (n = 24) at 1, 3, 5, 12, 26, 41, 54, 68, 81 d of the environmental challenge to measure heat shock protein (HSP) 70 concentration. Mammary biopsies were collected from another subset of cows (n = 30) at enrollment (baseline samples) and at d 7 and 56 of the environmental challenge to analyze gene expression related to heat shock response, apoptosis and anti-oxidative enzymes, and to examine apoptosis and cell proliferation using immunohistochemistry. Supplemental Zn source did not affect milk yield but NC cows produced less milk than CL cows. Supplemental Zn source had no effect on mammary gene expression of HSP27, 70, and 90 or plasma concentrations of HSP70. The NC cows had greater mammary gene expression of HSP than CL cows. Circulating HSP70 of NC cows gradually increased and was higher at 81 d of environmental challenge compared with CL cows. Relative to IOZ, ZMC cows tended to have lower total mammary cell proliferation but greater mammary apoptosis. There was a tendency of greater TNFRSF1A mRNA expression for ZMC compared with IOZ cows, which may suggest upregulated extrinsic apoptosis. At d 7 of environmental challenge, NC cows had numerically higher mammary apoptosis than CL cows although not statistically significant. The NC cows tended to have greater mRNA expression of CAT and SOD3 regardless of time, and had greater mRNA expression of GPX1 at d 56 and FAS at d 7 of the environmental challenge than CL cows. Relative to CL cows, mammary cell proliferation rate was higher for NC cows at d 56 of the environmental challenge. In conclusion, dietary source of supplemental Zn has substantial effect on mammary cell turnover in lactating dairy cows, and prolonged exposure to heat stress increases mammary cell proliferation.

Short communication: Effect of supplemental zinc source with and without evaporative cooling on systemic and mammary metabolism of lactating dairy cows during summer

The negative effects of heat stress partly result from disturbed systemic metabolic responses and possibly altered mammary gland metabolism of lactating dairy cows. Our previous research reported that supplemental dietary Zn sources may affect milk fat synthesis of lactating cows during summer. Thus, our objective was to evaluate the systemic and mammary metabolism of cows fed 2 supplemental Zn sources under 2 environmental conditions. Multiparous lactating Holstein cows (n = 72; days in milk: 99.7 ± 13.4 d; parity: 2.9 ± 0.3) were randomly assigned to 4 treatments in a 2 × 2 factorial arrangement. Treatments included 2 different environments: cooled (CL) using fans and misters or noncooled (NC), and 2 supplemental Zn sources: 75 mg of Zn hydroxychloride/kg of DM (IOZ) or 35 mg of Zn hydroxychloride/kg of DM + 40 mg of Zn-Met complex/kg of DM (ZMC). The 168-d experiment was divided into baseline and environmental challenge phases, 84 d each. During the baseline phase, all cows were cooled and fed respective dietary treatments, and during the environmental challenge phase cows continued receiving the same diets but NC cows were deprived of cooling. Temperature-humidity index averaged 77.6 ± 3.8 and 77.8 ± 3.8 for CL and NC pens, respectively, during the environmental challenge phase. Plasma was collected before the baseline phase and at 1, 3, 5, 12, 22, 26, 41, 54, 61, 68, 75, and 81 d of the environmental challenge phase for metabolites and insulin analyses. Mammary biopsies were collected before the baseline phase and at 7 and 56 d of the environmental challenge phase to measure mRNA abundance of proteins related to mammary metabolism. Compared with CL, NC reduced plasma glucose, nonesterified fatty acids, β-hydroxybutyrate, and triglyceride concentrations, but increased insulin concentration. Cows fed ZMC had greater plasma triglyceride concentration than IOZ. Treatments had no effect on mRNA abundance of protein related to mammary fatty acid and glucose metabolism except that NC cows had greater mammary mRNA abundance of 6-phosphogluconate dehydrogenase and ATP-dependent 6-phosphofructokinase than CL cows. In conclusion, deprivation of evaporative cooling influenced the metabolism of lactating dairy cows but dietary Zn source had no apparent effect.

PRL/microRNA-183/IRS1 Pathway Regulates Milk Fat Metabolism in Cow Mammary Epithelial Cells

The aim of the study was to understand the internal relationship between milk quality and lipid metabolism in cow mammary glands. A serial of studies was conducted to assess the molecular mechanism of PRL/microRNA-183/IRS1 (Insulin receptor substrate) pathway, which regulates milk fat metabolism in dairy cows. microRNA-183 (miR-183) was overexpressed and inhibited in cow mammary epithelial cells (CMECs), and its function was detected. The function of miR-183 in inhibiting milk fat metabolism was clarified by triglycerides (TAG), cholesterol and marker genes. There is a CpG island in the 5'-flanking promoter area of miR-183, which may inhibit the expression of miR-183 after methylation. Our results showed that prolactin (PRL) inhibited the expression of miR-183 by methylating the 5' terminal CpG island of miR-183. The upstream regulation of PRL on miR-183 was demonstrated, and construction of the lipid metabolism regulation network of microRNA-183 and target gene IRS1 was performed. These results reveal the molecular mechanism of PRL/miR-183/IRS1 pathway regulating milk fat metabolism in dairy cows, thus providing an experimental basis for the improvement of milk quality.

Short communication: Effects of mammary biopsy in the dry period on activity and feeding behavior of dairy cows

In dairy cattle, mammary biopsies are commonly used to study development and function of the mammary gland. The objective of this study was to investigate changes in activity and feeding patterns following the mammary biopsy procedure. Pregnant, nonlactating Holstein dairy cows (20 d before expected calving date) were exposed to either (1) a biopsy procedure, in which a mammary tissue sample (60 × 4 mm in diameter) was obtained from cows (n = 9) using a biopsy tool from the rear left quarter, following administration of a sedative (xylazine, 20 µg/kg of body weight) and local anesthetic (3 mL of lidocaine), or (2) a sham procedure, in which cows (n = 8) were removed from the pen and restrained for a similar duration of time as for the biopsy procedure. Behavior of cows was monitored for 5 d, beginning on the day following biopsy (approximately 14 h after the procedure). Cows were fitted with accelerometers to record daily lying time, lying bout frequency, and lying side. Daily individual feed intake was recorded using the Calan Broadbent feeding system, and feeding time and meal characteristics were determined from a subset of cows (n = 6 per treatment) using a change-of-state data logger to record the times the cows were accessing the feed bunk. Total daily lying time did not differ between treatments [13.9 h/d; standard error (SE) = 0.56], but biopsied cows had more frequent, shorter lying bouts on the biopsied side on d 1 following the procedure (6.67 vs. 4.25 bouts/d, SE = 1.03, and 70.0 vs. 97.0 min/bout, SE = 8.6; left vs. right side), whereas control cows had no side preference. We found no effects of treatment on feed intake and feeding time but, on the first day after treatment, biopsied cows had meals that were more frequent (7.2 vs. 4.6 meals/d; SE = 0.93) and tended to be shorter (28.2 vs. 60.9 min/meal; SE = 11.8) than control cows. In conclusion, we did not detect effects of mammary biopsy on feed intake or lying time during our time frame of observation, but activity patterns were altered, which could be indicative of increased overall restlessness and specific pain in the biopsied quarter.