Validating a heat stress model: The effects of an electric heat blanket and nutritional plane on lactating dairy cows

Abstract

The efficacy of an electric heat blanket (EHB) has previously been confirmed as an alternative method to evaluate heat stress (HS). However, a pair-feeding design has not been used with the EHB model. Therefore, study objectives were to determine the contribution of the nutritional plane to altered metabolism and productivity during EHB-induced HS. Multiparous Holstein cows (n = 18; 140 ± 10 d in milk) were subjected to 2 experimental periods (P); during P1 (4 d), cows were in thermoneutral conditions with ad libitum feed intake. During P2 (4 d), cows were assigned to 1 of 2 treatments: (1) thermoneutral conditions and pair-fed (PF; n = 8) or (2) EHB-induced HS with ad libitum feed intake (n = 10). Overall, the EHB increased rectal temperature, vaginal temperature, skin temperature, and respiration rate (1.4°C, 1.3°C, 0.8°C, and 42 breaths/ min, respectively) relative to PF cows. The EHB reduced dry matter intake (DMI; 47%) and, by design, PF cows had a similar pattern and extent of decreased DMI. Milk yield decreased in EHB and PF cows by 27.3% (12.1 kg) and 13.4% (5.4 kg), respectively, indicating that reduced DMI accounted for only ~50% of decreased milk synthesis. Milk fat content tended to increase (19%) in the EHB group, whereas in the PF cows it remained similar relative to P1. During P2, milk protein and lactose contents tended to decrease or decreased (1.3 and 2.2%, respectively) in both EHB and PF groups. Milk urea nitrogen remained unchanged in PF controls but increased (34.2%) in EHB cows relative to P1. The EHB decreased blood partial pressure of CO 2 , total CO 2 , HCO 3 , and base excess levels (17, 16, 17, and 81%, respectively) compared with those in PF cows. During P2, the EHB and PF cows had similar decreases (4%) in plasma glucose content, but no differences in circulating insulin were detected. However, a group by day interaction was detected for plasma nonesterified fatty acids; levels progressively increased in PF controls but remained unaltered in the EHB cows. Blood urea nitrogen increased in the EHB cows (61%) compared with the PF controls. In summary, utilizing the EHB model indicated that reduced nutrient intake explains only about 50% of the decrease in milk yield during HS, and the postabsorptive changes in nutrient partitioning are similar to those obtained in climatecontrolled chamber studies. Consequently, the EHB is a reasonable and economically feasible model to study environmental physiology of dairy cows.

Changes in Blood Metabolites and Immune Cells in Holstein and Jersey Dairy Cows by Heat Stress

“…To better understand the direct impact of heat stress on dairy cows, specific experimental methods should be used, such as a climate control chamber system or an electric blanket, for dairy cow studies [63,64]. To elucidate the functional outcome from heat stress-induced impaired immune response, immune challenges model could be applied for future study.…”

The effects of zinc amino acid complex on biomarkers of gut integrity, inflammation, and metabolism in heat-stressed ruminants

“…Muscle protein catabolism makes available gluconeogenic precursors to fuel-activated immune cells (Wannemacher et al, 1980) and provides additional amino acids for APP synthesis (Iseri and Klasing, 2013), although, as aforementioned, we curiously did not detect an increase in circulating APP. Consequently, protein metabolism is affected by HS, as muscle catabolism biomarkers such as BUN are increased during HS (Yoshizawa et al, 1997;Yunianto et al, 1997;Pearce et al, 2013a;Al-Qaisi et al, 2020). In agreement, BUN levels were increased in HS steers irrespective of the Zn form fed and substantially increased compared with the PF steers, although ZAHS had numerically reduced BUN relative to ZSHS, whereas ZAHS did not statistically differ from ZSCON, ZSPF, or ZAPF BUN values.…”

“…The increase in NEFA is bioenergetically expected, because both groups were on a lowered plane of nutrition, and adipose mobilization is a homeorhetic response to maintain energy supply for metabolic processes. Our group has previously reported that heat-stressed ruminants do not mobilize as much adipose tissue as their PF counterparts (Rhoads et al, 2009;O'Brien et al, 2010;Al-Qaisi et al, 2020). In this study, we utilized an ad libitum control, and this likely explains why we detected a small increase in NEFA in HS steers.…”

“…A negative outcome of this survival strategy is that blood and nutrient delivery to the gastrointestinal tract is decreased, leading to hypoxia, increased reactive oxygen species production, extracellular membrane damage, and disruption of enterocyte tight junction complexes; this is thoroughly described in rodent and other animal models (Kregel et al, 1988;Hall et al, 1999). Consequently, there is a loss in intestinal barrier integrity and increased susceptibility to antigen permeability and subsequent immune activation and inflammation, as demonstrated in pig and ruminant models (Pearce et al, 2013b;Gabler et al, 2018;Koch et al, 2019;Al-Qaisi et al, 2020). Interestingly, nutrient restriction (a consequence of heat stress) itself negatively affects barrier function in a variety of animal models (Welsh et al, 1998;Ferraris and Carey, 2000;Pearce et al, 2013c), including ruminants (Zhang et al, 2013;Kvidera et al, 2017c).…”

Common and Differential Dynamics of the Function of Peripheral Blood Mononuclear Cells between Holstein and Jersey Cows in Heat-Stress Environment

“…Thus, our study represents natural changes of immunity of two breeds of dairy cow in the mid-lactation period from normal to heat-stress environmental conditions. To better understand the direct impact of heat stress on immune responses, in future studies, a chamber system or electric blanket should be applied to induce heat stress [37,78]. In this study, we found several altered genes related to critical immune functions in dairy cows by high THI environmental condition.…”