Salivary biomarkers of acclimatization in dairy cows with different milk yield potential

Abstract

Environmental heat stress affects the productive performance of animals, especially those of high genetic merit. The Mediterranean region is characterized by sudden and prolonged heat periods. Although animals can adapt to warm environmental conditions, in these conditions they are less likely to acclimate. Saliva testing is a non-invasive and inexpensive test that can be a source of biomarkers. Results from our team suggested that the salivary levels of Hsp70 could function as a putative biomarker of thermal stress. The main objective of this work was to study the acclimatization process in dairy cows with high milk yield potential (HP; > 8000 kg of milk at 305 days in lactation) and low milk yield potential (LP; ≤ 8000 kg of milk) and to relate physiological parameters with salivary protein profiles. 6 HP and 6 LP animals were followed during four days in two periods: Summer - high environmental temperatures (animals under heat stress) and Winter – low environmental temperature (animals in thermoneutrality). Environment temperature was evaluated using a black globe thermometer (BGT) placed outside (BGTsun) and inside the facility (BGTshade). Rectal temperatures (RT) and respiratory rate (RR) were measured. On each period samples of saliva were collected through cotton rolls (Salivettes ®) and samples of blood from the coccygeal vein. BGT, RT and RR were significantly higher (P<0.05) in Summer (BGTsun 35.71±4.71°C; BGTshade 23.88±2.05°C; 38.80±0.10°C; 64.13±3.69 mov.min.) comparatively to Winter (BGTsun 14.21±2.61°C; BGTshade 6.15±1.01°C; 38.07±0.02; 36.13±2.21 mov.min.), but no differences were observed between HP and LP. Regarding T3, in Summer, HP had significatively lower values than LP, which indicated a more intense acclimatization. Higher values of salivary pH were observed in Summer in both HP and LP group. No significant differences were observed among periods in SC, however there was a significative negative correlation between SC and RT (r=-0.615, P=0.03). In Winter, HP had higher levels of SC than LP cows, which could be associated with metabolic heat production. Salivary albumin was higher in HP, during Summer. The results reinforce the concept that saliva can be useful in monitoring temperature adaptation in milk-producing animals.