Effects of solar radiation and feeding time on behavior, immune response and production of lactating ewes under high ambient temperature

A 6-wk trial was performed with 40 late-lactation Comisana ewes, which were either exposed to or protected from solar radiation and fed either in the morning (EXPM, PROM) or afternoon (EXPA, PROA) during summer in a Mediterra nean climate. Behavioral traits of ewes were recorded once per week from 08 00 to 2000 h. Rectal temperature (RT) and respiration rate (RR) were measur ed twice weekly at 1430 h. The phytohemagglutinin (PHA) skin test was perfo rmed to induce nonspecific delayed-type hypersensitivity at d 10, 20, and 3 2 of the experiment. Jugular blood samples were taken from ewes at the begi nning and at d 21 and 42 of the experiment. Ewe milk yield was recorded dai ly. Individual milk samples were analyzed weekly for milk composition, coag ulating properties, somatic cell count (SCC) and polymorphonuclear neutroph il leukocyte counts (PMNLC) and every 2 wk for bacteriological characterist ics. Solar radiation and the interaction of solar radiation x time of feedi ng had significant effects on rectal temperatures. EXPM ewes had higher rec tal temperatures than EXPA ewes, which in turn exhibited higher RT compared with FROM and PROA ewes. EXP groups also had significantly higher respirat ion rates than PRO groups. Immune response was lower in EXPM ewes at d 10 a nd in EXPM, EXPA, and FROM animals at d 20 compared with PROA ewes. Exposur e to solar radiation resulted in decreased plasma concentrations of alanine amino-transferase; alkaline phosphatase, potassium, and magnesium, as well as in increased levels of nonesterified fatty acids and aspartate amino-tr ansferase. Milk yield and composition were not changed by exposure to solar radiation and time of feeding, but the EXPM treatment resulted in lower yi elds of casein and fat and reduced clot firmness compared with the three ot her treatments. Milk SCC was similar across treatments, but PMNLC was highe r in EXPM than in FROM and PROA milk. EXPM animals also had the greatest am ounts of total and fecal coliforms and of Pseudomonadaceae as well as the h ighest number of mastitis related pathogens in their milk. Results suggest that provision of shaded areas can play a major role in helping lactating e wes to minimize the adverse effects of high ambient temperatures on thermal balance and energy and mineral metabolism. Changing the time of feeding to late afternoon may be beneficial to exposed ewes in lowering their heat lo ads during the warmest hours of the day, thereby reducing the detrimental i mpact of thermal stress on immune function and udder health.