Within-day variation and effect of acute stress on plasma and milk cortisol in lactating goats

Abstract

An experiment was carried out to study the effect of acute stress on cortisol concentration in goat milk (milk cortisol; MC) and its suitability for stress assessment. Additional variables studied were plasma cortisol (PC), blood glucose (BG), and somatic cell count (SCC). Ten goats free of mastitis at 2 mo of lactation were divided into 2 groups. One group of animals was exposed to acute stress (visual and auditory, but not physical, contact with a barking dog for 3 min) immediately before the 1000 h sampling (STR), and the other group was considered as the control group, not exposed to acute stress (CON). The animals were gradually accustomed to the sampling schedule for 1 wk before the stress treatment (pre-experimental period). The variables PC, MC, BG, SCC, and milk composition (fat, lactose, whey protein, true protein, and casein) were recorded at 0600, 1000, 1130, 1400, 1800, 2200, and 0200 h. Milk variables were recorded in both glands separately. The right gland (n=10) was completely milked and the left gland (n=10) was milked to 30 mL at every sampling except at 1000 h, when complete milking was carried out on both glands. Variables were analyzed by using a linear mixed model. Both PC and MC concentrations varied throughout the day, with values being highest in the morning. Higher PC levels were recorded in the STR group immediately after treatment compared with CON (36.9 vs 16.3 ng/mL). For MC, differences between treatments were noted 1.5h after STR treatment (1.27 vs 0.25 ng/mL). Blood glucose increased immediately after treatment in STR animals, being different from CON until 1.5h after treatment sampling (101 vs. 58 mg/dL). The SCC was not increased by STR treatment, showing higher values in the morning and afternoon compared with evening and night (5.6±0.13 to 5.87±0.13 log10 SCC). The STR treatment had no significant effect on milk composition, and overall milk yield of a complete day after stress stimulus of both groups was similar (STR: 2,067±280 g/d; CON: 2,134±427 g/d). We conclude that plasma and milk cortisol concentrations in control dairy goats varied throughout the day; MC showed significant differences in the STR group if samples were taken 1.5h after the stressing stimulus, whereas PC showed significant differences in samples taken immediately after the stressing stimulus. Additionally, MC sampling has the advantage of being noninvasive compared with blood sampling.

Effect of stress on somatic cell count and milk yield and composition in goats

“…This is a difference compared to the effect of estrus, as this factor also produces an augmentation of SCC in primiparous goats (Mehdid et al, 2013). Romero et al (2015) did not find that acute stress for 5 minutes increased the SCC, but these authors only used primiparous IMI-free goats, which would coincide with what we observed in the present work. Other authors did not find that the stress induced by 45 minutes of transportation or by application of ACTH (Gaiato et al, 2012) affected SCC, but in both studies the distribution of goats according to parity number was not described and, therefore, we cannot know if it differs with our results.…”

“…In ewes aged from to 6 years subjected to stress (isolation test for 10 minutes), Caroprese et al (2010) observed that SCC was higher in high-cortisol ewes than in low-cortisol ewes, but the differences were small (geometric means of 0.426 and 0.223 million cells/ml, respectively). Regarding the cortisol records in our experiment, we must specify that in order to rule out any possible circadian variation, the blood samples were taken at the same time each day, at 13:00 h, that is, at a time of day when the cortisol levels are low in non-stressed goats (Kokkonen et al, 2001;Romero et al, 2015). Two hypotheses could be formulated to explain the different behavior of the goats with three or more lactations compared to the younger goats.…”

“…The aim of the study was to test this hypothesis using goats with different parities (primiparous and multiparous) and mammary health status (with or without intramammary infection-IMI) and to challenge them with a short and acute stress. Milk yield and composition were also determined, and blood cortisol concentration was recorded as a physiological indicator of stress level suffered by the animals (Romero et al, 2015).…”

Factors affecting milk cortisol in mid lactating dairy cows

“…Moreover, Verkerk et al [ 20 ] suggested that milk cortisol can reflect serum concentration only within 2–4 h after the response to acute stressors of lactating cows. Similarly, Romero et al [ 23 ] in goats reported a delay of 1.5 h between blood and milk cortisol increase in response to an acute stress. According to Fox et al [ 24 ], adrenal cortisol secretion is transferred from blood to milk rapidly (within 4 h), but in the absence of sustained activation of HPA axis the transfer rate declines and cortisol is diluted later, as a function of milk yield and milking interval.…”

A Survey of Naturally-Occurring Steroid Hormones in Raw Milk and the Associated Health Risks in Tangshan City, Hebei Province, China

“…This difference may reflect individual differences among cows [ 26 ]. Moreover, Romero et al (2015) and Verkerk et al (1998) suggested that milk cortisol content was influenced by the response to acute stressors in lactating cows and goats [ 27 , 28 ]. In addition, Sgorlon et al (2015) found that breed is a factor affecting milk cortisol concentration [ 18 ].…”