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

Abstract

[EN] There is little information about the effect of the stress on Somatic Cell Count (SCC) and milk yield and composition in goats. A total of 40 goats in their 4th month of lactation were assigned to two groups: stress (STR) and untreated (CON). Goats of STR were exposed to acute stress (visual and auditory stimulus from a barking dog for 20 min on day 0). After the stress, average values of plasma cortisol were higher in STR than CON (P < 0.001); likewise, in STR group cortisol was lower in parity 1 + 2 goats than parity >= 3 goats (P < 0.05). Stress caused a considerable increase in SCC in parity >= 3 goats (P < 0.05), but not in parity 1 + 2 goats. On average, this increase of SCC was 6-fold compared to values prior to the stress, and it was observed in both healthy and infected mammary glands. This increase was transient, as SCC returned to normal values after 1 to 3 days. On day 1, stressed goats of parity >= 3 produced 11% less milk compared with day 0 and, regarding milk composition, only lactose showed a significant drop. Stressed parity 1 + 2 goats showed no changes in SCC and milk yield and composition. We conclude that, in goats, stress is a non-infectious factor that can interfere in the use of SCC as an indirect method of intramammary infection (IMI) detection or, in bulk tank milk, as a commercial milk quality parameter.