Physiological responses of dietary tryptophan fed Labeo rohita to temperature and salinity stress

Two experiments were conducted to elucidate the possible effects of dietary L‐tryptophan (TRP) in Labeo rohita based on growth performance and physio‐biochemical responses. In the experiment I, a 60‐day feeding trial was carried out to elucidate the effects of dietary TRP enrichment on growth performance and physio‐biochemical responses. In the experiment II, the TRP pre‐fed L. rohita, from experiment I, was exposed to temperature and salinity stress to evaluate stress‐mitigating efficacy of TRP. In L. rohita, dietary supplementation of TRP showed significant effect on weight gain percentage and feed conversion ratio but not on blood glucose. A significant increase in RNA content and RNA/DNA ratio upon TRP supplementation was observed and was positively correlated with growth performance. The results of experiment II indicated that weight gain percentage, serum T3 and T4 levels were significantly reduced in groups that were exposed to temperature and salinity stress and fed diets without TRP supplementation. However, dietary supplementation of TRP significantly augmented weight gain percentage in stress‐exposed groups. Tryptophan supplementation helped in bringing back T3 and T4 levels comparable with control. A significant increase in superoxide dismutase, catalase, Adenosine triphosphatase, blood glucose and serum cortisol was observed in temperature‐ and salinity‐exposed groups fed without TRP‐supplemented diets. However, TRP supplementation was found to be effective in restoring the above parameters. The results of these experiments suggest that dietary TRP supplementation augments growth, lowers energy demand and helps in mitigating thermal and salinity stress in L. rohita.     

Analysis of weaning‐induced stress in Saanen goat kids

In young ruminants’ life, weaning often coincides with a period of growth stasis and poor welfare. The present study aimed at evaluating the effect of coping with the new diet on behavioural and haematological stress indicators in goat kids subjected to a commonly adopted weaning practice. Immediately after birth, male Saanen goat kids were divided into two groups: MILK and WMIX. All were fed colostrum for the first 3 days and then goat milk to the age of 29 days. After that, MILK kids continued to receive milk, while the WMIX kids underwent weaning and were completely weaned by day 48. Animal behaviour was recorded daily. From day 23–50, blood samples were taken weekly and analysed for indicators of stress and immune function. No abnormal behaviour, such as injurious behaviours or stereotypies, was observed in either of the experimental groups throughout the experimental period. During the last week, fasting plasma cortisol level was significantly lower, whereas plasma activity of both alanine aminotransferase (ALT) and aspartate aminotransferase (AST) was significantly higher in WMIX kids, in relation to the MILK ones. Anyway, data were within the normal physiological range and no difference was observed neither in plasma haptoglobin, ceruloplasmin, albumin and antithrombin III, nor in plasma immunoglobulin A and G, at any time, signalling no stressful condition. Therefore, differences observed in cortisol, ALT and AST could be the consequence of the metabolic changes that occur during the transition from pre‐ruminant to ruminant state. The gradual weaning at 48 days of age did not result in any stressful condition and had no negative effect on weight gain. Results suggest that parameters commonly adopted to provide information on animal stress, such as cortisol and aminotransferase activity, can vary in relation to the physiological status of the animals and may bias stress assessment.     

Hair cortisol as a marker of hypothalamic-pituitary-adrenal axis activation in Friesian dairy cows clinically or physiologically compromised

This study was designed to assess hypothalamic-pituitary-adrenal (HPA) axis activation in lactating cows clinically or physiologically compromised. Cortisol was measured in the hair of 475 multiparous cows of Italian Friesian breed. The cows were classified into Groups A (n=218) and B (n=257). Group A included cows clinically compromised that had recently suffered a disease (e.g. metritis, laminitis, mastitis) or physiologically compromised that calved 1 month prior to hair sampling. Group B were clinically normal lactating cows at least 60 days after calving with somatic cell counts of less than 200,000 cells/ml in milk. Animals in Group A showed higher hair cortisol levels than those in Group B (P<0.01). Significant positive correlation (rpb=+0.352, P<0.001) was detected between hair cortisol and cows clinically or physiologically compromised. The area under the receiver operating characteristic curve was 0.701 (SE 0.024) and a cut-off value of 4.17 pg/mg was found to discriminate between groups A and B with a sensitivity of 62.4% and specificity of 69.3%. The hair cortisol test emerged as useful to determine HPA activation and to enhance current understanding on the involvement of this axis in clinically or physiologically compromised cows.     

Effect of lactation stage, season and parity on milk cortisol concentration in Holstein cows

This experiment was designed (1) to study the effects of lactation stage, season, and parity on milk cortisol concentrations in Holstein cows, and (2) to elucidate the relationships between milk yield, quality, and milk cortisol concentration. Subjects of this study were 24 dairy cows kept in a free stall barn. Milk samples were taken on test day in May, August, November, and February. Data of milk yield, quality, and cortisol concentration were collected. Random effects of animals and fixed effects of lactation stage, test day, and parity on milk yield, quality, and cortisol concentration were analyzed using mixed models. We estimated the best linear unbiased prediction of each trait (BLUP) which was an animal-specific value. Correlation among milk yield, quality, and cortisol concentration was calculated using raw data and BLUP. The effect of the lactation stage on milk cortisol concentration was significant: the value observed in early lactation was higher than in other stages. However, the correlation between milk yield and cortisol concentration was low. The beginning of lactation might be a strong stressor for every cow. Calculated with raw data, milk cortisol concentration had respectively significant negative correlation with milk protein contents and solid not-fat contents. Calculated with BLUP, milk cortisol concentration showed a significant and negative correlation with milk protein contents. The lactation stage and milk protein contents should be considered for measurement of milk cortisol concentrations.     

Hair cortisol levels of lactating dairy cows in cold‐ and warm‐temperate regions in Japan

We compared the hair cortisol levels of lactating dairy cows in a cold‐ and a warm‐temperate region out of four climatic zones in Japan. We simultaneously investigated the effects of calving number, lactation period and month of hair sampling. Hair of nine Holstein lactating cows chosen from each region (i.e. 18 cows per sampling) was sampled in March, June, September and December. Number of calvings (1, 2, ≥3) and lactation duration (early: <100, middle: 101–200, and late: >201 days) were balanced between regions. Cortisol was extracted from hair by methanol, and its level was determined with a cortisol immunoassay kit. A multi‐way analysis of variance revealed that the effects of month of hair sampling (P < 0.001) and its combination with region (P < 0.05) were significant. In a multiple comparison test, significant differences (P < 0.01) in hair cortisol level (pg/mg of hair) were found between June (13.0 ± 1.0) and the other 3 months, and between September (1.6 ± 0.2) and December (4.5 ± 0.3). The rise in cortisol level from March to June was more intense in the cold‐temperate region. These results demonstrate the necessity of considering seasonal variations in each climatic region when we use hair cortisol level as an indicator of stress.     

Docosahexaenoic acid (C22:6n‐3) alters cortisol response after air exposure in Prochilodus lineatus (Valenciennes) larvae fed on enriched Artemia

This study investigated the effect of different proportions of dietary docosahexaenoic acid (DHA) and arachidonic acid (ARA) on the growth, survival and stress response of curimba (Prochilodus lineatus Valenciennes) larvae, an omnivorous freshwater species, fed on enriched Artemia. Six different experimental emulsions were formulated to have two levels of ARA (A‐0.5 and A‐1.0), two levels of DHA (D‐0.5 and D‐1.0) two combinations of ARA and DHA (AD‐3:1 and AD‐1:3). There were no significant effects of treatments on curimba standard length and survival at the end of the experiment. The results showed a negative correlation between dietary DHA and whole‐body cortisol after 60 s of air exposure. The resting concentration of cortisol was not affected by the diets (p = .424). After air exposure, all treatments except for D‐1.0 (p = .137) and D‐0.5 (p = .545) exhibited a marked cortisol rise. These results showed that DHA supplementation can have an attenuating effect on cortisol response after air exposure.