Epsilon Archive for Student Projects

Abstract

This thesis is based upon two studies carried out at a commercial organic dairy farm, in the southwest of Sweden.
The aim of the first study was to evaluate the effects of suckling and subsequent weaning after a nursing period of 9 weeks in foster cows with previous high somatic cell count (SCC) on their saleable milk yield (total milk minus discarded milk due to a high California Mastitis Test score), milk composition, udder health and behaviour during milking. Seven foster cows (calves suckling) and seven control cows (with no calves suckling) were used in the experiment. Four alien calves had suckled each foster cow for 9 weeks and the calves were free to suckle at any time.

Behavioural observations were made during afternoon milking and milk samples were taken at 0, 1, 2, 3, 7, 10, 14, 17, 21 and 24 days after weaning. The saleable milk yield of the foster cows was significantly lower than the control cows during the first ten days after weaning. One day after weaning, the foster cows moved significantly more during milking and vocalizations were recorded (as yes or no) in five foster cows while none of the control cows vocalized. Four of the seven foster cows had mastitis towards the end of the study. The fat content in strip milk was significantly lower in the foster cows than in the control cows on the day of weaning, indicating a disturbed milk ejection. However, the day after weaning no such difference was observed. The foster cows had a significantly lower fat content in composite milk on the day of weaning. This fat content increased rapidly, and 10 days after weaning the foster cows had significantly higher fat content in composite milk than the control cows.

In conclusion, the suckling by four calves on foster cows with high SCC or mastitis, resulted in a higher fat content in composite milk after weaning. However, after 9 weeks nursing their udder-health condition did not seem to improve and the saleable milk yield was lower than in the control group. Furthermore, the weaning in addition to the beginning of milking seem to be a stressful situation as indicated by cows vocalizing more and moving more during milking.

The aim of the second study was to investigate the relationship between plasma and salivary cortisol response to stress in dairy cattle. To activate the cortisol stress response, six cows were separated from their calves at 4 d after calving, and six calves were separated from a group of four peers at 8 wk of age. In addition, all 8 the animals were moved to an unfamiliar surrounding after the social separation. Jugular catheters were placed on the animals 1 d before sampling, blood and saliva samples were taken simultaneously before and after separation. Samples were taken at a 10 min interval during the first 2 h and further samples were taken every 15 min. In response to the stressors, there was an increase in plasma cortisol reaching peak mean values 25 min after the first sample. However, peak values in saliva cortisol in cows and calves were observed 35 min after the first sample. Plasma cortisol correlated well with saliva cortisol (r = 0.626). However, plasma cortisol explained more of the variation in the cortisol concentrations from saliva samples taken 10 to 15 min after (AIC = 727.0; P < 0.001) than in the saliva samples taken at the same moment as the plasma samples (AIC = 810.7; P < 0.001) and no significant effects of breed or group (cow or calf) were found in the models. The correlation coefficient for plasma and saliva-lag was r = 0.744. These results suggest a time lag between plasma cortisol values and associated changes in saliva cortisol values in dairy cattle.

In conclusion, salivary cortisol assessment seems to be a valid method to detect responses of the HPA axis following acute stress in cows and calves. This study suggests a time lag between plasma and saliva cortisol values and this should be considered when using saliva samples as the only measure of the stress response in cattle.