Cow performance, adrenal function, and milk quality under varying levels of competition

Twelve dairy cows were used to determine behavior with varying numbers of free stalls and length of feed trough. A least squares procedure, which regressed for numbers of observations, was adapted for obtaining dominance values. Available free stalls were 1.0, .83, .67, .50, .33 per cow. With 1.0 free stalls, linear feed trough was .5, .4, .3, .2, .1 m per cow changed at 7-day intervals. Cow behavior and locations were quantified by time-lapse photography at I-minute intervals during the last 3-days of each treatment. Spatial recommendations for dairy cattle can be greatly reduced. Behavior was altered only when less than .67 free stalls or .2 m of linear trough was available per cow. Minimum stalls needed per cow without altering daily free stall usage = [14.2 hours (average use)]/[hours per day free stalls are available to the herd X .93 (maximum. efficiency before crowding)]. Linear feed trough of .2 m appears adequate to ensure desired amount of eating time when individuals have access to feed in trough 21 hours per day. Estimated individual dry matter intakes were the same at .5 m and .25 m of trough per cow. Intake was affected by time spent eating for .25 m. In 10-variable models for various levels of competition, time spent eating, or in free stalls, and individual dry matter intake were described predominantly by production variables, not dominance values.

Adrenal responsiveness to 200 IU adrenocorticotrophic hormone (ACTH) was determined by quantifying plasma corticosteroids in two groups of lactating Holstein cows. One group of 18 cows received ACTH via jugular catheter 0, 2, or 9 days after introduction to an established group in restricted space (3.96 m2 lot space and .67 free stalls per cow). Differences in total plasma corticoids (area under curve) in response to ACTH were not statistically different although corticoid response 2 and 9 days of stress tended to be greater than day O. A second group of 16 cows received ACTH at 0, 1, 2, or 3 days after introduction to a new group and crowding (2.97 m2 lot space and .5 free stalls per cow). Mean corticoid response to ACTH (area under the curve, ng/ml ± SD) were 161.6 ± 12.6, 158.2 ± 28.2, 227.7 ± 32.2 and 229.9 ± 40.3 for cows inject~d days 0, 1, 2, and 3 respectively, days 2 and 3 differed from day 0 (P<.OS). Bacteriological status of quarter milk samples was not changed by stress. In non-infected quarters of 24 stressed cows, 8 quarters increased above 150,000 somatic cells/ml while 5 quarters decreased below 150,000 cells/m1 of milk after 4 days of stress when compared to 2 and 6 days prior to stress. Stress did not affect milk production relative to controls.