Effect of Season and Stage of Lactation on Performance of Holsteins

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Abstract
Ninety-seven Holstein cows were used to evaluate the effects of season and stage of lactation on physiological measurements, behavior, and milk production. Skin and rectal temperatures and respiration rates were lowest in winter and highest in summer. Skin temperatures increased .39.degree. C per degree rise in ambient temperature, whereas rectal temperature and respiration rate changed .017.degree. C and 1.74 breaths/min per degree increase in air temperature. Eating activity in winter was 5.6 h and decreased to 4.2 h during summer. Lying activity decreaed from winter to summer, whereas standing activity increased. Drinking, defecation, and urination frequency increased from winter to summer. Monthly milk yield was highest during the spring and lowest in winter. Highest milk yield for early and midlactation cows was in the spring, whereas late lactation cows performed best in the summer. Midlactation cows were most adversely affected by summer conditions, and early and late lactation cows were most affected by winter conditions. These data show differential response of cows in different stages of lactation to changes in the environment.