Influence of season and microclimate on fertility of dairy cows in a hot-arid environment.

Records were obtained over a 3 year period from six Holstein dairy farms of 300 to 500 cows each in the Phoenix, Ariz. area. Dairies were selected on the basis of similar management practices, herd size, milk production and facilities (with the exception of cooling systems). Microclimatic modifications (two dairies each) were shade only (approximately 3.7 m2/cow), evaporative-cooled shades and low-pressure water foggers under the shades. Data were categorized by season of calving (spring, Feb.-May; summer, June-Sept.; and fall, Oct.-Jan.). Traits evaluated were calving interval, days open and services/conception. Calving interval was shortest for cows calving in the spring (378 days), intermediate in fall (382 days) and longest in summer (396 days). Similar seasonal trends were observed for days open (103, 103 and 119 days, respectively) and services/conception (1.54, 1.81 and 1.93, respectively). All differences between spring and summer were significant (P less than 0.05). Calving interval and days open were less for evaporative-cooled groups (374 and 98 days, respectively), with no difference between shade only and foggers (391 and 392 days, 112 and 116 days, respectively). Services/conception were similar for all groups (1.72 to 1.79). A significant interaction between microclimate and season for services/conception could be interpreted as (i) smaller season differences for evaporative-cooled groups than for shade or foggers, or (ii) a change in the ranking of control and fogger groups during summer versus fall. Evaporative cooling was more effective than fogging for reducing the detrimental effects of seasonal high temperatures on fertility.

Failure of hair analysis to reflect excessive sodium chloride ingestion by Holstein heifers.

Mineral analysis of hair samples was to assess its value as an indicator of excessive salt ingestion. Ten pregnant Holstein heifers averaging 499 +/- 32 kg were group-fed 9 kg of alfalfa hay cubes and 2 kg of a 14% dairy concentrate mix per head per day. Salt and dicalcium phosphate were available free choice. Prior to treatment animals received fresh water containing 450 ppm total dissolved salts. During treatment, sodium chloride was added to the fresh water at 3500 ppm. Hair samples together with blood and urine were taken immediately prior to start of the experiment and at 30 and 60 days after initiation. Hair samples from two previously marked areas were composited, washed with hot detergent, rinsed, dried with ethanol and then acetone, and wet-ashed. Blood electrolytes and hair and urinary minerals were measured by atomic absorption spectrophotometry. Analysis yielded no significant treatment effects for sodium, potassium, calcium, magnesium in hair and blood serum, and no correlations between hair, blood serum, and urinary minerals. Only urinary sodium reflected the increased sodium ingestion.

Effect of stress on blood leucocyte and milk somatic cell counts in dairy cows.

Blood and milk samples from Holstein cows were examined for total blood leucocyte count, differential blood leucocyte count, milk quality test, and somatic cell count in milk while the cows were stressed by corticotropin injection, confinement in a heat-humidity chamber, or environmental-heat stress by exposure during the hot summer months of June through November in southern Arizona. All three stressing conditions resulted in a moderate blood leucocytosis. Modest increases in somatic cell counts of milk were associated with corticotropin injection and environmental-heat stress. Positive correlations were recorded between blood leucocytes and somatic cell counts of milk in mastitis-free cows injected with corticotropin and between percent blood neutrophils and somatic cell counts of milk in environmental-heat stressed cows with no evidence of current mastitis.