Environmental profile and critical temperature effects on milk production of Holstein cows in desert climate.

The environmental profile of central Arizona is quantitatively described using meteorological data between 1971 and 1986. Utilizing ambient temperature criteria of hours per day less than 21 degrees C, between 21 and 27 degrees C, and more than 27 degrees C, the environmental profile of central Arizona consists of varying levels of thermoneutral and heat stress periods. Milk production data from two commercial dairy farms from March 1990 to February 1991 were used to evaluate the seasonal effects identified in the environmental profile. Overall, milk production is lower during heat stress compared to thermoneutral periods. During heat stress, the cool period of hours per day with temperature less than 21 degrees C provides a margin of safety to reduce the effects of heat stress on decreased milk production. Using minimum, mean and maximum ambient temperatures, the upper critical temperatures for milk production are 21, 27 and 32 degrees C, respectively. Using the temperature-humidity index as the thermal environment indicator, the critical values for minimum, mean and maximum THI are 64, 72 and 76, respectively.

Physiological, productive, and economic benefits of shade, spray, and fan system versus shade for Holstein cows during summer heat.

During the 1984 summer, effects of spray and fan in freestall areas and feeding areas on milk yield, plasma growth hormone and prolactin, freestall utilization, and economic significance for Holstein cows were studied. Weekly milk and rectal temperatures at morning and afternoon milkings were higher for cows in shade than in shade with spray and fan cooling. Compared with rectal temperature, milk temperature measured in the clawpiece provided a more reliable indicator of heat stress than in the milk meter. Diurnal pattern of rectal temperature from 4-h measurements showed an average of 12 h in which maximal rectal temperatures of cows in shade were greater than 39 degrees C, but cows in the shade plus spray plus fan group had rectal temperatures below 39 degrees C all day. Plasma growth hormone was higher and prolactin lower for cows in shade plus spray and fan than cows in shade only. Cows cooled with spray and fan under shade produced 2 kg/cow per d more than cows in shade alone. Economic analysis showed a net income of 22 cents/cow per day for spray plus fan under shade. Results suggest that milk temperature is a practical technique to assess heat stress in dairy cattle, and the use of spray plus fan is a profitable means to maximize cow comfort and lessen stress-induced decline in milk production.

Spray cooling effects on milk production, milk, and rectal temperatures of cows during a moderate temperate summer season.

During summer 1982, responses of lactating Holstein and Guernsey cows were measured by milk temperature recorded by a Digital Dataloger with thermocouples attached to Boumatic flow meters. Maximum air temperature and temperature-humidity index averaged 30.8 degrees C and 75.6 for July. Breed did not affect milk temperature, but within-breed milk temperature increased with production. In a second study, benefits of spray cooling were evaluated with 24 Holsteins in midlactation assigned randomly to two groups of 12 and maintained under loose-housing conditions. Spray nozzles were installed in the walkways and under the manger shade for the spray treatment group. Maximum temperature and temperature-humidity index during the spray study were 27 degrees C and 73.9. Rectal temperature taken following milking averaged less for treatment than control (38.8 versus 39.1 degrees C). Milk temperature was similar (37.8 versus 38.1 degrees C). Daily milk yield was .70 kg higher than controls. Milk temperature may provide reliable indication of climate stress similar to rectal temperature, and spray cooling improves cow comfort and lessens summer decline of milk production.

Seasonal variations in rectal temperature of Yankasa sheep.

From measurements of rectal temperature (Tre) at 06:00h (06:00Tre) and at 14:00h (14:00Tre), meteorological stress was determined in six Yankasa ewes in terms of per cent rise of 14:00Tre over 06:00Tre reference values during the harmattan and hot-dry seasons. Absolute and mean Tre values were significantly higher (P less than 0.05) during the harmattan than the hot-dry season. In both seasons, mean 14:00Tre was significantly higher (P less than 0.01) than 06:00Tre. The mean diurnal difference between 14:00Tre and 06:00Tre, i.e. delta Tre was about 1 degrees C during the harmattan but ranged between 0.5 and 0.7 degrees C during the hot-dry season. All animals were observed to shiver during harmattan nights.

Effect of season on estrous cycle of Yankasa sheep.

An investigation was conducted to establish the effects of harmattan and hot-dry season on estrous cycle length, onset, and duration of estrus in Yankasa sheep indigenous to the Nigerian guinea savanna zone. Mean cycle lengths were 16.8 +/- 0.58 and 16.4 +/- 0.53 days during harmattan and hot-dry seasons, respectively; short cycles, 5-13 days, and long cycles, 21 to 30 days, were observed during both seasons. During the harmattan season, 57.1% of estrus began at night while 70% started at night during the hot-dry season. The duration of normal estrus observed during the harmattan, 33.6 +/- 5.87h, significantly decreased (P0.05) during the hot-dry season (24.0 +/- 5.45h). It is suggested that twice daily observation at 12-hour intervals will suffice to detect estrus in this breed of sheep.