Evaporative cooling of ventral regions of the skin in heat-stressed laying hens.

Laying hens held in battery cages in naturally ventilated poultry houses in hot countries usually develop hyperthermia, which adversely affects their performance. The present means of cooling alleviate to some degree, but cannot eliminate, the stress imposed by heat. A new approach to cooling of laying hens was developed, based on wetting the skin and promoting evaporation of water from the ventral regions of the bird. The type of plumage in the ventral regions and the exposed skin of the apteria enable more efficient wetting than is possible with dorsal cooling. A ventral cooling regime, comprising an initial period of frequent wettings followed by intermittent wetting for 10 s every 30 min was able to maintain normothermia of laying hens subjected to a 10-h period of heat exposure. Dorsal cooling was less efficient; body temperature and respiration rate were higher and skin temperatures were lower than in ventrally cooled hens. During 10 d of heat exposure, ventrally cooled hens maintained egg weight and shell index (mg/cm2), whereas their food intake decreased moderately. In contrast, egg weight, shell index, and food intake all decreased markedly in uncooled or dorsally cooled hens. Transient alterations in plasma concentrations of corticosterone, progesterone, and estradiol were noted in uncooled and dorsally cooled hens but not in ventrally cooled hens. Results indicate that ventral cooling is an efficient method to alleviate heat stress in laying hens during summer. Successful implementation of ventral cooling in poultry houses will depend on optimal installation of sprinklers and on minimal wetting of manure.

Two methods of inducing low plasma progesterone concentrations have different effects on dominant follicles in cows.

The effects of two methods of inducing low progesterone concentrations on the shape of the plasma progesterone curve and on follicular characteristics in lactating cows were studied. A low ascending progesterone curve was elicited by three PGF2alpha injections on d 3 to 4 of the estrous cycle; a low constant curve by induction of corpus luteum regression on d 6 and insertion of two progesterone-containing intravaginal devices from d 6 to 15 of the cycle. Plasma progesterone concentration was highest in the untreated control group, intermediate in low ascending group, and lowest in the low constant group. On d 15, both control and low ascending groups had one large healthy and one large atretic follicle, suggesting a turnover of follicular waves; in the low constant group, the presence of only one very large healthy follicle indicated follicular persistence. Estradiol concentration in the follicular fluid and its production by granulosa cells were highest in the low constant, intermediate in the low ascending, and lowest in the control group. Androstenedione concentration in the follicular fluid and its production by theca cells were higher in the low constant than in the low ascending and control groups. The results indicate that the low ascending progesterone curve affected follicular development and steroidogenesis differently from the low constant curve. We suggest that the low ascending curve mimics the effects of naturally occurring low plasma progesterone concentrations better, and it might, therefore, be used as a model for studying the effects of low plasma progesterone on fertility.

Seasonal and acute heat stress effects on steroid production by dominant follicles in cows.

The present study concerned the seasonal and acute effects of heat stress on steroid concentrations in follicular fluid and on steroid production by granulosa and theca interna cells, in bovine dominant follicles. Three groups of cows were studied: summer (n = 5), autumn (n = 5) and winter (n = 9) cows. During the winter season, another group of cows was acutely heat-stressed from days 3 through 5 of the estrous cycle (n = 5). On day 7 of the estrous cycle, follicular fluid from first-wave dominant follicles was aspirated, and dispersed granulosa and theca cells from each seasonal group were incubated for 18 h at normothermic (37.5 degrees C) or high (40.5 degrees C) temperatures. Cells were incubated in media only or in media containing testosterone (300 ng ml-1, for granulosa cells) or forskolin (4 micrograms ml-1, for theca cells). In follicular fluid the 17 beta-estradiol concentration was high (P < 0.05) in winter and low in autumn, and summer, the androstenedione concentration was high in summer (P < 0.05), low in autumn, and intermediate in winter. During the winter season, acute in vivo heat stress increased follicular fluid androstenedione and decreased estradiol to levels comparable with those prevailing in summer. Basal and forskolin-stimulated androstenedione production by theca cells was higher (P < 0.05) in the winter group than in the summer and autumn groups, and also higher than in the cows that were heat-stressed during winter, which suggests that theca cell function is susceptible to chronic (summer), short-term (winter) and delayed (autumn) heat stresses. In vitro incubation at high temperature (40.5 degrees C) reduced the high, forskolin-stimulated androstenedione production in winter (P < 0.05). Estradiol production by granulosa cells was high in winter and autumn, and low in summer (P < 0.05). Acute heat stress in winter did not alter estradiol production relative to winter controls, whereas a high incubation temperature (40.5 degrees C) reduced (P < 0.05) estradiol production only in the autumn, when the highest production rate was recorded. The results indicate a differential effect of heat stress on the functions of granulosa and theca cells. Both concurrent and delayed effects of heat stress on the steroidogenic capacity of ovarian follicles in cattle are presented.

Effect of heat stress on tonic and GnRH-induced gonadotrophin secretion in relation to concentration of oestradiol in plasma of cyclic cows.

Effects of acute and seasonal heat stress on tonic and GnRH-induced LH and FSH secretion were examined during the early follicular phase of the oestrous cycle of cows (n = 40). Prostaglandin F2 alpha was injected on day 11 +/- 1 of the oestrous cycle and on the next day blood samples were collected at intervals of 15-20 min for 14 h, and i.m. injection of GnRH was given after 7 h. Treatments compared were control versus acute heat stress during blood sampling in winter, and cooled versus chronic heat stress in summer. Before GnRH injection, chronic heat stress in summer did not affect basal concentrations of plasma LH, but did lower LH pulse amplitude. However, in cows with low plasma oestradiol (1.9 +/- 0.2 pg ml-1), the mean and basal concentrations and amplitude of tonic LH pulses were reduced by heat stress (3.1, 2.1 and 4.8 versus 1.9, 1.4 and 2.5 ng ml-1, respectively). In cows with high plasma oestradiol (6.3 +/- 0.5 pg ml-1), these parameters were not affected. In chronically heat stressed cows in summer, GnRH-induced increases in plasma LH and FSH concentrations were the same as in the cooled controls. However, in cows with low plasma oestradiol, mean concentrations of FSH in plasma (31.8 versus 25.5 ng ml-1), the peak of the GnRH-induced FSH and LH surge (FSH 47.4 versus 35.6 ng ml-1, LH 50.7 versus 37.3 ng ml-1) and the shape of the GnRH-induced FSH and LH curves (treatment by time interaction) were significantly lower in non-cooled versus cooled controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorption of protein, fatty acids and minerals in young turkeys under heat and cold stress.

1. Absorption of protein, fatty acids, calcium, phosphate and potassium by young turkeys maintained at thermoneutral (24 degrees C), hot (35 degrees C) and cold (8 degrees C) conditions was examined. 2. Non-acclimatised, heat-stressed birds absorbed less potassium and phosphate, whereas absorption of nitrogen, fatty acids and calcium was not altered, as compared with birds at 24 degrees C. Non-acclimatised, cold-stressed birds absorbed less calcium than control birds and more nitrogen than non-acclimatised, heat-stressed birds. 3. Heat acclimatization might reduce the adverse effect of heat stress on potassium and phosphate absorption.

Upper critical temperatures and forced ventilation effects for high-yielding dairy cows in a subtropical climate.

Upper limit of thermal stability and subsequent rise of thermoregulatory functions as affected by forced ventilation were examined. Rectal temperature, respiratory frequency, ear skin temperature, body weight, and milk yield were recorded biweekly July to March over 2 yr for 170 Israeli-Holstein cows (305-day milk yield 9000 kg/cow) at air temperatures 10 to 36 degrees C. Cows were in an open shelter. One side was force ventilated over 2.5 m along the stanchions (air velocity 1.5 to 3 m/s) from 0500 to 2200 h. Control side mean air velocity was .5 m/s. Within the 10 to 24 degrees C range, rectal temperature was not affected by air temperature or forced ventilation but increased by .02 degrees C/kg fat-corrected milk in animals producing above 24 kg/day. Between 26 and 36 degrees C rectal temperature increased with air temperature in both groups; rate of rise was halved by forced ventilation. In this range of air temperature, rectal temperature increased with rising milk yield, as in the lower air temperature range, in both high-producing and lower-producing cows in forced ventilation. Body weight or parity did not have significant effects. Mean ear skin temperature was higher for control animals, but its rate of increase with air temperature was similar in both groups. Forced ventilation reduced mean respiratory rate. An upper critical temperature is 25 to 26 degrees C and is independent of milk yield or acclimatizational state of cows exposed to the natural sequence of climate.