Estrous cyclicity in nonlactating and lactating Holsteins and Jerseys during a Pakistani summer

Coping with a challenging environment: effects of seasonal variability and reproductive status on glucocorticoid concentrations of female baboons (Papio cynocephalus)

Environmental stressors impact physiology and behavior in many species of animals. These effects are partly mediated through changing concentrations of glucocorticoids, which also vary with reproductive state and social conditions. Prior research has focused largely on seasonal breeders, but the close temporal linkage between season and reproductive state in these species hinders ability to disentangle environmental effects from those of the animal's reproductive status. Here we assessed the effects of environmental challenges on the fecal glucocorticoid (fGC) levels of non-seasonal breeders, female baboons (Papio cynocephalus) of Amboseli, Kenya. Amboseli is characterized by a long dry season, during which food and water become scarce, and by extreme temperatures above 40 degrees C in the shade during some months of the year. We found that after accounting for female reproductive status and individual variability, females exhibited higher fGC levels during the dry season than during the wet season. Further, during the wet season, fGC levels were higher in months of high average daily maximum temperatures. During the dry season, fGC levels were elevated both in hotter months and in months during which the baboons spent a relatively high proportion of time feeding. In spite of these stressors, female baboons reproduce during all months of the year in Amboseli, unlike most other mammals in this environment. This may be attributable to their extreme adaptability, specifically their diversified diet, and their ability to modify their behavior, including their activity profiles.

The effects of GnRH administration postinsemination on serum concentrations of progesterone and pregnancy rates in dairy cattle exposed to mild summer heat stress

The objective of this study was to evaluate whether administration of GnRH postinsemination would improve reproductive performance in heat-stressed dairy cattle. Estrous cycles of Holstein cows were synchronized using the OvSynch protocol and cows were artificially inseminated. Cows were then administered the following treatments: control (no GnRH; n=37), GnRH (100 microg) on Day 5 (GnRH-D5; n=34), or GnRH (100 microg) on Day 11 (GnRH-D11; n=34) postinsemination. Cows were provided access to both fans and sprinklers, and environmental data was collected hourly. Rectal temperatures and blood samples were obtained from cows on Days -9, -2, 0 (AI) and on alternate days from Day 5 to Day 19 postinsemination. Blood serum was collected for the analysis of progesterone (P(4)) by RIA. In a subset of cows (n=6/treatment) ultrasonography was performed on alternate days from Day 5 to Day 19 postinsemination to assess numbers of corpora lutea (CL) and CL cross-sectional areas. Pregnancy status of cows was confirmed at Day 30 postinsemination. Environmental data indicated that cows experienced mild heat stress during the trials (mean daily THI=73-77). Serum P(4) was greater (P<0.05) after Day 9 for GnRH-D5 cows and after Day 15 for GnRH-D11 cows through Day 19 postinsemination. The number of CLs present for GnRH-D5 cows was greater (P<0.05) on Day 17 than in either the control or GnRH-D11 treatment groups. On Day 17 postinsemination, both the GnRH-D5 and GnRH-D11 cows were observed to have greater (P<0.05) total CL tissue area than control cows. The interval from insemination to when serum P(4) returned to <1 ng/ml (i.e. luteolysis and return to estrus) did not differ (P>0.10) among treatment groups. Control cows (19%) tended to exhibit lower pregnancy rates (P<0.08) compared to the GnRH-D5 and GnRH-D11 treatment groups combined (35%). In summary, the treatment of heat-stressed dairy cows with GnRH postinsemination (Day 5 or 11) results in the appearance of more CL tissue, increased serum concentrations of P(4) and a tendency toward greater pregnancy rates.

An Alternative AI Breeding Protocol for Dairy Cows Exposed to Elevated Ambient Temperatures before or after Calving or Both

Our objective was to determine if a timed artificial insemination (AI) protocol (Ovsynch) might produce greater pregnancy rates than AI after a synchronized, detected estrus during summer. Lactating Holstein cows (n = 425) were grouped into breeding clusters and then assigned randomly to each of two protocols for AI between 50 and 70 days in milk. All cows were treated with GnRH followed 7 d later by PGF2alpha. Ovsynch cows then were treated with a second injection of GnRH 48 h after PGF2alpha and inseminated 16 to 19 h later. Controls received no further treatment after PGF2alpha and were inseminated after detected estrus. Pregnancy was diagnosed once by transrectal ultrasonography (27 to 30 d after AI) and again by palpation (40 to 50 d). Based on concentrations of progesterone in blood collected before each hormonal injection, only 85.4% of 425 cows were considered to be cycling. Although conception rates were not different between protocols at d 27 to 30, AI submission rates and pregnancy rates were greater after Ovsynch (timed AI) than after detected estrus. A temperature-humidity index > or = 72 was associated with fewer controls detected in estrus with lower conception than for controls detected in estrus when index values were < 72, whereas the reverse was true for cows after the Ovsynch protocol. We concluded that a timed AI protocol increased pregnancy rates at d 27 to 30 because its success was independent of either expression or detection of estrus. However, because of poorer embryonic survival in Ovsynch cows during heat stress only (39.5 vs. 69.2% survival for Ovsynch and control, respectively), pregnancy rates were not different by d 40 to 50 after timed AI.

Effect of gonadotropin-releasing hormone at estrus on subsequent luteal function and fertility in lactating Holsteins during heat stress

The experiment used lactating Holstein cows (n = 94) from three herds in Mississippi. The experiment was conducted during late summer when temperatures were hot enough to cause a measurable stress response in cows in order to determine the effect of GnRH administration during estrus on fertility and subsequent luteal function of cows under these conditions. The mean ranges for ambient temperature, relative humidity, and temperature-humidity index during the study were 21.4 to 32.8 degrees C, 67 to 95%, and 21.6 to 29.6, respectively. After injection of PGF2 alpha for synchronization of estrus, cows were alternately injected with 100 micrograms of either GnRH or saline (control) at detection of estrus, followed by AI 10 to 12 h later. From 14 treated cows and 14 control cows, blood samples were drawn by venipuncture just prior to treatment and at 5-d intervals until 30 d after treatment. Serum progesterone concentrations were determined by radioimmunoassay. Mean progesterone concentrations were higher for the cows treated with GnRH than for the controls. The pregnancy rate from first AI was 28.6% for all treated cows and 17.7% for control cows. On d 20, 42.8% of the treated cows and 57.1% of the control cows exhibited progesterone concentrations that were typical of pregnancy. When pregnancy was diagnosed in these cows after d 45, pregnancy rates had decreased significantly for controls but not for cows given GnRH at estrus, suggesting greater embryonic survival in treated cows. We concluded that GnRH treatment enhanced secretion of luteal progesterone and embryo survival.

Corpus luteum growth and function in lactating Holstein cows during spring and summer

Corpus luteum growth and function were monitored daily for a complete estrous cycle by ultrasonography and peripheral serum progesterone in lactating, cyclic Holstein cows during spring (n = 8) and summer (n = 8). For spring and summer, respectively, daily ambient temperatures (mean +/- SEM) were 21.2 +/- .9 and 31.1 +/- .3 degrees C. In summer compared with spring, early morning rectal temperatures were higher on d 1, 2, and 3, when the corpus luteum was forming, and on d 15 and 19. The length of the luteal phase and the corpus luteum cross-sectional area were similar for the two seasonal groups. Central luteal cavities were observed during spring and summer. Serum progesterone secreted between d 6 and 18 was lower during summer. In addition, progesterone concentrations during the entire luteal phase and the peak magnitude of progesterone tended to be lower during summer. Suppressed luteal function may contribute to low fertility when cows are inseminated during summer.

Estrous and endocrine responses of lactating Holsteins to forced ventilation during summer

Fourteen lactating and cycling Holsteins in each of two summers were assigned randomly to pens in a free-stall barn either with or without overhead fans to study the effect of fan cooling on certain endocrine and behavioral responses during the estrous cycle. After an adjustment period of 8 d in the first summer and 21 d in the second summer, jugular cannulas were inserted, and 25 mg of PGF2 alpha were injected. After injection, blood samples were collected frequently for 84 h in the first summer and 88 h in the second summer, followed by collection three times weekly for 3 wk thereafter each summer. Rectal temperatures were lower in the group cooled by fans than in the control group each summer. Luteal progesterone secretion tended to be greater in the fan group each summer; area under the luteal phase curve was significantly higher than for controls during the second summer. There was tendency for more preovulatory surges of LH and higher estrous responses rates in the fan group during the second summer. Thus, fan cooling of lactating dairy cows for several weeks before anticipated breeding provides potential for more efficient reproductive performance during the summer.