Environmental effects on pregnancy rate in beef cattle1

Abstract

Ten years of calving records were examined from Bos taurus crossbred cows (mean of 182 cows/ yr) to quantify the effects of environmental conditions during the breeding season on pregnancy rate. Estimated breeding dates were determined by subtracting 283 d from the calving date. Relationships were determined between the proportion of cows bred during the periods from the beginning of the breeding season until d 21, 42, and 60 of the breeding season and the corresponding environmental variables. Weather data were compiled from a weather station located approximately 20 km from the research site. Average daily temperature and relative humidity were used to calculate daily temperature-humidity index (THI). Daily averages for each environmental variable were averaged for each period. Minimum temperature (MNTP) and THI for the first 21 and 42 d of the breeding season were negatively associated (P < 0.001) with pregnancy rate. For the 0-to 21-d, 0-to 42-d, and 0-to 60-d breeding periods, respective r 2 for average temperatures were 0.32, 0.37,

Environmental factors affecting daily water intake on cattle finished in feedlots

“…Morrison (1983) reported that RH affects the rate of evaporation from surfaces, so it would be expected to also affect evaporative heat loss. Likewise, SR has been found to influence body temperature and DWI Amundson et al, 2006;Mader et al, 2006).…”

“…In general, a THI of 70 or 72 would be considered a decreased threshold, although differences among animals do exist with high producing animals with increased metabolic heat load having decreased heat stress thresholds (Mader, 2003). Inflection points would possibly represent a threshold or shift in some physiological or biological response due to changing environmental conditions (Amundson et al, 2006). In addition, Mader (2003) and Amundson et al (2006) established the importance of Tmin in energy balance of cattle, mainly used as a strategy to dissipate heat during the night.…”

“…Inflection points would possibly represent a threshold or shift in some physiological or biological response due to changing environmental conditions (Amundson et al, 2006). In addition, Mader (2003) and Amundson et al (2006) established the importance of Tmin in energy balance of cattle, mainly used as a strategy to dissipate heat during the night. Amundson et al (2006) found Tmin inflection point to range from 10.0 to 16.7°C in reproducing females.…”

“…In addition, Mader (2003) and Amundson et al (2006) established the importance of Tmin in energy balance of cattle, mainly used as a strategy to dissipate heat during the night. Amundson et al (2006) found Tmin inflection point to range from 10.0 to 16.7°C in reproducing females. Therefore, a Tmin that is greater than the threshold (12°C) could indicate that feedlot cattle heat loss through convection and conduction during summer nights is no longer at optimum physiological capacity.…”

Metabolic and hormonal acclimation to heat stress in domesticated ruminants

“…In females, heat stress compromises oocyte growth by altering progesterone, luteinizing hormone and follicle-stimulating hormone secretion and dynamics during the estrous cycle (Ronchi et al, 2001). Moreover, heat stress may reduce summer fertility in dairy and beef cows by causing poor estrous expression due to reduced estradiol secretion from the dominant follicle developed in a low luteinizing hormone environment (Biggers et al, 1987; De Rensis and Scaramuzzi, 2003;Amundson et al, 2006). About a 20% to 27% drop in conception rates (Lucy, 2002; Chebel et al, 2004) or decrease in 90-day non-return rate to the first service in lactating dairy cows (Al-Katanani et al, 1999;Ravagnolo and Misztal, 2002) occurs in summer.…”