Effect of biostimulation on the expression of estrus in postpartum Angus cows

The objective of this study was to evaluate the effect of biostimulation by bull exposure on the expression of estrus in postpartum Angus cows. Ninety Angus cows and their calves were allocated by parity and body frame to three pens (30/pen). From 1-week post partum, one epididectomized mature Angus bull was placed with Groups A and B (BE), whereas Group C served as a Control (NE). Data for duration of estrus (DE), total mounts received (TMR), and intensity of estrus (IE) were recorded using HeatWatch^®. At either the first or second postpartum estrus, there were no differences between BE and NE cows for DE, TMR and IE. However, the period after onset of estrus, cow within treatment and the interaction treatment by period exerted a significant influence on IE. Overall, the greatest IE (P < 0.0001) was observed during the first two periods (6 h). At the first postpartum estrus, IE tended (P < 0.11) to be greater in BE than NE cows during the first 3 h after onset of estrus. However, IE was greater (P < 0.02) in NE cows than BE cows during 4-6 h after onset of estrus. At the second postpartum estrus, IE did not differ between BE and NE cows during the first 3 h after onset of estrus. However, from 4 to 9 h after onset of estrus, IE was greater (P < 006) in NE cows than BE cows. From the results of this study, it was concluded that DE, TMR and IE were not influenced by biostimulation. However, the manner in which mounting activities were distributed across the duration of estrus was influenced by the presence of bulls. © 2005 Elsevier Inc. All rights reserved.