|Chase, Chadwick - Chad|
Submitted to: Theriogenology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/27/2002
Publication Date: 6/27/2002
Citation: Landaeta-Hernandez, A.J., Yelich, J.V., Lemaster, J.W., Fields, M.J., Tran, T., Chase, C.C., Rae, D.O., Chenoweth, P.J. 2002. Environmental, genetic and social factors affecting the expression of estrus in beef cows. Theriogenology.57:1357-1370. Interpretive Summary: Artificial insemination (AI) is the most economical means to advance genetic progress in beef cattle. Effective estrous detection is critical to the success of AI in beef cattle. Knowledge of factors that influence the expression of estrus should lead to more effective estrous detection and success in AI. Previous studies suggest that genotype and environment are factors that can influence the expression of estrus in beef cattle. The objectives of this study were to evaluate the effects of breed (Angus, Brahman, and Senepol) and social status (dominance) on the expression of estrus during synchronized (programmed) and spontaneous estruses. Cows under synchronized estrus conditions expressed a longer and more intense estrus than cows that exhibited spontaneous estrus. However, behavioral estrus data between synchronized and spontaneous estruses were confounded due to an increased temperature-humidity-index (THI) that occurred during spontaneous estrus, making it difficult to determine which factor(s) had the most influence on estrus expression. Breed had a significant effect on the interval to onset of synchronized estrus and duration of estrus. Dominant cows took longer to exhibit estrus than subordinate cows during synchronized estrus. It appears that the combination of heat stress and the frequent handling and restraint of cows during spontaneous estrus contributed to decreased estrus intensity. In conclusion, type of estrus, synchronized or spontaneous, and the potential interactions with THI and breed can exert significant effects on characteristics associated with behavioral estrus in Angus, Brahman, and Senepol cows, particularly when the breeds are managed together. These interactions can have significant implications for strategies implemented to detect estrus in cattle in subtropical climates.
Technical Abstract: Genetic, social and environmental factors affecting behavioral estrus were evaluated in Angus (n = 10), Brahman (n = 10) and Senepol (n = 10) cows during a synchronized estrus and subsequent spontaneous estrus. Cows were equally stratified by breed to two groups of 15. Both groups were pre-synchronized with a modified two-injection PGF protocol. At the start of the experiment, cows were treated with 25 mg PGF followed by a second and third administration of 12.5 mg PGF, 11 and 12 days later to induce synchronized estrus. The subsequent estrus was designated as spontaneous estrus. Behavioral estrus data including the onset and end of estrus, estrous duration and the total number of mounts received for the synchronized and spontaneous estruses were collected using HeatWatch. Interval from the third PGF treatment to the onset of a HeatWatch estrus occurred earlier (P < 0.05) in Angus (31 h) than Brahman (53 h) or Senepol (53 h) cows, with dominant Senepol and Brahman cows taking longer to exhibit estrus after PGF than subordinate cows. The duration of the synchronized estrus tended to be shorter (P < 0.06) in Senepol (12 h) than in Angus (19 h) or Brahman (17 h) cows. Behavioral estrus data between the two periods were confounded by greater temperature-humidity index (THI) values during spontaneous estrus. The THI during spontaneous estrus appeared (P = 0.09) to affect the duration of estrus (9 versus 16 h) and did affect (P < 0.0001) the total number of mounts received (8 versus 34 mounts) during spontaneous estrus compared to synchronized estrus. Breed had no effect (P > 0.10) on the duration and total number of mounts received during synchronized and spontaneous estruses. In conclusion, type of estrus (synchronized or spontaneous), THI, social dominance and breed exerted significant effects on characteristics associated with behavioral estrus in beef cattle in subtropical environments.