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Title: SOCIAL AND BREED EFFECTS ON THE EXPRESSION OF A PGF INDUCED OESTRUS IN BEEF COWS

Author
item LANDEATA-HERNANDEZ, A. - UNIV. OF ZULIA,VENEZULA
item PALOMARES-NEVADA, R. - UNIV. OF ZULIA,VENEZUELA
item SOTO-CASTILLO, G. - UNIV. OF ZULIA,VENEZUELA
item ATENCIO, A. - UNIV. OF ZULIA,VENEZUELA
item Chase, Chadwick - Chad
item CHENOWETH, P. - KANSAS STATE UNIVERSITY

Submitted to: Reproduction in Domestic Animals
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/14/2004
Publication Date: 11/1/2004
Citation: Landeata-Hernandez, A.J., Palomares-Nevada, R., Soto-Castillo, G., Atencio, A., Chase, C.C., Chenoweth, P.J. 2004. Social and breed effects on the expression of a pgf a induced oestrus in beef cows. Reproduction of Domestic Animals. Vol.39, pp 1-6.

Interpretive Summary: A limitation to the widespread use of artificial insemination (AI) in beef cattle is due to problems associated with the detection of estrus. Detection of estrus is dependent upon outward behavioral expression as well as duration and intensity of expression. Human factors such as time devoted to surveillance are important. Animal factors such as breed type appear to play a role and more recently social organization has been identified to play a role. The objective of this study was to determine the effect of social organization and breed type on the expression of an induced estrus (synchronized) in a mixed breed herd comprised of Angus (temperate adapted), Brahman (tropical adapted), and Romosinuano (tropical adapted) cows. Mounting activity was recorded using a radio-telemetric system (HeatWatch). Social order was determined by the assessment of each cow into one of three categories: dominant, intermediate, and subordinate based on visual observations. Breed type affected the length of time that elapsed from synchronization treatment to onset of estrus, the duration of estrus, and the total number of mounts recorded, but not the intensity of estrus. The intensity of estrus was greatest during the first 9 hours after the onset of estrus regardless of breed type. In general, dominant cows came into estrus later, had a longer duration of estrus, and had fewer total mounts recorded than subordinate cows. However, dominant Angus came into estrus earlier than subordinate Angus cows and dominant Senepol cows had a shorter duration of estrus. These results indicate that both breed type and social organization affect estrous behavior following an induced estrus. These results are useful to commercial cattle producers with mixed breed herds using artificial insemination as an economical means to advance genetic progress.

Technical Abstract: Social organization and breed effects following PGF2a were studied in mature Angus, Brahman and Senepol cows allocated into two groups (each A = 5, B = 5 and S = 5). Variables including interval to oestrus onset (IEO), oestrous duration (DE), total mounts received (TMR), and oestrous intensity (IE) were derived via HeatWatch. Breed-type influenced IEO (B = 42.6 h; S = 54.6 h; and A = 27.8 h; p < 0.003). Within breeds, dominant B (69.4 h) and S (65.5 h) cows were slower (p < 0.05) to be detected in oestrus than subordinate (38.1 h) and intermediate (40.6 h) cows. However, within A, dominant cows (16.4 h) were detected in oestrus earlier (p < 0.05) than intermediates (44.3 h) and subordinates (32.7 h). Angus (21.5 h) and B (22.1 h) cows had longer (p < 0.01) DE than S (9.1 h). Dominant (20.4 h) and intermediate (20.2 h) cows had longer DE (p < 0.04) than subordinates (12.1 h) although the interaction breed x social order showed that dominant S had shorter DE than dominant A and B (10.1, 34.8, and 20.0 h, respectively; p < 0.001). Angus cows had less TMR than B (p < 0.02) and tended to be less than S cows (p < 0.06). Overall, greatest (p < 0.008) IE occurred in the first 9 h after onset of oestrus with no breed effect (p > 0.05). Dominant cows tended (p < 0.10) to have less TMR (3.2 mounts) than subordinate (4.1 mounts) and intermediate (4.7 mounts) throughout, especially 3-6 h after oestrus onset (p < 0.07). Breed and social order both influence PGF2a-induced oestrus behavior.