Abstract
The estrus behavior was evaluated during an induced and natural subsequent estrus in twelve Guzera breed cows, in the winter and summer seasons in two consecutive years. The proportion of cows that responded to estrus synchronization was 84.8%. The effect of the interaction season x year of experiment on estrous cycle length was observed. Pro-estrus was longer in the summer (57.69±4.72h) and in the natural estrus (74.23±4.41h) than in the winter (38.95±4.02h) and in the induced estrus (22.40±4.36h). Estrus length was similar in the winter (11.48±0.70h) and in the summer seasons (13.40±0.82h) as well as among cows with induced (12.47±0.75h) and natural estrus (12.41±0.76h). The number of mounts accepted during estrus and the number of mounts accepted/ hour in estrus were similar in winter (29.17±2.86 and 2.59±0.22, respectively) and summer (31.45±3.36 and 2.42±0.26, respectively) as well as between induced (30.23±3.10 and 2.54±0.24, respectively) and natural estrus (30.40±3.14 and 2.47±0.24, respectively). The length and intensity of estrus were not influenced by synchronization or season of the year. Longer period of pro-estrus in summer may favor the identification of sexually active animals in this season.
Highlights
A high percentage of reproductive programs in tropical countries depends on natural mount
Prostaglandin is not effective during the first five days of the estrous cycle and can cause partial luteolysis with subsequent recovery of the corpus luteum function when administered before the 10th day (WRIGHT & MALMO, 1992)
In the estrus synchronization scheme with two prostaglandin applications at 11-day interval, the animals that responded to the first application were found to be between day 6 and day 9 of the cycle on the day of the second application (ODDE, 1990), a stage in which a luteal regression failure may occur
Summary
A high percentage of reproductive programs in tropical countries depends on natural mount. A growing interest in the use of artificial insemination (AI) has been observed in the last decades The success of this technology depends on several factors, with estrus detection being one of the most important. Correct estrus detection is still one the obstacles to obtain high pregnancy rates and is, many times, cited as the most common and expensive flaw in AI programs. Factors such as frequency, length, observation time (ORIHUELA et al, 1983) and number of cows simultaneously in estrus (LAMOTHE et al, 1995) may influence the efficiency of estrus detection programs.
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