Response to GnRH on day 6 of the estrous cycle is diminished as the percentage of Bos indicus breeding increases in Angus, Brangus, and Brahman × Angus heifers
Department of Animal Sciences, University of Florida, Gainesville, FL 32611, United States.Animal Reproduction Science (Impact Factor: 1.51). 01/2008; 103(1-2):38-51. DOI: 10.1016/j.anireprosci.2006.12.008
Angus (n=6), Brangus (5/8 Angus x 3/8 Brahman, n=6), and Brahman x Angus (3/8 Angus x 5/8 Brahman, n=6) heifers exhibiting estrous cycles at regular intervals were used to determine if the percentage of Bos indicus breeding influenced the secretory patterns of LH in response to a GnRH treatment on Day 6 of the estrous cycle. Heifers were pre-synchronized with a two-injection PGF(2 alpha) protocol (25 mg i.m. Day -14 and 12.5 mg i.m. Day -3 and -2 of experiment). Heifers received 100 microg GnRH i.m. on Day 6 of the subsequent estrous cycle. Blood samples were collected at -60, -30, and -1 min before GnRH and 15, 30, 60, 90, 120, 150, 180, 240, 300, 360, 420, and 480 min after GnRH to determine concentrations of serum LH. Estradiol concentrations were determined at -60, -30, and -1 min before GnRH. On Day 6 and 8, ovaries were examined by ultrasonography to determine if ovulation occurred. On Day 13, heifers received 25 mg PGF(2 alpha) i.m. and blood samples were collected daily until either the expression of estrus or Day 20 for heifers not exhibiting estrus to determine progesterone concentrations. There was no effect (P>0.10) of breed on ovulation rate to GnRH as well as size of the largest follicle, mean estradiol, and mean corpus luteum volume at GnRH. Mean LH was greater (P<0.05) for Angus (7.0+/-0.8 ng/mL) compared to Brangus (4.6+/-0.8 ng/mL) and Brahman x Angus (2.9+/-0.8 ng/mL), which were similar (P>0.10). Mean LH peak-height was similar (P>0.10) for Brangus (13.9+/-3.4 ng/mL) compared to Angus (21.9+/-3.4 ng/mL) and Brahman x Angus (8.0+/-3.4 ng/mL), but was greater (P<0.05) for Angus compared to Brahman x Angus. Interval from GnRH to LH peak was similar (P>0.10) between breeds. As the percentage of Bos indicus breeding increased the amount of LH released in response to GnRH on Day 6 of the estrous cycle decreased.
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ABSTRACT: Timely onset of postpartum ovarian activity is vital for optimal reproductive performance of dairy cows. Much depends upon genetic constitution of an animal although several factors interplay to govern the onset of postpartum ovarian activity. South Asian zebu cattle have much longer service period when compared with other exotic or crossbred cattle reared in the same Asian environment, which suggests differences in their genetic makeup. However, the cows with same genetic configuration expressed better reproductive potential when reared under different environment, such as in Brazil and Mexico, which suggests the role of extrinsic factors such as management, nutrition, environment and disease conditions. Better management of animals (provision of proper shade, water and housing, efficient oestrous detection and timely insemination), good quality nutrition supplemented with appropriate minerals and vitamins, prevention of diseases (vaccination, deworming, suitable therapeutic interventions) and application of biotechnology have helped in improving postpartum ovarian activity and, therefore, reproductive performance of zebu cattle in Asia. No comprehensive study appears to have been carried out on the various aspects of reproduction in zebu cattle reared under South Asian socio-agro-climatic conditions. This paper is a modest effort to collect what ever information available and to critically review the postpartum ovarian activity in zebu cattle with special reference to the effect of the various managemental practices and pharmacological interventions.
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ABSTRACT: The aim of this study was to compare the estrus response and pregnancy rate between the indigenous beef cows of Malaysia; Kedah-Kelantan (KK) and the exotic beef cows; Brangus (BR) following progesterone and prostaglandin-based estrus synchronization treatments. A total of 40 KK and 30 BR open cows were selected and each breed group was randomly divided equally into two. Cows in KK1 and BR1 were treated with estradiol benzoate (Cidirol, 1 mg, im) each at the time CIDR® was inserted (Day 0). Cloprostenol (Estrumate, 250 μg,im) was administered at the time of CIDR® removal on Day 9 while 1 mg of Estradiol Benzoate (EB) was injected on Day 10. On the other hand, KK2 and BR2 cows received intramuscular injections of 500 and 250 ug of cloprostenol, on Day 0 and 11, respectively. All cows were then observed for estrus signs and scanned per rectum for ovulation followed by AI upon detection of estrus. Pregnancy status was diagnosed 45 days after AI. Both treatments were effective in inducing observable estrus in all groups with synchrony of ovulation resulting in CL development and pregnancy. In the progesterone4)ased treatment groups, 84.2% of KK1 and 78.8% of BR1 responded. In the prostaglandingsed treatment groups, KK2 responded with the highest proportion (80.0%) compared with BR2 (50.0%). However, there was no significant difference in rate of ovulation (84.2 vs. 64.3%; 70.0 vs. 42.9%) and pregnancy (31.6 vs. 14.3%; 45.0 vs. 21.4%) among all the four experimental groups. The interval to ovulation from the last treatment time varied significantly among all the treatment groups with a higher variation observed in BR, ranging from 48 h when treated with CIDR to 84 h after treatment with PGF2α. These variations could be explained by the difference in ovarian status at the time of treatment. In conclusion, the result of this data showed KK cows had a better rate of ovulation and pregnancy than BR cows in both treatments though not statistically significant. It can therefore be gathered that KK and BR responded effectively to estrus synchronization and produce acceptable pregnancy rates by both progesterone and prostaglandn-based protocols for breeding and genetic improvement.
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