OPTIONS FOR ESTRUS SYNCHRONISATION IN CROSSBRED DAIRY CATTLE: EMPHASIS ON CONCEPTION RATE TO INSEMINATION ON ESTRUS OR SYNCHRONIZED OVULATION, EAST SHOA, ETHIOPIA
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Date
2019-06
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Abstract
The study was conducted from November 2018 to June 2019 to evaluate conception rate to different hormonal manipulation of the estrous cycle and insemination on estrus and without estrus at fixed time in crossbred dairy cattle. Before assigning cows to treatments ovaries were scanned by ultrasonography and postpartum cows (>60 days postpartum) were divided into corpus luteum positive (n= 15) and corpus luteum negative (n= 19). All cows with corpus luteum received single PGF2α and detected for estrus and inseminated at standing estrus. Cows without corpus luteum received GnRH at starting day and PGF2α at day seven, detected for estrus within 48 hours and while those in estrus inseminated (Selectsynch) those did not show estrus received second GnRH at day 9 and inseminated at 16-24 hours of the second GnRH (ovulation synchronization). Dairy heifers (≥2 years) were randomly assigned into two groups. One group (n=14) received CIDR and GnRH at starting day and PGF2α at day seven with CIDR removal. The second group heifers (n =13) received GnRH-on day of start (without CIDR) and PGF2α at day seven. All heifers were inseminated either at standing estrus (Selectsynch) or at fixed time (ovulation synchronization). The estrus response was 93.3% in cows treated with single PGF2α, 68.4% for cows receiving GnRH-PGF2α, 50% for heifer receiving CIDR-GnRH-PGF2α and 53.8% for heifers receiving GnRH-PGF2α. The estrus response for all groups was 67.2%. The conception rate was 66.6% to single PGF2α administration and insemination at estrus, 30.7% for GnRH-PGF2α protocol and insemination at estrus, 33.3% for GnRH-PGF2α protocol and timed insemination for cows. Overall conception rate was 71.4% for heifers receiving CIDR-GnRH-PGF2α protocol and 53.8% for GnRH-PGF2α protocol. The difference in conception rate was not statistically significant (P>0.05). In heifers receiving CIDR-GnRH-PGF2α and inseminated at estrus all conceived (100%), while only 42.8% heifers were conceived in CIDR-GnRH-PGF2α and fixed time insemination and difference was not significant (P>0.05). Conception rate was 57.1% in heifers receiving GnRH-PGF2α and inseminated at estrus while it was 50% in GnRH-PGF2α protocol with inseminated at fixed time insemination. BCS and parity showed statistically significant difference (P<0.05) on estrus response and conception in all treatment protocols. It could be concluded that ultrasound scanning for presence of corpus luteum, single PGF2α administration and insemination at standing estrus would give better conception rate in dairy cows than GnRH-PGF2α protocol. In dairy heifers CIDR-GnRH-PGF2α protocol improve conception rate than GnRH-PGF2α without CIDR in general and in particular CIDR-GnRH-PGF2α with insemination at standing estrus gives 100% conception rate.
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Msc Thesis
Keywords
Artificial insemination, Conception rate, Dairy cattle