| Fertility is an important economic traits of dairy cows.With the continuous improvement of dairy cow yield,the fertility of cows shows a downward trend,and reproductive regulation protocol,e.g.,TAI protocol,is an effective ways to improve the fertility.Double-Ovsynch(DO)and Presynch-Ovsynch(PO)are two widely used Ovsynch-TAI protocols.However,the regulation effects of the two protocols are reported inconsistently in different studies,resulting in the lack of scientific basis for reproductive management in production practice.Therefore,through correlation,regression and survival analysis with 14777 cows,this study clarified the reproductive regulation effect of the two protocols under different parity and ambience,which provided a scientific basis for the rational selection of TAI protocol.The main conclusions are as follows:1.Month,TAI protocol and parity affect conception rate for the first service(CR).CR was lower from July to September(36%-45%),compared to the rest months(48%-52%),and the influence of month on CR was related to Temperature-Humidity Index(THI);CR of cows treated with DO was increased by 8%;there was a negative correlation between parity and CR,CR of primiparous cows(53%)was higher than that of other parity,CR of multiparous cows with parity from 2 to 6(47%-42%)was lower and there was no difference among them,CR of multiparous cows with parity ≥7(37%-30%)was the lowest and there was no difference among them;in order to study the reproductive regulation effect of different TAI protocols on cows with different parity,cows were divided into groups according to primiparous,parity from2 to 6 and parity ≥ 7.2.DO improved the fertility of primiparous cows: Among 12 ambient indicators,the average THI during 21 days before first service(THI-b)had the highest correlation with CR,and when THI-b was 73,the CR of DO began to decrease linearly,whereas the threshold was 64 in PO;when THI-b <64,64≤THI-b<73 or ≥73,CR was improved under treatment of DO by 6,13 and 19 percent;when THI-b <64,DO reduced non-pregnant rate(hazard ratio=1.32),while no difference on calving interval between DO and PO;when THI-b ≥73,DO reduced non-pregnant rate(hazard ratio=1.42),shortened calving interval by 15 d.3.DO improved the fertility of multiparous cows(parity from 2-6): THI-b had the highest correlation with CR,and the threshold of two protocols was 67;when THI-b <67,DO improved CR by 7 percent,reduced non-pregnant rate(hazard ratio=1.95),and shortened calving interval by 12 d;when THI-b ≥67,DO improved CR by 15 percent,reduced non-pregnant rate(hazard ratio=2.17),and shortened calving interval by 14 d.4.No difference between DO and PO in reproductive regulation effect on CR of multiparous cow(parity ≥7): both effects from protocols and ambience on CR were not significant.5.The economic benefit of DO was greater: in primiparous cows,when THI<64or ≥73,DO improved economic benefit per cow by 290 or 1435 yuan,respectively;in multiparous cows(parity from 2-6),when THI<67 or ≥67,DO improved economic benefit per cow by 870 or 1605 yuan.The results showed that compared with the PO,DO can effectively improve the fertility of primiparous and multiparous cows(parity 2-6),especially in high THI-b;while in high parity cow(parity ≥7),the effects from two protocols were not different.The present paper studied on regulation effects of PO and DO on cows in different ambience and parity,and provided a scientific guidance for the selection of TAI protocol in actual production. |
