A case study of a regime using a progesterone releasing intravaginal device
(CIDR) and pregnant mare serum gonadotrophin (PMSG) as a treatment for
post-partum anoestrum in twenty-seven (27) Manawatu
seasonal supply dairy herds.
Diploma in Veterinary Preventative Medicine
1991
Clifton Bernard King
Abstract
Six hundred anoestrus dairy cows from 27 Manawatu dairy farms were treated with a
CIDR-B device for 7 days and with an injection of 400IU pregnant mare serum
gonadotrophin (PMSG) at the time of device removal. The reproductive performance
of these 600 cows was monitored, as was the reproductive performance of the 27
farms from which they came. The mean prevalence of anoestrum among cows in the
27 herds was 12.8%, ranging from 4.3% to 26.0%.
A mean of 59.1% of treated cows were mated within seven days of CIDR-B device
removal. The mean pregnancy rate to first insemination was 51.7%. The mean
interval between CIDR-B removal and conception was 22.3 days, and the nonpregnancy rate of treated cows at the end of the breeding season was 26.6%. There
was a wide variation of results between farms.
Submission rate after CIDR-B removal is not an effective method for assessing the
response, because of the high levels of non-oestrus inseminations after treatment.
Response to treatment should be assessed from in-calf rates confirmed by pregnancy
testing.
The interval to conception following treatment declined by 6.6 days for each unit
increase in body condition score at the time of treatment, and by 2.0 days for each 3
week unit increase in the post-partum interval at treatment. Herds that first treated
their anoestrus cows with CIDRs late in the breeding season achieved shorter
treatment to conception intervals than herds using CIDRs in the early breeding season
(p<0.01). The treatment to conception interval decreased by 0.28 days for each extra
day after the planned start of mating that anoestrus cows were first treated with
CIDRs. The interval between treatment and conception increased by 4.2 days for each
100 cow increase in herd size. Pregnancy rates by the end of the breeding season were
higher in cows with high body condition and with long post-partum intervals at
treatment, and on farms with high first service pregnancy rates and long breeding
periods following CIDR-B removal. The effects of cow condition score and postpartum interval at treatment are especially important in 2 year old cows, but appear of
little importance in older cattle.
Improved cow condition score at the time of treatment was the only factor associated
with a reduction in the planned start of mating to conception interval, resulting from
reduction in the calving to conception interval. The reduction in the planned start of
mating to conception interval associated with treating anoestrus cows earlier in the
breeding season was not the result of a reduction in the calving to conception interval.