SIX WEEK PREGNANCY RATES AVERAGE 70% AND SEXED SEMEN USE ON WANE
Breeding programmes for spring calving should now be nearing an end as cows served now will calve in the last week of April 2016. However, at farm level many farmers are considering leaving stock bulls far longer with the herd and to sell May 2016 calvers. There has been a market for these cows in previous years which has been better than cull cow price.
An alternative scenario arising on a number of farms is the establishment of an autumn calving section, whereby breeding stops in early July. Empty fit cows will be identified from a herd scan in September. These will then be bred in December and January.
Currently, our six week pregnancy rates for herd scans range between 54 and 81pc. We use this figure based on cows pregnant for the first six weeks of breeding as a percentage of cows milking in the herd on the day of scanning. There may be a weakness in that late calvers are included which may not have eligibility to establish pregnancy.
The six week targeted pregnancy rate of 90pc for grass-based milk production systems is not realistically feasible at farm level. Even the inclusion of 30pc replacement rates may not generate the targeted 90pc calving rate in six weeks. Calving spread has created its’ own issues regarding late calves as replacements for the dairy herd.
Pregnancy rates in maiden heifers should be close to 70pc for a given service. However, when we adjust for young maiden heifers in the breeding group, delayed puberty associated with previous stressors in development, six week pregnancy rates currently range between 70 and 85pc in our survey data. Therefore, we cannot achieve the desired 90pc six week pregnancy rate.
Sex semen was very much in favour in previous years to generate extra replacements for the dairy herd and associated expansion of same. However, farmers have moved away from the use of sexed semen this year. The costs of sexed semen and the associated reduction in pregnancy rates have been considered prohibitive.
Sexed semen will result in acceptable pregnancy rates if herd health is optimal. In my own experience, stressors in young stock such as coccidiosis, cryptosporidium and pneumonia will result in poorer reproductive performance when they reach 14 to 16 months of age.
Pregnancy rates of 40 to 45pc using sexed semen in first and second lactation cows have been routinely achieved where dry cow and early lactation transition management of the herd have been optimised. Pregnancy rates using AI with conventional semen are currently not above 50pc on a routine basis. Therefore, there are significant stressors at play in the background mitigating successful outcomes to a given breeding opportunity.
Farmers have become frustrated and lost faith in the use of sexed semen. There are differences between bulls in terms of their pregnancy rate using sexed semen and between batches of sexed semen from the same sire. Farmers will have to be given confidence that sexed semen will not result in their breeding programme being thrown into disarray.
Finally, selling sexed semen with a 90pc female bias is unacceptable when a farmer in Kerry discovers from our ScanMan Vet technology that 5 out of 14 pregnancies using sexed semen were bull calves! It should be noted that this was an exceptional case study, but farmers will always remember “the bull calf”.
A cautionary note at this time of year as stock bulls running with the dairy herd is the norm. Over the past month, farmers will either purchase a stock bull or remove a stock bull running with maiden heifers and introduce him to the dairy herd.
Consider the use of AI in association with the stock bull to avoid the 10pc risk of an infertile or subfertile bull. Do not take risks. Ensure a chain is placed on the bull ring at all times. Children are on holidays from school now and are more likely to have contact with livestock. Bulls are considered most dangerous in midsummer. Do not ask children to bring in cows for milking when stock bulls are running with the cows. A “playful” bull confined a client of ours from County Antrim to a wheelchair after he turned on him when the stock were bring moved to new pasture.
Dr. Dan Ryan is a bovine reproductive physiologist and can be contacted at www.cowsdna.com
Article written by Dr. Dan Ryan in the Farming Independent 14th July 2015