INFERTILE BULLS AND EMBRYO DEATH REDUCE 6 WEEK CALVING RATES
The improvement in weather for the past three weeks has provided an excellent opportunity to preserve top quality silage and get slurry spread in preparation for second cuts of silage. Farmers are now heeding the need to have extra reserves of silage to address the risk of an extended indoor feeding period.
Milk proteins are reduced significantly on many dairy units. One case study with a 170 cow dairy herd in Cork comes to mind. His milk protein is 0.28% less than that for average milk deliveries in May compared with this time last year. This alone has reduced his milk cheque by €2800. In addition he has had to spend an extra €3000 on concentrates.
Managing grass when weather conditions improved created a scenario of “famine to a feast” with a consequent improvement in grass quality available for grazing. Removing grazing blocks from the rotation to make silage has been essential to create a high quality sward regrowths.
Farmers are now in catch up mode as there is a continuous backlog of work to catch up on the farm. AI technicians have told me that there was a shorter period of intensive use of AI this season prior to introduction of stock bulls. Farmers are now using more synchronization programmes for their maiden heifers. This has enabled greater use of AI, where some of these programmes facilitate fixed line AI of all heifers on a given day. Scanning results in terms of first serviced pregnancy rate vary tremendously by farm. If the heifers are “fit” by breed and age, pregnancy rates of 65pc are the norm. However, these programmes used in conjunction with undersized pre-pubertal heifers have resulted in poor pregnancy rates and heifers either still in a pre-pubertal or cystic reproductive status.
A second concern with these synchronization programmes is the introduction of a stock bull to catch repeats. One has to be careful that there is sufficient bull power to address the repeats which will come in intensely over a 2 to 3 day period.
Infertile or sub-fertile bulls are now appearing on the radar with pregnancy scan data. This is a significant ongoing problem. Bull fertility tests just give a “picture on time”. Bull injuries and lack of libido are primarily causes of cows in heat not being bred. Our 3 week period of high temperatures exceeding 23 degrees centigrade also reduce the intensity and duration of bulling activity. Our scan data has also revealed that a significant number of cows scanned as being on heat had shown no signs of heat and there was no semen present in the vagina or uterus of these cows where a stock bull was running with the herd.
Farmers often introduce stock bulls to the herd and stop watching bulling activity. Do this at your peril. You need to ensure that bulls are completing the art of mating cows seen in heat. If more than 3 cows are seen bulling on a given day for stock bull available, it is best advised to supplement with AI on the following day. This will reduce the risks of infertility to a given service opportunity.
Injured stock bulls will not have the same interest or agility in mating cows in heat. It must, also be remembered that spermatogenesis or the production of semen ceases while a bull is injured. The “sperm belt” has a duration of approximately 6 weeks. Therefore it takes 6 weeks from the time sperm enter the production line until they are available for a natural service of a cow in heat. In essence, a bull injured today for a period of weeks will be sub-fertile or infertile when seemingly fit mating cows 6 week later.
We are now 5 weeks into spring breeding programmes on most farms. The big challenge to outcomes for your 6 and 9 week calving rates next spring will be the impact of the hidden cost of later embryo/foetal death. When cows are bred to AI or natural service, approximately 90% of the eggs are fertilized. The resultant embryo develops and hatches from its shell 7 to 8 days after breeding. It then elongates and its first challenge is to provide a signal to the cow of its presence between day 12 and 14. This stops the cow returning to heat between day 18 and 24. Embryo death after this stage will result in cows returning to heat anywhere up to 6 weeks after the time of embryo death. Unfortunately, your spring breeding programme will be over.
This later embryo death and other reproductive anomalies preventing cows establishing a successful pregnancy can be prevented by scanning your herd within 3 weeks of finishing your breeding programme.
Dr. Dan Ryan is a bovine reproductive physiologist and can be contacted at www.reprodoc.ie
Article written by Dr. Dan Ryan for the Farming Independent for the 19th June 2018