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Saturday 21 July 2018

Having enough 'bull power' for breeding finale is vital

Stock image.
Stock image.
Dan Ryan

Dan Ryan

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 0.28pc less than average milk deliveries this time last year.

This alone has reduced his milk cheque by €2,800. In addition, he has had to spend an extra €3,000 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 high quality sward regrowths.

Farmers are now in catch-up mode, as there is a continuous backlog of work on the farm. AI technicians have told me there was a shorter period of intensive use of AI this season, prior to the introduction of stock bulls. Farmers are now using more synchronisation 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.

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A second concern with these synchronisation 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 two- to three-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 three-week period of high temperatures exceeding 23C also reduced 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 bulls are actually bulling cows seen in heat. If more than three 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 six weeks. Therefore, it takes six 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 for mating cows six weeks later.

We are now five weeks into spring breeding programmes on most farms. The big challenge to outcomes for your six and nine-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 90pc of the eggs are fertilised. The resultant embryo develops and hatches from its shell seven to eight 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 six 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 three weeks of finishing your breeding programme.

Dr Dan Ryan is a bovine reproductive physiologist and can be contacted at www.reprodoc.ie

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