Not high urea but energy deficit – vet

14 August 1998




Not high urea but energy deficit – vet

By Emma Penny

ANALYSIS of urea level in bulk collected milk is useless, and in any case, infertility may not be related to high urea levels, but may be due to energy deficit.

Thats the belief of David Whitaker, of Edinburgh Universitys Dick vet school, who also runs a blood testing service for a major feed compounder.

Mr Whitaker, a speaker at next months Nottingham cattle fertility conference (see panel) has just completed a literature review, and concludes that theres no link between high urea levels and fertility difficulties.

"I am astonished at how weak the relationship is, and how ambivalent the work is. As scientists, we approach problems with an idea and therefore a prejudice; if were not careful we can interpret results in the light of that prejudice."

He points out that in some cases, the authors did not conclude that there was a link, but that other people, when interpreting results, had somehow twisted them to show that high urea levels led to infertility.

"Also, some papers looked at studies of high protein rations where cows did suffer infertility, but none looked at the levels of energy fed."

Mr Whitaker believes that energy is the key factor involved. "I have seen plenty of cows with high blood urea levels and perfectly good fertility."

Recently completed work in the USA looked at the difference in conception rate of maiden heifers fed on high and low protein rations. "Both groups were fed to 70% of their energy requirements – but increasing protein in the diet boosts milk production. More milk requires more energy. A bigger protein input induces a greater energy imbalance.

"Where producers find their cows have high urea levels they do one of two things – take their cows off grass or provide a source of fermentable energy. Either way, the cow receives more energy – as well as reducing urea levels – and it may be that correcting energy deficit is the key to better fertility," he explains

Backing up his case, Mr Whitaker quotes two on-going trials. At ADAS Bridgets, he says work so far has found no link between milk urea and fertility in a 500-cow trial. Irish research on high and low urea rations fed to heifers implanted with embryos shows no link between the rations and uterus conditions.

"Also, if you think logically, sheep are flushed on grass, which increases urea levels, before tupping to increase fertility – why should it be different for cows?"

He urges producers and researchers to be more open minded about the cause of infertility. "Many people think there is a link, but we need to question that thinking more and look at trials in greater detail.

"Producers also need to stop paying attention to bulk milk urea results. They are an average reading, tell you absolutely nothing and just lead to unnecessary worry.

"I started this review thinking I would have a long list of evidence for and against urea influencing fertility, but Ive found no evidence to support the theory at all," he concludes.

Fertility conference

Find out the latest research on cattle fertility and implications for genetic selection, herd management and vet treatment at the Nottingham cattle fertility conference. It is to be held at the Universitys Sutton Bonington campus on September 3 and is organised by the University and British Cattle Veterinary Association. Attendance is £25. Further details from Marilyn Prentice, Cattle Fertility Research Group, University of Nottingham, Sutton Bonington Campus, Loughborough LE12 5RD (0115 951 6321).

Fertility conference

Find out the latest research on cattle fertility and implications for genetic selection, herd management and vet treatment at the Nottingham cattle fertility conference.

It is to be held at the Universitys Sutton Bonington campus on September 3 and is organised by the University and British Cattle Veterinary Association. Attendance is £25. Further details from Marilyn Prentice, Cattle Fertility Research Group, University of Nottingham, Sutton Bonington Campus, Loughborough LE12 5RD (0115-951 6321).


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