Effect of Nitrogen Underfeeding and Energy Source on Milk Production in Dairy Cows

Reducing dietary nitrogen (N) decreases both milk yield and urinary N excretion irrespective of the dietary source of energy.
calendar icon 14 August 2012
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Animal Bytes

A large reduction in dietary N significantly decreases both milk yield and N excretion in the environment. Just one of the findings of a study, carried out by scientists in France, to determine the consequences of a decreasing dietary in N in dairy cows and its interaction with source of energy, on milk production and N partition.

Improving dietary N utilisation by dairy cows is a way to reduce N output in manure and is desirable due to global concerns about contribution of agricultural N to environmental pollution. “But this strategy should not impair animal performance,” Michel Doreau from INRA told delegates at this year’s British Society of Animal Science’s annual conference.

“It is hypothesised that the nature of digested energy may interact with protein digestion and metabolism. And we wanted to investigate that.”

His team’s trial used four lactating Holstein cows and the treatments were two N levels (low and high level) combined with two energy sources rich in starch (S) or fibre (F).

On a dry matter (DM) basis, the four diets had the same forage proportion. The high level of N (H) met 110 per cent of N cow requirements as expressed by the French protein digestible in the intestine (PDI) system, with an adequate supply in ruminal degradable N. The low level (L) covered 80 per cent of PDI requirements with a shortage of ruminal degradable N.

“And we found that dry matter intake was similar for both treatments and both milk production and urea content of the milk were higher with H than with L diets,” said Dr Doreau.

“Neither milk fat content nor milk protein content was affected by the N level of the diet. Milk protein was higher for S diets. And there was no interaction between the N level and the energy source for any parameter.

Daily output of N in urine and milk were 0.52 and 0.11 times lower with L diets than with H diets, respectively.

“When dietary N decreases, the percentage of transfer of N into milk increases, and there is a strong decrease in urinary losses, in percentage of N intake as in daily output. In this study, only milk fat and protein were changed by the energy source, whatever the N level was,” he added.

Full details: Fanchone A, Doreau M and Noziere P : “Effect of N underfeeding and energy source on milk production and N partition in dairy cows.”

To view proceedings, Advances in Animal Biosciences, of all summaries presented at the Annual Conference and Powerpoint presentations, please click here.

August 2012

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