Feeding Systems with Legumes to Intensify Dairy Farms - cgiar
Feeding Systems with Legumes to Intensify Dairy Farms - cgiar
Feeding Systems with Legumes to Intensify Dairy Farms - cgiar
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Defining Milk Urea Nitrogen Concentrations for Optimum<br />
Recommendations of Protein-<strong>to</strong>-Energy Ratios in<br />
Tropical Forage Diets<br />
Patricia Avila and Carlos Lascano<br />
CIAT, Colombia<br />
When there is an excess of nitrogen relative <strong>to</strong> energy in the rumen,<br />
ruminal ammonia concentration increases. Unused ruminal ammonia<br />
enters the portal blood through the rumen wall and is transferred <strong>to</strong> the<br />
liver where it is de<strong>to</strong>xified by conversion <strong>to</strong> urea. The liver also produces<br />
urea from deamination of amino acids rising from postruminal digestion and<br />
systemic protein turnover. Urea then circulates in the blood <strong>to</strong> the kidneys<br />
and is excreted <strong>with</strong> the urine or it can be diffused from the blood in<strong>to</strong> milk.<br />
When there is a deficiency of dietary proteins, ruminal ammonia<br />
concentrations are relatively low and the proportion of nitrogen recycled<br />
back <strong>to</strong> the rumen as urea increases. As a result of these metabolic<br />
transactions, blood urea nitrogen (BUN) is highly correlated <strong>with</strong> ruminal<br />
ammonia and milk urea nitrogen (MUN). Therefore, in healthy ruminants,<br />
MUN concentrations could be a good indica<strong>to</strong>r of the protein-<strong>to</strong>-energy ratio<br />
in the diet.<br />
The study aimed <strong>to</strong> determine the level of urea in the milk that could be<br />
used as reference <strong>to</strong> increase the protein content <strong>to</strong> supplement diets, <strong>with</strong> a<br />
high probability that cows will respond by increasing milk production.<br />
Materials and Methods<br />
The study was carried out between 1992 and 1995 at the CIAT-<br />
Quilichao experiment station on contrasting pastures of Andropogon<br />
gayanus and Brachiaria dictyoneura. Two groups of four Brahman x<br />
Holstein cows were submitted <strong>to</strong> grazing on each pasture, <strong>with</strong> a 7-day<br />
period <strong>to</strong> adjust cows <strong>to</strong> the diet and 7 days of measurements. Milk yields<br />
were recorded during the 7-day measurement period, and milk samples for<br />
urea content were taken on days 1, 4, and 7 of each period. A 4 x 4 Latin<br />
square experiment design was used.<br />
Results<br />
Figure 1 shows the relationship between milk yield increase and MUN<br />
of cows supplemented <strong>with</strong> Cratylia argentea and sugarcane. Four groups<br />
can be identified, one in each quadrant. In the first group, cows showed an<br />
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