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Title: Effect of dietary protein supply and forage type on efficiency of dietary nitrogen utilisation with a focus on diet digestion and splanchnic flux of amino acids and other nutrients in lactating dairy cows
Author: Barratt, Cassandra
Awarding Body: University of Reading
Current Institution: University of Reading
Date of Award: 2013
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Abstract:
The effect of altering dietary protein supply and forage type on milk production, the efficiency of converting dietary nitrogen (N) into milk protein, nutrient digestibility and the splanchnic flux of nutrients was measured using a 2 x 3 factorial design experiment. Six Holstein dairy cows in mid-late lactation, surgically prepared with a rumen fistula and splanchnic blood sampling catheters were fed ad libitum in equal meals provided hourly, total mixed rations consisting of a 50:50 mixture (dry matter (OM) basis) of forage:concentrate, with the forage comprised of either 25:75 or 75:25 grass:maize silage. Rations were formulated to contain dietary protein concentrations of 12.5, 15.0 and 17.5% diet OM providing metabolisable protein below, near, and above estimated requirement. The experiment was conducted as repeated 3 x 3 Latin Squares with 21 d treatment periods, with the effect of protein level tested within squares and forage source as the square effect. Dry matter intake, (OMl), N intake, milk yield and milk N yield increased with increasing dietary protein but were not different between forages. Efficiency of N utilisation decreased with increasing dietary protein and was not different between forages. Rumen ammonia concentrations increased with increasing dietary protein, and were higher when the grass-based diet was fed as N intake was higher for the grass-based diet. Arterial urea concentration and liver urea production increased with increasing dietary protein concentration. Liver release of glucose and Bhydroxybutyrate increased linearly as DMI increased. The net flux of amino acids (AA) were unaffected by dietary treatment, although arterial concentrations of individual essential AA and many nonessential AA increased with increasing dietary protein. The splanchnic flux of AA did not follow results seen for N intake and highlight the complexities of splanchnic metabolism as an integrator of supply and demand by other body tissues.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.627936  DOI: Not available
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