Abstract
Effects of Urea as a Source of Extra Dietary Nitrogen on Growth
Performance and Carcass Traits of Finisher Pigs.
Lee I. Chiba, Henry W. Ivey, Keith A. Cummins, and Brian E. Gamble
Background Information & Objectives
As the amino acid or nitrogen (N) content of diets increases, there is a concomitant
improvement in leanness of pigs. Numerous factors are responsible for this effect,
but essentially pigs fed a high-N diet have less energy available for excess
fat accretion, thus improving carcass leanness. Therefore, providing extra dietary
N might be a viable means to enhance the carcass quality of finisher pigs. Increasing
dietary N can be a costly method to enhance carcass leanness of pigs, but the
quantity of extra dietary N may be more important than the quality of N sources.
This contention implies that inexpensive N supplements can be used for this purpose.
Previous research indicated that extra dietary N provided by soybean meal (SBM)
or hydrolyzed feather meal was equally effective in enhancing the carcass quality
of finisher pigs. In addition, the improved carcass quality in response to the
increase in dietary N was independent of method of incorporating feather meal
in diets (i.e., iso-nitrogenous or iso-lysinic). The research described herein
was designed to investigate the potential value of urea as a source of extra
N to enhance carcass leanness, and to determine the effect of amino acid supplementation
of urea diets on growth performance and leanness of finisher pigs.
Experimental Procedures, Results & Conclusions
Forty-two crossbred pigs weighing 54.2 +/- 5.5 kg were used
to evaluate the value of urea as a source of extra N to enhance carcass leanness
of finisher pigs. Three SBM diets were formulated to contain 0.60 and 13.2% (Low),
0.73 and 15.5% (Med) or 0.85 and 16.7% (High) lysine and crude protein (CP),
respectively. Two urea diets were formulated to be iso-nitrogenous (Iso-N) to
the Med and High SBM diets. Two additional urea diets were formulated to be iso-lysinic
(Iso-Lys) to the Med and High SBM diets by incorporating crystalline amino acids.
The indispensable amino acid contents were at least 20.8 and 41.7% above the
current NRC requirements for the Med and High Iso-Lys diets, respectively. To
ensure an adequate supply of CP from common feed ingredients for pigs, corn and
SBM contributed 13.2% CP to four urea diets, and urea supplied additional CP
equivalent. Pigs were housed individually, and allowed ad libitum access to feed.
All pigs were slaughtered at an average weight of 103.2 +/- 4.5 kg. Pigs fed
the Low SBM diet tended to grow faster (P = .09) than those fed other diets.
However, the average backfat (BF; P < .05) and 10th rib BF (P = .10) were higher, and carcass specific gravity
(P < .05) and proportion of lean (P = .08) were lower in pigs fed the Low diet
than those fed the Med and High diets, indicating that a higher weight gain was
achieved by the increased rate of fat accretion. The level (Med vs High) and
source of lysine and(or) N [SBM vs urea and(or) amino acids] or amino acid supplementation
of urea diets (Iso-N vs Iso-Lys) had no effect on weight gain or carcass traits. The results indicated that the carcass quality was improved by increasing
lysine and(or) N levels from low to medium regardless of the source [SBM or
urea and(or) amino acids]. In addition, simply incorporating urea to increase
dietary N (Iso-N) from low to medium and amino acid supplementation of urea
diets (Iso-Lys) were equally effective in enhancing the carcass quality of
pigs, indicating that overall utilization of diets was improved by the inclusion
of urea. There was, however, no improvement in the carcass quality of finisher
pigs with further increases in dietary lysine and(or) N levels from medium
to high.
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