The use of different nutritional strategies and mathematical models to improve production efficiency, profitability, and carcass quality of feedlot cattle
Forty eight crossbred steers (BW = 296 ñ 16.7 kg) were fed four dietary
treatments for 56 d: AL-LS (low starch diet fed ad libitum for a rate of gain of 1 kg/d),
AL-HS (high starch diet fed ad libitum), LF-HS (a limit fed high starch diet designed to
be isocaloric with AL-LS), and AL-IS (a diet fed ad libitum for the midpoint daily
energy intake between AL-LS and AL-HS). On d 57 all steers were placed on AL-HS
for finishing until d 140. Steers that consumed more total energy (AL-HS and AL-IS)
throughout production achieved greater carcass fatness in the end of the 140 d period,
although these responses were difficult to evaluate via real-time ultrasound
measurements. No differences in insulin and glucose kinetics were observed. Data
suggested that energy source may influence energy partitioning during the growing
period, but these effects may be overcome by differences in energy intake. Higher
marbling scores (AL-HS and AL-IS) rewarded higher grid values and greater premiums,
which increased profitability. This data set was also used for a model evaluation that showed that mathematical models (CVDS and NRC) were able to explain most of the
variation in individual feed requirements of group- fed growing and finishing cattle.
Another data set was used for evaluation of a decision support system Cornell Net
Carbohydrate and Protein System (CNCPS) as a tool to minimize nutrient excretion
from fed cattle. One-hundred eight-four group- fed steers were fed a 13% crude protein
(CP) diet until reaching 567 kg of BW, when their diets were either maintained at 13%
or reduced to 11.5% or 10% CP. Data from the second half of the experiment were
modeled to predict urinary, fecal, and total N excretion. As dietary CP decreased from
13 to 11.5%, the model indicated a total N excretion of 16%. An even greater reduction
in total N excretion (26%) occurred when dietary CP was decreased from 11.5% to 10%.
The overall decrease from 13 to 10% CP resulted in a reduction of total N excretion by
38%. Data suggest that decision support sys tems can be used to assist in balancing diets
to meet environment restriction
