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Updating equations to estimate dry matter intake of Nellore and beef crossbred cattle
Dry matter intake is the most important variable that affects animal performance, mainly in beef cattle due to economic impact and its complex gastrointestinal system with peculiar metabolic functions. A database with 1,459 animals, being 1,188 Nellore and 271 beef crossbred cattle, was developed to generate equations estimating dry matter intake for animals raised on feedlot. Variables such as dry matter intake (DMI), body weight (BW), metabolic body weight (mBW), average daily gain (ADG), and level of concentrate (LC) were collected. First of all, a PROC CORR was utilized to evaluate whose variables are significantly correlated with DMI. The variables mBW, LC, and ADG presented the highest correlation with DMI being those chosen to be part of the equations generated. The range of DMI in this database was from 2.96 to 12.3 kg/d, while LC was from 0 to 100%, and ADG was from -0.36 to 2.26. After, all statistical models were fitted by the cross-validation procedure. Also, differences between genetic group (Nellore and beef crossbred cattle) were evaluated which allowed us to develop two different equations. Then, the following equations were developed to estimate DMI of Nellore and beef crossbred cattle, respectively: Nelore cattle: DMI = -2.406 + 0.064 × LC – 0.00065 × LC2 + 0.070 x BW0.75 + 4.384 × ADG – 1.255 × ADG2 (R2 = 0.797) and beef crossbred cattle: DMI = -4.355 + 0.0598 × LC – 0.00049 × LC2 + 0.128 x BW0.75 + 3.974 × ADG – 1.128 × ADG2 (R2 = 0.717). From this, if we derive these equations in function of level of concentrate, we can know which amount of concentrate each genetic group is able to reach the maximum DMI. Thus, Nellore cattle reach maximum DMI when 49.2% of concentrate is provided in diet while beef crossbred cattle reach this amount for 61.0% of concentrate. This statement proves that Nellore cattle are more sensible to high amounts of concentrate than beef crossbred cattle. Moreover, if we derive these equations in function of ADG, we are able to know which ADG the animals reach maximum DMI. For Nellore and beef crossbred cattle, the maximum DMI is reached when ADG is 1.75 and 1.76 kg/d, respectively. Therefore, Nellore cattle are more sensible when level of concentrate is increased in diet when compared to beef crossbred cattle.
Keywords: cross-validation, beef crossbred cattle , level of concentrate, Nellore