Energy nutritional requirements for females of Nellore, Nellore × Angus and Nellore × Simmental fed on two forage: concentrate ratios

Abstract

-The objective of this study was to determine the energy nutritional requirements for females of Nellore, Nellore × Angus and Nellore × Simmental fed on two levels of concentrate. Sixty heifers from three genetic groups were used: 20 Nellore, 20 Nellore × Angus and 20 Nellore × Simmental. Twelve belonged to the reference group (four of each genetic group) and were slaughtered at the beginning of the experiment. Another 12 heifers (four of each genetic group) were fed on the maintenance level and 36 heifers (12 animals of each genetic group) were kept in feeding system ad libitum with 30 (six in each group) or 50% (six of each group) dry matter concentrate. Animals were randomly assigned to six treatments in a 3 × 2 factorial arrangement (three genetic groups and two diets) with six replicates per treatment. Nine more heifers were used in a parallel experiment to estimate the apparent digestibility coefficients (three from each genetic group). Net energy requirements were estimated by the equation of retained energy as a function of metabolic empty body weight (EBW 0.75 ) and empty body weight gain (EBWg). Requirements of metabolizable and net energy were estimated for maintenance by the equation of heat production as a function of metabolizable energy intake. Using the combined equation RE (retained energy; Mcal/day) = 0.0703 × EBW .75 × EBWg 1.128 to predict net energy requirements for weight gain is recommended. The requirement of metabolizable and net energy for maintenance of all groups is 70.55 and 106.53 kcal/kgEBW 0.75 /day, respectively. Use efficiencies of metabolizable energy for gain and maintenance are 36.41 and 66.23%, for the three genetic groups respectively.

Protein requirements for females of Nellore, Nellore × Angus and Nellore × Simmental fed on two forage: concentrate ratios

“…Therefore, 1 kg BWF average daily gain is equivalent to 0.90 kg EBW. The ADG:EBW ratio found in this study was lower than the 0.92 found by Marcondes et al (2010) working on the same genetic groups (Nellore, Nellore × Angus and Nellore × Simmental). The highest ratio found by the authors is consistent, since they worked with males.…”

“…Thus, values found by these authors hypothesize that differences in nutritional requirements of proteins differ only between zebu and dairy crossbred. Using the RE estimation (4.15 Mcal/day) for a heifer weighing 350 kg body weight and 1 kg/day average daily gain, according to the RE equation as function of EBW and EBW gain (RE = 0.0611× EBW 0.75 × EBWg 0.6718 ) proposed by Souza et al (2012) with data from this experiment, 140.23 g/day retained protein (RP) could be found. Substituting these same values in the equations proposed by Moraes et al (2010) 75, 163.35, 157.10 and 145.99 were obtained, respectively.…”

“…According to Berg & Butterfield (1976), males deposit more lean tissue than females at the same age. Using the equation obtained in this study to estimate protein net requirements for gain and basing on the equations described by Souza et al (2012) to estimate the retained energy by these heifers (RE (Mcal/day) = 0.0703 × EBW 0.75 × EBWg 1.128 ), accounting for 3.88 g/kg EBW 0.75 /day metabolizable protein requirement for maintenance and considering 37.40% efficiency obtained by the regression between protein retained (g/EBW 0.75 /day) and metabolizable protein intake (g/EBW 0.75 /day), the net requirements of protein, metabolizable protein and total metabolizable protein (maintenance + gain) for heifers at different weights and different growth rates can be calculated (Table 4).…”

“…For calculation of protein requirements for maintenance, the model suggested by Valadares Filho et al (2010) was adopted first, in which the consumption of metabolizable protein was contrasted with the gain of empty body weight for animals on performance and maintenance: m PI = β0 + β1 × EBW in which m PI is metabolizable protein intake (g/day) and EBW is the gain of empty body weight (kg/day) and β0 and β1 are regression parameters. The division between this regression intercept by the average metabolic weight of animals allowed estimating the metabolizable protein requirements for maintenance (β0/BP 0.75 , g/BP 0.75 /day).…”

High-concentrate diets with fibrous by-products for feedlot Nellore heifers

“…The DMI intake prediction for Nellore Brazilian cattle at 250 kg, to obtain 1 kg/day is 6.05 kg/day with approximately 80% TDN (Valadares Filho et al 2006, Souza et al 2012 (Mendes et al 2010, Liu & Li 2017. The ratio between energy sources and soybean hulls was about 1:1 in diets with corn, while the ones with corn germ meal presented 1.4 times more than soybean hulls.…”