D. Zanetti

Creatinine excretion and relationship with body weight of Nellore cattle

The objective of this study was to estimate the urinary creatinine excretion by the shrunk body weight (SBW). In experiment I, 32 Nellore bulls with initial body weight of 259±24.9 kg and 14±1 months-old were used. The group was divided in four animals to maintenance and twenty eight animals feeding ad libitum and separated in four groups; each group was slaughtered at different times of feedlot (42, 84, 126 and 168 days). The diet was composed of corn silage and concentrate (55:45). Before the slaughters, the total urinary collection was realized during three days. A database of creatinine excretion was collected from other five studies that had been conducted with Nellore cattle. In all the studies, the total urinary collection was realized during at least three days. At the end of each collection, the animals were weighted. Urinary creatinine excretion (UCE) was related with the shrunk body weight and it can be estimated by the equation: UCE (g/day) = 0.0345 × SBW0.9491.

Reducing calcium and phosphorus in crossbred beef cattle diets: impacts on productive performance during the growing and finishing phase

Forty 3/4 Bos indicus × 1/4 Bos taurus bulls (initial bodyweight = 214 ± 4 kg; 11 ± 0.2 months) were used in the study. Four bulls were slaughtered as reference and the other 36 bulls were allowed ad libitum consumption of treatment diets following a completely randomised 3 × 3 factorial design. The design included three diet concentrations of calcium (Ca) and phosphorus (P): standard, 50% of standard, and 75% of standard and three periods of feedlot confinement: 8, 16, and 24 weeks with four bulls per treatment combination. The diets were isonitrogenous and consisted of 60 : 40 corn silage to concentrate. Dry matter intake, crude protein, ether extract, organic matter, non-fibrous carbohydrates, Ca, and P, expressed as kg/day, were greater (P 0.05) by Ca and P concentration of diet or by feedlot phase. Dressing were decreased (P < 0.05) for bulls that remained in confinement for a shorter period. The daily maintenance requirements of Ca and P were 13.66 and 21.51 mg/kg empty bodyweight, respectively, and the absorption coefficients of Ca and P were 0.70 and 0.67, respectively. We concluded that for crossbred cattle in the feedlot, dietary levels of Ca and P recommended by BR-CORTE (2010), NRC (2000), and AFRC (1991) could be reduced by 62%, 66%, and 57%, respectively, for Ca and by 14%, 15%, and 43%, respectively, for P with significant savings in costs. This study shows that Ca and P can be reduced to 1.8 and 2.2 g/kg DM respectively, in the diets for crossbred cattle in feedlot.

Energy and protein requirements of 3/4 Zebu × 1/4 Holstein crossbreds fed different calcium and phosphorus levels in the diet

The aim of this study was to determine the nutritional requirements of energy and protein for maintenance and weight gain of crossbred cattle, as well as their efficiencies. Fifty 3/4 Zebu × 1/4 Holstein crossbred bulls with initial weights of 214±4kg and aged 11±0.2 months on average were used in this experiment. Four animals were used in the reference group; ten bulls were fed at the maintenance level; and the remaining 36 bulls were fed ad libitum and distributed in a completely randomized design in a 3×3 factorial arrangement, which had three feedlot periods (56, 112 or 168 days) and three calcium and phosphorus levels (low, medium and normal) in the diet. Four of the maintenance animals had their heat production measured by respirometry at the Laboratory of Metabolism and Calorimetry of UFMG. After slaughter, composite samples, referred to as carcass and noncarcass samples were obtained from each animal. The net energy requirements for maintenance (NEm) and metabolizable energy for maintenance (MEm) were 68.9 and 90.1 kcal/EBW0.75/day, respectively. The efficiency (km) was 76.41%. The NEm requirement determined in the respirometry chamber was 85.5 kcal/kg0.75. The following equations were obtained for net energy for gain (NEg) and net protein for gain (NPg): NEg (Mcal/day) = 0.0505±0.000986 × EBW0.75× EBWG1.095 and NPg (g/day) = 162.79±18.2546 × EBWG - 1.30±5.3010 × RE. The efficiencies of fat and protein deposition were 70.04 and 15.12%, respectively. In conclusion, the requirements of NEm for growing and finishing non-castrated 3/4 Zebu × 1/4 Holstein crossbred cattle are 68.9 kcal/EBW0.75/day. Requirements of NEg and NPg can be obtained by the following equations: NEg(Mcal/day) = 0.05050.000986 × EBW0.75 × EBWG1.095and NPg (g/day) = 162.79±18.2546 × EBWG - 1.30±5.3010× RE.

Reducing mineral usage in feedlot diets for Nellore cattle: I. Impacts of calcium, phosphorus, copper, manganese, and zinc contents on microbial efficiency and ruminal, intestinal, and total digestibility of dietary constituents

This study evaluated intake, microbial efficiency, and ruminal, small and large intestinal, and total digestibility of DM, OM, CP, and NDF, as well as availability of Ca, P, Mg, Na, K, Cu, Mn, and Zn in Zebu cattle fed with or without supplemental sources of Ca and P or a micromineral premix. Five rumen- and ileum-cannulated Nellore bulls (BW = 200 ± 10.5 kg; 9 mo) were used in the experiment, distributed in a 5 × 5 Latin square design. The experiment was developed in a 2 × 2 + 1 factorial design to measure the effects of mineral supplementation on intake, digestibility, and site of nutrient absorption. The factors consisted of 2 Ca and P levels (macromineral factor; CaP+ or CaP-) and 2 microminerals levels (micromineral factor; CuMnZn+ or CuMnZn-). In addition, a treatment with alimentary restriction (REST) was evaluated at 1.7% of BW. Nutrient fluxes were measured in the omasum and ileum, in addition to intake and fecal excretion. Microbial efficiency was estimated using purine derivative excretion. Dry matter, OM, NDF, CP intake, and total digestibility were not affected ( ≥ 0.058) by the absence of Ca, P, Cu, Mn, and Zn supplementation. Intake of Ca, P, and Mg were reduced ( < 0.01) by CaP-. The absence of CuMnZn reduced ( < 0.01) Cu, Mn, and Zn intake. Ruminal recycling of P, Na, and K is significant for increasing the influx of these minerals to the digestive tract; however, influences of treatments were not observed. The small and large intestines contributed to mineral absorption in different proportions ( < 0.05), according to minerals and treatments. Because of the similarity ( > 0.05) of OM, NDF, and CP digestion sites and coefficients, we assume that omitting supplemental sources of Ca, P, Cu, Mn, and Zn may be an option in raising cattle on feedlots. If supplementation is viable, knowledge about the specific absorption site of each mineral could positively impact choices about the supplemental source.

Effects of roughage sources produced in a tropical environment on forage intake, and ruminal and microbial parameters

Our objective was to study the effect of different roughage sources produced in a tropical environment on intake, digestibility, and ruminal parameters of crossbred bulls. Five rumen-fistulated 30-mo-old Holstein × Bos indicus bulls (average BW =459 ± 32.5 kg) were utilized in a 5 × 5 randomized Latin square design. The experiment consisted of five 19-d experimental periods (10 d for adaptation and 9 d for data collection) and 5 treatments. Experimental diets consisted of corn (Zea mays L.) silage (CS), Brachiaria grass (Brachiaria decumbens Stapf.) silage (BGS), elephant grass (Pennisetum purpureum Schumach.) silage(EGS), Tifton 85 (Cynodon spp.) hay (T85), and fresh sugarcane (Saccharum officinarum L.; SC). Diets were formulated to have approximately 11% CP (DM basis)using a mixture of urea and ammonium sulfate (9:1 ratio) that was diluted in water and then mixed with roughage. Intake, ruminal outflow, digestibility coefficients,ruminal pool, intake, passage (kp) and digestion rates, microbial parameters, and pH data were assessed.D ry matter intake was greater (P < 0.01) for CS compared with SC. Among treatments, lesser (P < 0.01)potentially digestible NDF, ash- and protein-free NDF(apNDF), and digestible ash- and protein-free NDF intake values were observed for SC. Ruminal outflows of DM and nonfibrous carbohydrates were lesser (P <0.01) for SC compared with other treatments. Dry matter apparent digestibility and ruminal digestibility did not differ (P > 0.27) among treatments. No differences (P = 0.11) were observed for ruminal apNDF pool and ruminal kp of apNDF (P = 0.06) among treatments. No treatment effect (P > 0.28) was observed for DM and nitrogen of rumen-isolated bacteria, and microbial efficiency was greater (P = 0.02) for BGS among treatments.A treatment × time interaction (P < 0.01) was found for ruminal pH, with a quadratic pattern in terms of time for CS, BGS, EGS, and T85, whereas pH values for CA linearly decreased as a function of time. In summary, these roughages, when supplemented with an additional nitrogen sources, show similar overall apparent digestibility and ruminal pool values, but conversely, bulls fed sugarcane had less overall nutrient intake and lower ruminal outflow and digestion rate values. We conclude that fresh-cut sugarcane, when provided with urea, can affect digestion rate and, consequently, impact nutrient intake.

Technical note: Prediction of chemical rib section composition by dual energy X-ray absorptiometry in Zebu beef cattle.

It is expensive and laborious to evaluate carcass composition in beef cattle. The objective of this study was to evaluate a method to predict the 9th to 11th rib section (rib) composition through empirical equations using dual energy X-ray absorptiometry (DXA). Dual energy X-ray absorptiometry is a validated method used to describe tissue composition in humans and other animals, but few studies have evaluated this technique in beef cattle, and especially in the Zebu genotype. A total of 116 rib were used to evaluate published prediction equations for rib composition and to develop new regression models using a cross-validation procedure. For the proposed models, 93 ribs were randomly selected to calculate the new regression equations, and 23 different ribs were randomly selected to validate the regressions. The rib from left carcasses were taken from Nellore and Nellore × Angus bulls from 3 different studies and scanned using DXA equipment (GE Healthcare, Madison, WI) in the Health Division at Universidade Federal de Viçosa (Viçosa, Brazil). The outputs of the DXA report were DXA lean (g), DXA fat free mass (g), DXA fat mass (g), and DXA bone mineral content (BMC; g). After being scanned, the rib were dissected, ground, and chemically analyzed for total ether extract (EE), CP, water, and ash content. The predictions of rib fat and protein from previous published equations were different ( < 0.01) from the observed composition. New equations were established through leave-one-out cross-validation using the REG procedure in SAS. The equations were as follows: lean (g) = 37.082 + 0.907× DXA lean ( = 0.95); fat free mass (g) = 103.224 + 0.869 × DXA fat free mass ( = 0.93); EE mass (g) = 122.404 + 1.119 × DXA fat mass ( = 0.86); and ash mass (g) = 18.722 + 1.016 × DXA BMC ( = 0.39). The equations were validated using Mayers test, the concordance correlation coefficient, and the mean square error of prediction for decomposition. For both equations, Mayers test indicated that if the intercept and the slope were equal to 0 and 1 ( > 0.05), respectively, then the equation correctly estimated the rib composition. Comparing observed and predicted values using the new equations, Mayers test was not significant for lean mass ( = 0.26), fat free mass ( = 0.67), EE mass ( = 0.054), and ash mass ( = 0.14). We concluded that the rib composition of Nellore and Nellore × Angus bulls can be estimated from DXA using the proposed equations.