Protein requirements for pregnant dairy cows

We aimed to estimate the protein requirements of pregnant Holstein × Gyr cows. A total of 61 Holstein × Gyr (HG) cows were used, with an average initial body weight (BW) of 480 ± 10.1 kg and age 5 ± 0.5 yr. Cows were divided into 3 groups: pregnant (n = 43), nonpregnant (n = 12), and baseline (n = 6). Baseline animals were slaughtered before starting the experiment to estimate the initial body composition of the remaining animals. Pregnant and nonpregnant cows received 2 diets: maintenance and ad libitum. Pregnant cows were slaughtered at 139, 199, 241, and 268 gestation days (GD). First, we used data only from nonpregnant cows to determine the requirements for maintenance and growth in adult cows. The requirements of metabolizable protein for maintenance (MPm; grams of empty metabolic BW [EBW0.75] per day) were estimated using a linear regression between the metabolizable protein intake (MPI, g/d) and average daily gain (g/d), and the MPm was defined as the intercept divided by the average metabolic BW. Net protein requirements for gain (NPg; g/d) were estimated by the first derivative of the allometric equation between final crude protein in the body (kg) and the final empty BW (EBW; kg). The efficiency of use of metabolizable protein for gain (k) was calculated from the regression between the retained protein (g EBW0.75/d) and the MPI (g EBW0.75/d), and k was the slope of this regression. The MPI was estimated by combining microbial protein synthesis (purine derivatives) with the digestible rumen undegradable protein [(total protein intake - rumen-degradable protein) × intestinal digestibility]. Second, an exponential model was used to fit the protein accumulation in the gestational components in the function of GD. The first derivative of that model was considered the net requirement for gestation (NPgest). The efficiency of protein utilization for gestation (kgest) was calculated by the iterative method using the equation Δ = MPI - (MPm + NPg/kg + NPgest/kgest), where kg is efficiency of protein utilization for gain. The iteration was performed aiming at a zero deviation between observed MPI and metabolizable protein (MP) estimated by the requirements determined herein. We obtained a value of 3.88 g EBW0.75/d for MPm. The estimation of NPg can be calculated according to the following equation: NPg = 0.716 × (EBWopen-0.308) × EBGc, where EBWopen is the EBW (kg) for nonpregnant animals and EBGc is the empty body gain (kg/d) corrected for the gestational component. The k was determined as 0.347. The NPgest requirements were determined as NPgest (g/d) = 0.0008722 × exp(0.01784 × GD) × (calf weight/35). The kgest was 0.625. It is important to highlight that different methods of MP estimates should not be mixed and that the proposed method requires the estimation of microbial protein (estimated via urinary estimates), which might limit practical application. In conclusion, new studies should be conducted to validate our results and the methodology adopted to determine protein requirements for pregnancy in dairy cows. Due to the pattern of protein accumulation in the gestational components, we suggest an exponential model to describe protein requirements for pregnancy for dairy cows.

Development of equations to predict carcass weight, empty body gain, and retained energy of Zebu beef cattle

The accurate supply of energy is essential to optimize livestock productivity and profitability. Furthermore, replacing empty BW gain (EBG) with carcass gain (CG) might be a suitable alternative to estimate the retained energy (RE) of beef cattle. Thus, this multi-analysis study was conducted aiming to estimate and validate new equations to predict carcass weight (CW), EBG, and RE of Zebu, beef crossbred, and dairy crossbred. A database composed by 1112 animals encompassing bulls, steers, heifers of different genetic groups (Zebu, beef crossbred, and dairy crossbred), and two types of slaughter plants (commercial and experimental) was used for generating the new CW equation. For the development of the EBG and RE equations, a database of 636 observations composed of bulls, steers, and heifers of different genetic groups (Zebu, beef crossbred, and dairy crossbred) was assembled. The validation of new equations was performed using independent databases composed by 137 observations (80 for CW and 57 for EBG and RE). The new approaches for EBG and RE validation also included data from our research group studies (Inside) and independent data from literature publications (Outside). Furthermore, the new RE equation was compared to the current model devised by the nutritional requirements, diet formulation, and performance prediction of Zebu and crossbred cattle (BR-CORTE, 2016). Validation analyses were performed by using the Model Evaluation System (MES; 3.1.13, College Station, US). The CW was accurately estimated by the new equation when using both commercial and experimental data. Also, the equations developed in this study accurately estimated EBG and RE using both inside and outside data. In conclusion, equations proposed in this study accurately and precisely estimated CW, EBG, and RE of Zebu beef cattle that composed validation data set. Therefore, we suggest the following equations to estimate CW, EBG, and RE of Zebu cattle: CW, kg = -11.0_±1.56 + P + ((0.609_±0.005 + G + B) × SBW); EBG (kg) = 0.044_±0.017 + 1.47_±0.026 × CG; RE (MJ/d) = 4.184 × (0.082_±0.002 × EQEBW^0.75 × CG^0.777±0.039), where P = slaughter plant effect, if commercial = -10.98, if experimental =0; G = gender effect, if steer = 0, if bull = 0.008169 and if heifer = -0.00612; B = genotype effect, if Zebu = 0, if dairy crossbreds = -0.03301 and if beef crossbreds = -0.01595; SBW = shrunk BW; CG = carcass gain; EQEBW = equivalent empty BW.

Metabolizable amino acids and energy requirements of Nellore and crossbred Angus × Nellore bulls fed rations of different crude protein concentrations

Growth rate of cattle depends on their genetic makeup and nutrient intake. Moreover, increased growth rate may lead to increased amino acid (AA) requirements. Therefore, we evaluated the AA content of the empty body and estimated the net AA and energy requirements of purebred and crossbred beef bulls fed rations of different dietary CP concentrations. We performed a comparative slaughter experiment with 24 Nellore and 24 Angus × Nellore (A × N) bulls (8 months; initial shrunk BW: Nellore = 208.0 ± 12.78 kg; A × N = 221.9 ± 14.16 kg). Eight bulls (four Nellore and four A × N) were designated as the reference group, eight bulls (four Nellore and four A × N) were fed to maintenance level and 32 bulls (16 Nellore and 16 A × N) were fed ad libitum. The 32 bulls fed ad libitum were distributed using a completely randomized design in a 2 × 3 factorial scheme with two genetic groups (Nellore or A × N) and three dietary CP contents (100, 120 or 140 g CP/kg DM), being four groups with five bulls and two groups with six bulls. The experimental period lasted for 224 days. There were no interactions (P ≥ 0.056) between the dietary CP contents and genetic groups for any of the response variables. The dietary CP contents did not affect (P ≥ 0.062) the AA content in the empty body (g/kg empty BW [EBW]), with exception for Tryptophan (P = 0.027, linear effect). The dietary CP contents did not affect (P ≥ 0.051) AA content in the empty body (g/100 g of CP), with exception for Alanine (P = 0.013) that responded quadratically to dietary CP increase. The equations to estimate the net Lysine (Lys) and Methionine (Met) requirements (g/100 g of CP) were: Lys = 5.1 × EBW^0.0594 and Met = 1.7 × EBW^0.0255. Metabolizable Lys and Met to metabolizable energy (ME) ratios decreased as bulls EBW increased. Also, the metabolizable protein to ME ratio decreased as bulls EBW increased. In conclusion, the present study provides useful information regarding net and metabolizable requirements of AA of purebred and crossbred beef bulls. In the future, after the validation of the equations, these results can be used to calculate the AA requirements for growth of purebred and crossbred beef bulls. Nevertheless, it is important to highlight that the small sample size was one limitation of this present experiment.

Influence of a mineral supplement containing calcium, phosphorus and micronutrients on intake, digestibility, performance and mineral status of young Nellore bulls in a feedlot

We measured nutrient intake and digestibility, performance and mineral status of young Nellore bulls fed three diets with and without supplementation comprising calcium (Ca), phosphorus (P) and micro-minerals during the growing and finishing phases. Five bulls were slaughtered at the beginning of the experiment to measure initial mineral status. Forty-two young Nellore bulls (initial bodyweight (mean ± s.d.) 270.4 ± 36.6 kg, age 8 months) were assigned for 125 days to one of six treatments: sugarcane as a roughage source plus a concentrate based on soybean meal and soybean hull with (SH100) and without (SH0) supplementation; sugarcane as a roughage source plus a concentrate based on soybean meal and ground maize with (SC100) and without (SC0) supplementation; and maize silage as a roughage source plus a concentrate based on soybean meal and maize with (CS100) and without (CS0) supplementation. The experiment was conducted as a completely randomised design with a 3 × 2 factorial arrangement of treatments. Nutrient intake and digestibility, bone and serum parameters related to Ca and P metabolism, and liver mineral concentrations were measured. Nutrient intake, digestibility and performance were not affected (P > 0.10) by the mineral factor. Water intake was higher (P < 0.05) with SH100 than with all other diets. Rib-bone breaking strength and density according to dual-energy X-ray absorptiometry were reduced (P < 0.04) in the absence of supplementation. Metatarsus parameters were not affected (P > 0.10). Liver copper (Cu) content was reduced (P < 0.01) in diets without supplementation. In conclusion, the short-term absence of mineral supplementation did not influence intake and digestibility. However, depending on diet type, absence of Cu may reduce the hepatic Cu content, and a low Ca:P ratio may stimulate bone reabsorption without compromising performance. Therefore, under our conditions, mineral requirements are overestimated by nutritional systems.

Effect of duration of restricted-feeding on nutrient excretion, animal performance, and carcass characteristics of Holstein × Zebu finishing steers

Restricted-feeding may be a useful management tool available to reduce environmental impact in feedlots. Therefore, the objectives of the present study were to determine the effects of the duration of restricted-feeding on nitrogen (N) and phosphorus (P) excretion, growth performance and carcass characteristics of finishing steers. Twenty-five Holstein × Zebu steers (average initial bodyweight (BW) = 319 ± 16.2 kg; age = 19 ± 1 months) were used. Five steers were slaughtered to provide baseline empty BW (EBW) and empty body composition at Day 0. The remaining steers were randomly allotted to four groups of five steers, which were restricted to 85% ad libitum feed intake for either 0 (R0), 28 (R28), 42 (R42) or 84 (R84) days of an 84-day finishing period. All steers were fed a diet of 40% corn silage and 60% concentrate (DM basis) for 84 days. Total excretion of faeces and urine were collected during two periods: Days 25 to 27 (period 1) and Days 73 to 75 (period 2). The DM intake, average daily gain (ADG) and gain-to-feed ratio (G:F) were evaluated in three blocks, Days 0 to 28, Days 28 to 42 and Days 42 to 84. As expected, DM, N and P intakes were greater (P < 0.05) for R0 steers than R28, R42 and R84 steers when steers in R28, R42 and R84 treatments were restricted. When transitioned to ad libitum feeding, R28 and R42 steers had similar (P > 0.05) DM, N and P intakes compared with R0 steers. Faecal N and urinary P excretions did not differ (P ≥ 0.40) among restricted and ad libitum-fed steers in either period evaluated. However, greater (P < 0.05) faecal P excretions were observed in steers fed ad libitum intake in period 2 (R0). Phosphorus retention in period 2, and whole-body N retention were greatest (P < 0.05) in steers fed R28 and least (P < 0.05) in steers fed R84, steers fed R0 and steers fed R42 were intermediate and not different (P > 0.05). Final BW, overall ADG, G:F and carcass characteristics were not affected (P ≥ 0.11) by treatments. Restricted-feeding Holstein × Zebu steers to 85% of ad libitum intake for 84 days in the feedlot reduced DM intake and P excretion, without impairing steer growth performance or carcass characteristics. Nevertheless, it is important to highlight that the small sample size was one limitation of this present experiment.

A comparative study on the excretion of urinary metabolites in goats and sheep to evaluate spot sampling applied to protein nutrition trials

The main objective of this study was to establish a protocol to validate urine spot samples to estimate N excretion and microbial synthesis in goat and sheep; and to study factors that affect daily creatinine and purine derivatives (PD) urinary excretion. Also a performance trial was carried out to compare goat and sheep slaughtered after different feedlot periods. Twelve Boer goats (20.6 kg ± 3.4 initial BW) and 12 Dorper sheep (18.4 kg ± 2.3 initial BW), all 4-mo-old, males, were used. Eight animals (4 goats and 4 sheep) were randomly allocated to be slaughtered at 28, 56, and 84 d in feedlot. The experiment was conducted in a completely randomized design in a 2 × 3 factorial scheme, in which the factors were both species and the 3 feedlot periods. Diet consisted of 50% sorghum silage and 50% concentrate on a DM basis. Nutrient intake was higher (P < 0.01) for sheep than goats. Apparent digestibility of nutrients was similar (P > 0.05) in both species. Sheep had greater (P < 0.01) ADG and final BW than goats. Fat deposition and fat:muscle ratio was higher (P < 0.01) in sheep carcasses. Sheep had higher N urinary (P = 0.02) excretion and N retention (g/d; P < 0.01) than goats. Urinary N excretion increased linearly (P < 0.01) in response to feedlot period. However, feedlot did not affect (P = 0.20) N retention, but linearly reduced the relationship between N retained and ingested (P = 0.04) or apparently digested (P < 0.01). Microbial efficiency (P > 0.05) did not differ between species. Creatinine excretion (C mg/d; P < 0.01) was higher in sheep than goats. Purine derivatives (Ŷ) were related closely with OM intake (Ŷ = 0.013±0.0007X; r2 = 94). A difference (P < 0.01) was found between the allometric model for creatinine excretion (Ŷ) and muscle weight (X) for both species, and the following equations were obtained: Ŷ = 89.04(±31.44)X0.9797(±0.16) for goats and Ŷ = 109.8(±47.50)X0.8002(±0.20) for sheep. Creatinine concentration was greater during nocturnal than diurnal periods, with lower diurnal fluctuations. Sampling time did not affect (P = 0.27) the PD:C ratio. The urea (U):C ratio was higher (P < 0.01) in sheep than goats, and was also higher (P < 0.01) during diurnal than nocturnal sampling periods. Our results suggest that it is necessary to take 2 and 3 spot urine samples after feeding to estimate N compounds excretions in goats and sheep, respectively.

Dietary protein reduction on microbial protein, amino acid digestibility, and body retention in beef cattle: 2. Amino acid intestinal absorption and their efficiency for whole-body deposition

The objective of this study was to determine the apparent and true intestinal digestibility of total and individual AA, and to estimate the efficiency of whole-body AA retention from individual and total absorbed AA. Four Nellore animals (241.3 kg initial BW) and four crossbred Angus × Nellore (263.4 kg initial BW) cannulated in rumen and ileum were randomly allocated in two 4 × 4 Latin squares. The experiment lasted four 17 d periods, with 10 d for adaptation to diets and another 7 d for data collection. The diets consisted of increasing CP levels: 100, 120, or 140 g/kg of DM offered ad libitum, and restricted intake diet with 120 g CP/kg DM (experiment 1). In experiment 2, forty-four bulls (22 Nellore and 22 crossbred F1 Angus × Nellore) with 8 months and initial shrunk BW 215.0 ± 15.0 kg (Nellore = 208.0 ± 12.78 kg; Angus × Nellore = 221.9 ± 14.16 kg) were used. Eight of those animals were slaughtered at the beginning of the experiment. The remaining 36 bulls were allocated in a completely randomized design with six replicates, in a 2 (genetic groups) × 3 (CP contents) factorial scheme. The amount of essential AA (EAA) and nonessential AA (NEAA) reaching the small intestine increased linearly (P < 0.05) in response to CP content. The apparent digestibility of EAA was not affected (P > 0.05) by CP content, with exception for histidine (P = 0.07, linear effect), leucine (P = 0.01, linear effect), and methionine (P = 0.05, linear effect). Differences existed among AA when compared the apparent digestibility of NEAA. The apparent digestibility of alanine (P = 0.05), aspartic acid (P = 0.07), glutamic acid (P = 0.02), glycine (P = 0.05), proline (P = 0.02), and serine (P = 0.04) responded quadratically to CP content increase. However, the apparent digestibility of cystine and tyrosine was not affected (P > 0.05) by increasing dietary CP. The true intestinal digestibilities of total, essential, nonessential AA, lysine, and methionine were 75.0%, 77.0%, 74.0%, 77.0%, and 86%, respectively. The true intestinal digestibility of total microbial AA was 80%. The efficiency of utilization of total AA for whole-body protein deposition was 40%. The efficiency of utilization of lysine and methionine was 37% and 58%, respectively. It was concluded that the AA flow to the omasum increases in response to dietary CP content. In addition, there are differences among AA in the efficiency that they are used by beef cattle.

Assessment of body fat composition in crossbred Angus × Nellore using biometric measurements

This study was conducted to assess the body and empty body fat physical and chemical composition through biometric measurements (BM) as well as postmortem measurements taken in 40 F Angus × Nellore bulls and steers. The animals used were 12.5 ± 0.51 mo of age, with an average shrunk BW of 233 ± 23.5 and 238 ± 24.6 kg for bulls and steers, respectively. Animals were fed 60:40 ratio of corn silage to concentrate diets. Eight animals (4 bulls and 4 steers) were slaughtered at the beginning of the trial, and the remaining animals were randomly assigned to a 1 + 2 × 3 factorial arrangement (1 reference group, 2 sexes, and 3 slaughter weights). The remaining animals were slaughtered when the average BW of the group reached 380 ± 19.5 (6 bulls and 5 steers), 440 ± 19.2 (6 bulls and 5 steers), and 500 ± 19.5 kg (5 bulls and 5 steers). Before the slaughter, the animals were led through a squeeze chute in which BM were taken, including hook bone width (HBW), pin bone width, abdomen width (AW), body length (BL), rump height, height at the withers, pelvic girdle length (PGL), rib depth (RD), girth circumference (GC), rump depth, body diagonal length (BDL), and thorax width. Additionally, the following postmortem measurements were obtained: total body surface (TBS), body volume (BV), subcutaneous fat (SF), internal physical fat (InF), intermuscular fat, carcass physical fat (CF), empty body physically separable fat (EBF), carcass chemical fat (CFch), empty body chemical fat (EBFch), fat thickness in the 12th rib, and 9th to 11th rib section fat. The equations were developed using a stepwise procedure to select the variables that should enter into the model. The and root mean square error (RMSE) were used to account for precision and accuracy. The ranges for and RMSE were 0.852 to 0.946 and 0.0625 to 0.103 m, respectively for TBS; 0.942 to 0.998 and 0.004 to 0.022 m, respectively, for BV; 0.767 to 0.967 and 2.70 to 3.24 kg, respectively, for SF; 0.816 to 0.900 and 3.04 to 4.12 kg, respectively, for InF; 0.830 to 0.988 and 3.44 to 8.39 kg, respectively, for CF; 0.861 to 0.998 and 1.51 to 10.98 kg, respectively, for EBF; 0.825 to 0.985 and 5.96 to 8.46 kg, respectively, for CFch; and 0.862 to 0.992 and 5.54 to 12.19 kg, respectively, for EBFch. Our results indicated that BM that could accurately and precisely be used as alternatives to predict different fat depots of F Angus × Nellore bulls and steers are AW, GC, or PGL for CF estimation; HBW and RD for CFch estimation; and body lengths such as BL and BDL for InF and SF estimation, respectively.

Nutritional parameters of beef heifers fed diets with different roughages

The purpose of this study was to evaluate intake, digestibility and efficiency of microbial protein synthesis of beef heifers fed with sugarcane silage with different calcium oxide (CaO) levels (0, 7.5; 15 g/kg), fresh sugarcane and corn silage. The same concentrate was offered at 5 g/kg bodyweight (BW) for every diet. Five ruminally and abomasally fistulated beef heifers (373.8 ± 33.12 kg BW) were used in a 5 × 5 Latin square design. Heifers fed sugarcane silage diets presented lower dry matter (DM) intake than those fed fresh sugarcane. Corn silage provides greatest DM intake compared with other roughages. CaO levels had a quadratic positive effect (P < 0.05) on DM and total digestible nutrients (TDN). For TDN intake (3.43 + 4.39 CaO – 2.56 CaO2) the maximum TDN intake of 5.31 kg/day was obtained at 8.6 g/kg CaO. The total apparent digestibility for neutral detergent fibre increased with CaO levels. An increase in nitrogen balance was observed with the inclusion of CaO in the sugarcane silage. Corn silages-based diets provide greater DM intake and digestibility and nitrogen balance compared with the diets based on sugarcane. Adding CaO to sugarcane as it is ensiled improves DM intake and TDN than diet sugarcane silage without CaO. However, the use of high levels of CaO (15 g/kg) in sugarcane at ensiling decreases the diet intake. Based on the maximum energy intake, the use of 8.6 g/kg CaO in sugarcane at ensiling is recommended.

Stylosanthes cv. Campo Grande silage and concentrate levels in diets for beef cattle

The objective of this study was to evaluate the ruminal and intestinal digestion, the ruminal fermentation and the performance of beef cattle fed diets containing Stylosanthes silage (StS) and corn silage (CS). The treatments consisted of diets containing StS with different concentrate levels, based on dry matter (DM) (g/kg): 200 (StS-200), 400 (StS-400), 60 (StS-600), and a Control treatment with 600 g/kg CS and 400 g/kg concentrate (CS-400). In Experiment 1, 32 Nellore bulls, 364.28 ± 2.82 kg bodyweight, were distributed in a complete randomised design with eight replicates. Four Holstein × Zebu bulls (average bodyweight of 429 ± 15 kg) were used in Experiment 2, distributed in a 4 × 4 Latin square design. Nutrient intake was similar between StS-400 and CS-400 (P > 0.05), however, only StS-600 showed the same intake of total digestible nutrients as CS-400 (P < 0.05). Only the animals fed the StS-600 diet had similar (P > 0.05) average daily gain of carcass in comparison with those fed the Control diet. The StS-200 and StS-400 diets showed lower (P < 0.05) total tract digestibility of DM and crude protein than CS-400 (P < 0.05). Ruminal pH values of StS-200 and SE-400 were higher (P < 0.05) than in CS-400. The StS-600 diet showed a similar productive performance to CS in diets with 600 g/kg of concentrate, highlighting the potential use of this legume in diets for beef cattle in tropical conditions.

Does microbial nitrogen contamination affect the estimation of crude protein degradability of concentrate feeds?

The effects of microbial contamination (MC) on CP degradability of concentrate feeds are still controversial. Therefore, the aim of this study was to use N to estimate the impact of MC on estimations of CP fractions (the soluble fraction of CP [a], the insoluble but potentially degradable fraction of CP [b], and the rate of digestion of fraction b [kd]) of concentrate feeds. Twelve types of feed were evaluated: 6 energy concentrates-wheat bran ( L.), rice meal ( L.), ground corn ( L.), ground sorghum ( Pers.), ground corn cob ( L.), and soybean hulls [ (L.) Merr.]-and 6 protein concentrates-cottonseed meal ( L.), soybean meal [ (L.) Merr.], ground bean ( L.), peanut meal ( L.), sunflower meal ( L.), and corn gluten meal ( L.). The feeds were divided into 4 groups and were incubated in the rumen of 4 crossbred bulls. The samples were incubated for 0, 2, 4, 8, 16, 24, 48, and 72 h. To estimate the MC of the incubated residues, the ruminal bacteria were labeled with N via continuous intraruminal infusion of (NH)SO. There was no difference ( = 0.738) between corrected and uncorrected parameters a, b, and kd for all feeds that were evaluated. All of the feed tests followed an exponential model of degradation, and the model fitted well to the data, except for corn gluten meal, probably because the maximum incubation time that was used (72 h) was not long enough to allow for an accurate estimation of the degradation profile. Therefore, correction of ruminal protein degradation to MC is irrelevant with regards to the concentrates that were studied.

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.

Reducing mineral usage in feedlot diets for Nellore cattle: II. Impacts of calcium, phosphorus, copper, manganese, and zinc contents on intake, performance, and liver and bone status

Weaned Nellore bulls ( = 36; 274 ± 34 kg) were used in a randomized block design with a 2 × 2 factorial arrangement of treatments to evaluate intake, fecal excretion, and performance with different concentrations of minerals. Experimental diets were formulated with 2 concentrations of Ca and P (macromineral factor; diet supplying 100% of Ca and P according to BR-CORTE () [CaP+] or diet without limestone and dicalcium phosphate [CaP-]) and 2 concentrations of microminerals (micromineral factor; diet with supplementation of microminerals [Zn, Mn, and Cu; CuMnZn+] or diet without supplementation of microminerals [Zn, Mn, and Cu; CuMnZn-]). The factor CaP- was formulated without the addition of limestone and dicalcium phosphate, and the factor CuMnZn- was formulated without inorganic supplementation of microminerals (premix). The diets were isonitrogenous (13.3% CP). Intake was individually monitored every day. Indigestible NDF was used as an internal marker for digestibility estimates. The bulls were slaughtered (84 or 147 d on feed), and then carcass characteristics were measured and liver and rib samples were collected. Feed, feces, rib bones, and liver samples were analyzed for DM, ash, CP, ether extract (EE), Ca, P, Zn, Mn, and Cu. There were no significant interactions ( ≥ 0.06) between macro- and micromineral supplementation for any variables in the study. Calcium, P, and micromineral concentrations did not affect ( ≥ 0.20) intake of DM, OM, NDF, EE, CP, TDN, and nonfiber carbohydrates (NFC). Calcium and P intake were affected ( < 0.01) by macromineral factor. Animals fed without Ca and P supplementation consumed less of these minerals. Dry matter and nutrient fecal excretion (OM, NDF, EE, CP, and NFC) were similar ( ≥ 0.23) among all factors. Performance and carcass characteristics were similar ( ≥ 0.09) among diets. The content of ash in rib bones was not affected by diets ( ≥ 0.06). Plasma P and phosphatase alkaline concentrations were similar ( ≥ 0.52) among diets. Supplementation of microminerals decreased ( < 0.01) plasma Ca concentration; nevertheless, all analyzed blood metabolites were within the reference values. Supplementation of Ca and P increased ( < 0.01) fecal excretion of these minerals. These results indicate that mineral supplementation (Ca, P, Zn, Mn, and Cu) of conventional feedlot diets for Nellore bulls may be not necessary. Dietary reductions in these minerals would represent a decrease in the cost of feedlot diets. Dietary reduction in Ca and P content cause a decrease in fecal excretion of these minerals, which, in turn, represents an opportunity to reduce the environmental impact of feedlot operations.

Estimating mineral requirements of Nellore beef bulls fed with or without inorganic mineral supplementation and the influence on mineral balance

The objectives of this study were to quantify the mineral balance of Nellore cattle fed with and without Ca, P, and micromineral (MM) supplementation and to estimate the net and dietary mineral requirement for cattle. Nellore cattle ( = 51; 270.4 ± 36.6 kg initial BW and 8 mo age) were assigned to 1 of 3 groups: reference ( = 5), maintenance ( = 4), and performance ( = 42). The reference group was slaughtered prior to the experiment to estimate initial body composition. The maintenance group was used to collect values of animals at low gain and reduced mineral intake. The performance group was assigned to 1 of 6 treatments: sugarcane as the roughage source with a concentrate supplement composed of soybean meal and soybean hulls with and without Ca, P, and MM supplementation; sugarcane as the roughage source with a concentrate supplement composed of soybean meal and ground corn with and without Ca, P, and MM supplementation; and corn silage as the roughage source with a concentrate supplement composed of soybean meal and ground corn with and without Ca, P, and MM supplementation. Orthogonal contrasts were adopted to compare mineral intake, fecal and urinary excretion, and apparent retention among treatments. Maintenance requirements and true retention coefficients were generated with the aid of linear regression between mineral intake and mineral retention. Mineral composition of the body and gain requirements was assessed using nonlinear regression between body mineral content and mineral intake. Mineral intake and fecal and urinary excretion were measured. Intakes of Ca, P, S, Cu, Zn, Mn, Co, and Fe were reduced in the absence of Ca, P, and MM supplementation ( < 0.05). Fecal excretion of Ca, Cu, Zn, Mn, and Co was also reduced in treatments without supplementation ( < 0.01). Overall, excretion and apparent absorption and retention coefficients were reduced when minerals were not supplied ( < 0.05). The use of the true retention coefficient instead of the true absorption coefficient provided a better estimate of mineral requirements. Dietary mineral requirements were lower for P, Cu, and Zn and greater for Fe compared with previously published recommendations. This study provides useful information about mineral requirements and mineral supplementation to obtain adequate dietary mineral supply of Nellore cattle in tropical conditions.

Effect of different forage types and concentrate levels on energy conversion, enteric methane production, and animal performance of Holstein × Zebu heifers

The aim of this study was to evaluate the effect of diets containing corn silage (CS) or sugarcane (SC) with 300 or 500 g/kg of concentrate (on a DM basis) on energy conversion, enteric methane (CH4) production, and the animal performance of Holstein × Zebu heifers. An experiment was conducted while using comparative slaughter. Twenty Holstein × Zebu heifers with an average age of 12 ± 1.0 months and an average bodyweight of 218 ± 36.5 kg were used. Four heifers were assigned to a baseline group, whereas the remaining 16 heifers were distributed in a completely randomised design using a 2 × 2 factorial scheme (n = 4), with two types of roughage (CS or SC) and two levels of concentrate (300 or 500 g/kg) on a DM basis of the diet over the course of 112 days. For the evaluation of the apparent total-tract digestibility of diets and energy losses, a digestibility assay was performed by using the total collection of faeces and urine over three consecutive days. The enteric CH4 production was quantified by continuous analysis of regular samples of air excreted by the animals throughout the day. The greatest (P < 0.05) average daily gain was observed for heifers that were fed CS-based diets or with 500 g/kg of concentrate. Greater (P < 0.05) daily CH4 emissions were observed for heifers that were fed 500 g/kg of concentrate; CH4 production as a function of DM intake was greater (P < 0.05) for heifers that were fed SC-based diets. The efficiency of the conversion from digestible energy (DE) to metabolisable energy (ME) was not influenced (P > 0.05) by variables that were analysed in this study. However, the mean value that was observed in the present study was above those values proposed by the main evaluation systems of feedstuffs and nutrient requirements of ruminants. Therefore, we concluded that CS-based diets allow for better animal performance of Holstein × Zebu heifers in relation to SC-based diets. Also, the increased concentrate improves the performance of growing heifers. A greater inclusion of concentrate in SC-based diets can allow for a reduction of CH4 emissions per consumed unit and per gain unit. The mean suggested value for the ME : DE ratio based on this study is 0.86. However, more studies are necessary to validate this result.

Evaluation of equations to estimate body composition in beef cattle using live, linear and standing-rib cut measurements

Quick and reliable methods to estimate body and carcass composition of beef cattle are needed to predict the most profitable slaughter weight. This study evaluates body compositional equations using biometric measurements (BM), dissected fat (kg) at the 9–11th rib section and rib fat depth (cm). The present independent dataset used to evaluate the equations comprised of 48 F1 Nellore × Angus bulls (B) and steers (S); aged 12.5 ± 0.51 months with a mean shrunk BW (SBW) of 233 ± 23.5 and 238 ± 24.6 kg for B and S, respectively. Animals were fed a diet of 60% corn silage and 40% concentrate ad libitum. Eight animals were slaughtered at the beginning of the trial and the remaining animals were randomly assigned into a 2 (sex) × 3 (slaughter weights) factorial arrangement, and slaughtered when the average BW of the group reached 380 (6B and 5S), 440 (6B and 5S), 500 kg (5B and 5S). In addition, eight animals (4B and 4S) were fed at the maintenance level intake and slaughtered with the 500-kg group. Before slaughter, animals were led through a squeeze chute to collect BM, which included hook bone width, pin bone width, abdomen width, body length, rump height, height at withers, pelvic girdle length, rib depth, girth circumference, rump depth, body diagonal length, and thorax width. The following post-mortem measurements were included: total body surface, body volume (BV, m3), subcutaneous fat, internal fat, intermuscular fat, carcass physical fat (CF, kg), empty body fat (EBF, kg), carcass chemical fat (kg), empty body chemical fat (kg), fat thickness (cm) in the 12th rib, and 9–11th rib section fat. The predicted values were compared with the observed. Among all evaluated equations, only five were found to be adequate for F1 Nellore × Angus: Eqns (7): BV = 0.036 (±0.016) + 1.028 (±0.049) × BVcylinder (n = 28, RMSE = 0.016 m3, r2 = 0.942) and (8): BV = –0.011 (±0.004) + 9.8 × 10–4 (±1.84 × 10–5) × SBW (n = 27, RMSE = 0.003 m3, r2 = 0.997), to estimate BV; and Eqns (27): EBF = –16.8 (±2.68) + 0.142 (±0.008) × SBW (n = 36, RMSE = 4.17 kg, r2 = 0.897), (28): EBF = 0.011 (±0.002) × SBW + 1.22 (±0.024) × CF (n = 35, RMSE = 0.69 kg, r2 = 0.999), and (32): EBF = 1.445 (±0.010) × CF (n = 43, RMSE = 1.51 kg, r2 = 0.998), to estimate EBF. More research is needed to create a robust prediction of carcass and empty body fat using BM for animals of different breeds under diverse production conditions.

Effect of protein supplementation in the rumen, abomasum, or both on intake, digestibility, and nitrogen utilisation in cattle fed high-quality tropical forage

Effects of differing proportions of ruminal and abomasal protein infusion on intake, digestion, ruminal dynamics and the metabolic parameters of nitrogen (N) compounds were evaluated in beef bulls fed high-quality tropical forage (98.6 g crude protein, CP/kg dry matter) for ad libitum intake. Four Nelore bulls (280 ± 10 kg bodyweight) fitted with ruminal and abomasal cannulas were studied in a 4 × 4 Latin square. Treatments included: Control (no supplement) or 230 g/day of supplemental CP (as casein), with ratios of abomasal : ruminal infusion of 0 : 100, 50 : 50 or 100 : 0. Organic matter intake was not affected by treatments (P ≥ 0.30), though N intake increased by supplementation (P < 0.001). Total CP and organic matter digestibility were increased (P < 0.02) by protein supplementation. Nitrogen balance was 43% greater (P < 0.02) in the treatments with supplementation. Although supplementation did not affect (P = 0.98) the efficiency of absorbed N, a tendency towards a positive linear effect (P = 0.08) was observed when modifying the site of supplementation from the rumen to the abomasum. Supplementation increased (P < 0.01) ruminal ammonia-N, serum urea-N, urinary N and urea-N excretion, which subsequently decreased linearly (P < 0.01) by the displacement of supplementation from the rumen to the abomasum. The results indicate that protein supplementation, either in the rumen or abomasum produces similar effects on N retention. However, the metabolic mechanisms responsible for the improved N retention appear to differ between supplementation sites. Additionally, the efficiency of N utilisation increases with infusion of protein into the abomasum.

Effects of varying ruminally undegradable protein supplementation on forage digestion, nitrogen metabolism, and urea kinetics in Nellore cattle fed low-quality tropical forage

Effects of supplemental RDP and RUP on nutrient digestion, N metabolism, urea kinetics, and muscle protein degradation were evaluated in Nellore heifers () consuming low-quality signal grass hay (5% CP and 80% NDF, DM basis). Five ruminally and abomasally cannulated Nellore heifers (248 ± 9 kg) were used in a 5 × 5 Latin square. Treatments were the control (no supplement) and RDP supplementation to meet 100% of the RDP requirement plus RUP provision to supply 0, 50, 100, or 150% of the RUP requirement. Supplemental RDP (casein plus NPN) was ruminally dosed twice daily, and RUP supply (casein) was continuously infused abomasally. Jugular infusion of [NN]-urea with measurement of enrichment in urine was used to evaluate urea kinetics. The ratio of urinary 3-methylhistidine to creatinine was used to estimate skeletal muscle protein degradation. Forage NDF intake (2.48 kg/d) was not affected ( ≥ 0.37) by supplementation, but supplementation did increase ruminal NDF digestion ( < 0.01). Total N intake (by design) and N retention increased ( < 0.001) with supplementation and also linearly increased with RUP provision. Urea entry rate and gastrointestinal entry rate of urea were increased by supplementation ( < 0.001). Supplementation with RUP linearly increased ( = 0.02) urea entry rate and tended ( = 0.07) to linearly increase gastrointestinal entry rate of urea. Urea use for anabolic purposes tended ( = 0.07) to be increased by supplementation, and RUP provision also tended ( = 0.08) to linearly increase the amount of urea used for anabolism. The fraction of recycled urea N incorporated into microbial N was greater ( < 0.001) for control (22%) than for supplemented (9%) heifers. Urinary 3-methylhistidine:creatinine of control heifers was more than double that of supplemented heifers ( < 0.001). Control heifers reabsorbed a greater ( < 0.001) fraction of urea from the renal tubule than did supplemented heifers. Overall, unsupplemented heifers had greater mobilization of AA from myofibrillar protein, which provided N for urea synthesis and subsequent recycling. Supplemental RUP, when RDP was supplied, not only increased N retention but also supported increased urea N recycling and increased ruminal microbial protein synthesis.

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 Mayer's test, the concordance correlation coefficient, and the mean square error of prediction for decomposition. For both equations, Mayer's 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, Mayer's 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.

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.

Effects of Supplements with Different Protein Contents on Nutritional Performance of Grazing Cattle During the Rainy Season

The objective of this study was to evaluate the effects of supplements with different crude protein (CP) contents on grazing cattle intake, digestibility, ruminal fermentation pattern, and nitrogen (N) metabolism characteristics during the rainy season. Five ruminal and abomasal cannulated Holstein×Zebu steers (296 kg body weight, BW) were used in a 5×5 Latin square design. The animals grazed five signal grass paddocks (0.34 ha). The five treatments evaluated were: Control (no supplement) and 1.0 g of supplement/kg BW with 0, 330, 660, and 1,000 g of CP/kg as-fed. The supplement was composed of starch, soybean meal, urea, and ammonium sulphate. There was a positive linear effect (p≤0.033) of the CP content in the supplements on the organic matter (OM), CP, and digested OM intakes. The provision of supplements did not increase (p≥0.158), on average, total and ruminal digestibilities of OM and CP. However, the increase in CP content in the supplements caused a positive linear effect (p≤0.018) on ruminal digestibilities of OM and CP. Additionally, a quadratic effect of the CP contents of the supplements were observed (p = 0.041) for the ruminal digestibility of neutral detergent fiber corrected for ash and protein, with the highest estimate obtained with the CP content of 670 g/kg. The supply of supplements increased (p<0.001) the ruminal ammonia N concentration, which also changed linearly and positively (p<0.001) according to increase in CP content in the supplements. The apparent N balance and relative N balance (g/g N intake) were not, on average, changed (p≥0.164) by the supplements supply. However, both showed a tendency of a linear increase (p≤0.099) with increasing supplement CP content. The supplements increased (p = 0.007) microbial N production in the rumen, which also changed linearly and positively (p = 0.016) with increasing supplement CP content. In conclusion, protein supplementation in grazing cattle during the rainy season, while stimulating voluntary forage intake, results in higher efficiency of N utilization when compared to energy supplementation. This is a possible response to increased microbial protein synthesis in the rumen and improved N status in the animal body.

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) for bulls confined for longer periods. Nutrient digestibility and average daily gain was not affected (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.

Evaluation of Acid Digestion Procedures to Estimate Mineral Contents in Materials from Animal Trials

Rigorously standardized laboratory protocols are essential for meaningful comparison of data from multiple sites. Considering that interactions of minerals with organic matrices may vary depending on the material nature, there could be peculiar demands for each material with respect to digestion procedure. Acid digestion procedures were evaluated using different nitric to perchloric acid ratios and one- or two-step digestion to estimate the concentration of calcium, phosphorus, magnesium, and zinc in samples of carcass, bone, excreta, concentrate, forage, and feces. Six procedures were evaluated: ratio of nitric to perchloric acid at 2:1, 3:1, and 4:1 v/v in a one- or two-step digestion. There were no direct or interaction effects (p>0.01) of nitric to perchloric acid ratio or number of digestion steps on magnesium and zinc contents. Calcium and phosphorus contents presented a significant (p<0.01) interaction between sample type and nitric to perchloric acid ratio. Digestion solution of 2:1 v/v provided greater (p<0.01) recovery of calcium and phosphorus from bone samples than 3:1 and 4:1 v/v ratio. Different acid ratios did not affect (p>0.01) calcium or phosphorus contents in carcass, excreta, concentrate, forage, and feces. Number of digestion steps did not affect mineral content (p>0.01). Estimated concentration of calcium, phosphorus, magnesium, and zinc in carcass, excreta, concentrated, forage, and feces samples can be performed using digestion solution of nitric to perchloric acid 4:1 v/v in a one-step digestion. However, samples of bones demand a stronger digestion solution to analyze the mineral contents, which is represented by an increased proportion of perchloric acid, being recommended a digestion solution of nitric to perchloric acid 2:1 v/v in a one-step digestion.

Effects of day of gestation and feeding regimen in Holstein × Gyr cows: III. Placental adaptations and placentome gene expression

This study investigated the influence of day of gestation (DG) and feeding regimens (FR) on the expression of genes responsible for placenta development, nutrient transfer, and angiogenic factors in Holstein × Gyr cows. Forty pregnant multiparous Holstein × Gyr cows with an average initial body weight of 482±10.8kg and an initial age of 5±0.8 yr were allocated to 1 of 2 FR: ad libitum (AL; n=20) or maintenance level (ML; n=20). Maintenance level was considered to be 1.15% of body weight (dry matter basis) and met 100% of the net energy requirements and AL provided 190% of the total net energy requirements. Cows were slaughtered at 4 DG: 139, 199, 241, and 268d. After the cows were slaughtered, the placenta and uterus were separated and weighed. Caruncles and cotyledons were individually separated, counted, and weighed. Placenta expressed as kilograms and grams per kilogram of empty body weight (EBW) was heavier in ML- than in AL-fed cows at 268d of gestation. Placenta expressed as kilograms and grams per kilogram of EBW was the lightest at 139d of gestation, and the greatest mass was observed at 268d in ML-fed cows. However, in AL-fed cows, the heaviest placenta expressed as grams per kilogram of EBW was observed from 199d of gestation. Placentomes expressed as grams per kilogram of EBW were heavier in ML-fed cows during gestation, and the number of placentomes was greater in ML-fed cows at 268d of gestation. We observed that IGFR1 and IGFR2 were involved in placenta adaptations when ML was provided, as their expression in placentome cells was greater in ML-fed cows at 268d of gestation. The genes responsible for angiogenesis were also greater in ML-fed cows: VEGFA, GUCY1B3, HIFA, FGF2, and NOS3 were altered by FR and DG interaction and they were greater in ML-fed cows at 268d of gestation. In addition, VEGFB and ANGPT2 did not show interactions between FR and DG, but they were greater in ML-fed cows. Thus, we suggest that the placenta from an ML-fed cow develops adaptations to the reduced nutrient supply by altering its structure and gene expression, thereby developing mechanisms for potential increased nutrient transfer efficiency to the fetus.

Evaluation of predictive equations developed to assess body composition of F1 Nellore × Angus bulls and steers

We evaluated and compared empirical equations used for assessing beef cattle body composition, developed in 2010 (M10), 2012 (M12), 2006 (V06) and 1946 (HH46). Forty-eight F1 Nellore × Angus bulls and steers, aged 12.5 ± 0.51 months old, with initial shrunk bodyweight of 233 ± 23.5 kg and 238 ± 24.6 kg, respectively, were used in this experiment. The trial was a randomised factorial arrangement of treatments (two genders and five slaughter weights). The animals were randomly assigned to five slaughter-weight-based groups: baseline, maintenance, and 380, 440 and 500 kg. The diet comprised maize silage and concentrate (60 : 40). After slaughter, the 9th–11th rib section cut was dissected into muscle, fat and bone. The remaining carcass was similarly dissected. Other variables evaluated as partial predictors of body composition included empty bodyweight, dressing percentage, visceral fat percentage, and organ and viscera percentage. The values estimated with predictive equations were compared with observed values. For the physically separable carcass composition, only the M12 equation estimated precisely and accurately the amount of muscle (r2 = 0.98, root-mean-square error (RMSE) = 5.64 kg, concordance correlation coefficient (CCC) = 0.96) and fat (r2 = 0.94, RMSE = 4.91 kg, CCC = 0.96) tissue present in the carcass. The V06 and M10 equations estimated precisely and accurately the amount of carcass chemical components; HH46 could explain only the amount of crude protein (r2 = 0.84, RMSE = 4.71 kg, CCC = 0.90) content in the carcass. The equations used to predict empty body chemical composition failed to estimate correctly the amount of chemical contents present in the empty bodyweight. However, V06 can be used to estimate the crude protein (r2 = 0.91, RMSE = 5.97 kg, CCC = 0.93) content in the empty bodyweight. Furthermore, M10 could be used to estimate ether extract (r2 = 0.94, RMSE = 8.13 kg, CCC = 0.84) content, although this had to be analysed by gender, because such variables (i.e. ether extract) presented a pronounced effect, especially for steers, on total chemical fat.

Intake, digestibility, nitrogen efficiency, and animal performance of growing and finishing beef cattle fed warm-season legume (Stylosanthes capitata plus Stylosanthes macrocephala) silage replacing corn silage

It was hypothesized that Stylosanthes cv. Campo Grande (ES) silage could be used as the single source of dietary forage for beef cattle and that performance on ES would be similar to corn silage (CS) at a 50:50 forage:concentrate. The objectives of this study were to evaluate intake, total and partial digestibility of nutrients, ruminal pH, ruminal ammonia, and productive performance in growing beef cattle fed diets with varying proportions of ES silage replacing CS. Treatments consisted of diets with ratios of 0:100, 25:75, 50:50, 75:25, and 100:0% ES:CS. Two experiments were conducted simultaneously. In the first experiment, 10 crossbred Holstein-Zebu bulls with an average initial weight of 272 ± 86 kg were used. The bulls were rumen and abomasums fistulated. An experimental design of two 5 × 5 Latin squares (Exp. 1) was used. The second experiment used 40 Nellore bulls with an average BW of 386 ± 30 kg in a completely randomized design (Exp. 2). Results showed a linear increase in CP intake (P < 0.05) in response to increased dietary ES. An increase in the proportion of ES in the diet had a negative linear effect on TDN. Apparent ruminal digestibility of CP increased linearly, and apparent intestinal digestibility of nonfibrous carbohydrates increased with the addition of ES to the diet (P < 0.05). Intestinal digestibility of DM exhibited a quadratic response (P < 0.05). Nitrogen balance, excretion of urinary urea, and plasma urea nitrogen did not respond to the inclusion of ES in the diet (P > 0.05). There was also no effect (P > 0.05) of ES inclusion on animal performance. Ruminal pH was not affected by an increased proportion of ES in the diet (P > 0.05), but ruminal pH was affected (P < 0.05) by the time of collection, for which a cubic model fit the data. There was an interaction (P < 0.05) between treatment and collection time for ruminal ammonia nitrogen concentration. It can be concluded that ES silage can be used as a source of roughage in the diet of beef cattle during the growing and finishing phases at a proportion of 50% of DM in the total diet. Therefore, ES silage is a promising alternative dietary ingredient and the use of this alternative source of silage will depend on availability and economic factors.

Grazing behavior and locomotion of young bulls receiving different nutritional plans in a tropical pasture

The objectives of this study were to compare visual observation and an electronic grazing time method and to evaluate the effects of nutritional plans on intake, grazing behavior and horizontal and vertical locomotion of young bulls in a tropical pasture. Thirty-nine Nellore young bulls with an average body weight of 345±9.3 kg kept in pasture were used. The experimental treatments consisted of: restricted: animals kept in a plot with a low mass of forage receiving mineral mixture only; control: animals receiving mineral mixture only; HPHC: a high protein and high carbohydrate supplement; HPLC: a high protein and low carbohydrate supplement; LPHC: a low protein and high carbohydrate supplement; LPLC: a low protein and low carbohydrate supplement. GPS collars equipped with activity sensors were used. Information about head position, latitude, longitude and altitude were recorded. Daytime grazing behavioral patterns monitored by a continuous focal animal recording method was compared to behavior estimated by the activity sensor. Feed intake was estimated by a marker method. The Restricted group presented lower (p<0.05) intake of dry matter and TDN. However, difference in dry matter intake was not found (p>0.05) between non-supplemented and supplemented animals. Difference was not found (p>0.05) in daytime grazing time obtained by visual observation or the activity sensor method. The restricted group showed longer (p<0.05) grazing time (9.58 h/d) than other groups, but difference was not found (p>0.05) in the grazing time between Control (8.35 h/d) and supplemented animals (8.03 h/d). The Restricted group presented lower (p<0.05) horizontal locomotion distance (2,168 m/d) in comparison to other groups (2,580.6 m/d). It can be concluded that the use of activity sensor methods can be recommended due to their being similar to visual observation and able to record 24-h/d. While supplements with high carbohydrates reduce pasture intake, they do not change grazing behavior. Moderate supplementation (until 50% of protein requirement and 30% of energy requirement) of beef cattle on tropical pasture has no effect on daily locomotion.

The impact of dietary sugarcane addition to finishing diets on performance, apparent digestibility, and fatty acid composition of Holstein × Zebu bulls

The objective of this study was to evaluate the influence of corn silage (CS) or sugarcane (SC) additions to finishing diets on voluntary intake, apparent digestibility, animal performance, and LM fatty acid (FA) composition in crossbred Holstein × Zebu bulls. Forty-two bulls (initial BW 328 ± 39.2 kg and an initial age of 23.5 mo) were used in this experiment. A completely randomized design was used to examine roughage source (CS vs. SC) and ratio of concentrate (CO) on nutrient utilization and production. The experimental diets consisted of 1) 60% CS and 40% CO on DM basis fed for 84 d (CS60:40), 2) 60% CS and 40% CO on DM basis fed for 42 d and 40% CS and 60% CO on DM basis fed for 42 d (CS reverse diet [CSR]), 3) 40% CS and 60% CO on DM basis fed for 84 d (CS40:60), 4) 60% SC and 40% CO on DM basis fed for 84 d (SC60:40), 5) 60% SC and 40% CO on DM basis fed for 42 d and 40% SC and 60% CO on DM basis fed for 42 d (SC reverse diet [SCR]), and 6) 40% SC and 60% CO on DM basis fed for 84 d (SC40:60). Dry matter and NDF intakes were greater (P < 0.01) in bulls fed CS-based diets than bulls fed SC-based diets. The greatest (P < 0.01) DM and CP digestibility were observed in bulls fed SC-based diets. Bulls fed CSR and CS40:60 had greater (P < 0.01) ADG than bulls fed SC-based diets. However, ADG was similar (P = 0.52) in bulls fed CS60:40, CSR, and SC40:60 diets. The percentage of C18:3 n-3 and C20:5 n-3 were greater (P < 0.01) in LM of bulls fed SC-based diets. The percentage of CLA was greater (P < 0.01) in LM of bulls fed SC60:40 than those fed CS-based diets. The findings of the present study indicate that SC40:60 can replace CS60:40 and CSR in finishing diets and, moreover, roughage source significantly altered the FA composition of crossbred Holstein × Zebu bulls LM.

Predicting efficiency of use of metabolizable energy to net energy for gain and maintenance of Nellore cattle

Twenty-six comparative slaughter studies were used (n = 752 animals) and coded within each experiment by gender (431 bulls, 204 steers, and 117 heifers) and breed (447 Nellore and 305 Bos indicus and Bos taurus crossbreds) to develop equations to predict the efficiency of use of ME to NE for growth (kg) and ME to NE for maintenance (km). The retained energy (RE) was regressed on ME intake (MEI) available for gain using orthogonal regression to obtain the kg within each experiment. The estimated kg was regressed on RE as protein (REp) according to the following equation: kg = a/(b + REp). Gender and breed effects were not tested because of limited number of experiments. The km was estimated as the intercept of the following equation: HP = β0 × e((β1 × MEI)), in which HP is heat production, β0 and β1 are coefficients, and e is the natural logarithm. The ME for maintenance (MEm) was computed assuming MEI equals to HP at maintenance. The km was obtained using the stepwise procedure of a multiple regression including ADG, empty body gain (EBG), empty BW (EBW), EBW(0.75), kg, and energy content in the EBW. A random coefficient model, assuming a random variation for study effects, was used to test breed and gender effects to identify the best model to estimate km. The overall equation to predict kg was 0.327 (±0.142)/[0.539 (±0.317) + REp], with an R(2) of 0.963. The equation to predict km was 0.513 (±0.024) + 0.173 (±0.061) × kg + a × EBG, R(2) = 0.92, in which a = 0.100 (±0.021) for B. indicus or a = 0.073 (±0.021) for crossbreds. Our results indicated that B. indicus were more efficient to use ME for maintenance. We concluded that km can be predicted from kg and EBG and that B. indicus × B. taurus crossbreds can affect km. Furthermore, kg can be predicted from REp and neither gender nor crossbreeding (B. indicus × B. taurus) affected kg. Because our database consisted of Nellore and B. indicus and B. taurus crossbreds, it is necessary to further evaluate differences between B. taurus and B. indicus regarding the kg.