L. O. Tedeschi

Characterization of feed efficiency traits and relationships with feeding behavior and ultrasound carcass traits in growing bulls

The objectives of this study were to characterize feed efficiency traits and to examine phenotypic correlations between performance and feeding behavior traits, and ultrasound measurements of carcass composition in growing bulls. Individual DMI and feeding behavior traits were measured in Angus bulls (n=341; initial BW=371.1+/-50.8 kg) fed a corn silage-based diet (ME=2.77 Mcal/kg of DM) for 84 d in trials 1 and 2 and for 70 d in trials 3 and 4 by using a GrowSafe feeding system. Meal duration (min/d) and meal frequency (events/d) were calculated for each bull from feeding behavior recorded by the GrowSafe system. Ultrasound measures of carcass 12th-rib fat thickness (BF) and LM area (LMA) were obtained at the start and end of each trial. Residual feed intake (RFIp) was computed from the linear regression of DMI on ADG and midtest BW(0.75) (metabolic BW, MBW), with trial, trial by ADG, and trial by midtest BW(0.75) as random effects (base model). Overall ADG, DMI, and RFIp were 1.44 (SD=0.29), 9.46 (SD=1.31), and 0.00 (SD=0.78) kg/d, respectively. Stepwise regression analysis revealed that inclusion of BW gain in BF and LMA in the base model increased R(2) (0.76 vs. 0.78) and accounted for 9% of the variation in DMI not explained by MBW and ADG (RFIp). Residual feed intake and carcass-adjusted residual feed intake (RFIc) were moderately correlated with DMI (0.60 and 0.55, respectively) and feed conversion ratio (FCR; 0.49 and 0.45, respectively), and strongly correlated with partial efficiency of growth (PEG; -0.84 and -0.78, respectively), but not with ADG or MBW. Gain in BF was weakly correlated with RFIp (0.30), FCR (-0.15), and PEG (-0.11), but not with RFIc. Gain in LMA was weakly correlated with RFIp (0.17) and FCR (-0.19), but not with PEG or RFIc. The Spearman rank correlation between RFIp and RFIc was high (0.91). Meal duration (0.41), head-down duration (0.38), and meal frequency (0.26) were correlated with RFIp and accounted for 35% of the variation in DMI not explained by MBW, ADG, and ultrasound traits (RFIc). These results suggest that adjusting residual feed intake for carcass composition will facilitate selection to reduce feed intake in cattle without affecting rate or composition of gain.

Phenotypic and genetic relationships of residual feed intake with performance and ultrasound carcass traits in Brangus heifers.

The objective of this study was to characterize residual feed intake (RFI) and to estimate phenotypic and genetic correlations with performance and ultrasound carcass traits in growing heifers. Four postweaning feed efficiency trials were conducted using 468 Brangus heifers. The complete Brangus pedigree file from Camp Cooley Ranch (Franklin, TX), which included 31,215 animals, was used to generate genetic parameter estimates. The heifer progeny from 223 dams were sired by 36 bulls, whereas the complete pedigree file contained 1,710 sires and 8,191 dams. Heifers were individually fed a roughage-based diet (ME = 1.98 Mcal/kg of DM) using Calan gate feeders for 70 d. Heifer BW was recorded weekly and ultrasound measures of 12th- to 13th-rib fat thickness (BF) and LM area (LMA) obtained at d 0 and 70. Residual feed intake (RFIp) was computed as actual minus predicted DMI, with predicted DMI determined by linear regression of DMI on mid-test BW(0.75) (MBW) and ADG with trial, trial x MBW, and trial x ADG as random effects. Overall means for ADG, DMI, and RFI were 1.01 (SD = 0.15), 9.51 (SD = 1.02), and 0.00 (SD = 0.71) kg/d, respectively. Stepwise regression analysis revealed that inclusion of gain in BF and final LMA into the base model increased the R(2) (0.578 vs. 0.534) and accounted for 9% of the variation in DMI not explained by MBW and ADG (RFIp). Residual feed intake and carcass-adjusted RFI (RFIc) were strongly correlated phenotypically and genetically with DMI and FCR, but not with ADG or MBW. Gain in BF was phenotypically correlated (P < 0.05) with RFIp (0.22), but not with FCR or RFIc; however, final BF was genetically correlated (P < 0.05) with RFIp (0.36) and RFIc (0.39). Gain in LMA was weakly phenotypically correlated with FCR, but not with RFIp or RFIc; however, gain in LMA was strongly genetically correlated with RFIp (0.55) and RFIc (0.77). The Spearman rank correlation between RFIp and RFIc was high (0.96). These results suggest that adjusting RFI for ultrasound carcass composition traits will facilitate selection phenotypically independent of growth, body size, and carcass composition; however, genetic relationships may still exist between RFI and carcass composition.

Evaluation of feeding glycerol on free-fatty acid production and fermentation kinetics of mixed ruminal microbes in vitro

Ruminant-derived foods contain high proportions of saturated fats as a result of ruminal biohydrogenation that rapidly saturates and thus limits the availability of free unsaturated fatty acids for assimilation. The objective of this study was to evaluate the effects of glycerol on ruminal free-fatty acid (FFA) production rates and in vitro fermentation kinetics of alfalfa hay. In vitro incubations demonstrated 48% and 77% reductions in rates of FFA accumulation in incubations supplemented with 2% and 20% glycerol as compared to controls. In vitro incubations with alfalfa hay demonstrated that increasing levels of glycerol did not affect NDF digestibility of the hay. Additionally, increasing amounts of glycerol decreased the acetate to propionate ratio in the rumen. These results suggest that inhibiting bacterial fat degradation may promote ruminal passage of total lipid, thereby providing greater proportions of beneficial unsaturated fat for incorporation into beef products.

Relationship between the rumen microbiome and residual feed intake-efficiency of Brahman bulls stocked on bermudagrass pastures.

Residual feed intake (RFI) testing has increased selection pressure on biological efficiency in cattle. The objective of this study was to assess the association of the rumen microbiome in inefficient, positive RFI (p-RFI) and efficient, negative RFI (n-RFI) Brahman bulls grazing ‘Coastal’ bermudagrass [Cynodondactylon (L.) Pers.]under two levels of forage allowance (high and low stocking intensity). Sixteen Brahman bulls were previously fed in confinement for 70 d to determine the RFI phenotype. Bulls were then allotted 60 d stocking on bermudagrass pastures to estimate RFI using the n-alkane technique. At the conclusion of the grazing period, rumen liquid samples were collected from each bull by stomach tube to evaluate the rumen microbiome. Extraction of DNA, amplification of the V4-V6 region of the 16S rRNA gene, and 454 pyrosequencing were performed on each sample. After denoising the sequences, chimera checking, and quality trimming, 4,573 ± 1,287 sequences were generated per sample. Sequences were then assigned taxonomy from the Greengenes database using the RDP classifier. Overall, 67.5 and 22.9% of sequences were classified as Bacteroidetes and Firmicutes, respectively. Within the phylum Bacteroidetes, Prevotella was the most predominant genus and was observed in greater relative abundance in p-RFI bulls compared with n-RFI bulls (P = 0.01). In contrast, an unidentified Bacteroidales family was greater in relative abundance for n-RFI bulls than p-RFI (26.7 vs. 19.1%; P = 0.03). Ruminococcaceae was the third most abundant family in our samples, but it was not affected by RFI phenotype. No effect of stocking intensity was observed for bacterial taxa, but there was a tendency for alpha diversity and operational taxonomic unit richness to increase with lower stocking intensity. Results suggested the rumen microbiome of p-RFI Brahman bulls has greater levels of Prevotella, but the bacterial community composition was unaffected by stocking intensity.

Influence of different levels of concentrate and ruminally undegraded protein on digestive variables in beef heifers.

This experiment evaluated the effect of 2 levels of diet concentrate (20 and 40% of DM) and 2 levels of ruminally undegraded protein (RUP: 25 and 40% of CP) on nutrient intake, total and partial apparent nutrient digestibility, microbial protein synthesis, and ruminal and physiological variables. Eight Nellore heifers (233 +/- 14 kg of BW) fitted with ruminal, abomasal, and ileal cannulas were used. The animals were held in individual sheltered pens of approximately 15 m(2) and fed twice daily at 0800 and 1600 h for ad libitum intake. Heifers were allocated in two 4 x 4 Latin square designs, containing 8 heifers, 4 experimental periods, and 4 treatments in a 2 x 2 factorial arrangement. All statistical analyses were performed using PROC MIXED of SAS. Titanium dioxide (TiO(2)) and chromic oxide (Cr(2)O(3)) were used to estimate digesta fluxes and fecal excretion. Purine derivative (PD) excretion and abomasal purine bases were used to estimate the microbial N (MN) synthesis. No significant interaction (P > 0.10) between dietary levels of RUP and concentrate was observed. There was no effect of treatment (P = 0.24) on DMI. Both markers led to the same estimates of fecal, abomasal, and ileal DM fluxes, and digestibilities of DM and individual nutrients. Ruminal pH was affected by sampling time (P < 0.001), but no interaction between treatment and sampling time was observed (P = 0.71). There was an interaction between treatment and sampling time (P < 0.001) for ruminal NH(3)-N concentration. A linear decrease (P = 0.04) over sampling time was observed for the higher level of RUP, whereas a quadratic effect (P < 0.001) of sampling time was observed for the lower level of RUP. The higher level of dietary concentrate led to greater MN yield regardless of the level of RUP. The MN yield and the efficiency of microbial yield estimated from urinary PD excretion produced greater (P < 0.01) values than those estimated by either TiO(2) or Cr(2)O(3), which did not differ (P = 0.63) from each other. However, all methods yielded values that were within the range reported in the literature. In conclusion, no interactions between dietary levels of RUP and concentrate were observed for ruminal and digestive parameters. Neither RUP nor concentrate level affected DMI. Titanium dioxide showed to be similar to Cr(2)O(3) as an external marker to measure digestibility and nutrient fluxes in cattle.

Effects of chemical composition variation on the dynamics of ruminal fermentation and biological value of corn milling (co)products.

The objectives of this study were to evaluate the dynamics of gas production of several corn (co)products, to develop equations to predict the rate of ruminal fiber digestion, to estimate total digestible nutrients (TDN) and net energy for lactation (NE(L)), and to assess the stochasticity of chemical composition and nutritive value variability. Four corn milling (co)products were evaluated in this study: high protein dried distillers grains (HP-DDG), corn bran (BRAN) and dehydrated germ (GERM), and a dried distillers grains plus soluble produced with a low-heat drying process (BPX). Alfalfa hay was used as an internal standard feed in the in vitro fermentation dynamics analysis. Standard chemical analyses, in vitro digestibility, and in vitro gas production techniques were used to obtain the necessary physicochemical characterization of feeds. The in vitro dry matter digestibility at 24 and 48 h of incubation decreased exponentially as acid detergent insoluble nitrogen increased. However, the degree of in vitro dry matter digestibility reduction was more accentuated at 24 than at 48 h of incubation. The difference among these feeds regarding the dynamics of the anaerobic fermentation within different substrates (intact feed, and fiber and defatted residues) was evaluated. Results suggested that the proportion of fiber digested in the rumen was affected by the degree of sample processing and fat removal. Fractional fermentation rate (kf) of neutral detergent residue (without sodium sulfite) and defatted fiber residue for BRAN, GERM, HP-DDG, and BPX was estimated to be 0.0635 and 0.0852 h(-1), 0.0803 and 0.0914 h(-1), 0.118 and 0.117 h(-1), and 0.0695 and 0.0844 h(-1), respectively. The most influential variables affecting kf(NDR) of HP-DDG and BPX also affected the predicted TDN, suggesting that fiber quality is essential to ensure higher TDN values for these feeds. Our study indicated that it is possible to routinely quantify the rate of fiber digestion and this approach may be based on common analytical procedures namely estimates of neutral detergent fiber, acid detergent fiber, acid detergent insoluble nitrogen, ether extract, and acid detergent lignin. Our simulations of TDN values demonstrated that differences in fermentability and chemical composition of these corn (co)products might considerably affect the supply of energy to lactating dairy cow. The analytical methods developed in this study may serve as a valuable tool to assess nutrient quality and uniformity when samples differ in chemical composition.

Evaluation of protein fractionation and ruminal and intestinal digestibility of corn milling co-products

Novel corn milling co-products developed from technological advancements in ethanol production vary widely in chemical composition and nutrient availability. The objectives of this study were to characterize feed protein fractions and evaluate differences in rumen-undegradable protein (RUP) and its digestible fraction (dRUP), amino acid concentration, and in vitro gas production of 7 corn milling co-products. The crude protein (CP; % of dry matter) of co-products was 12.7 for germ, 26.9 for dried distillers grains plus solubles that had no heat exposure before fermentation (DDGS1), 45.4 for high-protein dried distillers grains (HPDDG), 12.7 for bran, 30.2 for wet distillers grains plus solubles (WDGS), 23.1 for wet corn gluten feed (WCGF), and 26.0 for dried distillers grains plus solubles that had heat exposure before fermentation (DDGS2). Two ruminally and duodenally fistulated Holstein steers weighing 663+/-24 kg were used to determine RUP and dRUP with the in situ and mobile bag techniques. Samples of each feed were ruminally incubated for 16 h, and mobile bags were exposed to simulated abomasal digestion before insertion into the duodenum and subsequent collection in the feces. Protein fractions A, B(1), B(2), B(3), and C were characterized as follows (% CP): germ=30.0, 15.0, 38.1, 13.5, 3.4; DDGS1=17.0, 7.0, 67.0, 4.8, 4.2; HPDDG=7.4, 0.6, 82.4, 8.8, 0.8; bran=33.5, 4.0, 54.3, 6.0, 2.2; WDGS=18.6, 2.4, 53.1, 11.0, 14.9; WCGF=36.6, 15.9, 33.2, 10.1, 4.1; and DDGS2=17.9, 2.1, 41.1, 11.1, 27.9. The proportions of RUP and dRUP were different and are reported as follows (% CP): DDGS2=56.3, 91.9; HPDDG=55.2, 97.7; WDGS=44.7, 93.1; DDGS1=33.2, 92.1; bran=20.7, 65.8; germ=16.5, 66.8; and WCGF=11.5, 51.1. The concentrations of Lys and Met in the RUP were different and are listed as follows (% CP): germ=2.9, 2.0; DDGS1=1.9, 2.0; HPDDG=2.0, 3.2; bran=3.2, 1.5; WDGS=1.9, 2.3; WCGF=3.5, 1.6; and DDGS2=1.9, 2.4. In vitro gas production (mL/48h) was highest for germ (52.1) followed by bran (50.1), WDGS (40.7), DDGS2 (40.1), WCGF (39.0), DDGS1 (38.6), and HPDDG (37.5). Comparison of co-products defined differences in chemical composition, protein fractionation, ruminal availability, and microbial fermentation.

Effects of feeding three types of corn-milling coproducts on milk production and ruminal fermentation of lactating Holstein cattle

Two experiments were conducted to determine the effects of feeding 3 corn-milling coproducts on intake, milk production, ruminal fermentation, and digestibility of lactating Holstein cows. In experiment 1, three corn-milling coproducts were fed at 15% of the diet dry matter (DM) to 28 Holstein cows averaging (+/-SD) 625 +/- 81 kg of body weight and 116 +/- 33 d in milk to determine effects on DM intake and milk production. In experiment 2, the same rations were fed to 4 ruminally fistulated, multiparous Holstein cows averaging 677 +/- 41 kg of body weight and 144 +/- 5 d in milk to determine the effects on ruminal fermentation and digestibility. In both experiments, cows and treatments were assigned randomly in 4 x 4 Latin squares over four 21-d periods. Treatments were formulated by replacing portions of forage and concentrate feeds with 15% coproduct and included 1) 0% coproduct (control), 2) dried distillers grains plus solubles (DDGS), 3) dehydrated corn germ meal (germ), and 4) high-protein dried distillers grains (HPDDG). Feed intake was recorded daily, and milk samples were collected on d 19 to 21 of each period for analysis of major components. Rumen fluid was collected at 10 time points over 24 h post feeding on d 21 of experiment 2. In experiment 1, DM intake was greater for the germ (24.3 kg/d) and DDGS treatments (23.8 kg/d), but DDGS was not different from the control (22.9 kg/d) and HPDDG treatments (22.4 kg/d). Milk production paralleled DM intake and tended to be greater for the germ (32.1 kg/d) and DDGS treatments (30.9 kg/d), but the DDGS treatment was not different from the control (30.6 kg/d) and HPDDG treatments (30.3 kg/d). However, yields of milk fat, milk protein, and 3.5% FCM were similar and averaged (+/-SEM) 1.1 +/- 0.1, 0.9 +/- 0.03, and 31.7 +/- 1.3 kg/d. Milk urea nitrogen was greater for the HPDDG (15.9 mg/dL) and germ treatments (15.5 mg/dL) than for the control (15.0 mg/dL) and DDGS treatments (14.9 mg/dL). In experiment 2, DM intake and milk production were not different across treatments and averaged 26.1 +/- 2.3 and 28.3 +/- 3.9 kg/d. Ruminal pH (6.26 +/- 0.08) and total concentration of volatile fatty acids (125.3 +/- 4.2 mM) were similar. Acetate concentration was higher for the control treatment than the DDGS, germ, and HPDDG treatments (81.7 vs. 75.8, 75.0, and 78.4 mM). Concentrations of propionate and butyrate were not different and averaged 27.8 +/- 1.2 and 14.3 +/- 0.9 mM across treatments. The acetate:propionate ratios for the control, germ, and HPDDG treatments were greater than for the DDGS treatment (3.02, 2.88, and 2.91 vs. 2.62). Dry matter, organic matter, and neutral detergent fiber digestibilities were similar across treatments and averaged 63.5 +/- 2.7, 67.3 +/- 2.2, and 43.5 +/- 4.2%. Milk production followed DM intake in experiment 1, and yield of major milk components was not affected. Results of these experiments indicate that dairy rations can be successfully formulated to include 15% of diet DM as corn-milling coproducts while maintaining or increasing DM intakes and yields of milk and milk components.

A generalized compartmental model to estimate the fibre mass in the ruminoreticulum: 2. Integrating digestion and passage.

Models used to predict digestibility and fill of the dietary insoluble fibre (NDF) treat the ruminoreticular particulate mass as a single pool. The underlying assumption is that escape of particles follows first-order kinetics. In this paper, we proposed and evaluated a model of two ruminoreticular sequential NDF pools. The first pool is formed by buoyant particles (raft pool) and the second one by fluid dispersed particles (escapable pool) ventrally to the raft. The transference of particles between these two pools results from several processes that reduce particles buoyancy, assuming the gamma distribution. The exit of escapable pool particles from the ruminoreticulum is exponentially distributed. These concepts were evaluated by comparing ruminoreticular NDF masses as 43 and 27 means from cattle and sheep, respectively, to the same predicted variable using single- and two-pools models. Predictions of the single-pool model were based on lignin turnover and the turnover associated to the descending phase of the elimination of Yb-labelled forage particles in the faeces of sheep. Predictions of the two-pool model were obtained by estimating fractional passage rates associated to the ascending and descending phases of the same Yb excretion profiles in sheep faeces. All turnovers were scaled to the power 0.25 of body mass for interspecies comparisons. Predictions based on lignin turnover (single pool) and the two-pool model presented similar trends, accuracies and precisions. The single-pool approach based solely on the descending phase of the marker yielded biased estimates of the ruminoreticular NDF mass.

Validation of a system for monitoring feeding behavior in beef cattle.

The objective of this study was to evaluate the use of an electronic radio-frequency-identification-based system (GrowSafe System Ltd., Airdrie, Alberta, Canada) to measure feeding behavior traits in beef cattle fed a high-grain diet. Feeding behavior data were recorded by the GrowSafe system and time-lapse video using 10 heifers over a 6-d period. Observed bunk visit (BV) and meal event data (frequency and duration) were compared with electronic feeding behavior data generated by the GrowSafe system at 5 parameter settings (MPS; 30, 60, 100, 150, and 300 s), which are used to define the maximum duration between consecutive electronic identification recordings to initiate a subsequent BV event. A random coefficient model was used to compare video and electronic data using orthogonal contrasts. Video data were regressed on the electronic feeding behavior data to obtain an estimate of precision (r(2)) and other statistical estimates, including mean square error of prediction and concordance correlation coefficient, to access the adequacy of the electronic system predictions. The variation in MPS values affected BV data, but not meal event data. Electronic meal frequency and duration data were not different (P > 0.50) from observed values, and were not affected by electronic MPS values. The optimal MPS value for prediction of BV and meal event frequency and duration traits was 100 s. Our evaluation indicated the GrowSafe system 4000E was able to predict BV and meal event data when the 100-s MPS was used to analyze the feeding behavior data.