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Effect of feeding protocol on intake by Angus bulls

February 1, 2014

Whisnant, S


Individual intakes are required to evaluate rate and efficiency of gain in young bulls. The objectives were to confirm use of alkanes as acceptable markers to calculate DMI of corn silage-based diets and to assess changes in DMI by Angus bulls (288 to 402 kg of BW) in response to individual feeding or group feeding. An 80:20 corn silage:supplement TMR was offered to 12 Angus bulls in each of 2 yr. The bulls were housed together and fed individually (period 1), group fed in a bunk (period 2), then again fed individually (period 3). Periods lasted 21 d. In addition to the TMR, each bull consumed 0.908 g/d of 50:50 corn grain:soybean hulls. Feed intake was recorded daily. Fecal grab samples were collected during the last 5 d of each period to calculate TMR DMI from feed and fecal content of hentriacontane and dotriacontane. Measured and calculated TMR DMI did not differ (P < 0.16) in period 3. Although average daily TMR DMI of the bulls did not change from period 2 (2.58 kg of DM/kg of BW, calculated with markers) to 3 (2.42 kg of DM/kg of BW, P < 0.11), 21 of the 24 bulls gained or lost DMI rank by 2 or more positions among pen mates as the method of feeding changed among periods. Changes in DMI for a given bull ranged from 0.15 to 3.2 kg/d. Feeding method may not affect DMI of the top-ranked or bottom-ranked bulls, but intermediate bulls may change rank in response to individual or bunk feeding.

Key words: alkane, bull, feeding protocol, intake


Animal managers have selected breeding stock based on visual appraisal and individual productivity for centuries. The use of breeding values and EPD has advanced selection into the realm of pedigrees and prediction for progeny. Current efforts focus on the importance of knowing individual feed intake and BW gain in a natural environment to assess efficiency under production conditions. A key component of that assessment is quantitative information on individual feed intake and change in BW, with the former being a larger challenge than the latter. There are feed intake data available on effects of a feeding strategy among groups of animals (Friend et al., 1977; Pritchard and Bruns, 2003; Schwartzkopf-Genswein et ah, 2003) and individual DMI or intake behavior within groups of animals (Friend et ah, 1977; DeVries and von Keyserlingk, 2006; Huzzey et al., 2006; Golden et al., 2008), but we are unaware of any information on feed intake within groups of animals to compare individual to group feeding.

Alkanes are used to measure feed intake in group-fed animals (Mayes et al., 1986; Elwert and Dove, 2005; Olivan et al., 2007; Morris et al., 2010), but their use in silage-based diets fed to cattle is associated with lesser concentrations of alkanes upon which to base the calculations (Garcia et al., 2000; Graf et al., 2005). The objectives of the current research were to measure changes in DMI in response to a switchback in feeding protocols and to verify validity of use of alkanes as DMI and DM digestibility (DMD) markers in corn silage-based diets.


All animal procedures were reviewed and approved by the animal care and use committee of North Carolina State University. Purebred Angus bulls were born and raised on the Upper Piedmont Research Center in Reidsville, North Carolina, weaned at 5 to 7 mo, preconditioned for 45 d at Reidsville, moved to feeding facilities in Butner, North Carolina, and adapted to individual Calan feeding gates. A total of 24 bulls (12 in yr 1, 12 in yr 2) was fed a TMR containing on a DM basis 79% corn silage and 21% supplement (Huntington et ah, 2012) for 42 d in August and September, then proceeded through three 21-d periods. Bulls were weighed periodically before feeding and were fed once daily in the morning. Bulls consumed 0.9 kg of additional supplement before TMR feeding. The additional supplement was corn graimsoybean hulls 1:1 and contained dotriacontane (C32) and hexatriacontane (C36) for the last 14 d of periods 2 and 3. Bulls continued to be fed individually in period 1, were group fed at a bunk in period 2 (7.1 m of bunk space for 12 bulls), and then returned to individual feeding in period 3. During period 2, bulls went to their individual gates daily in the morning to consume supplement and then returned to a common pen for the rest of the day. Water was available ad libitum. Feed offered and refused was recorded daily. Daily measured intake during period 2 was the total pen intake divided by 12; therefore, measured intake was the same for each bull on a given day. Daily feed intakes that were measured during the last 14 d of each period were included in calculations and statistical analysis of results. Orts were placed in 4 categories based on physical appearance ranging from similar to TMR (category 1) to corn cobs (category 4). Samples of corn silage and TMR were collected periodically during the experiment, and daily grab samples of supplement were composited within periods. During the last 5 d of each period, fecal grab samples were collected from each bull at 1230 to 1330 h.

Silage and TMR samples were freeze-dried to determine DM and then ground through a 0.5-mm screen (Cyclotec, Foss Analytical, Hilleroed, Denmark). Orts and fecal samples were dried to a constant weight at 60C, composited within categories, and then ground through a 0.5-mm screen. Feces were dried to a constant weight at 60C and then ground through a 0.5-mm screen. Alkane concentrations in feeds, orts, and feces were determined as described by Chavez et al. (2011).

Dry matter intake of TMR was calculated from feed and fecal concentrations of hentriacontane (C31) and C32 as described by Mayes et al. (1986). Means of alkane concentrations from sample analyses were used to provide values for the DMI calculations. Fecal output was calculated by dividing the daily supply of C31, C32, or C36 by the fecal concentrations of those alkanes, and DMD was calculated for each of the alkanes. For uniformity of calculations, C31 concentrations were used to calculate DMD and digestible DMI in all periods.

Within bulls and periods 2 or 3, C31 content of the TMR was adjusted for amount of orts and C31 content of orts, and DMI was again calculated with this adjusted concentration. Paired-t differences between measured and calculated DMI in periods 2 and 3 were used to assess the validity of the alkane technique.

Effects of feeding protocol on DMI and other dependent variables were assessed with the General Linear Models procedure of SAS (SAS Institute Inc., Cary, NC) in a statistical model that included year, period, and their interaction tested against residual mean squares. One model included all periods and a second model included periods 2 and 3, when alkanes were included in the supplement. Paired-t differences between measured and calculated DMI in periods 2 and 3 were used to assess the validity of the alkane technique. Dry matter digestibilities were calculated with C31, C32, and C36 as alkane markers were compared in a model similar to the one described above, except that it considered alkane marker and interactions as sources of variation. Bulls were ranked on the basis of DMI within year and period, and then paired-t differences in rank among comparisons of the preliminary period and periods 1, 2, and 3 were used to evaluate change in rank in response to the change from individual to bunk feeding and then the return to individual feeding. The Correlation procedure of SAS was used to generate Pearson correlation coefficients between response variables.


The supplement contained 22.5 mg of C31 and 488 mg of C32 per kilogram of DM in yr 1 and 18 mg of C31 and 563 mg of C32 per kilogram of DM in yr 2. The TMR contained 22.6 mg of C31 per kilogram of DM in yr 1 and 29.7 mg of C31 in yr 2. None of the TMR samples contained C32 or C36, concentrations of tritriacontane (C33) in the TMR were lower than C31, and pentriacontane was not detected, so DMI was calculated with C31 and C32.

Mean SE ADG and G:F were 1.73 0.03 kg/d and 0.22 0.01 g/g in yr 1 and 1.79 0.05 kg/d and 0.22 0.01 g/g in yr 2. Bulls in yr 2 weighed more and ate more feed than bulls in yr 1 (Table 1). Dry matter intake and BW increased with time (Table 1), but DMI per kilogram of BW decreased from 27 to 24 g/kg as the bulls grew larger and older. Measured and calculated DMI during periods 2 and 3 differed by 4 g or less per 100 g of measured DMI (Table 1). Mean SE orts were 42 5 g/kg of DM offered in yr 1 and 131 2 g/kg of DM offered in yr 2. Adjustment for C31 concentration in orts had minimal effect on the C31 concentration used in the calculations, hence had no effect on calculated DMI. Measured or calculated DMI during bunk feeding (period 2) did not differ from similar DMI during period 3 when the bulls returned to individual feeding (Table 1).

Calculated daily fecal output, hence DMD, was similar for C31 and C32 as markers, both of which had greater calculated fecal outputs and lower DMD than C36 as the marker (Table 2). Bulls had greater DMD in yr 1 than in yr 2, and a year x feeding period interaction was caused by a trend for increased DMD for bulls during gate feeding (period 2) versus gate feeding (period 3) during yr 1, and a significant decrease between period 2 and 3 during yr 2 (Table 2).

Ranking of bulls on DMI within period and year changed, based on the criteria of a change equal to or greater than 2 SE units, which was a change in 3 positions in comparison of period 1 to period 2, 2 positions in comparison of period 2 to period 3, and 2 positions in comparison of period 1 to period 3. Figure 1A shows that decreased DMI for bulls that decreased rank from period 1 to period 2 ranged from -0.15 to -2.41 kg/d, with an average of -1.21 kg/d. Ten bulls (Including 7 that lost rank from period 1 to 2) increased rank and increased DMI from period 2 to 3, ranging from 1.42 to 3.20 kg/d with an average of 2.08 kg/d (Figure IB). Figure 1C shows that increased DMI for bulls that increased rank from period 1 to period 2 ranged from 1.42 to 2.48 kg/d, with an average of 1.84 kg/d. Eight bulls (including 5 that gained rank from period 1 to 2) decreased rank and on average decreased DMI from period 2 to 3, ranging from 0.98 to -1.03 kg/d with an average of -0.23 kg/d (Figure ID). Three of the 8 bulls actually increased DMI slightly from period 2 to 3 but lost rank relative to their pen mates. Of the 9 bulls that changed rank from period 1 to 2 or from period 2 to 3, 5 bulls gained rank, 1 bull lost rank, and 3 did not change rank from period 1 to 3. Of the 13 other bulls that changed rank from period 1 to period 3, 5 bulls gained rank and 8 bulls lost rank. Three of the 24 did not change rank in the comparisons of periods 1 to 2, and 2 to 3; one bull always ranked first, one bull ranked first or second in each period, and one bull always ranked eleventh.

A main goal of feeding trials with bulls is to evaluate bulls on the basis of rate and efficiency of BW gain; if they change rank relative to their pen mates in response to method of feeding during the evaluation period, that makes time on feed, feeding method, or both a potential factor, or source of error. Our results indicate that feeding method may not affect the topranked or bottom-ranked bulls, but intermediate bulls may change rank in response to individual or bunk feeding. That may not hold with longer feeding periods. The need to measure individual DMI on group-fed animals under normal production feeding methods was recently demonstrated in Angus heifers (Morris et al., 2010).

To assess the effect, if any, of changes in overall DMI, ADG, and feed efficiency on DMI ranking within a pen of bulls, we divided data from 317 Angus bulls (from previous experiments in the same facility, fed the same diet, over the 5 yr before the bulls in the present experiment) into low-, medium-, and high-DMI categories across years and pens (Table 3), based on average SD DMI for all bulls. The high-DMI bulls had greater DMI and ADG but lesser G:F than the mediumor low-DMI bulls. The DMI ranks correlated with average DMI for 84 d within pens and years, with lower-ranking bulls in the lower DMI category, the medium-ranking bulls in the medium category, and the high-ranking bulls in the highDMI category. As their feeding trials progressed through 84 d, bulls in the low-DMI category gained rank, and bulls in the high-DMI category lost rank (Table 2).

Over the years and including the present experiment, bulls did not exhibit aggressive behavior toward pen mates while they were in the pens. On days when the bulls were weighed or removed from the pens for activities that involved use of a squeeze chute, the bulls immediately began exhibiting aggressive behavior toward pen mates when they left the pen and then stopped that behavior when they returned to the pen. Apparently, that intermittent behavior did not affect how the bulls ate from their individual feeding gates.

Although alkane concentrations in the corn silage-based TMR were less than in feeds in other experiments (Garcia et al., 2000; Graf et al., 2005), in particular C33, lack of significant differences within bulls in measured and predicted TMR DMI during Calan gate feeding provides support for use of alkanes to predict DMI. Further support is shown by similar calculated fecal output and DMD when C31 or C32 was used as marker, consistent with the concept of Mayes et al. (1986) that alkane markers need similar indigestibilities for valid use to predict DMI. The DMD for C36 is consistent with the data of Mayes et al. (1986) and Olivan et al. (2007) that show less digestion, or greater indigestibility, of C36 versus alkanes of shorter chain length. Assuming indigestibility of C36, data in Table 2 indicate that DMD with C31 as a marker is underestimated by approximately 6 g/100 g of DMI, or about 11%. The predicted DMD (Table 2) was appreciably less than measured digestibility of the same TMR with 36 steers and 12 bulls over several years (72.3 g/100 g of DMI; Huntington et al., 2011). However, DMI in the previous study did not exceed 19.6 g/ kg of BW, less than 24.0 to 27.0 g/ kg of BW in the present study (Table 1). Furthermore, near-infrared reflectance spectroscopy spectra from fecal grab samples from 282 bulls of similar breeding, age, and weight, TMR, and the same facilities used in the present study were not similar to spectra from feces from measured digestibilities described above, indicating that equations generated with spectra from measured digestibilities were not statistically acceptable to predict digestibilities from fecal grab samples of the bulls, who ate on average 23 g of TMR DMI/kg of BW (Huntington et al., 2011).


Alkanes are suitable markers to measure individual DMI of bulls fed a corn silage-based diet in groups. At least in our feeding facility we conclude that the change in DMI rank for the bulls in the present study as they switched feeding protocol is attributable to the change from individual feeding gates to bunk feeding.


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G. Huntington,1 J. Cassady, PAS, S. F. Reis, M. Poore, M. Alley, and S. Whisnant

Department of Animal Science and College of Veterinary Medicine, North Carolina State University, Raleigh 27695

* Corresponding author: gerald_

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Source: Professional Animal Scientist

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