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Liquid supplement and forage intake by range beef cows¹

Montana State University, Bozeman 59717

² Correspondence:
Animal and Range Sciences (phone: 406-994-5563; E-mail:
jbowman{at}montana.edu).

	Abstract

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One hundred eighty crossbred cows were assigned to one of six native range pastures during two winters to evaluate forage and supplement intake as affected by liquid supplement (yr 1: 50% crude protein, 84% from urea; yr 2: 57% crude protein, 91% from urea) delivery method and cow age (2, 3, 4, 5, or 6 yr). Treatments were: 1) no supplement (Control); 2) a lick-wheel feeder containing liquid supplement (ADLIB); and 3) a computer-controlled lick-wheel feeder that dispensed 0.9 kg•cow^-1•d^-1 of liquid supplement (average 0.5 kg of dry matter•cow^-1•d^-1; Restricted). Each treatment was applied to two pastures. Forage digestibility was increased (P = 0.03) by supplementation. Supplemented cows lost less (P = 0.05) body condition than unsupplemented cows (average -0.3 vs -0.6). Blood urea nitrogen (BUN) was highest (P = 0.001) for ADLIB (8.7 mg/dL), intermediate for Restricted (6.2 mg/dL), and lowest for Control (2.3 mg/dL). Forage DMI was 31% higher (P = 0.01) in 1995 than in 1996, and was increased (P = 0.02) by supplementation both years. Cows supplemented with ADLIB consumed 23% more forage dry matter than Control cows, whereas Restricted cows consumed 21% more dry matter than ADLIB cows. Supplement intake by cows on ADLIB was greater (P = 0.001) than by cows on Restricted in both years. Supplement intake was lowest (P = 0.002) by 2-yr-old cows, intermediate by 3-yr-olds, and greatest by 4-, 5-, and 6-yr-old cows. Variation in supplement intake by individual cows was higher (P = 0.09) for cows in the Restricted treatment (coefficient of variation [CV] = 117%) than those on ADLIB (CV = 68%) during the first year, but did not differ between supplement treatments (average CV = 62%) in the second year. The proportions of cows consuming less than 0.3 kg/d of supplement dry matter intake (DMI) and consuming less than the target amount of supplement (0.5 kg DMI) were less (P = 0.001) for ADLIB than for Restricted during both years. ADLIB cows spent more (P = 0.001) time at the supplement feeder and had more (P < 0.002) supplement feeding bouts than Restricted cows during both years. During the first year, 2- and 3-yr-old cows spent less (P < 0.01) time at the feeder and had fewer feeding bouts per day than 6-yr-old cows. Age had no effect (P > 0.24) on feeding behavior during the second year. Supplementation of beef cows grazing winter range with 50 to 57% crude protein liquid supplement increased forage digestibility and intake. Restricting supplement access increased forage consumption and variability of supplement intake.

Key Words: Age • Animal Feeding • Cows • Feeding Behavior • Radio

	Introduction

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Supplementation programs for grazing cows have not always been shown to be effective, primarily because measures, such as subsequent pregnancy rate, calving interval, or calf growth, have not been consistently improved (DelCurto et al., 1990). Some of this inconsistency may be due to variation in supplement intake by individual cows. Variation in supplement intake can be influenced by supplement delivery method (Bowman and Sowell, 1997) and social interactions of individual cows within the herd (Wagnon, 1965). Social dominance within a herd is associated with age (Wagnon, 1965; Friend and Polan, 1974) and may be modified by supplement delivery method (Bowman et al., 1999). The objectives of this study were to evaluate the effects of liquid supplement delivery method and cow age on forage intake, supplement intake, and supplement feeding behavior by mixed-age groups of cows grazing native range.

	Materials and Methods

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One hundred eighty mixed-age, crossbred pregnant cows were assigned to one of six native rangeland pastures in the fall after weaning in each of 2 yr (1995 and 1996). Thirty cows (along with three ruminally cannulated cows) grazed each pasture from November 7, 1995 to January 4, 1996 and from November 12, 1996 to January 10, 1997. The study pastures were located at Ft. Keogh Livestock and Range Research Laboratory in Miles City, MT. Pastures averaged 253 ha in size, and ranged from 162 to 351 ha. Pastures were classified as a Northern mixed-grass prairie dominated by western wheatgrass (Agropyron smithii), needleandthread (Stipa comata), and blue grama (Bouteloua gracilis). Forage standing crop during the study averaged 1,000 kg/ha, and ranged from 738 to 1,523 kg/ha per pasture. Long-term annual precipitation was 356 mm, with temperatures ranging from 38°C in the summer to -40°C in the winter. Suggested stocking rates for these areas were 1.3 ha/animal unit month (AUM) (Lacey and Taylor, 1985). Our stocking rates for the six pastures were 1.3, 2.5, 3.8, 3.8, 4.3, and 4.5 ha/AUM, which were very conservative in order to ensure that intake was not limited by forage availability. The total snowfall during November and December 1995 was 26 cm, whereas the total snowfall for November and December 1996 was 58 cm (WRCC, 2000). In addition, two dates during the study in 1996 recorded record high snowfall, November 23 (8 cm; average for that date was 0.3 cm) and December 22 (12 cm; average for that date was 0.8 cm).

The distribution of cows by age in 1995 was 48 2-yr-olds, 41 3-yr-olds, 41 4-yr-olds, 24 5-yr-olds, and 24 6-yr-olds. The distribution of cows by age in 1996 was 59 2-yr-olds, 46 3-yr-olds, 37 4-yr-olds, 22 5-yr-olds, and 15 6-yr-olds. Cows from each age group were assigned to each pasture to determine forage and supplement intake as affected by cow age and liquid supplement delivery method. Supplement treatments were: 1) no supplement (Control), 2) ad libitum access to a lick-wheel feeder containing liquid supplement (ADLIB), and 3) access to a computer-controlled lick-wheel feeder that dispensed 0.9 kg•cow^-1•d^-1 of liquid supplement on an as-fed basis (average 0.5 kg DM•cow^-1•d^-1; Restricted; Regulate Liquid Feed Delivery System, Performix Nutrition Systems, Nampa, ID 83701). Each treatment was applied to two pastures. The ADLIB feeder had a capacity of 340 L in 1995 and 511 L in 1996, with two lick-wheels. The Restricted tank held approximately 360 L, with a smaller 26-L feeder tank containing two small lick-wheels. The Restricted delivery system was programmed in 1995 to dispense 29.7 kg/d of liquid supplement (0.52 kg DM•cow^-1•d^-1), divided into 12 equal aliquots every hour between 0700 and 1900. In 1996, the Restricted tank dispensed 29.7 kg/d of liquid supplement (0.53 kg DM•cow^-1•d^-1), in 24 equal aliquots every 30 min from 0700 to 1900. Both feeders contained the same liquid supplement formulation. In 1995, the liquid supplement contained a mixture of 50% cane and 50% beet molasses, with 84% of the CP provided by urea. In 1996, the liquid supplement was 100% cane molasses-based, with 91% of the CP provided by urea. No intake limiter was included in the liquid supplement. Liquid supplement in both tanks contained YbCl₃ hexahydrate as an external marker to estimate supplement consumption. Liquid supplement averaged 50.0% CP, 57.9% DM, and 1,046.5 parts per million (ppm) of Yb in 1995, and 57.0% CP, 58.7% DM, and 465.1 ppm of Yb in 1996. In addition, the liquid supplement contained 1.0% Ca, 1.6% P, 2.7% K, 0.67% Mg, 1.3% S, 866 ppm of Zn, 428 ppm of Cu, 387 ppm of Fe, 420 ppm of Mn, and 3 ppm of Se.

One wk prior to the beginning of the study, cows were confined in small lots with the supplement tanks to allow them to become familiar with the tanks. The supplement feeders remained in one location during both years to reduce confounding factors that might arise due to differences in proximity to water. Under commercial conditions, supplement feeders might have been moved as preferences for grazing areas changed.

Cows were weighed, body condition scored, and then turned on to their assigned pastures on d 1 of the study. Body condition scoring was done individually by three observers using a scale of 1 to 9, and the three values averaged. Cows on ADLIB and Restricted treatments had access to liquid supplement beginning on d 1. Ytterbium chloride was included in the liquid supplement from d 15 to 41 in 1995, and from d 21 to 46 in 1996. Liquid supplement was sampled from an individual tank each time supplement was added, a total of 31 times in 1995 and 16 times in 1996. The larger number of sampling times in 1995 was due to a smaller ADLIB tank. Liquid supplement was analyzed for DM, N (AOAC, 1997), and Yb by inductively coupled plasma emission spectroscopy (Fassel, 1978). On d 35 in 1996, venous blood samples were taken from cows via jugular puncture in nonheparinized tubes. Blood urea N (BUN) was measured using a Dade Behring Dimension clinical chemistry system (Dade Behring Inc., Newark, DE), which employed a urea/glutamate dehydrogenase-coupled enzymatic technique (Talke and Schubert, 1965). All cows (including the cannulated cows) were dosed with sustained release Cr₂O₃ boluses (Captec Chrome, Nufarm, Auckland, New Zealand) on d 22 and 23 in 1995, and d 26 and 27 in 1996 to estimate fecal output (FO). Fecal grab samples were taken on d 31, 34, and 36 in 1995, and d 35, 37, and 39 in 1996. Fecal samples were dried in a forced-air oven (60°C), ground through a 1-mm screen Wiley mill (Thomas Scientific, Swedensboro, NJ), and composited for each cow on an equal weight basis. Feces were analyzed for DM (AOAC, 1997), Cr by atomic absorption spectrophotometry (Ellis et al., 1982), and Yb by inductively coupled plasma emission spectroscopy (Fassel, 1978).

Fecal Cr concentration and daily Cr release rate were used to estimate FO using the following equation:

Three ruminally cannulated cows per pasture grazed along with the other 30 experimental cows throughout the study periods both years. The cannulated cows were used to collect diet extrusa samples on d 10 and 11 in 1995, and d 12 and 13 in 1996. Extrusa was air-dried and ground through a 2-mm screen in a Wiley mill (Thomas Scientific). Extrusa samples were analyzed for DM, OM, N (AOAC, 1997), NDF, and ADF (Van Soest et al., 1991).

The cannulated cows (aged 2 to 6 yr) used in this study were from a different herd and location than the rest of the cows, and had been used in other liquid supplement studies. Their supplement DMI ranged from 0.7 to 2.4 kg/d in 1995 and from 0.2 to 3.6 kg/d in 1996. The average supplement DMI by the cannulated cows (Table 1) on the ADLIB treatment matched well with the average supplement DMI of noncannulated cows on that treatment in 1995 and 1996 (average of 1.3 and 1.0 kg/d for cannulated cows in 1995 and 1996 compared with an average of 1.3 and 0.9 kg/d for noncannulated cows in 1995 and 1996; see Table 5). However, the cannulated cows on the Restricted diet consumed more supplement DMI than noncannulated cows on that diet during both 1995 and 1996 (average of 1.5 and 1.2 kg/d for cannulated cows in 1995 and 1996, compared with an average of 0.3 and 0.5 kg/d for noncannulated cows in 1995 and 1996). The amount of supplement intake by the cannulated cows on the Restricted diet in comparison to the rest of the Restricted cows indicates that digestibility estimates obtained using cannulated animals may not be representative of the entire herd. Therefore, we measured in situ DM disappearance (DMD) of the extrusa samples under more controlled conditions as described below and used those values to estimate forage intake.

One Cr₂O₃ bolus was weighed, placed in the rumen of each cannulated cow for 15 d in 1995 and 14 d in 1996, removed, and weighed again to estimate daily Cr release rate from the boluses. Chromium release rate averaged 1.03 g/d during both years.

Supplement consumption for individual cows was estimated by the following equation (Bowman et al., 1999):

Supplement use (kg DM•cow^-1•d^-1) was estimated by disappearance of supplement every time supplement was added to the tanks. Disappearance was calculated by measuring the change in depth of supplement in the tank (cm) and multiplying this by a calibrated volume per unit depth (L/cm) for each tank, and then by the density of supplement (1.13 kg/L). The calculated disappearance was corrected to DM basis and then divided by the number of days since the last measurement and by the number of cows per tank.

An antennae (GrowSafe, Inc., Calgary, Canada) was placed above the supplement feeder in one ADLIB and one Restricted pasture during both years. All cows in these pastures were fitted with a radio frequency (RF) eartag at the beginning of each study in order to electronically record each visit to the supplement feeder (Sowell et al., 1998; Earley et al., 1999). Each time the RF eartag was directly underneath and within 45 cm of the antennae, the reader panel identified the cow and the exact time it was present. Data were summarized by the hour in 1995, but in 1996, the equipment was reprogrammed to collect data every 1.25 s. The GrowSafe system was used to determine time spent at the feeder (min/d), visits/d (bouts/d), and supplement feeding bout duration (min/bout). In 1995, each hour a cow was identified as being present at the feeder was designated a feeding bout. For example, if a cow were present from 0830 to 0857, then that constituted one feeding bout; however, a cow’s presence from 0850 to 0910 constituted two feeding bouts. In 1996, a feeding bout was defined as a visit to the supplement feeder separated by 5 min of inactivity at the feeder.

Days that cows were handled, or that the computer failed, were excluded from the behavior data analysis. The behavior data from the cannulated cows were also excluded. Twenty-five (out of 52) days of behavior data for each cow were used in the data analysis in 1995. Prior to the beginning of the study in 1996, modifications to the computer system were made in order to improve reliability. Thirty-four (out of 43) days of behavior data for each cow were used in the data analysis in 1996.

Cows were weighed and body condition scored at the end of the study each year. Body condition scoring was done by three observers (1 to 9 scale), and the three values averaged. At calving, calf birth date and birth weight were recorded. At weaning, calf weaning weight (WW) was recorded and WW adjusted for age of calf was calculated using the following equation:

Cows were palpated for pregnancy diagnosis at weaning. In addition, the calf birth date the following year was recorded (calf birth date in 1997 for the November 7, 1995 to January 4, 1996 study, and calf birth date in 1998 for the November 12, 1996 to January 10, 1997 study).

Performance and intake data were analyzed as a split-plot design with the main effects of treatment, year, and their interactions tested by pasture(treatment x year). The subplot was cow age, and its interactions with year and treatment were included (SAS Inst., Inc., Cary, NC). Means were separated with LSD tests when a significant F-value was detected (P < 0.10). Performance and intake data from the cannulated cows were excluded from the statistical analysis. Pregnancy data were analyzed by ² using PROC CATMOD and PROC FREQ of SAS. Pregnancy data from the cannulated cows were excluded from the statistical analysis. Supplement intake distribution was analyzed as a 2 x 2 x 5 factorial, with year, treatment, and age as the main factors, and all with interactions tested. Each age group, within pasture, was used as the experimental unit for the following: the calculation of supplement intake CV and the proportion of cows with fecal samples without Yb (nonconsumers), with less than 0.3 kg of supplement intake, with 0.3 to 0.8 kg of supplement intake, with greater than 0.8 kg of supplement intake, and with below-target supplement consumption.

Each variable of electronically recorded behavior data was confirmed to be normally distributed prior to any analysis (Shapiro and Wilk, 1965). Data were analyzed using the GLM procedure of SAS to test the effects of treatment, date, treatment x date, age, and treatment x age. Individual cow was used as the experimental unit. Cow within treatment x age was used as the testing term for treatment, age and treatment x age, because repeated measures were made on each cow (Gill and Hafs, 1971). Means were separated with LSD tests when a significant F-value was detected (P < 0.10). No comparisons in supplement feeding behavior between years were made due to differences in electronic data collection methods between years. Behavior data from the cannulated cows were excluded from the statistical analysis.

	Results and Discussion

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The native range winter forage consumed by grazing cows was low quality as indicated by <6% CP and >77% NDF both years (Table 2). In situ DMD of the unsupplemented winter range forage at 48 h did not differ (P = 0.32) between years, and averaged 42.1%. Supplementation increased (P = 0.03) 48-h in situ DMD both years. When extrusa collected the first winter was supplemented with ADLIB and Restricted in situ DMD was increased by 34 and 47%, respectively, compared to the Control. Supplementation increased in situ DMD of extrusa collected the second year an average of 26%. Other researchers have reported 6 to 36% increases in DM and OM digestibility of forages due to liquid supplementation (Cohen, 1974; Garg and Gupta, 1992; Kalmbacher et al., 1995; Bowman et al., 1999).

Cow initial and final BW and BCS were lowest (P = 0.001) for 2-yr-old cows, followed by 3-yr-old cows, and highest for 4-, 5-, and 6-yr-old cows (Table 4). Two-year-old cows lost less (P = 0.01) weight than all other age groups; however, there was no difference (P = 0.88) in BCS change between age groups (average -0.4 BCS). Calf birth weight was lowest (P = 0.02) for 2-yr-old cows and highest for 6-yr-old cows. Age-adjusted WW was lower (P = 0.05) for 2-yr-old cows than for 3-, 4-, 5-, and 6-yr-old cows. A year x age interaction (P = 0.02) was seen for age-adjusted WW, with calves of 4- and 5-yr-old cows having higher age-adjusted WW than 2-, 3-, and 6-yr-old in the first year, and calves of 3-, 5-, and 6-yr-old cows having higher age-adjusted WW than 2- and 4-yr-olds in the second year. Fall pregnancy rate was not affected (P = 0.15) by cow age, although the 6-yr-old cows averaged 68% pregnant compared to an average of 80% for the other age groups. Cow age did not affect (P = 0.22) calving interval, which averaged 370 d.

Supplement use as estimated by disappearance of supplement from the tanks was 0.3 and 1.0 kg DM•cow^-1•d^-1 for Restricted and ADLIB cows, respectively, during the first year, and 0.4 and 0.9 kg DM•cow^-1•d^-1 for Restricted and ADLIB cows, respectively, during the second year. These estimates of supplement use are remarkably close to the average supplement intakes by individual cows as estimated using the Yb marker (0.3 and 1.3 kg DM•cow^-1•d^-1 for Restricted and ADLI cows, respectively, for 1995; 0.5 and 0.9 kg DM•cow^-1•d^-1 for Restricted and ADLIB cows, respectively, for 1996).

Blood urea nitrogen, measured in 1996, was highest (P = 0.001) for cows on the ADLIB supplement, intermediate for those on Restricted, and as might be expected, was lowest for Control cows that did not receive any supplemental N. Hammond (1997) reported that BUN levels less than 7 mg/dL indicated a deficiency of N relative to DE, and levels elevated above 19 to 20 mg/dL were sometimes associated with reduced reproductive performance. In our study, individual cow BUN levels ranged from 1 to 21 mg/dL, with only one cow having a BUN level above 19 mg/dL. Therefore, despite a wide range in supplement DMI (0 to 4.7 kg), and with urea providing 91% of the supplemental nitrogen, BUN levels were not high enough to cause concern relative to reproductive performance.

No treatment x age interactions (P > 0.23) were found for forage or supplement DMI or for BUN levels (Table 6). However, year x age interactions (P = 0.001) were seen for forage DMI expressed in kilograms and g/kg BW. During the first year, forage DMI was least (P = 0.001) by 2-yr-old cows (11.9 kg), higher by 3-yr-old cows (14.5 kg), higher still by 4- and 6-yr-old cows (average 16.2 kg), and greatest by 5-yr-old cows (18.4 kg). During the second year, forage DMI was least (P = 0.001) by 2-yr-old cows (10.5 kg), and not different by 3-, 4-, 5-, and 6-yr-old cows (average 12.1 kg). All age groups consumed less (P = 0.001) forage DM the second year compared with the first year. When expressed as g/kg BW, differences in forage DMI were not as large. During the first year, 2-yr-old cows had lower (P = 0.001) forage intake than3-, 4-, and 6-yr-old cows, with 5-yr-old cows having the greatest forage intake. However, during the second year, forage DMI in g/kg BW did not differ (P = 0.22) between age groups.

Liquid supplement intake distribution by individual cows is presented in Table 7. The largest range in supplement DMI by individual cows was seen on the ADLIB treatment, 0 to 4.7 kg/d in 1995 and 0 to 4.1 kg/d in 1996. The range in supplement DMI was smaller for cows on the Restricted diet (0 to 1.2 kg/d in 1995 and 0 to 1.5 kg/d in 1996) and may have been due to the controlled dispensing pattern of the supplement. There was a year x treatment interaction (P = 0.09) for CV of individual cow supplement DMI. The CV for individual cow supplement DMI was higher (P = 0.09) for Restricted cows than for ADLIB cows in 1995 (117 vs 68% CV), but not different (P = 0.69) for the two treatments in 1996 (56 vs 67% CV, for ADLIB and Restricted cows, respectively). The CV of supplement DMI for ADLIB was the same (P = 0.25) between years (average 62%). However, the supplement DMI CV for Restricted was lower (P < 0.01) the second year compared with the first (67 vs 117% CV, for 1995 and 1996, respectively). The change in the dispensing pattern of Restricted diets the second year, along with any other differences between years, could have contributed to the reduction in CV. Ytterbium was not detected in the feces of a greater (P = 0.03) proportion of cows (considered nonconsumers) on the Restricted treatment compared with cows on the ADLIB treatment (9.3 vs 1.7% for Restricted and ADLIB, respectively). This suggests that although the change in dispensing pattern of the Restricted feeder was effective in increasing the mean supplement intake and reducing the CV for supplement intake by that group of cows, it did not result in a reduction in non-consumers.

No effects of age (P > 0.11) and no year x age or treatment x age interactions (P > 0.12) were seen for supplement intake distribution (Table 8). The largest ranges in supplement intake were seen in 3- and 4-yr-old cows. Supplement intake CV ranged from 52% for 6-yr-old cows to 98% for 5-yr-old cows. Nonconsumers (cows without Yb in their fecal samples) averaged 5.4%. The proportion of cows that consumed less than 0.3 kg/d of supplement averaged 28.1%, those that consumed 0.3 to 0.8 kg/d of supplement averaged 38.2%, and 33.7% of cows consumed more than 0.8 kg/d. The proportion of cows that consumed below-target amounts of supplement averaged 40%.

Supplement feeding behavior as measured by the GrowSafe, Inc. System is presented in Table 9. One ADLIB and two Restricted cows were not electronically recorded as having visited the supplement feeder in 1995. In 1996, all ADLIB cows were electronically recorded as having visited the supplement feeder and two Restricted cows had no recorded time at the supplement feeder. Cows on ADLIB were present at the supplement feeder more (P < 0.001) days than Restricted cows, averaging 21 vs 12 d (out of 25) in 1995, and 30 vs 19 d (out of 34) in 1996. Wagnon (1965) reported that increasing supplement allowance increased the number of cows that responded to the call for supplement. Wagnon (1965) collected feeding behavior of hand-fed supplemented cattle for several years and reported that the percentage of cows responding to call differed between years (78 to 88%).

No comparisons of supplement feeding behavior can be made between years; however, cows in the ADLIB treatment spent more (P = 0.001) time at the tank, and had more (P < 0.002) feeding bouts than cows on the Restricted treatment in both 1995 and 1996 (Table 9). In addition, cows on ADLIB had longer (P = 0.001) feeding bout duration than Restricted cows during 1996.

Cow age affected (P < 0.01) feeding behavior during 1995, but not during 1996 (P > 0.24). In 1995, time spent at the feeder was highest (P = 0.01) for 6-yr-old cows (37 min/d), 35% less for 4- and 5-yr-old cows (average 24 min/d), and least for 3-yr-old cows (13 min/d). Time spent at the feeder by 2-yr-old cows (17 min/d) was intermediate between 3-, 4-, and 5-yr-olds. The number of feeding bouts per day was greatest (P = 0.01) by 4-, 5-, and 6-yr-old cows (average 3.3 bouts/d), and least by 3-yr-old cows (1.9 bouts/d). The number of bouts by 2-yr-olds (2.5 bouts/d) was not different (P > 0.10) from that by 3- or 5-yr-olds.

Arnold and Maller (1974) reported that in a mixed-age group of sheep, the oldest and youngest age groups were the least competitive. Friend and Polan (1974) also reported a quadratic relationship between average time spent eating and social rank of dairy cattle; however, the midranked cows spent the least amount of time eating. There were only four 6-yr-olds on study in 1996 and results for this age group could have been influenced by sample size.

Bowman et al. (1999) collected observations of cow behavior at the same ADLIB and Restricted lick-wheel feeders and used a 30-min separation interval to define different bouts. Based on 8 d of observations, they reported that cows visited the feeders 70% of the days. Cattle on the Restricted feeder averaged 14.1 min/d and 1.5 bouts/d, and cattle on the ADLIB feeder averaged 19.3 min/d and 1.1 bouts/d (Bowman et al., 1999). In addition, 2-yr-old cows visited ADLIB and Restricted supplement feeders less frequently and spent less time there than 3-yr-old cows (Bowman et al., 1999). Ernst (1973) reported that yearling heifers visited a roller lick feeder containing a urea-molasses mixture at least once a day and that bout duration averaged 4 min/bout. Ernst (1973) used a 5-min separation interval between bouts and reported that cows spent 26 min/d at the supplement feeder and averaged 6.5 bouts/d. Wagnon et al. (1966) reported that social rankings of individual cows fed forage in troughs remained constant between 2 yr. Time spent at the supplement feeder, frequency of supplement feeding bouts, and social interactions between age groups in the current study is in agreement with what has been previously reported in the literature.

	Implications

Top Abstract Introduction Materials and Methods Results and Discussion Implications Literature Cited

 
Supplying high-nitrogen liquid supplement (50 to 57% CP) to cows grazing low-quality winter native range can increase forage digestibility and intake, and reduce body condition loss. Delivery method of self-fed liquid supplement can influence the variation in supplement intake and the proportion of cows meeting target consumption. The proportion of nonfeeders in a herd will usually increase with restricted access, but that restriction may encourage grazing and forage intake. Restricting supplement access can increase the variability of supplement intake by individual cows. Social interactions by a mixed-age group of cows at liquid supplement feeders can result in lower supplement consumption by 2-yr-old cows compared with older cows.

	Footnotes

 
¹ This study was funded in part by NRICGP/USDA Strengthening Grant #9504239, the American Feed Industry Association, and Agri-Beef, Boise, Idaho.

³ Current address: USDA-ARS, Fort Keogh LARRL, Miles City, MT 59301.

Received for publication August 13, 2001. Accepted for publication September 16, 2002.

	Literature Cited

Top Abstract Introduction Materials and Methods Results and Discussion Implications Literature Cited

 


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