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ANIMAL PRODUCTION |
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* Department of Animal and Range Sciences, Clayton Livestock Research Center, Clayton 88415;
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Extension Animal Resources Department, New Mexico State University, Las Cruces 88003-0003; and
and
C. S. Cattle Co., Cimarron, NM 87714
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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Key Words: Cull Cows • Diet Adaptation • Management
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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); therefore, a 10% increase in net income from culled cows could nearly double ranch profitability. Several studies have evaluated the efficiency of increasing live and carcass weights of culled beef cows with high-intensity feeding periods (Swingle et al., 1979; Matulis et al., 1987; Cranwell et al., 1996). These gains consistently improved carcass characteristics (Wooten et al., 1979; Jones, 1983; Matulis et al., 1987). Increasing condition of culled cows to a BCS of 6 on a one-to-nine scale optimized live value (Apple, 1999). Culled cows are often thin (BCS < 5) and have the potential to express compensatory gain due to increased efficiency of energy use and nitrogen retention (Freetly and Nienaber, 1998).
Short feeding periods (45 to 60 d) optimize feed conversion to BW gain, and increasing energy density of diets fed to culled beef cows increases efficiency and rate of gain during short feeding periods (Swingle et al., 1979). However, with a short feeding period, adaptation to energy-dense diets may comprise as much as 50% of the feeding period, and DMI may be low with typical ad libitum adaptation strategies (Matulis et al. 1987).
Age may also have an influence on the performance of culled beef cows (Pritchard and Burg, 1993), although a report from young vs. mature Holstein cows found little difference in tissue accretion (Jones, 1983). The objectives of this study were to evaluate economic and performance responses to ad libitum feeding strategies for culled range cows of different ages.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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Culled beef cows (125 cows) were obtained from a cooperating ranch and delivered to the Clayton Livestock Research Center, 10 km east of Clayton, NM, in mid-January 2002. At the time of arrival, cows were offered a limited amount of long-stemmed wheat hay (4.5 kg/cow) and free access to clean water. Cows were processed 16 h after arrival. During processing, cows were individually weighed and assigned a BCS on a one-to-nine scale (1 = emaciated, 9 = obese). Dentition was noted, and cows received a vaccine against clostridial pathogens (Ultrabac 7, Pfizer Animal Health, New York, NY).
The majority of the cows had been year branded, and these brands, in combination with dentition, were used to block cows into age groups as follows: young = 3 and 4 yr olds, lowmid = 5 and 6 yr olds, highmid = 7 and 8 yr olds, and aged = 9 yr and older. Cows were predominantly of Hereford and Angus x Hereford breeding. Within age blocks, cows were assigned randomly to 10 m x 30 m soil surfaced pens (eight to 12 cows per pen; three pens per block). Initial BCS was 4.6, 4.5, 4.7, and 4.7 ± 0.2 for Young, LowMid, HighMid, and Aged blocks, respectively. Pens were equipped with concrete bunks and automatic water troughs. Age blocks were specifically constructed to evaluate age influences on cull cow performance independently from feeding management treatments.
Treatments
Within a block, pens were assigned randomly to one of three treatments designed to evaluate feeding management strategies. Body condition score was not used as a factor in treatment assignment. A conservative treatment (CSV) supplied a diet containing 30% roughage (DM basis) throughout the feeding period (Diet 1; Table 1). This treatment was designed to minimize disruption in intake patterns and to maximize intake through the feeding period. A moderate treatment (STD) that followed standard feed management for feeder cattle at this location consisted of five diets (30, 25, 20, 15, and 10% roughage) used in an adaptation program (Diets 1 through 5; Table 1). Diets for STD were changed after 5 d, so that the final diet (Diet 5) was supplied beginning on d 21. A more aggressive treatment (AGR) consisted of three diets (30, 20, and 10% roughage; Diets 1, 3, and 5; Table 1), also changed every 5 d, so that the final diet (Diet 5) was supplied on d 11, or half the time required to reach this diet compared with the STD approach. This treatment structure was designed to provide a strategy to maximize DMI (CSV), a strategy to maximize energy density and potentially NE intake (AGR), and a strategy intermediate to these approaches (STD).
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Measurements
Cows were weighed before feeding on d 0 (morning following arrival), 14, 28, 42, and 54. Average daily gain was calculated within these 14-d intervals. Gain efficiency was calculated based on 14-d ADG and 14-d average pen DMI.
On d 54, half the cows from each pen were selected randomly for shipment to a commercial processor, and the remaining cows were marketed live at a local auction. The decision to market cows in different channels was dictated by the cooperator. Hot carcass weight was measured following evisceration, and all other carcass data were collected after a 36-h chill by an independent data collection service (Cattlemen’s Carcass Data Service; West Texas A&M University, Canyon, TX). Measurements included fat thickness; LM area; kidney, pelvic, and heart fat; USDA yield grade; marbling score; bone, lean, and overall maturity scores; lean color; and fat color. Dressing percent was calculated using hot carcass weight and unshrunk final live weight (d 56).
Cost data were tracked for all pens. Diet costs were charged as delivered ingredient costs with a 10% markup and applied based on the amount delivered to the pen. A $0.25 cow/d yardage charge was also applied. Freight was charged at a flat rate of $7.50 per cow. Processing charges for vaccine and labor were assessed at $1.40 per cow. Cow initial value was charged at the local market rate for the week of delivery (USDA-AMS, 2002). Death losses were charged to the remainder of the pen of origin as initial value of the cow plus processing and yardage. Feed costs up to the time of death were inseparable from overall pen costs; therefore, they are implicitly included in per cow feed charges for that pen. Summation of feedlot costs (feed, yardage, processing, and death loss) was used to calculate cost of gain. A live-basis breakeven price was established using total costs and unshrunk final live weight. With these costs, performance, and carcass measurements, other economic projections can be extrapolated.
Statistical Analyses
All data were analyzed as a randomized complete block design, with feeding strategy and age group as effects in the model. Pen was the experimental unit for all measures, although data are expressed on a per-animal basis.
Data collected for interim weigh periods (ADG, DMI, G:F, NEm intake), as well as overall responses across the 54-d trial were of interest in this study due to the changes in diet imposed as treatments. All data were analyzed discretely using GLM procedures of SAS (v. 8.1, SAS Inst., Inc., Cary, NC). Feeding strategy responses were separated by F-protected Fisher’s LSD.
Although block data are typically not reported, initial analyses indicated that the block effect was a significant source of variation for many responses, and in most cases exceeded the effect of treatments. Therefore, in an effort to describe this source of variation, age effects were partitioned using orthogonal polynomial contrasts for a graded structure.
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Results and Discussion |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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shows the distribution of death losses and removals across feeding strategies, and Table 3 reports this data across age blocks. Mortality rates were similar for all feeding strategies (P = 0.66). Removal rates did not differ statistically (P = 0.26) but were numerically lower for AGR than for CSV or STD. Removal rates increased with age (P = 0.05), but mortality rate was not related to age (P = 0.24). Data from individuals that were removed were deleted from subsequent performance analyses. Brown et al. (2001) reported an approximately 2% removal rate and less than 1% death loss in a large group of culled cows, although in that trial, cows were sorted before the study based on defects and other preexisting conditions, whereas in this trial, all cows delivered were placed on feed.
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. Dry matter intake during the initial 14 d of the trial was low (1.2, 1.0, and 1.2% of BW for CSV, STD, and AGR, respectively) for cows under all management strategies. As a result of low DMI, the G:F estimates were negative for all treatments and were numerically (P = 0.16) lower for cows under STD management. Gain efficiency patterns were reflected in ADG; all cows lost BW initially. Based on estimates from NRC (1996), energy intake by all treatment groups should have been above maintenance requirements; therefore, it is assumed that these losses in measured BW were primarily caused by a decrease in gut fill. Additionally, diets during d 1 to 5 were identical for all treatments by design; therefore, any differential response due to treatment would have occurred only during d 6 to 14.
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Level 1 models were used to predict body condition change for each treatment group of cows based on diets fed and measured intake during d 15 to 28. Predicted condition changes and corresponding weight changes (NRC, 1996) were approximately equal to the sum of absolute weight loss during the initial 14 d (presumed fill loss) and observed weight change during d 15 to 28. Therefore, apparent compensation for losses during this period was due to fill replacement, and tissue gains were similar among treatments. During d 29 to 42, DMI was higher (P = 0.05) for cows managed with the CSV strategy than for cows receiving the higher energy diets (STD and AGR). Gain efficiency tended (P = 0.17) to be influenced by treatments, with CSV-managed cows exhibiting the lowest G:F and AGR-managed cow exhibiting the highest. The inverse relationship between intake and efficiency during this period resulted in no statistical differences (P = 0.39) in measures of ADG, but numerical differences followed increasing energy density in the diet.
Consistent with other studies (Swingle et al., 1979), feed conversion decreased for all treatment groups during the final 12 d of the feeding period (d 43 to 54) relative to the previous period, although a change in treatment rank was observed, as AGR-managed cows became the least efficient in this period. Cows under STD management expressed greater G:F in this period than CSV- or AGR-managed cows (P = 0.06). Intake continued to increase for all groups during d 43 to 54 relative to the previous 14-d period, with CSV cows continuing to consume more total feed than STD or AGR (P = 0.05). Aggressively managed cows had the lowest gains during this period, and STD-managed cows the greatest, with gains under CSV being intermediate (P = 0.10).
Although changes in treatment rank within interim periods are important due to the different patterns of live performance, differences across the entire 54 d are most important for application to management. Differences were observed among treatments for G:F (P = 0.05), with STD and AGR treatments having similar G:F, which were approximately 40% greater than CSV. Mean feed intake was similar for STD and AGR, and was approximately 9% lower with these treatments than with CSV (P = 0.05). Higher energy density in the diets combined with lower total intake resulted in a similar total intake of energy (calculated as total intake of NEm) for all treatments (P = 0.36; 1,217, 1,225, and 1,277 Mcal of NEm for CSV, STD, and AGR, respectively). Despite apparent differences in efficiency, variation in BW loss during the initial 14-d feeding period diluted differences in ADG across the 54-d trial (P = 0.26). Cows managed under the STD strategy tended to have the greatest ADG, and CSV management resulted in the lowest ADG. Although AGR-managed cows were statistically intermediate to STD and CSV, the numeric data indicated that cows fed more energy-dense diets (STD and AGR) had superior performance.
When culled cows were fed for 28, 56, or 84 d, patterns in ADG and intake similar to those in this study were observed by Matulis et al. (1987). These authors reported average DMI of 7.81 kg/d through 28 d on feed when using a three-diet step up program (37, 25, and 15% roughage), which is comparable to the level of intake observed for STD managed cows in this study. When cull cows were managed using a two-step program (72% silage, 40% silage; Cranwell et al., 1996), DMI after 28 d averaged 11.5 kg/d. Although intake of diets in the Cranwell et al. (1996) study was somewhat higher than those observed in our study, cows had been assembled before initiation of the study and thereby may have had decreased stress during the initial feeding period. This effect may have resulted in differences in intake in two studies utilizing single diet, limit-feeding strategies (Pritchard and Burg, 1993; Brown et al., 2001). In the former study, cows were assembled over time and fed hay plus wheat straw ad libitum until initiation of the trial. Over a 50-d feeding period, these authors observed an average DMI of 11.3 kg/d. In the latter study, cows were placed on feed immediately following arrival, and DMI over 57 d averaged 9.3 kg. Despite the expense of feeding roughage and the limited feeding period employed for culled cows, a 5- to 7-d period of feeding a high-roughage diet may encourage higher intake during the initial feeding period.
Other responses observed in our study were consistent with the increased energy density of the diets employed in the different feeding strategies (Swingle et al., 1979). However, limited data exist that compare ad libitum adaptation programs for culled cows, and reports using diets of similar peak energy density are confined to those using limit-feeding strategies.
Feeding strategy effects on carcass measures are summarized in Table 5. Hot carcass weight was influenced by feeding strategy (P = 0.04) and reflected trends in ADG. Cows managed under the CSV strategy had the lowest carcass weight, and those under STD had the greatest carcass weight, with carcass weights of AGR-managed cows being intermediate. Cows managed under the STD strategy also had greater fat thickness than those managed under CSV or AGR (P = 0.03). Occurrence of liver abscesses tended to be lowered (P = 0.13) for cows managed under AGR, despite the more aggressive step-up regimen. All diets contained equivalent density of antimicrobials (e.g., monensin and tylosin); therefore, this effect is difficult to explain. However, Brown et al. (2001) reported a variable rate of abscessed livers in cows fed diets containing similar levels of antimicrobials to those in the current study. Additionally, Price and Berg (1981) reported that 29% of culled cows exhibited liver damage before an intensive feeding program.
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Age Effects
In this trial, cows were initially blocked by age category as an imposition of local control of variation (Kuehl, 1994). Although it is not customary to report data related to block effects, in this trial, variability associated with blocks represented 40% to 60% of the total variability observed. Additionally, in the application of these data for future research or practice, some evaluation of the effect of age may help refine research approaches or improve application of these results. Table 6 summarizes performance responses across the 54-d trial. All responses were inversely related to age. Dry matter intake and G:F decreased linearly as age increased (P < 0.01), and resulted in decreasing ADG as age increased (P < 0.01). Pritchard and Burg (1993) observed similar trends in feedlot performance of cull cows, with performance decreasing as age increased.
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). Hot carcass weight decreased with increasing age, which reflected differences in live weight gain combined with decreased (P = 0.03) dressing percent with increased age. Fat thickness also decreased with increasing age (P < 0.01), but no effects on LM area or kidney, pelvic, and heart fat were observed (P > 0.41). These responses resulted in a decrease in calculated yield grade with increasing age (P < 0.02), although all yield grades were within ranges considered practically acceptable. Marbling score was related quadratically to age (P = 0.02), with middle-aged cows having higher marbling scores than young or aged cows. As expected, measures of maturity increased with increased age (P < 0.06). Lean color values tended to be darker as age increased (P = 0.11), and fat was more yellow in aged cows (quadratic, P = 0.02). Age effects on carcass traits seemed to be directly related to live performance; however, accretion rates of different tissue depots were not influenced by age in Holstein cows (Jones, 1983). As age increased in beef cows, lean carcass measures decreased, but little difference was observed in fat accretion (Pritchard and Burg, 1993). Decreasing age seemed to increase accretion of both lean and fat components in our study. It is likely that maturity and tissue deposition characteristics differ between dairy and beef cows, and that fat differences may have been masked in the study of Pritchard and Burg (1993) by pooling across increased days on feed.
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The results of this study indicate that although culled cows may achieve efficient short-term gains, an increase in market value during the feeding period is probably required to make a cow feeding enterprise profitable. Seasonality of the cull cow market must be capitalized on to make such an enterprise feasible. However, if adequate performance is achieved, this seasonality is sufficiently consistent to ensure long-run profitability (Little et al., 2002). More aggressive feed management may improve overall performance by rapidly increasing the energy density of the diet, although DMI can be maximized with a less energy-dense, single-diet approach. Because feeding costs are less than 25% of the total investment in a cow feeding enterprise (initial value of the cow is the greatest cost), and the total feeding period is of short duration, intake management during the initial 14 d of the feeding period is critical to ensuring optimal efficiency, regardless of the feeding strategy employed. Younger cows are more capable of responding to these strategies than older ones, and therefore have an economic advantage in a short-term feeding program.
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Implications |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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Footnotes |
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3 C. S. Cattle Co., Cimarron, NM 87714.
2 Correspondence: 2471 TAMU, College Station, TX 77843-2471 (phone: 979-845-5083; fax: 979-845-5292; e-mail: j-sawyer{at}tamu.edu).
Received for publication May 21, 2003. Accepted for publication August 17, 2004.
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Literature Cited |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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