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ANIMAL PRODUCTION |
USDA, ARS, Poisonous Plant Research Laboratory, Logan, UT 84341
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Abstract |
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 Top Abstract INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Key Words: body condition • cattle • intake • pine needle • Pinus ponderosa • toxic plant
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INTRODUCTION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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). Abortion risk is greatest in cows in the third trimester of gestation (James et al., 1989). The abortifacient compound in pine needles is isocupressic acid (ICA), a diterpene resin acid (Gardner et al., 1994, 1996). Pine needle consumption generally increases by grazing cows during cold weather when forage availability is limited by snow cover or lack of forage (Pfister and Adams, 1993; Pfister et al., 1998). Further, Short et al. (1994) reported that feeding high levels of protein increased consumption of needles by pen-fed cows.
Body condition may be an important factor influencing consumption of toxic plants (Pfister et al., 2002; Launchbaugh et al., 2007; Frost et al., 2008). Livestock in LBC may alter diet selectivity and feed intake to compensate for their poor nutrient status (Garnsworthy and Topps, 1982; Mellado et al., 2003; Lopez-Ortiz et al., 2007). Furthermore, livestock in LBC may have enhanced absorption and reduced elimination of some plant toxins compared with animals in HBC (Lopez-Ortiz et al., 2004). Sheep in LBC dosed with lupine (Lupinus caudatus) exhibited faster absorption and slower elimination rates of the teratogenic alkaloid, anagyrine, compared with HBC animals (Lopez-Ortiz et al., 2004). In addition, the reproductive success of cows is related to body condition (Pryce et al., 2001; Buckley et al., 2003), with fertility often decreasing in LBC cows.
No information is available on the influence of body condition on the ingestion of ponderosa pine needles. Thus, the objective of this study was to determine whether cows in HBC or LBC would consume differing amounts of pine needles in pen and field studies. Furthermore, we investigated the influence of dietary energy and protein status on pine needle intake.
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MATERIALS AND METHODS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Animals and Conditioning
Exp. 1. Eight mature (6- to 8-yr-old) Hereford cows that were naïve to pine needles were used in the study. These nonpregnant females were raised on treeless rangelands dominated by annual grasses near Ritzville, Washington (N latitude 46°57', W longitude 118°14'). Cows were housed in Logan, Utah, and randomly assigned to either high or low body condition groups (HBC or LBC, respectively; n = 4). By way of preconditioning, HBC cows were fed ad libitum a diet (DM basis) consisting of alfalfa (59.5%), corn (25.1%), soybean meal (9.7%), and molasses (5.7%). This diet provided 72% TDN, 19.7% CP, and 2.5 Mcal of ME/kg of DM. Cows in LBC were limited in DMI to 1.3% of BW, and fed a diet (DM basis) of alfalfa hay (40%) and barley straw (60%), which provided 51% TDN, 7.6% CP, and 1.86 Mcal of ME/kg of DM. After 14 wk on this feeding regimen, the mean BW and BCS were 689 ± 60 kg and 7.5 ± 0.2 BCS (1 = emaciated, 9 = obese) for HBC cows, and 458 ± 18 kg and 3.5 ± 0.4 BCS for LBC cows. An experienced observer from Utah State University who was blinded to the treatments assessed body condition visually.
Exp. 2 to 5. These studies were sequential and linked, and were separate from Exp. 1. Thirteen Angus x Hereford mature (5-yr-old) open cows were assigned randomly to 2 treatments: HBC (n = 6) and LBC (n = 7). Cows were naïve to pine needles because they were raised on desert rangelands near Twin Falls, Idaho (N latitude 42°30', W longitude 114°40'). Cows were fed individually for 12 wk in a barn as described in Exp. 1 to achieve desired body condition. All cows calved near the beginning of the conditioning period. Calves were removed 3 d after birth from cows allocated to the HBC treatment, but calves remained with cows in the LBC group. These calves were removed 10 d before the pine needle feeding studies began. Body weights and BCS, respectively, at the start of the feeding studies were 655 ± 24 kg and 7.5 ± 0.23 for HBC cows, and 484 ± 11 kg and 3.9 ± 0.25 for LBC cows.
Plant Collections
Pine needles for all pen studies were collected fresh from ponderosa pine trees (Pinus ponderosa C. Lawson var. scopulorum Engelm.) near Custer, South Dakota (N latitude 43°43', W longitude 103°38') during winter just before feeding in Exp. 1, and again immediately before Exp. 2 to 4. Branches were cut from trees, but needles were left on branches until used in the feeding studies, when needles were stripped from branches just before feeding. The needles were fed during winter; green needles were kept in a covered shelter at a temperature near or below freezing (0°C) before use, and were aromatic, green, and pliable when fed to cows. These needles were intended to mimic pine needles consumed by cows under grazing situations.
Pine Needle Feeding
Exp. 1. Maintenance Diet.
After conditioning, cows (n = 4 LBC, and n = 4 HBC) were placed into individual pens (4 x 4 m) in a heated barn (8°C) with ad libitum access to water and salt. To avoid refusals, the diet was restricted to commercial alfalfa pellets (Table 1) fed at 1.4% of BW (DM basis) during a 5-d acclimation period and the 14-d study. Maintenance was determined for mature, nonpregnant, nonlactating cows using the equation of DiCostanzo et al. (1990). Pellets were fed at 0800 h each morning, with any orts weighed the following morning. Pine needles (as-fed basis, hand-picked needles only, no woody material) were fed whole in a separate feeding box each morning at 0800 h, and any refusals were weighed back the following morning. Cows were fed pine needles ad libitum, and the feeding boxes were checked and replenished periodically to ensure a constant supply during each 24-h period.
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), CP (Leco FP-528 Nitrogen Analyzer, Leco Corp., St. Joseph, MI; Wiles et al., 1998), NDF (Ankom Fiber Analyzer system; Vogel et al., 1999), and in vitro true digestibility (Ankom Daisy II system; Holden, 1999). The NDF procedure was modified by addition of heat-stable amylase (Sigma Chemical, St. Louis, MO).
Pine needles in this and all studies were analyzed for ICA concentration, the abortifacient compound, using the procedures of Gardner et al. (1994, 1997). In brief, dry, ground needles were extracted by steeping twice with methylene chloride for 48 h. After additional extraction with hexane, samples were base extracted with NaOH and methylated with methyl iodide; the resulting methyl esters were analyzed by gas chromatography (Hewlett-Packard HP 5890, HP Corp., Palo Alto, CA).
Exp. 2. Maintenance Diet. Methods in this study were similar to those in the previous experiment, except that pine needle feeding was restricted to 8 h/d. Treatments were HBC (n = 6) and LBC (n = 7). We determined from the previous study that cows ate sufficient needles during the daytime that it was not necessary to provide 24-h access to needles. Water and trace mineral salt blocks were freely available in all experiments. After conditioning, cows were individually fed alfalfa pellets only (maintenance diet) for 7 d at 1.65% of BW (DM basis), then given the same amount of alfalfa pellets and also offered fresh pine needles ad libitum from 0800 to 1600 h each day in a separate feed box during a 10-d study. Refusals were weighed at the end of each day. Periodic samples were taken and analyzed as described for Exp. 1.
Exp. 3. High-Protein/Low-Energy Diet.
At the end of the 10-d pine needle feeding study, cattle from Exp. 2 were weighed, scored, and given only alfalfa pellets at 1.65% BW for 5 d. Cows were then shifted to a high-protein/low-energy (HPLE) diet at 1.65% BW for a 5-d adaptation period (Table 2). After the adaptation period, cattle continued to receive the HPLE diet at 1.65% BW and were also offered pine needles ad libitum from 0800 to 1600 h for 7 d.
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).
Exp. 5. Grazing Study.
At the end of Exp. 4, 6 HBC and 6 LBC cattle were transported to Rapid City, South Dakota for a 25-d field grazing study (N latitude 44°08.347', W longitude 103°15.013'; 1,060 m elevation). An 11-ha pasture with abundant pine trees was delineated with an electric fence. Water and a trace mineral salt block were freely available. Cows grazed in the pasture from January 26 to February 20, 2007. Daily bite counts were used to determine animal diets (Pfister et al., 1998). Beginning at 0700 h every day, individual animals were focally sampled (Altmann, 1974) in a predetermined random order. Each animal was observed in turn for 5 min. Bites were categorized as grasses, forbs, shrubs, and green (on the tree) or dry (litter) pine needles. We defined an individual bite as a single cropping motion, always indicated by a head jerk, often accompanied by a visible sweep of the tongue, and independent of chewing motions. After all animals had been observed, the process was repeated during all active grazing periods until approximately 1700 h (dusk), when cattle were placed in a corral for the night. Cows were group fed 50 kg of supplemental alfalfa hay each evening in the corral when snow covered the ground.
Pine tree density was determined by counting all trees 
2 m tall and >2 m tall in 20 randomly placed 10 x 10 m plots. Five randomly selected trees were sampled to determine ICA concentration in green needles. Forage availability was measured at the beginning of the study by clipping to ground level all nonwoody plant material in thirty 0.5 m2 plots randomly placed throughout the pasture; this material was separated into grasses, forbs, and pine litter, dried at 40°C, and weighed. A portable weather station (Campbell Scientific, Logan, UT) was located just outside the pasture and continuously recorded temperature, relative humidity, wind speed and direction, and barometric pressure. Snow depth was measured by using a 1 x 2 m unshaded snowboard; snow depth was measured several times each day during snowfall to capture maximum daily snow depth (Goodison et al., 1981).
Statistical Analysis
All analyses of pine needle intake in the pen studies were adjusted for BW (g/kg of BW). All studies were analyzed as a completely random design with 2 treatments. The model included treatment (LBC vs. HBC), with individual animals nested within treatments, and repeated measures over the multiday experiments. Animals were a random factor in the mixed linear model analysis (SAS Inst. Inc., Cary, NC). The primary dependent variable in the grazing study was percentage of total daily bites composed of pine needles. The variance-covariance matrix was chosen by an iterative process wherein the best fit was based on the Schwarz Bayesian criterion. The compound symmetry covariance model was typically the best fitting structure. When treatment numbers were not balanced, least squares means were used instead of unadjusted means. Treatment differences were separated by using predicted difference (PDIFF option in SAS) for significant interactions (P < 0.05) in the model. Preplanned pairwise comparisons between treatment least squares means were considered different at P < 0.05. Stepwise multiple regression (Stepwise option in SAS) was used to examine the relationship between pine needle consumption and weather variables. The multiple regression equation reported here used only observations from LBC cows.
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RESULTS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Alfalfa pellets were more nutritious than pine needles (Table 1). With one exception, animals consumed all of the pelleted basal ration each day. One cow in the HBC treatment did not eat approximately 10% of the pelleted basal ration on 13 consecutive days during the study. There was a day effect and a day x treatment interaction (P < 0.001), because daily pine needle consumption by cattle in LBC averaged 5.0 to 6.6 g/kg of BW. In contrast, cows in HBC consumed a small amount of needles until d 10 of the study, when their daily consumption peaked at 3.2 g/kg of BW (Figure 1).
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There was a day x treatment interaction (P = 0.001) because LBC cows consumed variable amounts of pine needles (Figure 1). Pine needle consumption by HBC cows was relatively constant over time and typically less (P < 0.01) than that of LBC cows.
Exp. 3. High-Protein/Low-Energy Diet
The LBC cattle ate more (P = 0.04) pine needles than did the HBC cattle (2.88 ± 0.22 g/kg of BW daily vs. 1.53 ± 0.15 g/kg of BW daily, respectively; Figure 2). There was no day effect or day x treatment interaction (P > 0.15).
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There was a day x treatment interaction (P = 0.001) because LBC cattle ate more pine needles than did HBC cattle for the initial 3 d of the study, and consumption by LBC animals decreased greatly during the last 3 d (Figure 2). Overall, HBC cattle consumed 1.6 ± 0.15 g/kg of BW daily compared with 2.6 ± 0.27 g/kg of BW daily for LBC animals.
Exp. 5. Grazing Study
Average pine tree density per 100 m2 plot was 10 ± 0.9 trees >2 m tall (range 2 to 16 trees), and 76 ± 24 trees <2 m tall (range 0 to 347 trees) across the experimental pasture. Initial forage biomass was primarily grass (510 ± 78 kg/ha), with some forbs (35 ± 10 kg/ha). Pine litter was abundant (446 ± 98 kg/ha). Concentration of ICA in green pine needles averaged 1.39% (DM basis). Composite grass samples averaged 72% NDF, 38% in vitro true digestibility, and 6.1% CP (DM basis).
Cows in LBC averaged 4.8 ± 0.6% of bites/day of pine needles overall, whereas HBC cows averaged 2.1 ± 0.3% of bites/day overall. There was a treatment effect (P = 0.006) and a day x treatment interaction (P = 0.001) because LBC animals consumed more pine needles on some days during the study (Figure 3a). The LBC cows differed (P < 0.05) in needle consumption from HBC cows on d 16, 18, 19, and 20 (Figure 3a). Days of greater pine needle consumption corresponded to days with greater snow depth (Figure 3b) and lower minimum daily temperatures (Figure 3c). The best-fitting (r2 = 0.60; P = 0.001) regression model relating weather with pine needle consumption by LBC cows was Y = 2.7 - 0.12 x minimum temperature (°C) + 0.81 x snow depth (cm), where Y = mean daily pine needle consumption (% of bites). The r2 value dropped to 0.32 (P = 0.03) when HBC cows were included.
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DISCUSSION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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). Further, adipose secretions are amplified in fat animals (Chilliard et al., 2000). Thus, the degree of adiposity of ruminants can have a marked effect on hormonal status and feeding behavior (Chilliard et al., 1998). In this study, LBC cows consumed much larger quantities of pine needles than did HBC cows. Cows in LBC may have a stronger drive to eat pine needles compared with HBC cows for several related reasons: 1) appetite differences related to metabolic changes; 2) increased feed intake to replenish fat stores (compensatory intake); and 3) hormonal changes from LBC. Physiological relationships between adiposity, feed intake, and metabolic and hormonal changes are extremely complex (Delavaud et al., 2002). This study was not designed to determine physiological reasons for intake differences. Thus, our discussion about possible causative factors is speculative.
During Exp. 1 and 2, HBC cows were switched from an unrestricted, high-quality diet to a maintenance diet restricted in the amount offered, and these animals lost an average of 10 and 12 kg during Exp. 1 and 2, respectively. In contrast, the LBC cattle gained 7 and 2 kg during Exp. 1 and 2, respectively. Thus, the dietary reduction in quality and quantity appears to have induced a mild or moderate negative energy balance in HBC cows even though they were not lactating. The apparent negative energy balance in HBC cows may have affected feed intake (Agenas et al., 2003) and intake of pine needles.
In the current study, cows in LBC may have increased pine needle consumption to replenish body fat stores (Chilliard et al., 2000). Forage intake typically increases as body condition decreases in grazing animals (Bines et al., 1969; Cowan, 1975). This inverse relationship has been shown for cattle (Garnsworthy and Topps, 1982; Jones and Garnsworthy, 1988; Hayirli et al., 2002), sheep (Sibbald, 1997), and goats (Frost et al., 2008). Bines and Morant (1983) reported that LBC cattle consumed 24% more forage than did HBC cattle. In other work, LBC sheep grazed longer and ate more forage than did HBC sheep, perhaps in part because the LBC animals were more motivated to eat (Sibbald and Kerr, 1994; Sibbald, 1997). As HBC or LBC ruminants attempt to restore homeostasis, it seems plausible that grazing preferences for specific foods will change (Provenza, 1995), but research is lacking on this point. In one recent study, HBC cattle selected less lupine while grazing than did LBC cows (Lopez-Ortiz et al., 2007), presumably because of physiological differences. Sprinkle et al. (2000) reported that bite rate was related to body condition in grazing cattle; bite rate increased as body condition decreased.
Pine trees produce large amounts of oleoresin, which is a complex mixture of terpenes consisting of monoterpenes, sesquiterpenes, and diterpenes (Phillips and Croteau, 1999). Mono- and sesquiterpenes are volatile, whereas diterpenes (resin acids) are nonvolatile. Terpenes at increased concentrations in the diet inhibit forage intake by ruminants (Personius et al., 1987), perhaps through negative effects on ruminal fermentation (Oh et al., 1967; Nagy and Tengerdy, 1968) or alterations in hepatic biotransformation and excretion (Foley et al., 1999). There was an apparent cyclicity (toxification-detoxification) in pine needle intake by LBC cows during Exp. 2 similar to that noted in cattle consuming toxic larkspur (Pfister et al., 1997). Supplementation may supply needed nutrients and enhance detoxification of terpenes by providing precursors required for conjugation and excretion, thus ameliorating toxic effects (Foley et al., 1999). The LBC cattle consumed more pine needles than did the HBC cattle (r2 = 0.60; P = 0.001) when only data from LBC cattle were used. when both were fed an HPLE diet; further, the daily intake pattern was relatively stable within treatments during the 7-d study. This suggests that LBC cows had sufficient energy and protein to maintain terpene intake over this period. This finding is supported by the work of Strickland et al. (1998), who reported that LBC cows given a protein supplement improved their tolerance for broom snakeweed toxins, suspected to be diterpene acids, compared with LBC cattle given supplemental energy. Villalba et al. (2002b) reported that terpenes added to sheep diets did not affect intake when foods had a greater protein:energy ratio.
When HBC and LBC cattle were fed an LPHE diet, LBC cattle initially had greater pine needle intake than did HBC cattle (4.5 g/kg of BW vs. 1.5 g/kg of BW, respectively), but by d 4 their intakes did not differ. These results indicate that LBC cattle were unable to tolerate increased quantities of pine needle terpenes on the LPHE diet. Several days may be required to deplete labile protein reserves (Swick and Benevenga, 1977). Foley et al. (1995) suggested that terpene-laden diets might lead to disturbances of the acid-base balance, and that these imbalances could be exacerbated by low protein intake. In addition, Villalba et al. (2006) found negative interactions between terpenes and sheep preference for grain-based (high-energy) diets. Endogenous fat in HBC animals did not appear to fuel detoxification of pine needle terpenes. The HBC cattle consumed approximately the same amount of pine needles on both the HPLE and LPHE diets, indicating that they were below a physiological threshold at which terpene ingestion would elicit negative effects; thus, HBC cattle showed no discernible effect on pine needle intake from modifying their dietary energy or protein intake.
Both HPLE and LPHE studies suggest that the protein:energy ratio may be an important factor in the ability of cattle to tolerate high levels of terpenes in the diet (Villalba et al., 2002a), perhaps overriding the importance of fat stores in needle intake. Villalba et al. (2002b) found that terpenes added to sheep diets depressed intake of a food with a low protein:energy ratio. Sheep and goats given high-protein supplements ate more high-terpene sagebrush than did animals given high-energy supplements, and sagebrush intake was depressed when animals were given a supplement high in energy and low in protein (Villalba et al., 2002a). Lambs consumed more terpene-containing food when the food contained moderate amounts of protein instead of low or high amounts (Villalba and Provenza, 2005). Similarly, goats ate more terpene-laden juniper when given a high-protein supplement (Campbell et al., 2007). Sheep given an opportunity to self-select energy and protein supplements while grazing on terpene-laden sagebrush rangelands selected a mixture of energy and protein that allowed a marked increase in sagebrush consumption (Dziba et al., 2007).
The increased intake of pine needles by LBC animals probably would have caused more abortions in LBC cows than in HBC cows if the cows had been pregnant. Cows typically must eat a substantial quantity of pine needles over several days to abort (Gardner et al., 1999a). The incidence of abortion is dependent on several factors, including stage of pregnancy, concentration of ICA in the needles, and individual susceptibility (Gardner et al., 1999a). Labdane terpenes such as the abortifacient compound ICA and its principal metabolites, agathic acid and dihydroagathic acid (Gardner et al., 1999b), are very lipophilic (Yalkowsky and He, 2003). Because of their lipophilicity (log P-values >3.5; Cronin et al., 2002; Chang et al., 2007), the pine needle diterpenes would probably be sequestered preferentially in adipose tissue (Rozman and Klaassen, 2001), which would reduce their abortifacient effect. The grazing study reported here indicates that HBC cows generally eat fewer pine needles than LBC cows during episodes of cold, snowy weather. Reduced needle consumption, in conjunction with the kinetics and lipophilicity of labdane terpenes, suggests that HBC cattle would have a lesser likelihood of abortions than LBC cows.
Grazing cattle eat more pine needles during cold weather, particularly when snow cover reduces the availability of standing forage (Pfister and Adams, 1993; Pfister et al., 1998). Cows in LBC responded to greater snow depth and colder winter temperatures by consuming more pine needles than HBC cows. Similarly, prolonged stimulation of energy expenditure by cold exposure markedly increased energy intake in rats (Vallerand et al., 1986). Therefore, the reduced availability of forage from grazing and snow cover may also be important in cattle responses. Sibbald and Kerr (1994) found that the difference in forage intake for LBC and HBC sheep was greater on a 5-cm-height sward than on a 10-cm-height sward. Olson and Wallander (2002) reported that winter grazing time was a trade-off between maximizing energy gain (thermal and forage), and minimizing heat loss from cold temperatures and grazing activity. This suggests that HBC cattle may be better adapted to deal with colder winter temperatures than are LBC cows.
The LBC cattle consumed more pine needles than did HBC cattle in all pen and field studies, except that pine needle ingestion by LBC cattle was reduced to a level equal to that of HBC cattle when both groups were fed an LPHE diet. These findings suggest that pregnant cows in LBC are at greater risk of pine needle abortion if provided access to pine needles. Grazing animals also increased pine needle intake during periods of cold weather when snow covered much of the available forage, but the increase was much greater for LBC cattle compared with HBC cattle. Past research has shown that pregnant cows in mid to late gestation should have restricted access to ponderosa pine needles (James et al., 1989). Maintaining cows in at least moderate body condition during gestation and calving is also beneficial for reproductive success in beef herds (Adams et al., 1987; Chilliard et al., 1998; Ciccioli et al., 2003). More study is needed to determine the possible benefits of feeding LPHE supplements to reduce needle consumption by pregnant cattle.
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Footnotes |
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2 Corresponding author: Jim.Pfister{at}ars.usda.gov
Received for publication March 3, 2008. Accepted for publication July 17, 2008.
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LITERATURE CITED |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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