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J. Anim. Sci. 2002. 80:2223-2233
© 2002 American Society of Animal Science

Metabolic characteristics of multiparous Angus and Brahman cows grazing in the Chihuahuan Desert1

B. S. Obeidat*, M. G. Thomas*,2, D. M. Hallford*, D. H. Keisler{dagger}, M. K. Petersen*, W. D. Bryant*, M. D. Garcia*, L. Narro* and R. Lopez*

* Department of Animal and Range Sciences, New Mexico State University, Las Cruces 88003 and and {dagger} Department of Animal Sciences, University of Missouri, Columbia 65211

2 Correspondence:
328 Knox Hall, MSC 3I (phone: 505-646-3427; fax: 505-646-5441; E-mail:
milthoma{at}nmsu.edu).


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 Implications
 Literature Cited
 
Understanding metabolic differences between breeds of cattle is important when selecting for production in semiarid environments. Spring-calving multiparous Angus and Brahman cows (n = 8/breed) grazing in the Chihuahuan Desert were used to evaluate metabolic hormone status in February (i.e., 3rd trimester of pregnancy), May (i.e., early lactation), and September (i.e., late lactation) 2000. Crude protein in ruminal digesta collected from grazing companion ruminally cannulated cows during these months was 5.6, 6.0, and 10.3%, respectively. Angus cows were heavier (P < 0.01) than Brahman cows across months. Body condition scores among breed groups were 4.4, 3.6, and 4.6 in February, May, and September with Brahman cows tending (P < 0.10) to have greater body condition than Angus cows in May. Brahman cows tended to have greater fecal output per 100 kg BW than Angus cows in February (0.9 > 0.7 ± 0.1, P < 0.10). Brahman cows had greater serum concentrations of leptin than Angus cows in September (1.8 > 0.70 ± 0.1 ng/mL; P < 0.05), and serum concentrations of insulin were greater (P < 0.01) in Brahman than Angus cows throughout the study. Brahman cows also had greater (P < 0.01) serum concentrations of glucose during February and May than Angus cows. Serum concentrations of triiodothyronine were greatest (P < 0.01) during September and lowest during February and May in both breed groups and were greater (P < 0.01) in Brahman than in Angus cows in February, May, and September. Pregnancy rate and 205-d adjusted weaning weights were similar (P >= 0.46) among breed groups. Results suggest that Brahman and Angus cows are sensitive to the seasonal dynamics of forage quality in the Chihuahuan Desert. Brahman cattle appear to have greater concentrations of metabolic hormones and metabolites than Angus cows in this environment, but Angus cows experience greater fluctuations in BW.

Key Words: Arid Climate • Cattle Breeds • Cows • Hormones • Leptin • Metabolism


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 Implications
 Literature Cited
 
Forages in semiarid environments tend to vary greatly in quality and quantity which subsequently affects diet composition and selectivity of grazing animals (Rosiere et al., 1975; De Alba-Becerra et al., 1998). Diet quality is known to influence metabolic state and performance in beef cattle. These qualifiers of well-being can also be influenced by numerous other factors such as genetics, physiological state, and ambient temperature (Ferrell and Jenkins, 1984, 1985). Thus, understanding metabolic differences and (or) adaptability of breeds is important when designing beef production systems for semiarid environments.

Bos indicus-influenced cattle are often utilized in beef production systems in semiarid environments because they are adapted to high ambient temperature and maximize heterosis when challenged with poor forage quality (Frisch and Vercoe, 1977; Hunter and Siebert, 1985; Winder et al., 2000). Physiological differences have been described between B. indicus (Brahman) and Bos taurus (Angus) cows in subtropical environments (Segerson et al., 1984; Simpson et al., 1997; Alvarez et al., 2000). Data characterizing these types of relationships in cows grazing in desert environments are currently limited.

The Chihuahuan Desert is the largest desert in North America with forage growth primarily occurring during the summer (Pieper and Herbel, 1982). Sustaining beef cattle production systems on these rangelands is challenging. Thus, understanding adaptability of breeds to this environment is of economic relevance. The objectives were to assess the quality and availability of potentially consumed range forage and to evaluate metabolic status of grazing Angus and Brahman cows which are common constituents in Chihuahuan Desert beef cattle grazing systems. Evaluations were made in spring-calving multiparous cows grazing in February, May, and September which represent seasons of differing forage quality and ambient temperature and differing physiologic states.


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 Implications
 Literature Cited
 
Study Area
Experimentation was conducted at the New Mexico State University Chihuahuan Desert Rangeland Research Center (32.3° latitude and 106° longitude). The pasture encompassed 480 ha at an elevation of 1,220 m above sea level and was classified as semidesert rangeland. At this locale, June is the warmest month with an average maximum high temperature of 36°C, and January is the coldest month with an average maximum low temperature of -3°C. This locale typically experiences 9 d per annum of temperatures that exceed 37°C. Most of the annual rainfall and forage growth occurs between June and September (Pieper and Herbel, 1982). Figure 1Go displays measured rainfall during the years 1992 to 1999 and the year 2000 at the Chihuahuan Desert Rangeland Research Center. Data in the current study were collected during the months of February (winter), May (spring), and September (autumn) 2000. Historically, these months represent a period of dormant forage with cool ambient temperature (i.e., February; mean daily maximum = 16°C; CP of primary grasses = 4.5%), a period of dormant forage and high ambient temperature (i.e., May; mean daily maximum = 29°C; CP of primary grasses = 5.3%), and a period of growing forage and high ambient temperature (i.e., September; mean daily maximum = 30°C; CP of primary grasses = 8.9%; Nelson et al., 1970; Pieper and Herbel, 1982; Malm, 1994).



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  		Figure 1. Monthly precipitation (cm) for the years 1992 to 1999 and the year 2000, at the Chihuahuan Desert Rangeland Research Center.

 
Forage Quality and Availability
Two techniques were used to assess the quality and availability of potentially consumed forage by Angus and Brahman cows. The first technique evaluated forage standing crop by identifying species of forage and then by clipping quadrats within an area identified to be frequently grazed. The second technique utilized ruminally cannulated cows commingled with the experimental animals to obtain rumen digesta from these identified locations. Common grazing areas were identified by marking the locations of the cattle within the pasture each time they had to be gathered for sample collection using a global positioning receiver (Geo Explorer II; Trimble Inc., Sunnyvale, CA) and the Universal Transverse Mercado coordinate system differentially corrected using Pathfinder software (Trimble Inc.).

Forage Standing Crop.
Available forage (kg/ha) was measured from 10 transects in the pasture location determined to be frequently grazed during each month. Fifty 0.18-m2 quadrats were clipped at ground level (five quadrats/transect). Between quadrats, a number of paces ranging between 0 and 25 were randomly selected within a line that bisected the key grazing area. The percentage of each plant species was identified in each quadrat, and then the forage was clipped and divided into three categories: grass, forbs, and broom snakeweed (Gutierrezia sarothrae). Honey mesquite (Prosopis glandulosa) was excluded from the measurements because the leaves of this shrub are not typically grazed by cattle in the Chihuahuan Desert, and samples were collected when there was limited presence of its beans (De Alba-Becerra et al., 1998). Forage DM was determined by drying samples at 55°C for 72 h and then weighing.

Ruminal Digesta Sampling.
Four ruminally cannulated cows of mixed breeds were used to assist in evaluating quality of potentially consumed forage as described in Hakkila et al. (1987) and De Alba-Becerra et al. (1998). These cows were commingled with the studied Angus and Brahman cows except when used to estimate consumable forage. From these cows, forage extrusa samples were collected on d 1 and 5 of each month after the cows were allowed to graze the area determined to be frequently grazed. Collection of ruminal digesta involved penning the animals 24 h before sample collection to prevent grazing. The next morning (0600) the rumen was evacuated according to the procedures of Lesperance et al. (1960). After evacuation, cows were transported to the identified grazing area and allowed to graze for 1 h before being returned to the working facility for collection of ruminal digesta. The cows were not allowed to drink before collection of ruminal digesta. After collection, extrusa samples were subsequently dried at 55°C for 72 h and then ground through a Wiley mill with a 2-mm screen before quality analyses.

Forage Quality Analyses.
Samples of clipped forage and samples of ruminal digesta were dried overnight at 105°C to determine DM content. Additional samples were ashed for 3 h at 550°C in a muffle furnace to determine OM content. Dry matter, OM, and ash were determined by standard procedures, and CP was determined by the Kjeldahl method (AOAC, 1990). Neutral and acid detergent fibers were determined using procedures of Goering and Van Soest (1970). In situ disappearance of the collected ruminal digesta were also evaluated using dacron nylon bags (9 x 16 cm; pore size 44 µm; Bar Diamond, Inc., Parma, ID) containing 4 g of dried ruminal digesta. Triplicate bags for each sample plus a blank were incubated in the rumen of the four cannulated cows for 24 h to evaluate digestion rate and for 96 h to determine OM disappearance. After removal from the rumen, bags were rinsed with tap water until effluent was clear. The bags were then dried at 55°C for 72 h and at 100°C for 1 h. Bags plus indigestible materials were weighed and recorded.

Herd Descriptions and Management
In the autumn of 1998, pregnant multiparous Angus (n = 14) and Brahman (n = 14) cows as described in Thomas et al. (2002) were moved to the Chihuahuan Desert Rangeland Research Center. These cows were pastured together until the breeding season of 1999. During the 1999 breeding season of May 1 to August 1, the Angus cows were pastured separately from the Brahman cows with an Angus bull used to breed the Angus cows and a Brahman bull used to breed the Brahman cows. In January of 2000, the two herds of cattle were again commingled. During 2000, cows were maintained in the study area for 30 d before and during each month of data collection. Because the pasture was not large enough to support the cows for all months in 2000, cows were rotated to an adjacent pasture when cows were not being used for metabolic evaluations. This rotation allowed for a conservative harvest of the available forage (i.e., estimated removal of 30% of the forage).

Cows received nutritional and mineral supplementation during the spring of 2000. The supplementation strategy provided a protein-based supplement (CP = 40%; TDN = 70%) during calving and peak lactation (i.e., March 1 to May 1). This supplement was delivered at 0.9 kg•cow-1•d-1 with delivery being on every-other-day. An energy-based supplement (CP = 17%; TDN = 79%) was provided to the cows from May 1 until forage quality was enhanced with the initiation of summer rain and forage growth (Figure 1Go). This supplement was delivered at a rate of 1.8 kg•animal-1•week-1 with the delivery occurring three times/week.

Birth weights were collected the day after parturition for calves in these herds, and weaning weights were determined on September 15, 2001, and weights were adjusted to 205 d of age according to the procedures described in the guidelines of BIF (1996). Weaning and palpation for pregnancy occurred in mid-October. Nonpregnant cows were culled, and pregnancy rate in each breed group was determined.

Animal Procedures and Measurements
All animal-related procedures were approved by the Institutional Animal Care and Use Committee of New Mexico State University (#99-0011). In February 2000, eight spring-calving Angus and eight spring-calving Brahman cows were randomly selected from the herds of 14 Angus and Brahman cows to initiate the study. Cows used in the study did not share common ancestory based on a three-generation pedigree and were 8.7 ± 0.6 yr of age. Seven days before each data collection period (i.e., February, May, September), cows were orally administered intraruminal controlled release boluses containing chromium sesquioxide to evaluate fecal output. Boluses were designed to release 1.4 g of chromic oxide/day (Captec Chrome; Captec NZ limited, Auckland, NZ). After 7 d, fecal samples were collected per rectum from all cows for 8 consecutive days at 30-h intervals and stored at -20°C for subsequent analyses. The collection times were 0600 on d 1, 1200 on d 2, 1800 on d 3, and 2400 on d 4. Then the collection times were repeated. One hour before each collection, cows were driven to the corral, and the grazing location was identified with a global positioning receiver. After d 8, fecal samples were thawed and dried in an oven at 55°C for 72 h. Samples were then ground through a Wiley mill with a 2-mm screen, and fecal output was determined by estimating concentration of chromium using atomic absorption spectroscopy (Faichney, 1975).

Hip height was recorded on the first day of sampling in February. Body condition score (1 = emaciated to 9 = obese) was assigned at the start of each month, and BW was recorded each day immediately after fecal sample collection. A 10-mL blood sample was also collected via caudal venipuncture (Corvac serum separator; Sherwood, St. Louis, MO) each day at the time of fecal sample collection. Blood samples were allowed to clot and then centrifuged at 1,000 x g for 20 min at 4°C. Serum was frozen in plastic vials at -20°C until analyzed for concentrations of hormones and metabolites indicative of metabolic status. Hormones used in these evaluations were those known to be involved in carbohydrate and lipid metabolism and metabolic rate. These hormones were insulin, GH, IGF-I, and triiodothyronine. Metabolites used in these evaluations were urea nitrogen, glucose, and NEFA.

Hormone and Metabolite Measures
Hormone concentrations were determined using RIA. Concentrations of GH were determined in a single assay using the procedure of Hoefler and Hallford (1987). The within assay CV was 19%. Serum concentrations of insulin were determined in two assays using Coat-A-Count Kit (Diagnostic Products Corporation, Los Angeles, CA) according to manufacturer’s instructions and the procedures of Reimers et al. (1982). The intra- and inter-assay CV were 8.3 and 10.8%, respectively. Serum concentrations of IGF-I were determined using the procedures of Berrie et al. (1995) in one assay. The intra-assay CV was 9.4%. Serum concentrations of triiodothyronine were also determined with Coat-A-Count Kit (Diagnostic Products Corporation) according to manufacturer’s instructions in two assays. The intra- and inter-assay CV were 14.6 and 7.4%, respectively. Leptin concentrations were measured in three assays by the procedures of Delavaud et al. (2000). The intra- and inter-assay CV were 13.8 and 10.6%, respectively.

Serum concentrations of glucose and urea nitrogen were determined with enzymatic reagents and modified procedures of the Sigma-Aldrich Co. (St. Louis, MO). The intra- and inter-assay CV for nine assays were 3.7 and 3.6% for glucose and 3.9 and 4.8% for urea nitrogen. Serum concentrations of NEFA were determined using NEFA C kit (Wako Chemicals USA, Inc., Richmond, VA; Cat. No. 994-75409E). The intra- and inter-assay CV for nine assays were 4.3 and 4.1%, respectively.

Serum concentrations of leptin, glucose GH, NEFA, and urea nitrogen were determined for all blood samples collected (i.e., d 1 to 8 in each month). Serum concentrations of IGF-I were determined only on d 1 and 5, and serum concentrations of triiodothyronine were determined on d 1, 3, 5, and 7 in each month. Thus, d 1 and 5 represented samples obtained in the early morning (i.e., 0600), and d 3 and 7 represented samples obtained in the evening (i.e., 1800).

Statistical Analyses
Data analyses were conducted using SAS (SAS Inst. Inc., Cary, NC). Available forage was determined by averaging the data from individual quadrats (n = 5) within each transect. Thus, data from 10 transects were available for analyses for each month. Estimated proportion of plant species, DM of clipped forage, and quality measures of clipped forages (i.e., forbs, grass, snakeweed) were analyzed with a model that used month as an independent variable within PROC GLM. Organic matter, measures of composition of OM, and in situ digestibility of forage samples obtained from ruminally cannulated cows (n = 4) were analyzed with a model that included month, day, and the interaction month x day using PROC MIXED. If an interaction (P < 0.05) was detected, means were separated using preplanned pair-wise comparisons of least squares means generated with the PDIFF function. If no interaction was detected, but a main effect was detected, then the main effect means were separated with a similar procedure. Adjusted weaning weight was analyzed with a GLM using breed as an independent variable. Chi-square analyses using PROC FREQ were used to evaluate pregnancy rate.

Body condition score was analyzed using the procedures of PROC MIXED for repeated measures. The model included breed, month, and breed x month with cow (breed) used as the repeated term. Body weight, daily fecal output, fecal output per 100 kg of BW, and serum concentrations of hormones and metabolites were also analyzed with these procedures. The model included breed, month, time-of-day, and the interactions of these terms, and cow(breed) served as the repeated term. The appropriate covariance structure of the data was chosen for each analysis from the structures of compound symmetric, autoregressive order one, and unstructured using Akaike’s Information Criterion and Schwarz’s Bayesian Criterion. When an interaction was detected, means were subsequently separated with preplanned pair-wise comparisons using the PDIFF function associated with generation of least squares means. If no interaction was detected, but a main effect was detected, similar analyses were used to separate the means.


   Results
Top
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 Implications
 Literature Cited
 
Forage Availability and Quality
Percentage of ground cover by each plant species observed in February, May, and September 2000 is presented in Table 1Go. Six grass species were observed in the identified grazing areas. Harvard threeawn, mesa dropseed, and black gramma were found in greater (P < 0.05) proportions in February and May than in September. Tobosa was in greater (P < 0.05) proportions in May and September than in February with annual grasses being observed in much greater (P < 0.05) proportions in September than in February and May.


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  		Table 1. Percentage of ground cover by each plant species observed (n = 10 transects, n = 5 frames/transect) in February, May, and September 2000 at the Chihuahuan Desert Rangeland Research Center
 
Seven species of forbs in the defined grazing areas were observed. Leatherweed croton and desert holly were in greater (P < 0.05) proportions in September than in February and May, whereas James rushpea and spectaclepod were in greater (P < 0.05) proportions in February than in May and September. Various annual forbs were in greater (P < 0.05) proportions in February than in May, and snakeweed was in greater (P < 0.05) proportions in May than in February and September. Collectively, analyses of weights from clipped quadrats indicated that in February, May, and September 132.7, 436.2, and 554.8 kg of grass/ha, respectfully, were available for grazing. In these months, the amount of available forbs was 222.3, 57.3, 258.8 kg/ha and snakeweed was 116.8, 70.0, 181.2 kg/ha. Concomitantly, more than 69% of each evaluated quadrat was bare ground.

Results of quality analyses of clipped forages are presented in Table 2Go. In brief, DM in snakeweed was greater (P < 0.05) in May and September than in February. A tendency was detected (P < 0.10) for DM in forbs and grasses to be greater in May and September than in February. The percentage of CP in forbs was greater (P < 0.05) in September than in May and greater (P < 0.05) in May than February. Grasses and snakeweed had greater (P < 0.05) CP percentage in September than in February and May. Neutral detergent fiber appeared to decrease (P <= 0.10) in forbs from February to May and May to September. Acid detergent fiber tended to be greater (P < 0.10) in forbs in February than in May and September.


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  		Table 2. Composition of DM of clipped forage at the Chihuahuan Desert Rangeland Research Center in February, May, and September 2000 (n = 10 transects)
 
No effect of day or interactions of day x month were detected (P > 0.10) in samples of ruminal digesta. However, DM of ruminal digesta was greater (P < 0.05) in February than in May and September, whereas CP and ADF were greater (P < 0.05) in September than in February and May (Table 3Go). Twenty-four and 96 h in situ digestibility measures of the previously collected ruminal digesta were greater (P < 0.05) in September than in February and May (Table 3Go).


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  		Table 3. Quality measure of ruminal digesta collected from ruminally cannulated cows (n = 4) grazing at the Chihuahuan Desert Rangeland Research Center in February, May, and September 2000
 
Animal Measures
Brahman cows had greater (P < 0.01) hip height than Angus cows (i.e., 160.9 > 155.3 ± 1.7 cm). Pregnancy rate was similar (P = 0.46) between Angus (75%) and Brahman (57%) cows. Calving dates of cows (March 1 ± 10 d), birth weights (36.2 ± 2 kg), and adjusted weaning weights (227.5 ± 8.9 kg) of calves were similar (P >= 0.67) among breed groups. However, differences were found in other measures of cow performance (Table 4Go). Angus cows were heavier (breed x month, P < 0.01) than Brahman cows in February, May, and September as all cows were heavier (P < 0.02) in February than in September, and in September, cows were heavier (P < 0.02) than in May. Brahman cows tended to have greater (breed x month; P < 0.10) body condition score than Angus cows in May, and body condition scores tended (P < 0.10) to be lowest in both breeds in May relative to February and September.


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  		Table 4. Least square means of body weight (BW), body condition score (BCS), and fecal OM output (FO) estimates in spring-calving multiparous Angus and Brahman cows (n = 8 cows breed) grazing at the Chihuahuan Desert Rangeland Research Center in February, May, and September 2000
 
Cows in both breeds had greater (P < 0.01) daily fecal OM output in September than in May and greater (P < 0.01) output in May than in February (Table 4Go). Brahman cows tended to have more (breed x month; P < 0.10) fecal output/unit of BW in February than Angus cows. Fecal output per unit of BW tended (P < 0.10) to increase from February to May to September in both breeds.

Metabolic Hormones and Metabolites
Serum concentrations of leptin, triiodothyronine, IGF-I, GH, and glucose in February, May, and September in Angus and Brahman cows are listed in Table 5Go. Brahman cows had greater (breed x month; P < 0.05) serum concentrations of leptin in September than Angus cows. Concentrations of triiodothyronine were greater (breed x month; P < 0.05) in Brahman cows than in Angus in February, May, and September. Concentrations of triiodothyronine were greater (P < 0.05) in September than in February and May in both breed groups. No effects of breed or interactions involving breed were detected (P >= 0.34) in serum concentrations of GH. However, Brahman cows tended (breed x month; P = 0.11) to have greater concentrations of IGF-I across the 3 mo than Angus cows.


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  		Table 5. Serum concentrations of metabolic hormones and glucose in spring-calving multiparous Angus and Brahman cows (n = eight cows per breed) grazing at the Chihuahuan Desert Rangeland Research Center in February, May, and September 2000
 
Brahman cows had greater (breed x month; P < 0.05) concentrations of serum glucose than Angus cows in the months of February and May. Brahman cows tended (P < 0.10) to have greater concentrations in September than Angus cows. Brahman cows also had greater (P < 0.05) concentrations of glucose in the month of February than in the months of May and September. A breed x month x day interaction (P < 0.01) was detected in serum insulin. Concentrations of insulin were similar (P > 0.10) across time-of-day in Angus cows, whereas concentrations appeared (P < 0.05) dynamic across time-of-day in Brahman cows (Figure 2Go). Brahman cows consistently had greater P < 0.05) concentrations of insulin than Angus cows (Figure 2Go).



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  		Figure 2. Serum concentrations of insulin in spring-calving multiparous Angus and Brahman cows (n = 8 cows per breed) grazing in the Chihuahuan Desert during February, May, and September 2000. Pooled SE for the three graphs were 0.1, 0.08, and 0.08, respectively.

a,bDiffer among breeds at each time (P < 0.05).

 
Brahman cows had greater (breed x month x time-of-day; P < 0.05) concentrations of urea nitrogen than Angus cows on time-of-day 0600 and 2400 in May (Figure 3Go). Brahman cows also had greater concentrations (P < 0.05) than Angus cows on time-of-day 0600, 1800, and 2400 in September. Serum concentrations of NEFA were greater (breed x month x time-of-day; P < 0.05) in Angus cows than in Brahman cows on times 1200 and 2400 in February (Figure 4Go). Similar relationships were detected at times 0600 to 2400 in the month of May. Brahman cows also had greater concentrations of NEFA (P < 0.05) than Angus cows on time-of-day 0600 in September. Furthermore, in both breeds, serum concentrations of NEFA were less (P < 0.05) in September than in February and May (Figure 4Go).



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  		Figure 3. Serum concentrations of urea nitrogen in spring-calving multiparous Angus and Brahman cows (n = 8 cows per breed) grazing in the Chihuahuan Desert during February, May, and September 2000. Pooled SE for the following graphs were 1.0, 1.1, and 1.1, respectively. a,bDiffer among breeds at each time (P < 0.05).

 


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  		Figure 4. Serum concentrations of NEFA in spring-calving multiparous Angus and Brahman cows (n = 8 cows per breed) grazing in the Chihuahuan Desert during February, May, and September 2000. Pooled SE for the following graphs were 123, 137, and 85, respectively.

a,bDiffer among breeds at each time (P < 0.05).

 

   Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
Implications
 Literature Cited
 
Rainfall pattern was typical of this region of the Chihuahuan Desert, and forage quantity and quality were similar to previous reports (Figure 1Go, Tables 2Go and 3Go; Nelson et al., 1970; Pieper and Herbel, 1982; Malm, 1994). Even though these studies describe forage available for grazing, forage is sparse in this region of the Chihuahuan Desert with shrubs (honey mesquite, soaptree yucca, and mormon tea) accounting for 38% of the plant canopy (De Alba-Becerra et al., 1998). Cumulatively, the cows were sampled in a month of dormant forage with cool ambient temperature (February), a month of dormant forage and high ambient temperature (May), and a month of growing forage and high ambient temperature (September). These were also time periods of the third trimester of pregnancy (February), early lactation (May), and late lactation (September).

Because rainfall and forage growth do not typically occur in the Chihuahuan Desert until mid-summer, achieving performance levels that can be profitable is a challenge for traditional spring-calving beef herds (Winder et al., 2000). The Angus and Brahman cows calved in the spring and birth weights, weaning weights, and measures of reproductive performance were similar among breed groups. Even though the cows received nutritional supplementation in March and April, BW and body condition scores were lowest in May, which was the month of poorest forage quality (Tables 2Go to 4Go). Thus, peak lactation most likely occurred when forage quality was inadequate to meet the nutritional requirements for cows to maintain body condition. Even with supplementation, both breed groups experienced relatively low pregnancy rates.

Fecal output appeared to parallel forage quality across months, and a tendency was observed among breed groups as Brahman cows appeared to have greater fecal output than Angus cows in February (Tables 2Go through 4Go). These observations could have been due to differences in the kinetics of digestion of poor-quality forage that has been observed between these two breeds (Hunter and Siebert, 1985, 1986; Forbes et al., 1998) or differences in diet selectivity that has also been observed among grazing cattle of various genotypes in the Chihuahuan Desert (Herbel and Nelson, 1966; Winder et al., 1995; De Alba-Becerra et al., 1998). A challenge to the interpretation of the data is that quality of selected dietary forage is typically greater than the quality of forage obtained from clipping quadrats in the Chihuahuan Desert. This is primarily due to diversity of forage available for grazing (Hakkila et al., 1987; Alba-Beccera et al., 1998). Because Angus and Brahman cattle are common constituents of beef cattle grazing systems in the Chihuahuan Desert, additional investigations of diet selectivity comparing the two breeds are needed.

Even though the current study cannot delineate metabolic differences that were a consequence of diet selection, alterations in BW and body condition scores across months demonstrated that the breed groups were influenced by diet quality and physiologic state (i.e., gestation versus lactation in February versus May; Tables 2Go through 4Go). It appeared that Angus cows were more sensitive to environmental challenges than the Brahman cows as BW differed greatly across months (Table 4Go). The dynamics of varying forage quality and physiologic state across months was also observed in serum concentrations of leptin in Angus cows (Table 5Go). Leptin is a hormone secreted by adipose tissue that is known to be involved in regulating metabolic rate and appetite (Houseknecht et al., 1998; Ahima et al., 2000). Recently, it was determined that serum concentrations of leptin increased dramatically in developing Angus bulls but not in Brangus or Brahman bulls (Thomas et al., 2002). The cows sampled in the present study were in marginal to poor body condition and had relatively low concentrations of serum leptin; however, data suggest that serum leptin appears to be more dynamic in Angus cattle than in Brahman cattle.

Leptin is influenced by, or associated with, hormones secreted by the thyroid that are involved in regulating metabolic rate (Ahima et al., 2000). In the current study, serum concentrations of triiodothyronine were greater in Brahman cows relative to Angus cows in February, May, and September (Table 5Go). These results agree with the report of Cowley et al. (1971) comparing Brahman cattle with Hereford cattle and with the report of Carstens et al. (1997) comparing Angus calves with Brahman calves. The cattle evaluated in the present study were more likely exposed to heat stress rather than to cold stress in the months of May and September (Malm, 1994). Thus, the data derived from the Brahman cattle are in contrast to observations in Bos taurus cattle because cold stress typically elevates thyroid hormone levels (Godfrey et al., 1991).

Metabolic rate can also be influenced or regulated by several hormones involved in carbohydrate metabolism. These hormones include insulin, GH, and IGF-I (Davidson, 1987; Breier, 1999). Serum concentrations of insulin are dependent on availability of glucose (Harmon, 1992), and Brahman cows appeared to have greater concentrations of glucose than Angus cows even though concentrations in both breeds were very low for multiparous cows (Table 5Go; Vizcarra et al., 1998). Concentrations of glucose varied across months in Brahman cows, and a dynamic relationship was observed in serum concentrations of insulin with time-of-day in Brahman cows. Concentrations of glucose appeared static in Angus cows (Table 5Go and Figure 2Go). These observed differences between Angus and Brahman cows support previous findings (Simpson et al., 1994, 1997; Alvarez et al., 2000). However, they are contrary to the report of Thomas et al. (2002) in which serum insulin was similar in growing Angus and Brahman bulls consuming a diet rich in starch. Cumulatively, these studies suggest that insulin secretion, sensitivity, and/or resistance in cattle may be influenced by breed, gender, age, and/or diet quality. The differences in serum insulin observed in Brahman cows could have been due to dissimilarity in daily grazing behavior that may exist between these breeds (Forbes et al., 1998).

Serum concentrations of IGF-I were greater in Brahman cows than in Angus cows as in previous reports (Table 5Go; Simpson et al., 1994, 1997; Alvarez et al., 2000). These finding were in contrast to observations of Thomas et al. (2002) in which growing Angus bulls had greater concentrations than Brahman bulls. Insulin-like growth factor-I is secreted from the liver or local tissues in response to GH (Underwood et al., 1994). Serum concentrations of GH were similar between the Angus and Brahman cows, and this result is in contrast to previous reports (Simpson et al., 1994, 1997; Alvarez et al., 2000). This result could have been a consequence of the uncoupling of the physiological linkage between GH and IGF-I observed when an animal is in poor body condition (Roberts et al., 1997; Thissen et al., 1999; Lalman et al., 2000) or due to the influence of the suboptimal nutritional state on the pulsatile secretion pattern of GH (Thomas et al., 1991; Breier, 1999).

Pituitary secretion of GH is typically elevated in animals that are in a negative energy balance, and because of this hormone’s role in lipid metabolism, it increases serum concentrations of NEFA (Davidson, 1987; Thomas et al., 1991; Vizcarra et al., 1998). In this study, serum samples were collected during three physiologic states: third trimester of pregnancy (February), early lactation (May), and late lactation (September). Concentrations of NEFA were different in May and February than in September in both breed groups. This was most likely due to inadequacies of consumed forage to meet maintenance and lactation requirements (Tables 1Go through 3Go). Serum concentrations of NEFA were greater at various time-of-day across month in Brahman cows relative to Angus cows (Figure 4Go). These observations imply that differing mechanisms may exist between Angus and Brahman cows in regard to maintenance and mobilization of adipose tissue.

Serum concentrations of urea nitrogen can be used as an indicator of protein intake or protein catabolism. Since the cows in this study consumed forage that was inadequate relative to requirements of their physiologic state, concentrations of urea nitrogen were greater in months of lactation (i.e., May and September). May was also a month of poor forage quality (Tables 2Go and 3Go). Thus, protein catabolism probably occurred. Brahman cows appeared to have greater concentrations of urea nitrogen in these months relative to Angus cows as in other studies comparing Angus and Brahman cows (Figure 4Go; Simpson et al., 1994, 1997; Alvarez et al., 2000). These reports and the results of this study suggest that differing mechanisms may exist between Angus and Brahman cows for use of protein tissues as an energy source for maintenance and production.

Selecting for optimal biological type and breed composition and the knowledge of their management remains a challenge for beef cattle operations in semiarid climates. Previous studies conducted at the Chihuahuan Desert Rangeland Research Center suggest that herd productivity can be enhanced with use of B. indicus-influenced cattle (Winder et al., 1992). Nevertheless, Kattnig et al. (1993) suggested that cow efficiency calculations using cows of several breeds in this environment is greatly influenced by mature cow size. The objectives of this study were to assess the quality and availability of range forage and to evaluate the metabolic status of two breeds, Angus and Brahman. Evaluations were made in spring-calving multiparous cows in the months of February, May, and September. These months represent seasons of differing forage quality and ambient temperature in the Chihuahuan Desert and the differing physiologic states which are a result of management for spring-calving (i.e., third trimester of pregnancy, early lactation, and late lactation). Results suggest that both breeds were sensitive to the seasonal dynamics of forage quality. However, Brahman cows appear to have greater concentrations of metabolic hormones and metabolites than Angus cows, and Angus cows had more dynamic BW across months.


   Implications
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Implications
Literature Cited
 
Increased knowledge of the influence of the environment on metabolism may be useful in choosing breeds or breed combinations for production systems in semiarid climates. This study suggested that metabolism in Angus and Brahman cows is sensitive to the environmental challenges of the Chihuahuan Desert. However, Brahman cows, which are adapted to high ambient temperature, have greater concentrations of metabolic hormones and metabolites than Angus cows, and Angus cows appear to have more dynamic BW as forage quality and physiologic state change across seasons. These results contribute to the knowledge that is needed to determine the most suitable combinations of breeds in crossbreeding or composite systems in the Chihuahuan Desert.


   Footnotes
 
1 Experimentation was supported by the New Mexico Agricultural Experiment Station (Hatch project # 180674), the NIH-SCORE program (GMO8136-26), the NIH-RISE program (GM61222), and the Western Region Coordinating Committee in Beef Cattle Breeding Research (WCC-1). Appreciation is expressed to J. Hernandez, R. Randel, R. Beck, C. Bailey, R. McNeely, J. Sawyer, C. Löest, R. Waterman, and A. Stalker for assistance in conducting this experiment. Appreciation is also to expressed to NHPP-NIDDK and Dr. Parlow for supplying reagents for GH assays and to Marta Remmenga for statistical assistance. Back

Received for publication November 20, 2001. Accepted for publication May 7, 2002.


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


Ahima, R. S., C. B. Saper, J. S. Flier, and J. K. Elmquist. 2000. Leptin regulation of neuroendocrine systems. Front. Neuroendocrinol. 21:263–307.

Alvarez, P., L. J. Spicer, C. C. Chase, Jr., M. E. Payton, T. D. Hamilton, R. E. Stewart, A. C. Hammond, T. A. Olson, and R. P. Wettmann. 2000. Ovarian and endocrine characteristics during an estrous cycle in Angus, Brahman, and Senepol cows in a subtropical environment. J. Anim. Sci. 78:1291–1302.[Abstract/Free Full Text]

AOAC. 1990. Official methods of Analysis. 15th ed. Assoc. Anal. Chem., Arlington, VA.

Berrie, R. A., D. M. Hallford, and M. L. Galyean. 1995. Effect of zinc source and level on performance, carcass characteristics, and metabolic hormone concentrations of growing and finishing lambs. Prof. Anim. Sci. 11:149–156.

BIF. 1996. Guidelines for Uniform Beef Improvement Programs. In: C. Bailey (ed.), Writing and Business Support. 7th ed. Beef Improvement Fed., Reno, NV.

Breier, B. H. 1999. Regulation of protein and energy metabolism by the somatotropic axis. Domest. Anim. Endocrinol. 17:209–218.[Medline]

Carstens, G. E., P. M. Mostyn, M. A. Lammoglia, R. C. Vann, R. C. Apter, and R. D. Randel. 1997. Genotypic effects on norepinephrine-induced changes in thermogenesis, metabolic hormones, and metabolites in newborn calves. J. Anim. Sci. 75:1746–1755.[Abstract/Free Full Text]

Cowley, J. J., J. H. Gutierriz, A. C. Warnick, J. F. Hentges, Jr., and J. P. Feaster. 1971. Comparison of thyroid hormone levels in Hereford and Brahman Cattle. J. Anim. Sci. 32:981–983.[Abstract/Free Full Text]

Davidson, M. B. 1987. Effect of growth hormone on carbohydrate and lipid metabolism. Endocr. Rev. 8:115–131.[Medline]

De Alba-Becerra, R. D., J. Winder, J. L. Holecheck, and M. Cardenas. 1998. Diets of 3 cattle breeds on Chihuahuan desert rangeland. J. Range Manage. 51:270–275.

Delavaud, C., F. Bocquier, Y. Chillard, D. H. Keisler, A. Gertler, and G. Kann. 2000. Plasma leptin determination in ruminants; effects of nutritional status and body fatness on plasma leptin concentration assessed by a specific RIA in sheep. J. Endocrinol. 165:519–526.[Abstract]

Faichney, G. J. 1975. The use of markers to partition digestion within the gastrointestinal tract of ruminants. In: I. W. McDonald and A. C. I. Warner (ed.). Digestion and Metabolism in the Ruminant. University of New England Publication Unit, Armidale, Australia.

Ferrell, C. L., and T. G. Jenkins. 1984. Energy utilization by mature, nonpregnant, nonlactating cows of different types. J. Anim. Sci. 58:234–243.[Abstract/Free Full Text]

Ferrell, C. L., and T. G. Jenkins. 1985. Cow type and the nutritional environment: nutritional aspects. J. Anim. Sci. 61:725–741.[Abstract/Free Full Text]

Forbes, T. D. A., F. M. Rouquette, Jr., and J. W. Holloway. 1998. Comparisons among Tuli-, Brahman-, and Angus-sired heifers: intake, digesta kinetics, and grazing behavior. J. Anim. Sci. 76:220–227.[Abstract/Free Full Text]

Frisch, R., and J. Vercoe. 1977. Food intake, eating rate, weight gains, metabolic rate and efficiency of feed utilization in Bos taurus and Bos indicus crossbred cattle. Anim. Prod. 25:343–358.[Medline]

Godfrey, R. W., S. D. Smith, M. J. Guthrie, R. L. Stanko, D. A. Neuendorff, and R. D. Randel. 1991. Physiological responses of newborn Bos indicus and Bos indicus x Bos taurus calves after exposure to cold. J. Anim. Sci. 69:258–263.[Abstract]

Goering, H. D., and P. J. Van Soest. 1970. Forage fiber analyses (apparatus, reagents, procedures, and some procedures). Agricultural Handbook NO. 379, USDA-ARS, Washington, DC.

Hakkila, M. D., J. L. Holechek, J. D. Wallace, D. M. Anderson, and M. Cardenas. 1987. Diet and forage intake of cattle on desert grassland range. J. Range Manage. 40:339–342.

Harmon, D. L. 1992. Impact of nutrition on pancreatic exocrine and endocrine secretion in ruminants: A review. J. Anim. Sci. 70:1290–1301.[Abstract]

Herbel, C. H., and A. B. Nelson. 1966. Species preference of Hereford and Santa Gertrudis cattle on a southern New Mexico range. J. Range Manage. 19:177–181.

Hoefler, W., and D. M. Hallford. 1987. Influence of suckling status and types of birth on serum hormone profiles and return to estrus in early postpartum spring lambing ewes. Theriogenology 27:887–895.

Houseknecht, K. L., C. A. Baile, R. L. Matteri, and M. E. Spurlock. 1998. The biology of leptin: a review. J. Anim. Sci. 76:1405–1420.[Abstract/Free Full Text]

Hunter, R. A., and B. D. Siebert. 1985. Utilization of low quality roughage by Bos taurus and Bos indicuscattle. 1. Rumen digestion.Br. J. Nutr. 53:637–648.[Medline]

Hunter, R. A., and B. D. Siebert. 1986. The effects of genotype, age, pregnancy, lactation, and rumen characteristics on voluntary intake of roughage diets by cattle. Aust. J. Agric. Res. 37:549–560.

Kattnig, R. M., J. A. Winder, J. D. Wallace, and C. C. Bailey. 1993. Evaluation of biological efficiency of free-grazing beef cows under semidesert conditions.1993.J. Anim. Sci. 71:2601–2607.[Abstract]

Lalman, D. L., J. E. Williams, B. W. Hess, M. G. Thomas, and D. H. Keisler. 2000. Effect of dietary energy on milk production and metabolic hormones in thin, primiparous beef heifers. J. Anim. Sci. 78:530–538.[Abstract/Free Full Text]

Lesperance, A. L., V. R. Bohman, and D. W. Marble. 1960. Development of techniques for evaluating grazed forage. J. Dairy Sci. 43:682–689.[Abstract/Free Full Text]

Malm, N. R. 1994. Climatic guide, Las Cruces, 1892–1991, 100 years of weather records. NM. Agric. Exp. Sta. Rpt. 682, Las Cruces.

Nelson, A. B., C. H. Herbel, and H. M. Jackson. 1970. Chemical composition of forage species grazed by cattle on an arid New Mexico range. NM State Univ. Agric. Exp. Sta. Bull. 561, Las Cruces.

Pieper, R. D., and C. H. Herbel. 1982. Herbage dynamics and primary productivity of a desert grassland ecosystem. NM Agric. Exp. Sta. Bull. 695, Las Cruces.

Reimers, T. J., R. G. Cowan, J. P. McCann, and M. W. Ross. 1982. Validation of a rapid solid-phase radioimmunoassay for canine, bovine, and equine insulin. Am. J. Vet. Res. 43:1274–1278.[Medline]

Roberts, A. J., R. A. Nugent, III, J. Klindt, and T. G. Jenkins. 1997. Circulating insulin-like growth factor I, insulin-like growth factor binding proteins, growth hormone, and resumption of estrus in postpartum cows subjected to dietary energy restriction. J. Anim. Sci. 75:1909–1917.[Abstract/Free Full Text]

Rosiere, R. E., J. D. Wallace, and R. F. Beck. 1975. Cattle diets on semi-desert grassland: nutritive content. J. Range Manage. 28:94–96.

Segerson, E. C., T. R. Hansen, D. W. Libby, R. D. Randel, and W. R. Getz. 1984. Ovarian and uterine morphology and function in Angus and Brahman cows. J. Anim. Sci. 59:1026–1046.[Abstract/Free Full Text]

Simpson, R. B., C. C. Chase, Jr., L. J. Spicer, J. A. Carroll, A. C. Hammond, and T. H. Welsh, Jr. 1997. Effect of exogenous estradiol on plasma concentrations of somatotropin, insulin-like growth factor I, insulin-like growth factor binding protein activity, and metabolites in ovariectomized Angus and Brahman cows. Domest. Anim. Endocrinol. 14:367–380.[Medline]

Simpson, R. B., C. C. Chase, Jr., L. J. Spicer, R. K. Vernon, A. C. Hammond, and D. O. Rae. 1994. Effect of exogenous insulin on plasma and follicular insulin-like growth factor I, insulin-like growth factor binding protein activity, follicular oestradiol and progesterone, and follicular growth in superovulated Angus and Brahman cows. J. Reprod. Fertil. 102:483–492.[Abstract/Free Full Text]

Thissen, J. P., L. E. Underwood, and J. M. Ketelslegers. 1999. Regulation of insulin-like growth factor-I in starvation and injury. Nutr. Rev. 57:167–176.[Medline]

Thomas, G. B, J. T. Cummins, H. Francis, A. W. Sudbury, P. I. McCloud, and I. J. Clark. 1991. Effect of restricted feeding on the relationship between hypophyseal portal concentrations of growth hormone (GH)-releasing factor and somatostatin, and jugular concentrations of GH in ovariectomized ewes. Endocrinology 128:1151–1158.[Abstract]

Thomas, M. G., R. M. Enns, D. M. Hallford, D. H. Keisler, B. S. Obeidat, C. D. Morrison, J. A. Hernandez, W. D. Bryant, R. Flores, R. Lopez, and L. Narro. 2002. Relationships of metabolic hormones and serum glucose to growth and reproductive development of performance-tested Angus, Brangus, and Brahman bulls. J. Anim. Sci. 80:757–767.[Abstract/Free Full Text]

Underwood, L. E., J. P. Thissen, S. Lemozy, J. M. Keteslegers, and D. R. Clemmons. 1994. Hormonal and nutritional regulation of IGF-I and its binding proteins. Horm. Res. 42:145–151.[Medline]

Vizcarra, J. A., R. P. Wettemann, J. C. Spitzer, and D. G. Morrison. 1998. Body condition at parturition and postpartum weight gain influence luteal activity and concentrations of glucose, insulin, and nonesterfied fatty acids in plasma of primiparous beef cows. J. Anim. Sci. 76:927–936.[Abstract/Free Full Text]

Winder, J. A., C. C. Bailey, M. Thomas, and J. Holechek. 2000. Breed and stocking rate effects on Chihuahuan Desert Cattle Production. J. Range Manage. 53:32–38.

Winder, J. A., B. J. Rankin, and C. C. Bailey. 1992. Maternal performance of Hereford, Brangus, and reciprocal crossbred cows under semidesert conditions. J. Anim. Sci. 70:1032–1038.[Abstract]

Winder, J. A., D. A. Walker, and C. C. Bailey. 1995. Genetic aspects of diet selection in the Chihuahuan Desert. J. Range Manage. 48:549–553.


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