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Biomedical subjects

T D Forbes

Publications and source records attributed to T D Forbes.

11 recordsLinked to original sources
PubMed2000

Digesta kinetics, energy intake, grazing behavior, and body temperature of grazing beef cattle differing in adaptation to heat.

The objective of this study was to determine whether digesta kinetics, energy intake (EI, kcal ME intake x kg(-.75) x d(-1)), grazing behavior, or body temperature differed by breed, lactational state, or season of the year among cattle presumed to vary in adaptability to the subtropics. Two-year-old lactating and nonlactating Brahman x Angus (BA; n = 5, n = 5), Tuli x Angus (TA; n = 5, n = 4), and Angus (A; n = 4, n = 4) cows were used. During both early (ES) and late summer (LS), lactating cattle vs nonlactating cattle had greater gastrointestinal tract load (CM2) and EI (P < .01), although passage rate did not differ (P > .48). During LS, lactating cattle had decreased early morning rectal temperatures (P < .05) and spent more time grazing during the day compared with nonlactating cattle (P < .001). Among breeds, A had the largest CM2 (P < .01 compared with BA and P = .068 compared with TA) and accumulated the greatest heat during the day (P < .05). Due to greater daytime shading (P < .01) and less daytime grazing (P < .05), A had lower (P < .05) early morning and comparable (P > .26) late afternoon rectal temperatures compared with BA and TA. With data pooled over both grazing trials, BA cattle had the smallest CM2 (P < .01), and in ES they spent the least amount of time in the shade (P < .001). The TA spent more time in the shade than did BA (P < .001) during ES and less during LS (P < .001) and had similar (P > .28) early morning rectal temperatures compared with BA during ES and LS. During LS, TA spent more time in the sun and less time in the shade than did either A or BA (P < .001). During ES, EI did not differ among breeds (P > .50). During LS, EI for lactating A was greater than for BA and TA (P < .05), and EI for nonlactating BA was less than for A and TA (P < .05). Bite rate per minute for lactating cattle during ES was reduced (P < .03) by increased body condition score. Tuli x Angus cattle appear to be comparable to BA with respect to heat adaptation. It appears that EI demands are greater in a hot environment.

Adaptation, Physiological↗
PubMed2000

Effect of supplements on growth and forage intake by stocker steers grazing wheat pasture.

This experiment was conducted with stocker steers to determine the effects of supplementary fiber and grain on ruminal acid concentrations and OM intake following abrupt dietary change to lush, primary-growth wheat (Triticum aestivum) pasture and to measure the effects of those supplements on weight gain at different levels of herbage mass (HM). Each of four irrigated wheat pastures (2.4, 3.6, 4.9, and 6.1 ha) was stocked with nine Angus crossbred steers (mean = 189 kg). In each pasture, three steers were individually fed a daily supplement of 11.3 g of cottonseed hulls (CSH)/kg BW(.75), three steers were fed a supplement mixture of 11.3 g CSH/kg BW(.75) and 8.5 g corn grain/kg BW(.75), and three steers remained as controls. Body weight and HM changes were measured at 28-d intervals throughout the experiment. Ruminal samples for VFA determination were collected twice during the 1st wk on pasture. Organic matter intake calculations were based on fecal output and OM digestibility estimates made during the 2nd wk on pasture. Fecal outputs were estimated from nonlinear least squares analyses using a two-compartment rumen model of excretion patterns of Yb following a single oral dose. Digestibility of OM was estimated using indigestible NDF in feed and feces as an internal marker. Dietary supplements had no detectable effect on ruminal VFA characteristics. The magnitude of changes in ruminal acetate:propionate ratios between d 3 and 7 on pasture was significantly and negatively related to ADG during the first 28-d growth measurement period. Body condition scores taken on d 0 also had a significant, negative relationship to ADG. Average fecal output was greater for steers fed supplements (36 g/kg BW(.75)) than for control steers (30 g/kg BW(.75)) (P < .03). The supplements also significantly reduced estimates of total diet OM digestibility. However, supplements had no measurable effect on BW changes. Herbage mass up to 1,000 kg/ha had a significant and positive effect on ADG, which was 1.44 kg during Period 1, when HM was apparently not limiting in any pasture. The deduced threshold level of the influence of HM on ADG was 850 kg/ha. Under the conditions of this experiment, the effects of supplemental fiber and(or) grain on fecal output and OM digestibility were detected. However, in the amounts fed, these supplements had no detectable effect on ADG at any level of HM.

Animal Feed↗
PubMed1999

Effects of supplemental feeding interval on adult cows in western Texas.

Two experiments involving Brangus and Hereford x Brangus cows (3 to 10 yr) were conducted at four locations in western Texas to determine the effects of supplemental feeding interval on serum urea nitrogen (SUN) patterns, intake of supplement and forage, and winter changes in live body weight and condition score. Treatments were control (Control; no supplemental feed) and the equivalent of .91 kg/d of cottonseed meal (CSM) fed daily (Daily), three times per week (3T/WK), or one time per week (WK). At each location, one pasture group was given all four treatments (four cows/treatment) using Calan gates. In Exp. 1, conducted in 1994-95, blood samples were obtained for determining SUN during the last week of the study. Experiment 2, conducted in 1995-96, included both an individually fed herd and four additional herds at each location that were group-fed the four treatments. Experiment 2 included estimates of intakes of both CSM and forage in both individually fed and group-fed herds. A bolus containing chromium (Cr-bolus) was used to estimate fecal output in the individually fed cows. A double marker technique was used to determine total (Cr-bolus) and CSM (Yb) intakes in the group-fed cows. Data included initial and final cow weights and condition scores (Exp. 1 and 2), SUN patterns (Exp. 1), and supplement, forage, and total intakes (Exp. 2). Feeding CSM to range cows increased SUN concentrations (Exp. 1), reduced losses in live body weight and body condition score (Exp. 1 and 2), and tended to decrease forage intake by the approximate amount of the supplement (Exp. 2). Generally, providing supplement as infrequently as once per week reduced losses in live body weight and body condition score compared with control and was as effective as once daily supplementation. For the group-fed cows, supplement intake, forage intake, and live body weight change were more variable within groups with once daily feeding than when supplement was fed less frequently. These data indicate that feeding as infrequently as one time per week can be effective nutrition management for adult cows grazing native range.

Animal Feed↗
PubMed1998

Comparisons among Tuli-, Brahman-, and Angus-sired heifers: intake, digesta kinetics, and grazing behavior.

As part of an evaluation of Tuli crossbred cattle, forage intake, digesta kinetics, and grazing behavior were estimated in two Texas environments. In humid east Texas, Tuli x Brahman heifers were compared with purebred Angus and Brahman and Angus x Brahman heifers. Fecal output, forage intake, compartmental mass, and compartmental residence time did not differ among breeds. Angus and Brahman heifers had different (P < . 02) gastrointestinal residence times (51.1+/-1.56 vs 43.1+/-1.56 h, respectively), but values for the purebreds did not differ from those for Tuli x Brahman or Angus x Brahman heifers. Angus heifers had shorter (P < .05) 24-h grazing times (398+/-15.4 min/d) and fewer (P < .05) grazing periods (7+/-.4) than Tuli x Brahman (552+/-16.8 min/d and 10+/-.4), Angus x Brahman (507+/-18.4 min/d and 9+/-.5), and Brahman (560-/+ 16.8 min/d and 9+/-.4, respectively) heifers. In semiarid southwest Texas, Tuli x Angus heifers were compared with purebred Angus and Brahman and Brahman x Angus heifers. Fecal output and forage intake were similar in Tuli x Angus and Brahman x Angus heifers (14.2+/-.69 and 14.9+/-.91 g fecal DM/ [d.kg BW] and 24.5+/-1.33 and 25.6+/-1.75 g/d of forage DMI, respectively) but higher (P < .05) than those of purebred Brahman heifers (12.2+/-.64 and 20.3+/-1.23 g/[d.kg BW] of fecal DM and forage DMI, respectively). Grazing times did not differ among breeds. We conclude that Tuli-sired heifers are likely to be as productive as Brahman crossbred heifers in Texas, based on the similarities in intake, digesta dynamics, and grazing behavior.

Animals↗
PubMed1997

Effect of dietary phenolic amines on testicular function and luteinizing hormone secretion in male angora goats.

To test the effect of dietary phenolic amines on pituitary-gonadal functions, 24 postpubertal male Angora goats were assigned during the breeding season to a control diet or to graze on a pasture dominated by phenolic amine-containing vegetation (PA). Compared with control bucks, bucks grazing PA had decreased (P < .001) serum concentrations of testosterone, increased (P < .001) triiodothyronine (T3) and thyroxine (T4), greater (P < .001) reduction in scrotal circumference (SC), lower (P < .001) body weight gains, and reduced (P < .01) semen volume. Sperm concentration and progressive motility were not affected by treatment. On d 75 of treatment, endogenous and GnRH-stimulated LH secretion were greater (P < .01), but endogenous and stimulated testosterone secretion tended (P < .10) to be reduced in the PA bucks relative to the controls. Endogenous serum concentrations of LH and testosterone were positively correlated in the controls, whereas no correlation was detected in the PA males. We conclude that during the breeding season, increased consumption of plants with a high concentration of phenolic amines can affect the reproductive competence of male goats in a manner that suggests a premature ending of the active reproductive phase. The concurrent influence of dietary phenolic amines on serum T3 and T4, and the relationship of these hormones with expression of seasonal reproduction in domestic and wild ruminants, warrants further analysis of the relationship between dietary phenolic amines, thyroid function, and reproduction in these species.

Acacia↗
PubMed1995

Growth and subsequent feedlot performance of estradiol-implanted vs nonimplanted steers grazing fall-accumulated endophyte-infested or low-endophyte tall fescue.

A growing-finishing study using Angus steer calves was conducted in three phases: 1) grazing stockpiled 'Kentucky-31' tall fescue (Festuca arundinacea Schreb.) with high (65%; HE KY-31) and low (0%; LE KY-31) infestation rates of Acremonium coenophialum Morgan-Jones and Gams and 'Kenhy' and 'Johnstone' tall fescue with low (< 1%) infestation rate of Acremonium coenophialum from October 24 to December 19; 2) drylot feeding of Johnstone and HE KY-31 haylage (December 19 to April 10); and 3) feedlot finishing on a common high-concentrate diet (April 11 to August 1). In Phase 1, ADG was greatest (P < .05) for Kenhy, intermediate for Johnstone and LE KY-31, and lowest (P < .05) for HE KY-31. Implantation with estradiol 17-beta increased ADG (P < .01) by 23, 27, 7, and 2% for steers grazing Johnstone, HE KY-31, LE KY-31, and Kenhy, respectively. Dry matter digestibility and DMI of stockpiled Johnstone and HE KY-31 were not different (P > .10). During Phase 2, steers consuming Johnstone haylage had greater (P < .01) DMI, ADG, and gain:feed ratio (G:F) than steers consuming HE KY-31 haylage. During Phase 3, steers previously consuming Johnstone had greater DMI (P < .10); however, steers previously fed HE KY-31 had greater ADG (P < .05) and G:F (P < .01). By the end of the study, steer body weights were not different (P > .10) between treatments. These data indicate that growth-decreasing effects of endophyte-infested fescue were evident at hypothermal-ambient temperatures.(ABSTRACT TRUNCATED AT 250 WORDS)

Acremonium↗
PubMed1994

Follicular dynamics, embryo production, and hormonal responses in Brahman heifers following sympathetic stimulation.

The purpose of this experiment was to characterize adrenal and ovarian responses to N-methyl-beta-phenethylamine (NMP) or ACTH. Thirty-three heifers with functional midcycle corpora lutea were placed on a 4-d superovulation regimen. They were injected twice daily with FSH-P and either saline (Control), ACTH (80 IU), or NMP (1 mg/kg BW). An initial blood collection preceded jugular delivery of saline, NMP, or ACTH, i.m. delivery of FSH and PGF2 alpha (d 3), and ultrasound (d 1 to 4). A second blood collection was made 6 min after treatment. Sampling continued daily until d 13. Embryos (age 6 to 7 d) were collected and evaluated. Concentrations of cortisol (posttreatment minus pretreatment) were greatest (P < .05) in NMP- and ACTH-treated heifers. Treatment did not affect mean numbers of small (< 4 mm), large (> 8 mm), or total follicles on d 2 to 4. Heifers receiving NMP had fewer medium follicles (4 to 8 mm) on d 2 and 3, and ACTH-treated heifers had fewer medium follicles on d 4 (P < .07). Mean estradiol concentrations on d 2 to 4 were unaffected by treatment (P > .32). Following PGF2 alpha, time to onset of standing estrus was less (P < .05) in Control than in ACTH- and NMP-treated heifers (41.4 vs 47.9 and 58.9 h, respectively). A greater frequency (P < .05) of reproductive anomalies (no estrus; no ovulation [i.e., progesterone < 1 ng/mL]; luteal failure [i.e., progesterone < 1 ng/mL but embryos recovered]) occurred in NMP (5/11) than in Control (0/10) or ACTH (2/10) heifers.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenocorticotropic Hormone↗
PubMed1994

Effects of phenolic monoamines on release of luteinizing hormone stimulated by gonadotropin-releasing hormone and on plasma adrenocorticotropic hormone, norepinephrine, and cortisol concentrations in wethers.

Eighteen Suffolk and Suffolk x Hampshire wethers (56.3 +/- 1.3 kg) were used to determine the effects of naturally occurring amines, N-methyl-beta-phenethylamine (NMP) and tyramine (T), on plasma cortisol, norepinephrine (NE), ACTH, and GnRH-stimulated LH concentrations. In each experiment, wethers were assigned randomly to treatments with six replicates/treatment. In Exp. 1, treatments consisted of saline, 2 mg of NMP/kg BW (NMP2), or 4 mg of NMP/kg BW (NMP4). In Exp. 2, treatments consisted of saline, 4 mg of NMP/kg BW (N), or 2 mg of NMP + 4 mg of T/kg BW (NT). All treatments were given via indwelling jugular catheters in single doses of 2 mL. In Exp. 1, no effects of time after treatment on response were detected. The NMP2 wethers had lower cortisol and LH peak amplitudes (PKAMP) than other wethers (P < .03 and .05, respectively). Time to peak (PKT) concentration of NE was significantly shorter in NMP4-treated wethers (P < .004). In Exp. 2, significant interactions between time and treatment were detected for cortisol, NE, and LH. Cortisol and NE concentrations were increased (P < .0001 and P < .03, respectively) in N- and NT-treated wethers compared with controls, whereas LH was reduced (P < .003). The N and NT treatments increased cortisol PKT, peak height (PKHT), and PKAMP above that of controls (P < .02, < .006, and < .02, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenocorticotropic Hormone↗
PubMed1993

Technical note: an improved method for extraction and quantification of toxic phenethylamines from Acacia berlandieri.

N-methyl-beta-phenethylamine (NMPEA) has been previously identified as the toxin causing locomotor ataxia in sheep and goats grazing the browse plant, Acacia berlandieri. We describe a simplified procedure for extraction and quantification of naturally occurring beta-phenethylamines from this Acacia species. Dried, ground plant tissue was extracted (1:20 wt/vol) with 1% glacial acetic acid and filtered. The filtrate was passed through a high-sulfonated polymeric solid-phase extraction (SPE) tube, which retained the compounds of interest (tyramine, hordenine, NMPEA) but allowed many impurities co-extracted from the plant tissue to be washed through. Amines were eluted from the tube, then separated and detected by reversed-phase HPLC. Extracted amines were resolved by HPLC in < 15 min, and UV-absorbance spectra matched those of authentic standards. Recovery efficiency of amine standards (125 micrograms/mL) from SPE tubes averaged 97, 101, and 98% for tyramine, hordenine, and NMPEA, respectively. Excess sample loss was prevented and the large volumes of solvents required for liquid-liquid extraction eliminated by use of solid-phase extraction techniques.

Acacia↗
PubMed1988

Researching the plant-animal interface: the investigation of ingestive behavior in grazing animals.

Profitable livestock production from forages largely depends on efficiency of converting forages into products. Efficient grazing management systems require an understanding of the roles of system components. However, experimentation should be conducted with regard to the system as a whole rather than on the systems components in isolation. This may necessitate development of computer models. The short-term intake of forage by grazing animals is controlled both by the structure of the forage and by effects of the ingested forage on gut fill as moderated by the hunger-satiety complex. Intake can be defined as the product of bite size, rate of biting and grazing time. Measurement of these variables is facilitated by the use of esophageally fistulated animals and automatic recording devices. Bite size has the greatest influence on intake, with rate of biting and grazing time being compensatory variables. Sward structure influences bite size to varying degrees. In temperate grass swards, leaf surface height appears to be the dominant influence on bite size. But in tropical grass swards, leaf density and leaf:stem ratio have a greater influence on bite size than does leaf surface height. Alternative techniques to conventional grazing trials are described. Diversity of environments and forages in the U.S. requires further research into the development of grazing systems. In the future, small-scale trials and computer simulation techniques likely will be used to a greater extent.

Animal Feed↗