Joint work and power for both the forelimb and hindlimb during trotting in the horse.

The net work of the limbs during constant speed over level ground should be zero. However, the partitioning of negative and positive work between the fore- and hindlimbs of a quadruped is not likely to be equal because the forelimb produces a net braking force while the hindlimb produces a net propulsive force. It was hypothesized that the forelimb would do net negative work while the hindlimb did net positive work during trotting in the horse.

Additional food folate derived exclusively from natural sources improves folate status in young women with the MTHFR 677 CC or TT genotype.

The effectiveness of additional food folate in improving folate status in humans is uncertain particularly in people with the common genetic variant (677 C-->T) in the methylenetetrahydrofolate reductase (MTHFR) gene. To examine the effect of a doubling of food folate consumption on folate status response variables, women (n=32; 18-46 years) with the MTHFR 677 CC or TT genotype consumed either 400 (n=15; 7 CC and 8 TT) or 800 (n=17; 8 CC and 9 TT) microg/day of dietary folate equivalents (DFE) derived exclusively from naturally occurring food folate for 12 weeks. A repeated measures two-factor ANOVA was used to examine the effect of the dietary treatment, the MTHFR C677T genotype and their interactions on serum folate, RBC folate and plasma total homocysteine (tHcy) during the last 3 weeks of the study.

The glycine N-methyltransferase (GNMT) 1289 C->T variant influences plasma total homocysteine concentrations in young women after restricting folate intake.

Glycine N-methyltransferase (GNMT) is a key regulatory protein in folate metabolism, methionine availability, and transmethylation reactions. Perturbations in GNMT may lead to aberrations in homocysteine metabolism, a marker of numerous pathologies. The primary objective of this study was to examine the influence of the GNMT 1289 C-->T alone, and in combination with the methylenetetrahydrofolate reductase (MTHFR) 677 C-->T variant, on plasma total homocysteine concentrations in healthy young women (n = 114).

A long-term controlled folate feeding study in young women supports the validity of the 1.7 multiplier in the dietary folate equivalency equation.

The presence of folic acid in enriched cereal grain products and the higher bioavailability of folic acid than food folate led to the expression of the 1998 folate RDA, 400 microg/d, as dietary folate equivalents (DFE). DFE are defined as: mug natural food folate + 1.7 x microg synthetic folic acid.

In vivo muscle function vs speed. II. Muscle function trotting up an incline.

Different locomotor tasks, such as moving up or down grades or changing speed, require that muscles adjust the amount of work they perform to raise or lower, accelerate or decelerate the animal's center of mass. During level trotting in the horse, the triceps had shortening strains of around 10.6% while the vastus shortened 8.

In vivo muscle function vs speed. I. Muscle strain in relation to length change of the muscle-tendon unit.

The activity of muscles can be concentric (shortening), eccentric (lengthening) or isometric (constant length). When studying muscle function it is important to know what the muscle fascicles are actually doing because the performance of muscle is strongly influenced by the type of activity: force decreases as a function of shortening velocity during concentric contractions; force produced during eccentric contractions can be stronger than maximum isometric force, and force production is enhanced if a concentric contraction follows an eccentric phase. It is well known that length changes of muscle fascicles may be different from length changes of the overall muscle-tendon unit because of the compliance of the series elasticity.

Energetic and kinematic consequences of weighting the distal limb.

Reason For Performing Study: It is well known that adding a load to a horse's back increases its energetic costs of locomotion, but the magnitude of increase obtained by loading the most distal portion of limb has not been measured.

Objectives: To measure oxygen consumption in horses with mass added to the back and hooves. Because such mass distribution alters inertial parameters of the limbs, kinematic measurements were made to quantify the magnitude of change in limb movement.

Ground reaction forces in horses trotting up an incline and on the level over a range of speeds.

Although the forces required to support the body mass are not elevated when moving up an incline, kinematic studies, in vivo tendon and bone studies and kinetic studies suggest there is a shift in forces from the fore- to the hindlimbs in quadrupeds. However, there are no whole-animal kinetic measurements of incline locomotion. Based on previous related research, we hypothesized that there would be a shift in forces to the hindlimb.

Moments and power generated by the horse (Equus caballus) hind limb during jumping.

The ability to jump over an obstacle depends upon the generation of work across the joints of the propelling limb(s). The total work generated by one hind limb of a horse and the contribution to the total work by four joints of the hind limb were determined for a jump. It was hypothesized that the hip and ankle joints would have extensor moments performing positive work, while the knee would have a flexor moment and perform negative work during the jump.

Methylenetetrahydrofolate reductase 677C-->T variant modulates folate status response to controlled folate intakes in young women.

A common genetic variant in the methylenetetrahydrofolate reductase (MTHFR) gene involving a cytosine to thymidine (C-->T) transition at nucleotide 677 is associated with reduced enzyme activity, altered folate status and potentially higher folate requirements. The objectives of this study were to investigate the effect of the MTHFR 677 T allele on folate status variables in Mexican women (n = 43; 18-45 y) and to assess the adequacy of the 1998 folate U.S.

The energetics of the trot-gallop transition.

Two studies have focused on potential triggers for the trot-gallop transition in the horse. One study concluded that the transition was triggered by metabolic economy. The second study found that it was not metabolic factors but, rather, peak musculoskeletal forces that determine gait transition speeds.

Heterogeneity in the prevalence of methylenetetrahydrofolate reductase gene polymorphisms in women of different ethnic groups.

Objective: To determine the prevalence of methylenetetrahydrofolate reductase (MTHFR) gene polymorphisms in women of different ethnic groups and to relate these common mutations to plasma homocysteine, red cell folate, and serum folate.

Design: A one-time fasting blood sample was obtained for MTHFR genotype (C677T and A1298C) determinations (n=433). Serum folate, red cell folate, and homocysteine analyses were performed in nonfolic acid supplement users (n=215).

Metabolic and osmoregulatory function at low and high (3800 m) altitude.

Altitude evokes physiological adjustments that include not only respiratory and cardiovascular properties, but also metabolic function, renal and endocrine responses. The purpose of the present study was designed to expand our understanding of the physiological process involved with acclimatisation to high altitude in equids. The study examined temporal effects on metabolic and osmoregulatory function in horses (n = 6) at rest and postexercise at 3800 m.

Hindlimb net joint energies during swing phase as a function of trotting velocity.

Net joint powers and energies have been described in walking horses during the swing phase of the stride in the fore- and hindlimb (Clayton et al. 2001). During trotting, swing phase net joint powers have been described in the forelimb but not in the hindlimb.

Effect of trotting speed, load and incline on hindlimb stance-phase kinematics.

The objective was to understand how the stance-phase kinematics of the hindlimb of trotting horses change with speed under 3 conditions (level, loaded and incline), to compare our results with the predictions of the spring-mass model and to help focus our future studies of muscle function. Video recordings were made of 5 Arabian horses trotting on a treadmill. Five consecutive strides were digitised and averaged for each trial.

The cost of transport in an extended trot.

We hypothesised that trotters during an extended trot have lower energetic costs of locomotion (CT) than horses not bred for this behaviour. VO2 was measured as a function of speed in 7 Arabian horses (3 trained to extend their trotting speeds) and in 2 horses, of similar mass, bred to trot (Hackney). Both oxygen consumption and CT increased with speed and there was, contrary to our hypothesis, no difference between breeds.

Intracellular S-adenosylhomocysteine concentrations predict global DNA hypomethylation in tissues of methyl-deficient cystathionine beta-synthase heterozygous mice.

Because S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH) are the substrate and product of essential methyltransferase reactions; the ratio of SAM:SAH is frequently used as an indicator of cellular methylation potential. However, it is not clear from the ratio whether substrate insufficiency, product inhibition or both are required to negatively affect cellular methylation capacity. A combined genetic and dietary approach was used to modulate intracellular concentrations of SAM and SAH.

Folate status in women of childbearing age residing in Southern California after folic acid fortification.

Objective: The purpose of this study was to investigate folate status in healthy, nonpregnant women (18 to 45 years) following folic acid (FA) fortification of the food supply.

Design: This was a cross-sectional study design in which a fasting blood sample was obtained from socio-economically advantaged (n=85) and disadvantaged (n=50) women residing in Southern California who had not consumed supplemental FA within the past 12 months. Serum folate (SF), red cell folate (RCF) and plasma homocysteine (tHcy) concentrations were measured and methylene tetrahydrofolate reductase (MTHFR) genotype (C677T) was determined.

Effect of load on preferred speed and cost of transport.

Horses have a tendency to utilize a relatively narrow set of speeds near the middle of a much broader range they are capable of using within a particular gait, i.e., a preferred speed.

Preferred speed and cost of transport: the effect of incline.

Preferred speed is the behavioral tendency of animals to utilize a relatively narrow set of speeds near the middle of a much broader range that they are capable of using within a particular gait. Possible explanations for this behavior include minimizing musculoskeletal stresses and maximizing energetic economy. If preferred speed is determined by energetic economy (cost of transport, C(T)), then shifts in preferred speed should produce shifts in C(T).

High-altitude effects on respiratory gases, acid-base balance and pulmonary artery pressures in equids.

Arterial and venous blood were analysed at rest and post exercise for pH, PCO2, and PO2, and bicarbonate ([HCO3-]), base excess (BE), and strong ion difference (SID) were calculated in response to a 10 day sojourn to 3800 m. Pulmonary artery pressures (PAP) were measured at rest. Post exercise samples were restricted to venous blood.

Time of contact and step length: the effect of limb length, running speed, load carrying and incline.

Using published values for twelve species of birds and mammals, we investigated the effects of limb length and running speed on time of contact and step length. In addition, we measured the time of contact in horses trotting up a 10 % incline and when carrying a load averaging 19 % of their body mass. From these values, we calculated stride period and step length.

Serum luteinizing hormone, progesterone, and estradiol levels in relation to broodiness in the turkey (Meleagris gallapavo).

Changes in nesting frequency, serum LH, progesterone, and estradiol were measured in relation to the onset of broodiness in turkeys. In each of two experiments the frequency of nest visits increased about four-fold in the 5 to 7 day interval before oviposition of the last egg associated with the onset of broodiness. In the 9 day period prior to oviposition of this egg LH levels declined from about 12 ng/ml to 6 to 7 ng/ml (Experiment 1) and from about 9 ng/ml to less than 5 ng/ml (Experiment 2).

The effect of luteinizing hormone releasing hormone (L.H.R.H.) on serum L.H. and ovarian growth in turkeys.

Serum L.H. of non-laying hens (NL.