A note on the effects of a commercial tryptophan product on horse reactivity

Evaluation of behaviour in stabled draught horse foals fed diets with two protein levels

The present work is aimed at evaluating the behaviour of Italian Heavy Draught Horse (IHDH) foals reared in semi-covered stables and fed two isoenergetic total mixed rations with different dietary protein levels (13.2% and 10.6% of CP on dry matter). The study was prompted by the restrictions for nitrate emissions in farms of the European Nitrate Directive. One suggested solution is to reduce dietary protein while maintaining normal performance and welfare, but there is a lack of literature in studies of horses. The behaviours of 20 foals of 437±60 kg of BW, aged 379±37 days and stabled in four pens by sex (S) and diet (D) were video recorded and analysed to build a suitable ethogram including 18 behaviours in six categories: ingestion, resting, maintenance, movement, social activities, other. The percentage of the daily time spent in each behavioural category and single behaviours was analysed via a single traits GLM including S, D and their interaction. Daily activity was consistent with existing literature: foals spent about 33% of the day in ingestion activities and 41% in resting, whereas social interactions constituted 8% of the time and individual maintenance <2%. Concerning diet, foals fed high protein spent more time in movement (19.62±0.73% of day v. 10.45±0.73% in low-protein (LP) foals; P⩽0.001), whereas the LP group increased resting (43.42±1.12% v. 38.02±1.12%; P⩽0.001). No stereotypies were found, and daily activity followed the typical values for draught breeds for foals in both dietary groups, a result that suggests the maintenance of well-being after dietary protein reduction. This result, together with the findings of a companion study showing no changes in growth performances of foals, showed that a reduction of CP in foal diet is reconcilable with the maintenance of performance and welfare.

Randomised clinical trial on the effect of a single oral administration of l-tryptophan, at three dose rates, on reaction speed, plasma concentration and haemolysis in horses

Tryptophan (TRP) is marketed as a calmative for horses despite reservations about its efficacy. The aim of this study was to measure the effect of oral TRP administration on the reaction speed of horses. Sixty mature horses were used in a two stage randomised, blind, cross-over study, receiving a placebo and an oral dose of TRP (30, 60 or 120 mg/kg body weight), before undergoing a reaction speed test. Blood samples were taken up to 96 h after TRP administration, to identify signs of acute haemolytic anaemia. Plasma TRP concentrations were increased (P <0.001) by the administration of TRP paste. However, TRP had no effect on the reaction speed of horses when startled. There was no evidence of alterations in clinical pathology parameters in 432 blood samples. While the safety of these doses of TRP can be confirmed, there was no evidence to suggest that a single dose of TRP is an effective calmative for horses.

A pilot study to determine if a dietary mineral supplement can affect reactivity to stimuli by horses in training

Trainers have reported horses to be calmer and easier to train after receiving a calcium- and magnesium-rich mineral supplement derived from a calcified algae source. The purpose of this study was to test whether horses receiving this supplement were calmer than horses receiving a placebo. Fourteen 2-year-old Arabians in training were subjected to a ‘moving object reactivity test’ (MORT) and ‘handling reactivity test’ (HRT). The MORT involves quickly raising a bag suspended from the ceiling and scoring horses' reactions. The HRT involves placing horses into breeding stocks and scoring the horses’ nervousness. Horses were equipped with heart rate (HR) monitors and were scored by four observers blinded to treatment. Reactivity scores and HR were used to randomly striate the horses into two groups: a treated group (MIN) receiving 100 g of Aquacid/horse/day and a control group (CO) receiving a placebo. After supplementation for 60 days, horses were retested. Using PROC Mixed, changes from day 0 were examined. In the MORT, CO had an increase of 29 bpm (P=0.001), while MIN only showed a trend to increase (12 bpm; P=0.1). There was no difference between treatments (P=0.12). Reactivity scores during the MORT were not different between treatments (P=0.14) with CO horses increasing by 0.58 (1 to 5 scale) and MIN horses by 0.31. In the HRT, the peak HR of CO increased from day 0 by 17 bpm (P=0.009), but only by 11 bpm in the MIN (P=0.08). Reactivity scores for MIN horses improved by 0.45 (scale from 1 to 4) while the CO worsened by 0.04. Neither HRT measurement was significant (P=0.41 and P=0.33, respectively). Limited treatment differences suggest greater subject numbers were needed due to variability in behavioural responses despite some outcomes favouring MIN. Though inconclusive, results suggest anecdotal claims of calming effects may warrant further investigation.

Role of diet and feeding in normal and stereotypic behaviors in horses

This article reviews the effects of diet on equine feeding behavior and feeding patterns, before considering the evidence that diet affects reactivity in horses. A growing body of work suggests that fat- and fiber-based diets may result in calmer patterns of behavior, and possible mechanisms that may underpin these effects are discussed. In contrast, there is little evidence that herbal- or tryptophan-containing supplements influence equine behavior in any measurable way. The role of diet in the development of abnormal oral behaviors, particularly the oral stereotypy crib-biting, is also reviewed, and suggestions for future work are presented.