Agricultural and Food Science, Vol. 17 (2008): 338-350 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 17 (2008): 338–350. 338 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 17 (2008): 338–350. 339 Although the thermoregulatory mechanisms of horses have been studied to some extent (Morgan et al. 1997, Morgan 1998, Morgan et al. 2002), the nutrition of horses in a cold environment has received little study. In particular the demand for © Agricultural and Food Science Manuscript received February 2008 Energy intake and growth of weanling horses in a cold loose housing system Elena Autio1*, Ulla Sihto1, Jaakko Mononen2 and Minna-Liisa Heiskanen1 1 Equine Information Centre, PO Box 1627, FI-70211 Kuopio, Finland 2 University of Kuopio, Department of Biosciences, PO Box 1627, FI-70211 Kuopio, Finland *e-mail: elena.autio@hevostietokeskus.fi The demand for information relating to the nutrition of horses in a cold environment is increasing with the popularity of loose housing of horses. This study examined the energy intake and growth of 10 weanling horses from November to March (22 weeks) in a loose housing system (paddock and insulated sleeping hall with deep-litter bed). The horses were measured weekly for body condition and body weight, and the feed- ing was adjusted according to a horse’s body condition. Metabolizable energy (ME) intake was compared to Finnish (MTT 2006) and Swedish (SLU 2004) nutrient requirements for 6–12-month-old horses. ME intake (75.5 ± 11.8 MJ d-1, mean ± SD) was on average 24.6% above the requirements. The intake varied in a non-linear fashion in the course of the winter: y = 0.086x2 – 0.902x + 71.5, where x is weeks from November to March (p<0.001, R2=0.63). Low ambient temperature increased ME intake by about 1.8% in November (p<0.001), 0.5% in December (p<0.001) and 0.2% in January (p<0.05) per 1 °C decrease in ambient temperature when compared to nutrient requirements, but not in February and March. We conclude that the amount of extra energy needed decreases during the winter as the horses grow and acclimatize to the cold housing environment, i.e. as their body insulation increases. Horses gain weight at or above expected rates in cold conditions when the increased energy need is taken into account in the feeding. Key-words: horse, housing, temperature, energy intake, growth Introduction In the last 20 years, there has been a great increase in scientific knowledge of the nutrition of horses (Juliand and Martin-Rosset 2004, NRC 2007). A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 17 (2008): 338–350. 338 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 17 (2008): 338–350. 339 information relating to the nutrition and feeding management of growing horses in a cold environ- ment has grown with the popularity of cold loose housing in northern countries. Cold housing may have dramatic effects on horses’ energy needs. Average daily digestible en- ergy (DE) intakes were 33 % higher than mainte- nance energy requirement in growing horses housed outdoors in Canadian winter weather (Cymbaluk and Christison 1989a), and were increased by more than 50 % in horses in severely cold conditions (< –25 ºC) (Cymbaluk and Christison 1990). Wean- ling horses were reported to gain weight normally in the cold when fed readily digested diets ad libi- tum (Cymbaluk and Christison 1989a), but when horses were fed according to nutrient recommen- dations, cold-housed (–5 ºC) horses gained weight about 30% slower than warm-housed (10 ºC) hors- es (Cymbaluk 1990). Growing horses were found to require about 1–2% more DE per 1 °C decrease below the lower critical temperature (LCT) of 0 ºC to guarantee maintenance and growth in the cold. Mature horses required about 2.5% more ME for maintenance per 1 °C decrease below the LCT of –15 ºC (McBride et al. 1985). Nutrient requirements of horses have been de- termined in the US by the National Research Coun- cil (NRC 2007). In Europe, several different en- ergy systems and nutrient requirements have been performed and published for horses (INRA 1990, GfE 1994, CVB 2004, SLU 2004, MTT 2006). In Northern Europe, e.g. in Sweden and Finland, the nutrient requirements commonly used are SLU (2004) and MTT (2006) requirements, of which the SLU requirements include guidelines for feeding horses in a cold environment. Feeding of growing horses according to the requirements is important, since imbalanced nutrition may cause weight loss or weight gain, retard or increase growth rate, weaken the bones and increase the risk of developmental orthopaedic diseases (Thompson et al. 1988, Cym- baluk et al. 1989a, Cymbaluk et al. 1989b, Cym- baluk et al. 1990, Donabédian et al. 2006, NRC 2007). In practice, balancing nutrient intake is dif- ficult for horse breeders because they do not often know the nutrient concentrations of the feeds they use and do not take into account differences in nu- trient requirements for growing horses of various ages in the feeding strategies (Gibbs and Cohen 2001). Cold housing makes balancing even more difficult, since it is important to ensure adequate energy intake for maintenance and growth, and to avoid excess intake of nutrients. For example, in Central Finland, weanling horses’ body condition has been noticed to decrease quite often in cold loose housing conditions (E. Lappeteläinen, DVM, personal communication, August 16, 2007). In this preliminary study, the objective was to observe the level of energy intake and growth of weanling horses in a cold loose housing system, when the feeding was balanced to meet energy need in the cold by adjusting energy intake from silage and concentrates according to the horses’ body condition. Energy intake was compared to the Finnish (MTT 2006) and Swedish (SLU 2004) nutrient requirements. Material and methods Animals and housing The study was carried out between November 2002 and March 2003 (22 weeks) in a loose housing system at the Vocational Institute of Ylä-Savo in Kiuruvesi, Finland (latitude 63°29’ N, longitude 26°38’ E). Ten weanling horses participated in the study. Seven of them were Standardbred horses (SB) (three fillies and four colts) and three were Finnish coldblood horses (FC), i.e. Finnhorses, (two fillies and one colt). In the autumn before weaning, the horses were housed in box stables at night and kept in outdoor paddocks in the day. The horses were weaned and brought to the loose house in October. The age of the horses ranged from 118 to 224 d (average 160 ± 31 d, i.e. 5.3 months) at the beginning of the study in November. The horses were vaccinated and treated against internal parasites regularly. The loose house was an unheated, insulated facility consisting of two identical sleeping halls with a deep-litter bed, roofed entrance shelters and A G R I C U L T U R A L A N D F O O D S C I E N C E Autio, E. et al. Energy intake of loose housed weanling horses 340 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 17 (2008): 338–350. 341 paddocks. The facilities were the same as those de- scribed in the study by Autio and Heiskanen (2005). The ambient temperature (Ta) in the sleeping halls was a few degrees higher than the outdoor Ta. At night-time (16:00–07:00), the horses were kept in two groups (five horses in each group), which spent the evenings and nights on their own sides of the facility. In the daytime (07:00–16:00) both groups had free access to a large paddock (0.64 ha); in the evenings and nights, groups had access to smaller paddocks (0.08 ha). In the results and analyses, both groups were combined. The daily average Ta’s were obtained from the meteorological recording station at Vieremä (Finnish Meteorological Institute), lo- cated about 30 km from the study site. The average daily Ta of the study site correlated closely with the Ta recordings obtained from the meteorological recording station (mean difference 0.1 ºC). Feeds and feeding The diet was composed of hay and silage supple- mented by concentrates (Table 1). The horses were fed hay in one group during the daytime while silage and concentrates were individually fed during the daytime. Timothy hay was fed ad libitum outdoors in the paddocks. Hay was placed in off-the-ground feeding troughs fixed to the wall outside the sleeping halls. Intake was daily determined by measuring refusals every morning before the subsequent distri- bution. Silage was fed twice a day (0600 and 1600) and concentrates (oats, protein supplement (Rac- ing Protein, Suomen Rehu Oy, Helsinki, Finland), concentrate supplement (Mella leseleike, Suomen Rehu Oy, Helsinki, Finland), mineral and vitamin supplement (Steel Joint, Oy Steel Joint Ltd, Lahti, Finland)) three times a day (0600, 1030 and 1600) indoor in the sleeping halls. The horses were tied to the wall beside the feed buckets inside the halls during the feeding of concentrates and silage. Salt blocks and automatic waterers were located inside the halls. Refusals of all feeds were daily determined and deducted from consumption. The nutrient compositions of hay, silage and oats were analysed by the regional laboratory of Valio Oy (Lapinlahti, Finland) (Artturi –feed anal- ysis) by the standard NIR-method (Nousiainen et al. 2003) (Table 1). The nutrient compositions of protein and concentrate supplement were analysed by the laboratory of Suomen Rehu Oy (Turku/ Seinäjoki, Finland) by the standard methods (Min- istry of Agriculture and Forestry 2006) (dry matter , Hay Silage Oats Protein supplement Concentrate supplement1 Mineral and vitamin supplement DM, g kg-1 830 600 860 890 880 850 DCP, g kg-1 93 130 126 202 100 Ca, g kg-1 3.0 7.6 0.8 11.2 4.6 164.7 P, g kg-1 2.4 3.2 3.5 4.5 1.0 0.4 Lys, g kg-1 4.6 8.3 3.3 48.3 FFU, kg-1 0.77 0.84 1.05 1.12 1.25 ME, MJ kg-1 9.0 9.8 12.3 13.1 14.6 DM = dry matter, DCP = digestible crude protein, Lys = lysine, FFU = Finnish feed unit, ME = metabolizable energy. 1 Consisting of wheat bran, sugar beet and molasses. Table 1. Nutrient composition and feed values of feeds used in the study (DM basis). A G R I C U L T U R A L A N D F O O D S C I E N C E Autio, E. et al. Energy intake of loose housed weanling horses 340 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 17 (2008): 338–350. 341 DM): 71/393/ETY, crude protein (CP): 93/28/ETY, calcium (Ca) and phosphorus (P): plasma emission spectrometry, lysine (Lys): 98/64/EY). The labo- ratories of Valio Oy and Suomen Rehu Oy deter- mined feed values (Finnish feed unit (FFU) and digestible crude protein (DCP)) of the forages and concentrates by using MTT (2006) formulas and feed tables. The nutrient composition of mineral and vitamin supplement was analysed by Outo- kumpu Mining Services (Outokumpu Oyj, Espoo, Finland) by the standard x-ray fluorescence spec- troscopy (XRF) method. In October, the horses were brought to the loose house, where they were fed a diet sufficient to supply the nutrient requirements of 6–12-month- old horses expected to reach a mature BW of 500 kg (MTT 2006) until the beginning of the study (transitional period). The amount of silage and con- centrates fed was adjusted according to voluntary hay intake; the nutrients received from hay and the amount of other feeds fed was calculated so that the nutrient requirements of ME, DCP, Ca, P and Lys were met. After the beginning of the study in early November, the horses’ body condition score (BCS), which reflects a horse’s energy status, was assessed once a week on a subjective scale of one (poor: Animal extremely emaciated. Spinous processes, ribs, tailhead, tuber coxae and ischii projecting prominently. Bone structure of withers, shoulders and neck easily noticeable. No fatty tissue can be felt.) to nine (extremely fat: Obvious cease down back. Patchy fat appearing over ribs. Bulging fat around tailhead, along withers, behind shoulders and along neck. Fat along inner thighs may rub together. Flank filled with fat.) (Henneke et al. 1983). Moderate BCS (Back level. Ribs cannot be visually distinguished but can be easily felt. Fat around tailhead beginning to feel spongy. Withers appear rounded over spinous processes. Shoulders and neck blend smoothly into body), i.e. a score of 5, was regarded as an indicator of adequate energy intake and was the target score. Thus, according to each horse’s BCS, energy intake was adjusted individually by changing the amount of silage and/or concentrates fed to the horse. If a horse became leaner than the target score, the amount of silage and/or concentrates fed was increased, and if a horse became fatter than the target score, the amount was decreased. At the same time, the intakes of other nutrients (DCP, Ca, P, Lys) were adjusted so that at least minimum nutrient require- ments were met. During the experiment, the diets were revised on average twice a month according to BCS. Nu- trient intake was calculated using Hopti software (Equine Information Centre, Kuopio, Finland). For energy, intake was calculated in ME according to SLU (2004) system and in FFU according to MTT (2006) system. The energy need was determined on the basis of the performance of the growing horses during the experiment. ME intake was compared to the prediction of energy intake, which was based on the MTT (2006) and SLU (2004) requirements. Body weight and BCS measurements The horses were measured weekly for body weight (BW) and wither height (distance from the ground to the highest point of the withers). The wither height measurements were started on the first day of the study. The BW measurements were started in De- cember due to technical problems with the weighing scale. The growth of the SB horses was compared with the growth data presented in Sandgren et al. (1993) and the growth of the FC horses with the growth data presented in Ahtila and Saastamoinen (2005), and Saastamoinen and Koskinen (1993). Statistical analyses Statistical analyses were made using SPSS 14.0 for Windows. The average weekly energy intakes of the horses were compared with the energy requirements by the One-Sample t-Test. BCS was compared with the target score by the non-parametric Wilcoxon Signed-Rank test. Since the comparisons were made separately for repeated measurements, the p-values were multiplied by the Bonferroni correction. The effect of time (Model 1) and Ta (Model 2) on daily total (MJ) and mass-specific (MJ per 100 kg BW) A G R I C U L T U R A L A N D F O O D S C I E N C E Autio, E. et al. Energy intake of loose housed weanling horses 342 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 17 (2008): 338–350. 343 ME intake was tested using the Linear Mixed Model (LMM): Model 1: Yij = α + β × time + θ × time 2 + γi + εij where, Yij = daily ME intake for animal i at week j, i = animal 1…10, j = week 1…22 (time), α = intercept, β = regression coefficient for the linear trend, θ = regression coefficient for the polynomial (2nd order) trend, γi = random effect for i th animal, εij = residual for the i th animal at time j. Random effects γi and residuals εij were assumed normally distributed. Model 2: Yij = α + β × temp.j + θ × timej + γ × temp. × time + Δ i + εij where, Yij = daily ME intake for animal i at week j, i = animal 1…10, j = day 1…154, α = intercept, β = regression coefficient for temperature, θ = regression coefficient for time, γ = interaction of temperature and time, Δ i = random effect for i th animal, εij = residual for the ith animal at day j. The effect of Ta on daily ME intake was tested by the LMM, where Ta was tested as a continuous or categorical variable. The aim of the latter analy- sis was to see whether the LCT of –11 °C defined for cold-housed weanling horses in earlier stud- ies (Cymbaluk and Christison 1989a, Autio et al. 2007) could also be valid for the weanling horses in the present study. Therefore, in the mixed model, Ta’s were divided into two categories: warm (Ta > –11 °C) and cold (Ta < –11 °C). Results Feed intake The voluntary hay intake of the horses was on average 4.4 ± 1.2 kg DM d-1 (mean ± SD) (1.5 ± 0.4 kg DM per 100 kg BW); it increased during the study being 3.7 ± 1.1 kg DM d-1 in November, 4.0 ± 0.8 kg DM d-1 (1.5 ± 0.3 kg DM per 100 kg BW) in December, 4.3 ± 0.9 kg DM d-1 (1.5 ± 0.3 kg DM per 100 kg BW) in January, 4.3 ± 0.9 kg DM d-1 (1.4 ± 0.3 kg DM per 100 kg BW) in February and 5.6 ± 1.1 kg DM d-1 (1.8 ± 0.4 kg DM per 100 kg BW) in March. Silage was given on average 1.6 ± 0.4 kg DM d-1, oats 1.0 ± 0.2 kg DM d-1, protein supplement 0.5 ± 0.2 kg DM d-1, concentrate supplement 0.09 ± 0 kg DM d-1 and mineral and vitamin supplement 0.01 ± 0.01 kg DM d-1. The forage: concentrate ratio ranged from 72:28 to 86:14 (DM basis) and averaged 80:20 during the study. Total DM intake from forages and concentrates was on average 7.5 ± 1.3 kg d-1 (2.6 ± 0.5 kg DM per 100 kg BW). DM intake was about 6.6 ± 1.2 kg d-1 in November, 7.2 ± 0.8 kg d-1 (2.7 kg ± 0.4 kg DM per 100 kg BW) in December, 7.3 ± 0.9 kg d-1 (2.5 kg ± 0.4 kg DM per 100 kg BW) in Janu- ary, 7.3 ± 0.9 kg d-1 (2.4 kg ± 0.4 kg DM per 100 kg BW) in February and 9.0 ± 1.2 kg d-1 (2.8 kg ± 0.5 kg DM per 100 kg BW) in March. Energy intake ME intake was on average 75.5 ± 11.8 MJ d-1 (mean ± SD) (26.0 ± 4.5 MJ per 100 kg BW) during the study, which is about 30 % above the MTT (2006) requirements and SLU (2004) requirements for slow growth and about 15 % above the SLU (2004) requirements for rapid growth (Fig. 1). ME intake increased with time and differed from the MTT requirements and the SLU requirements for slow growth from week 2 onwards (p<0.001), and from the SLU requirements for rapid growth approxi- mately from week 8 onwards (p<0.05). Ta increased the total ME intake of the horses by about 0.5 % (0.3 MJ) per 1 °C increase in Ta during the whole study period (p<0.001, LMM), but the effect of Ta varied in the course of the winter (Fig. 2). In November total ME intake in- creased by 1.8 % (1.1 MJ) (p<0.001), in December by 0.5 % (0.3 MJ) (p<0.001) and in January by 0.2 % (0.1 MJ) (p<0.05) per 1 °C decrease in Ta. In February and March, ME intake increased by 0.7 % (0.4 MJ) and 1.3 % (0.8 MJ), respectively, per 1 °C increase in Ta (p<0.001). Mass-specific A G R I C U L T U R A L A N D F O O D S C I E N C E Autio, E. et al. Energy intake of loose housed weanling horses 342 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 17 (2008): 338–350. 343 y = 0.086x2 2 - 0.9023x + 71.5 R = 0.63 50 60 70 80 90 100 110 1 2 Nov Dec Jan Feb Mar 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 Week ME (MJ d -1) ME Intake MTT SLUs SLUr Polyn. (ME intake) Fig. 1. Mean weekly metab- olizable energy (ME) intake (MJ d-1) of the weanling horses compared with the nutrient re- quirements of MTT (2006) and SLU (2004) for slow growth (SLUs), and SLU (2004) for rapid growth (SLUr). Nov Dec Jan Feb Mar -30 -25 -20 -15 -10 -5 0 5 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 Week °C 0 0.2 0.4 0.6 0.8 1 1.2 ME (MJ ºC-1) ME Intake Ambient temperature Fig. 2. Mean weekly outdoor temperature and the increase in ME intake per 1 °C degree decrease in ambient tempera- ture (Nov, Dec, Jan) and per 1 °C degree increase in ambient temperature (Feb, Mar) in dif- ferent months. Nov Dec Jan Feb Mar 3 4 5 6 7 8 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 Week BCS (1-9) BCS Henneke et al. 1983 SB FC Fig. 3. Mean weekly body condi- tion score (BCS) of the weanling horses (SB = Standardbreds, FC = Finnish coldblood horses). A G R I C U L T U R A L A N D F O O D S C I E N C E Autio, E. et al. Energy intake of loose housed weanling horses 344 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 17 (2008): 338–350. 345 ME intake increased in December by 0.29 % (0.06 MJ per 100 kg BW) (p<0.01) and in January by 0.34 % (0.07 MJ per 100 kg BW) (p<0.01) per 1 °C decrease in Ta. In February, mass-specific ME intake increased by 0.39 % (0.08 MJ per 100 kg BW) (p<0.01) per 1 °C increase in Ta. Ta affected ME intake when Ta was a categori- cal variable in the statistical models (LMM). In the whole study period, total ME intake was on aver- age 0.5 % (0.3 MJ) higher at Ta above –11 °C than at Ta below –11 °C (p<0.05), but the magnitude of the effect varied between the months. In No- vember, ME intake was on average 16.1 % (10.8 MJ), and in December, 6.8 % (4.7 MJ) (p<0.001) higher at Ta below –11 °C than at Ta above –11 °C. In February, ME intake was on average 4.7 % (3.3 MJ) higher at Ta above –11 °C than at Ta below –11 °C (p<0.01). Mass-specific ME intake was on average 6.3 % (1.3 MJ) and 4.4 % (0.9 MJ) higher at Ta below –11 °C than at Ta above –11 °C in December and January, respectively. DCP, Ca and P intakes followed ME intake during the study period, and were, therefore high- est in late winter. The average DCP intake was 848 ± 128 g d-1 (293 ± 53 g per 100 kg BW) dur- ing the study. DCP to ME ratio was 11g DCP per MJ ME. The average Lys intake was 58.8 ± 9.1 g d-1 (19.6 ± 4.5 g per 100 kg BW), and Lys to ME ratio 0.8 ± 0.1 g per MJ ME. The average Ca and P intakes were 43.1 ± 7.8 g d-1 (14.8 ± 2.4 g per 100 kg BW) and 24.9 ± 5.1 g d-1 (8.4 ± 1.3 g per 100 kg BW), respectively, during the study. The Ca:P ratio ranged from 1.6 to 1.8. Body weight and BCS Individual growth curves of the weanling horses are presented in Fig. 4. Median BW of the horses was 262 kg at 6 months of age, 290 kg at 7 months of age, 296 kg at 8 months of age, 319 kg at 9 months of age and 340 kg at 10 months of age. Median av- erage daily gain (ADG) decreased during the study being 0.82 kg d-1 at 6 months of age, 0.71 kg d-1 at 7 months of age, 0.64 kg d-1 at 8 months of age and 0.38 kg d-1 at 9 months of age. Median ADG of the horses during the whole study period was 0.61 kg d-1. Median BCS was 5.5 from November to January and 6.0 from February to March, and 5.5 during the whole study period. The BCS differed from the target score of 5 in weeks 1,5,10 and 11, and from week 13 onwards (p<0.05) (Fig. 3). Fig. 4. Individual growth curves (body weight BW, kg) of the weanling Standardbred (1–7) (a) and Finnish coldblood horses (8–10) (b) compared with the reference curves (Ref. 1 = Sandgren et al. 1993: max., Ref. 2 = Sandgren et al. 1993: min., Ref. 3 = Saastamoinen and Koskinen 1993: max, Ref. 4 = Saastamoinen and Koskinen 1993: min, Ref. 5: Ahtila and Saastamoinen 2005). 150 200 250 300 350 400 450 148 168 188 211 232 253 273 294 315 336 357 377 Age (d) BW (kg) 1 2 3 4 5 6 7 Ref. 1 Ref. 2 a) 150 200 250 300 350 400 450 175 190 205 215 229 242 257 270 286 299 313 Age (d) BW (kg) 8 9 10 Ref. 3 Ref. 4 Ref. 5 b) A G R I C U L T U R A L A N D F O O D S C I E N C E Autio, E. et al. Energy intake of loose housed weanling horses 344 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 17 (2008): 338–350. 345 Discussion The present preliminary study examined energy intake and growth of weanling horses in a cold loose housing system. In the examination, man- agement practices followed general loose housing practices, where horses are group-housed and fed forages ad libitum. In addition, the energy intake of the horses was adjusted according to common practice in field conditions, i.e. on the basis of predicted energy requirements of growing horses determined by SLU (2004) and MTT (2006), and on the basis of BCS. Therefore, energy intake was not adjusted according to actual BW and predicted BW of the following study period, as was done, for example, in the study of Donabédian et al. (2006). The French nutritional models used in the study of Donabédian et al. (2006) have been established by INRA (1990). In these French models, the total energy requirement of a growing horse is determined on the basis of actual metabolic BW, ADG and com- position of weight gain (Martin-Rosset et al. 1994). In the present study, MTT (2006) and SLU (2004) requirements were used because these requirements are generally used in the Nordic countries. In these requirements, the predicted energy requirements of a growing horse is the sum of the energy needed for maintenance (based on average, estimated BW of a growing horse expected to reach a mature BW of 500 kg) and the energy needed for gain (based on age and average, estimated ADG of a growing horse expected to reach a mature BW of 500 kg) (SLU 2004). Because energy adjustments were based on predicted energy requirements and actual BCS, and the composition of diet was not constant during the study, it is possible that this adjustment method may have slightly overestimated the energy requirements of the weanling horses, and thus also the effect of Ta on energy need. It should also be noted that the voluntary activity of the horses in a loose housing system may affect their energy need. However, in the present study, the weanling horses were known to be quite inactive during the winter (see Autio and Heiskanen 2005). The energy intake (75.5 ± 11.8 MJ d-1, 26.0 ± 4.5 MJ per 100 kg BW) of the weanling horses in the present study was on average 24.6 % above the MTT (2006) and SLU (2004) predicted energy re- quirements for weanling horses expected to reach a mature BW of 500 kg, with the horses being fed good quality hay ad libitum and the amount of si- lage and concentrates being adjusted according to the horse’s BCS. Also DCP, Ca and P intakes were mostly above the requirements because their in- takes followed energy intake. Of all the measured nutrient intakes, Ca and P intakes and Ca:P ratio re- mained most within the limits of the requirements, perhaps due to the adjustment of the amount of mineral supplement fed with the aid of the equine feeding program. Ca intake (43.1 ± 7.8 g d-1, 14.8 ± 2.4 g per 100 kg BW) was on average 30 % above the Ca requirements (MTT 2006: 33 g d-1, SLU 2004: 29–37 g d-1), and P intake (24.9 ± 5.1 g d-1, 8.4 ± 1.3 g per 100 kg BW) was on average 23 % above the P requirements (MTT 2006: 22 g d-1, SLU 2004: 17–21 g d-1) for horses expected to reach a mature BW of 500 kg. DCP intake (848 ± 128 g d-1, 293 ± 53 g per 100 kg BW) was on average 60 % above the DCP requirements (MTT 2006: 500 g d-1, SLU 2004: 493–610 g d-1). Also the average DCP to ME ratio (11g DCP per MJ ME) and Lys to ME ratio (0.8 ± 0.1 g per MJ ME) were slightly higher than the requirements (SLU 2004: 8.5–10.0 g DCP per MJ ME, 0.5–0.6 g Lys per MJ ME). These facts indicate that the protein content of the feeds used in the present study was too high. When considering the results, it should be noted that, since the horses were group housed, daily hay intake values were calculated from group hay intake and were uniform for all of the horses. Variation in the total nutrient intakes (consisting of nutrient intakes from hay, silage and concen- trates) is therefore slightly underestimated in the results . Both the total and mass-specific ME intakes of the weanling horses were increased by low Ta in early winter but not in late winter, which may reflect the progressive acclimatization of the horses to their cold housing environment. Therefore, the cold resistance of the horses apparently improved during the winter. Since the energy intake in rela- tion to Ta decreased, this signifies that improved cold resistance resulted from increased body insu- A G R I C U L T U R A L A N D F O O D S C I E N C E Autio, E. et al. Energy intake of loose housed weanling horses 346 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 17 (2008): 338–350. 347 lation. However, it is unclear whether the improved insulation was caused by increasing coat insulation or by the decreasing ratio between heat dissipat- ing surface area and heat productive/retaining body mass of the growing horses, or by both of these. The results are in accordance with an earlier study, where Ta affected the DE intake of weanling horses in early winter but not in late winter (Cym- baluk and Christison 1989a). In the present study, total ME intake increased by 1.8 % in November, 0.5 % in December and 0.2 % in January per 1 °C decrease in Ta. During these months, the lowest daily Ta was generally near or lower than the LCT of –11 °C determined for cold-housed weanling horses (Cymbaluk and Christison 1989a, Autio et al. 2007), and the amount of concentrates fed had to be increased to maintain the moderate BCS of the horses. In the present study, the two-category analysis showed that the LCT also was approxi- mately –11 °C at least in early winter, since ME intakes were higher at Ta below –11 °C than at Ta’s above –11 °C. The results indicate that the winter period has an effect on the energy needs of the weanling horses in a cold housing environ- ment and that the climatic energy need is high- est in early winter. Accordingly, a drop in Ta to –20 °C increased the energy need of the horses by approximately 18 % in November, 5 % in Decem- ber and 2 % in January. In February and March, daily Ta fluctuations had little effect on energy need because Ta was mostly above the LCT. In addition, the increasing energy need of the weanling horses in late winter, which was apparently related to in- creasing BW (maintenance energy need increases) and changing composition of weight gain (the pro- tein content of gain decreases and fat content in- creases as age increases) (Frape 1998, NRC 2007), probably outweighed the effect of Ta. The increase (i.e. 0.2–1.8 % more energy per 1 °C decrease in Ta) in energy need in Ta below the LCT in the present study is in accordance with earlier studies (Cymbaluk 1990, Cymbaluk et al. 1989a, but see also Cymbaluk and Christi- son 1989a). Increased energy need in a cold hous- ing environment is taken into account in the SLU (2004) energy requirements. According to the SLU, ad libitum fed growing horses need 1.4 % more maintenance energy in a cold environment for each 1 °C decrease in Ta below –11 °C. The present study confirms that SLU’s advice is valid in early winter, but may lead to excess weight gain if followed rigidly throughout the winter. In contrast to the early winter, the ME intake of the horses in late winter increased as Ta increased, which resulted from increased voluntary hay intake. DM intake from forages was about 2 % of BW per day during the study except in March, when DM intake increased to 2.4 % of BW per day. There- fore, average daily DM and ME intakes increased with time (age). This is in agreement with earlier studies in growing horses, in which daily DM and DE intakes increased with BW and were accord- ingly related to age (Cymbaluk and Christison 1989a, Cymbaluk et al. 1989a). Increasing body size and changes in the composition of weight gain apparently explain the increased energy need of the weanling horses, and thus increased energy intake in late winter (NRC 2007). The horses were also probably adapted to large feed intake during the winter. Nevertheless, the increased DM intake in late winter at warmer Ta caused the positive rela- tion of ME intake to Ta, in opposition to the early winter, when the relation was negative. In February (week 15), the horses reached on average 9 months of age, after which the rate of weight gain declines (Frape 1998). At the same time, Ta was rising. Increased hay intake combined with the slower growth rate and higher Ta meant that the BCS of the horses became greater than the target score, although the amounts of concentrates fed were reduced. The horses probably compen- sated for dietary energy dilution by increasing DM intake by eating more hay, as has been previously noted in forage-fed growing horses (Cymbaluk and Christison 1989b). This is supported by the fact that the average DM intake of the weanling horses (2.4 and 2.8 kg DM per 100 kg BW in February and March, respectively) was approximately the same as in ad libitum fed weanling horses in pre- vious studies (2.5 to 3.1 kg DM per 100 kg BW) (Cymbaluk and Christison 1989a, Cymbaluk et al. 1989a). This indicates, that the reduction in the concentrates fed was not sufficient to prevent a rise in BCS and excess nutrient intake, and that, A G R I C U L T U R A L A N D F O O D S C I E N C E Autio, E. et al. Energy intake of loose housed weanling horses 346 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 17 (2008): 338–350. 347 therefore, hay intake should also have been regu- lated. Feeding forages ad libitum, so that growing horses are allowed to eat to their energy needs, is a common practice in Finnish loose housing sys- tems. Since ad libitum-fed growing horses tend to generally have a higher nutrient intake than their nutritional needs (Cymbaluk and Christison 1989a, Cymbaluk and Christison 1989b, Cymbaluk et al. 1989a), this predisposes horses to excess nutrient intakes and imbalanced nutrition (Cymbaluk et al. 1989a, Cymbaluk et al. 1989b, Cymbaluk et al. 1990). The excess protein intake may also lead to depressed growth since the catabolism of excess amino acids consumes energy (Yoakam et al. 1978, Ahtila and Saastamoinen 2005). Therefore, ad li- bitum forage feeding practices in loose housing systems should be reconsidered, especially in late winter when the horses are cold-acclimatized. In early winter when the horses are not cold-acclima- tized, ad libitum forage feeding is more reasonable because forages are heat productive during diges- tion (see Vermorel et al. 1997). In an earlier study, weight gain in cold-housed SB horses was noted to be slower than in warm- housed horses when the increased energy need in the cold was not taken into account in the feeding (Cymbaluk 1990). When fed ad libitum, horses gained weight normally in the cold in the study of Cymbaluk and Christison (1989a). In the present study, the average BW of the SB horses was about the same as that presented for SB horses with same age and withers height (131 cm and 135 cm at 5 and 8 months of age, respectively) in Sandgren et al. (1993). However, the FC horses weighed about 19 % more than FC horses with the same withers height (129 cm and 140 cm at 6 and 10 months of age, respectively) in the studies of Saastamoinen and Koskinen (1993) and Ahtila and Saastamoin- en (2005), because the FC horses in the present study were in a moderately fleshy or fleshy body condition. The ADG of the SB horses during the study (0.57 kg d-1) was similar or slightly lower than in SB horses of similar age in earlier studies (Sandgren et al. 1993: 0.51–0.94 kg d-1, Andrew et al. 2006: 0.72 kg d-1, Forsmark 2006: 0.6/0.9 kg d-1), whereas the ADG of the FC horses (0.62 kg d-1) was similar or slightly higher than in earlier studies in FC horses (Saastamoinen 1993: 0.56 kg d-1, Saastamoinen and Koskinen 1993: 0.54/0.67 kg d-1, Ahtila and Saastamoinen 2005: 0.51 kg d-1). The weanling horses in the present study seemed to gain weight at or above expected rates in a cold housing environment when the level of energy in- take was sufficient. However, it should be noted that there might be large individual variation in weight gain and that the number of horses in the present study was small. Therefore, the growth of different horse breeds in a cold housing environ- ment should be studied more extensively in future studies. Adjusting the energy intake of growing horses in a cold group housing system seems to be a far from simple task even under well-controlled exper- imental conditions due to changing circumstances. The difficulties in regulating the energy intake and BCS of horses result from the changes in both the environment (fluctuating Ta) and the animals (changes in age, level of cold acclimatization and capacity for forage intake), and from the ad libitum forage feeding. The energy intake of growing hors- es should be adjusted according to BW, ADG, BCS, the level of acclimatization and changing weather conditions to guarantee maintenance and normal growth in cold conditions. Although regular body condition scoring is a practical method to evaluate the adequacy of a horse’s energy intake in field conditions, the method does not take into account the effect of BW and composition of weight gain on energy need. The French (INRA 1990, Martin- Rosset et al. 1994) horse feeding system, which is based on net energy, provides models to predict energy and protein requirements and allowances of horses using BW, ADG and BCS as variables. The French system provides thus accurate models for matching the energy requirements of growing horses. However, since systems based on ME are usually used in the Nordic countries (SLU 2004) and the NE based system lacks information about the NE values of all feeds of all classes of horses and is also more complex as it accounts for more heat losses (NRC 2007), the French model (INRA 1990, Martin-Rosset et al. 1994) is not necessarily very applicable in the Nordic countries. A G R I C U L T U R A L A N D F O O D S C I E N C E Autio, E. et al. Energy intake of loose housed weanling horses 348 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 17 (2008): 338–350. 349 This study revealed that the complete regula- tion of nutrient intake and BCS requires that both concentrate and forage intakes are individually controlled in loose-housed horses. This is impor- tant especially in late winter, when the weather gets warmer and the voluntary DM intake of growing horses increases. These facts pose high demands on the planning and implementation of feeding of group-housed growing horses in a cold environ- ment to avoid overweight which is harmful for the musculoskeletal development. Conclusions The cold housing environment increased the energy needs of the weanling horses in early winter but not in late winter, which signifies that the horses accli- matized to the cold housing environment. 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Energy intake of loose housed weanling horses 350 SELOSTUS Vieroitettujen varsojen energiankulutus ja kasvu kylmäpihatossa Elena Autio, Ulla Sihto, Jaakko Mononen ja Minna-Liisa Heiskanen Hevostietokeskus ja Kuopion yliopisto Hevosten pihattokasvatuksen yleistyessä tarvitaan tie- toa hevosten energiantarpeesta kylmissä olosuhteissa. Tutkimuksessa selvitettiin 10 vieroitetun varsan ener- giankulutusta ja kasvua marras- ja maaliskuun välisenä aikana (22 viikkoa) pihatossa (jaloittelutarha ja lämpö- eristetty makuuhalli, jossa kestokuivikepatja). Varsojen lihavuusaste ja paino mitattiin kerran viikossa, ja niiden ruokintaa suhteutettiin lihavuuskunnon mukaan. Muuntokelpoisen energian (ME) kulutusta verrattiin suomalaisiin (MTT 2006) ja ruotsalaisiin (SLU 2004) 6–12 kuukauden ikäisten varsojen ruokintasuosituk- siin. ME:n kulutus (75.5 ± 11.8 MJ d-1, ka ± SD) oli keskimäärin 24.6 % ruokintasuosituksia suurempaa. Kulutus vaihteli talven aikana epälineaarisesti: y = 0.086x2 –0.902x + 71.5, missä x on viikot marraskuusta maaliskuuhun (p<0.001, R2=0.63). Alhainen ympä- ristön lämpötila lisäsi ME:n kulutusta marraskuussa 1.8 % (p<0.001), joulukuussa 0.5 % (p<0.001) ja tammikuussa 0.2 % (p<0.05) yhden asteen lämpötilan laskua kohti ruokintasuosituksiin verrattuna, mutta ei vaikuttanut kulutukseen helmi- ja maaliskuussa. Tu- lokset osoittavat, että lisäenergiantarve vähenee talven aikana varsojen kasvaessa ja sopeutuessa kylmään elinympäristöön, eli kehon eristyksen lisääntyessä. Varsat kasvavat normaalisti kylmissä olosuhteissa, kun lisäenergiantarve huomioidaan ruokinnassa. Energy intake and growth of weanling horses in a cold loose housing system Introduction Material and methods Animals and housing Feeds and feeding Body weight and BCS measurements Statistical analyses Results Feed intake Energy intake Body weight and BCS Discussion Conclusions References SELOSTUS