Growth rates and feeding management of Irish thoroughbred foals

Limited studies have focused on the growth of Irish Thoroughbred (TB) foals. The objectives of this study were to track the growth of foals and to monitor growth rates based on nutritional intakes. The growth of 72 foals, on eight Irish stud farms were monitored monthly from birth to six months of age. Body weight (BW), average daily gain (ADG), wither height (WH), body length (BL), heart girth (HG) and cannon bone circumference (CC) were measured monthly. Representative samples of grass, conserved forages and feed offered to foals were taken and grazing grass heights were measured at each visit. Managers completed daily feed budget calendars for all foals. DM, OM, CP, NDF, ADF, ADL and GE contents of all samples were analysed. Data was checked for normality and statistically analysed using appropriate tests in SPSS. Mean foal birth weight was 53.9 ±1.57 kg. From one to six months of age, BW increased by 150% from 101.1 ±1.99 kg to 253.2 ±2.82 kg (P<0.001), ADG decreased by 54% from 1.52 ±0.059 kg/day to 0.69 ±0.044 kg/day at 6 months of age (P<0.001). The ADG of colts decreased linearly, however, the ADG of fillies was more variable. WH increased by 19.1% over the study period (112.8 ±0.59 cm at 1 month to 134.3 ±0.45 cm at 6 months; P<0.001), HG increased by 34.8% (101.0 ±1.52 cm at 1 month to 136.1 ±0.70 cm at 6 months; P<0.001), BL increased by 11.3% (94.2 ±0.71 cm at 1 month to 131.5 ±0.57 cm at 6 months; P<0.001). Gender did not have a significant effect on the growth of foals. CC increased by 24.8% over the study period (12.5 ± 0.10 cm at 1 month to 15.6 ± 0.09 cm at 6 months of age; P<0.001), gender however, had a significant effect on the CC of all foals (P<0.05). Post foaling, the median hours spent grazing was four hours/day. This increased to 17 hours at two months of age and from four to six months of age, all study foals were grazing for 24 hours/day. This coincided with a 306.3% increase in BW. Mean grass heights were 14.6 ±0.36 cm; ranging from 6.4 cm to 24.6 cm across the study period. Highest grazing heights of 17.4 ±3.52 cm were recorded in June. Mean DM content of grass offered to foals was 23.7 ±0.59%; highest grass DM of 33.2 ±0.80% was recorded in June. The NDF and ADF content of the grazing sward ranged from 454.1 ±1.30% and 19.4 ±0.47%, respectively, in April, to 56.2 ±0.78% and 19.2 ±0.46%, respectively, in October. CP in the grazing sward was highest (19.0 ±0.72%) during the early and latter ends of the grazing period, decreasing to 13.5 ±0.76% in June, while mean GE of the grazing sward was 17.9 ±0.04 MJ/kg. Growth rates showed variation which could be a reflection of the changing nutritional intake over the grazing season. Foal BW and ADG were significantly correlated with quantities of CP, GE and NDF offered to foals on a daily basis from the grazing sward. Regression analysis was used to model foal BW based on age. The best fit models were quadratic (R2 = 0.896, P <0.001), cubic (R2 = 0.896, P <0.001), power (R2 = 0.892, P <0.001) and linear equations (R2 = 0.886, P <0.001). Resulting BW prediction equations were formulated. In conclusion, during the first six months of life, Irish TB foals grow in proportion, overall the growth of colts was similar to those of fillies. The growth of foals was significantly correlated to grass quality and quantity. Foal BW was accurately predicted by age.