PG . 39
Genetics accounts for around 25 % of the risk . Joint and cartilage development is an intricate , complex process and interruption of any of the myriad of steps can result in defective cartilage . Nutritionally , above average gains in height and weight are associated with the occurrence of lesions . So , the question of what is an appropriate growth rate to minimise developmental problems remains unanswered . Whilst it is relatively simple to measure weight if scales are available , it is important to take weights at the same time of day so errors related to gut fill and time of feeding do not occur . However , skeletal growth - measured as girth , cannon bone circumference and height at the withers - is equally important , easier to measure and yields practical , useful information .
As with body weight , there is a pattern in height increases . The most rapid growth periods for bone growth are :
• from 3 months before until one month after birth
• between 6-12 months of age
• just after puberty
These periods of intense growth are similar under different climatic conditions and the same pattern occurs regardless of breed .
To support the first period of rapid bone growth requires that the mare be correctly fed during the last 3 months of pregnancy . Quality hays and pasture are good feeds for broodmares but the amino acid and mineral composition . Mares and foals are sensitive to the amino acid content of their feed , which is reflected in the amino acid profile of the blood and eventually expressed in rates of growth . The effects of amino acid imbalance are most pronounced during the last 90 days of pregnancy and the first 90 days of birth - when bone growth spurts occur .
The essential amino acid lysine – used in the building of bone and muscle is high in lucerne hay , but other essential amino acids , such as methionine , are low – and even lower in grass / cereal hays . Hay can be supplemented with linseed , soybean or other oil-meals to provide adequate protein . If hay has been in storage longer than 3 months , there will be deterioration in the fat-soluble vitamins A , D and E . Most hays and pasture are deficient in copper , zinc , magnesium iodine and selenium . Individual vitamin , mineral and protein supplements can be added to the diet , but is often easier and cheaper to provide a wellformulated complete to balance the deficiencies inherent in all hays and pastures .
The reason correctly fed yearlings achieve greater gains in whither height , reach mature height earlier and deposit less fat is because their essential amino acid requirements are met . Two horses may be gaining similar amounts of weight , but one may be building bone and lean muscle mass and another depositing fat . Although body weight
AQHA NOVEMBER / DECEMBER ISSUE 2022