Charlotte Westwood, Veterinary Nutritionist, PGG Wrightson Seeds
Autumn pasture doesn’t always translate into optimal animal performance, and animals may gain little or no liveweight for many weeks. This is called autumn ill thrift, and several remedial strategies may be necessary to compensate for it. Charlotte Westwood, Veterinary Nutritionist for PGG Wrightson Seeds offers the following advice.
Compared with summer pasture, autumn pasture is highly digestible, containing low levels of physically effective neutral detergent fibre (NDF) and high levels of crude protein (CP). High digestibility, low NDF and too much rapidly degradable CP contribute to a dark coloured scour often seen as part of autumn ill thrift challenges.
Rumen microbes need to adjust quickly from digesting rough summer pasture to lush, leafy autumn pasture. This transition can take days or weeks for the rumen microbes to adjust from summer to autumn pasture. The liver must also ‘ramp up’ capacity to detoxify ammonia (from CP) to urea. This process is energetically demanding and may contribute to autumn ill thrift.
Given time, the rumen and liver will successfully adapt to leafy autumn pasture. Offering supplementary feed (baleage, hay and/or silage) for 7-14 days through early autumn offers two key benefits:
- Summer pasture rots and decays leaving less total dry matter available until new growth rebuilds pasture mass. Supplementary feeds offset the decrease in pasture dry matter (DM) on offer maintaining appropriately high feeding levels for stock.
- Supplements help the rumen and liver adapt to lush autumn pasture. Silage, baleage and hay contain more effective NDF than green pasture, stabilising rumen function. Supplementary feeds such as maize silage and cereal grains contain less protein than autumn pasture, diluting the intake of pasture protein and reducing the quantity of ammonia delivered to the liver for detoxification to urea.
Reducing stocking rate and/or continuing to offer supplementary feed can help offset the temporary ‘dip’ in pasture availability.
Demand for selenium and vitamin E increases due to high levels of polyunsaturated fatty acids (PUFA) in lush leafy green pasture. This is particularly important in areas that have seen little green pasture for 2-3 months or more. This can contribute to reduced vitamin E reserves in stock over summer. Added selenium supplementation may be required. Talk with your veterinarian about liver or blood testing.
Increased moisture in autumn can cause an increase of parasitic L3 larvae, whereby young stock become laden with internal parasites resulting in clinical or sub-clinical disease. Summer pasture rot supports the growth of fungi including Pithomyces Chartarum responsible for facial eczema. While counts remain high it is important to monitor with spore counts and continue with zinc treatment. Other mycotoxins are also produced that are partly responsible for signs of autumn ill thrift. Mycotoxin binder products mixed with supplementary feeds may help counteract non-specific mycotoxin-associated challenges but won’t help with facial eczema prevention.
Ryegrasses infected with the ‘wildtype’ or ‘standard’ endophyte produce alkaloids causing ryegrass staggers, heat stress, scouring and ill thrift. Modern ryegrass cultivars that contain novel endophytes such as AR37, reduce the risk of endophyte associated challenges during autumn.
Autumn pasture and the impact of warm and potentially wet weather supports a range of animal health challenges that can contribute towards autumn ill thrift.