Falling pasture quality over the coming months can dramatically affect the performance of milking animals and young stock, but countermeasures are available.
Spring calving cows should be “in their groove” by November – they will have peaked in production and now be gradually easing back while regaining condition as best they can. Carefully reared calves should be benefiting from increased rumen capacity to use as much of the leafy pasture on offer as they can. Unfortunately nature can throw some spanners in the works, with grasses slipping into reproductive mode and the sun slipping behind clouds that often bring shade rather than rain.
If pasture fibre levels rise and sugar levels drop, cattle on a predominantly pasture-based diet are hit by a double whammy – higher fibre pasture takes longer to ferment so dry matter intake falls; and because digestibility falls, the metabolisable energy per kilogram also drops. If neutral detergent fibre (NDF) levels rise by 10 percentage points (say from 40 percent to 50 percent), ME falls by about 1MJ.
A drop in ME from 12 to 11MJ/kg DM doesn’t sound very dramatic but if at the same time DMI drops suddenly, milk production is dropping and cows that were holding their own are dropping condition. Young or thin cows are going to be harder to get in-calf and recently weaned calves are going to struggle to meet growth targets. Cattle can be full and appear content but are not fully fed to meet demands for production, growth and reproduction.
Maintaining high quality pasture through attentive pasture management to stop post-grazing residuals rising through late spring may help to keep leafy pasture available to stock but increasing sunlight hours is beyond the ability of even the most progressive farm manager.
Continuing supplementary feeding or even increasing levels is one way to help counter falling pasture quality. Continuing to feed 1kg pellets per day to calves can make a significant difference to those with a total dry matter intake of 3-4kg/day. Although there will be some substitution when “hard feed” (grains, compound feed or straights) rates are increased and pasture management will have to ensure the pasture not eaten is well used, energy intake by cows should still increase and the risk of a negative energy balance reduced.
The NDF in hard feeds is less rumen filling than the NDF in forages – imagine forage being like the volume of a hotel compared with hard feed being like a demolished hotel – the cells of fresh and conserved forages fill the rumen much more than fibre in hard feeds. Fonterra’s new Fat Evaluation Index is undoubtedly focusing some farmers’ interest in reducing palm kernel usage, with resurgence in demand for compound feeds and blends across New Zealand.
Rumen-protected fats offer one way to supplement energy intake without compromising dry matter intake. Ionophores can help improve feed efficiency while helping to reduce the risk of bloat but interest is also growing in the use of yeast-based additives. Various sorts are available that can help fibre digestion by supporting fibre-digesting rumen microflora.
Options are available when nature works against progressive farmers.
For more information, contact your local Nutrition Specialist.
Article by Dr. Rob Derrick, Nutritionist, Farmlands.