Increasing starch-based supplements (e.g. maize grain or barley) in the diet can increase the concentrations of circulating hormones such as insulin and insulin-like growth factor 1 (IGF-I). In theory, these elevated levels of insulin and IGF-I can lead to earlier cycling, improving reproductive performance in pasturebased systems.
The actual effect
However, the effect of increasing IGF-I on cycling and other reproductive measures is inconsistent. New Zealand research indicates that IGF-I levels explain only three percent of the variation in cycling (time to first oestrus). Additionally, increased levels of these hormones post-mating can lead to embryo death.
Further evidence for the lack of effect produced when feeding cows starch-based supplements comes from a large-scale farmsystems experiment (through the Pillars of a New Dairy System* research programme – see the full results at dairynz.co.nz/pillars). This 2014 study involved three commercial farms and about 1000 cows.
In this experiment, half of each farm’s herd was fed a starchbased concentrate. The other half received the same energy from a fibre-based feed.
Reproductive performance was recorded throughout the four-month study. The results highlighted there was no benefit of feeding starch-based supplements compared with fibre based feeds on any reproductive measures. In fact, there was evidence of a risk of reduced pregnancy rates when cows consumed the high-starch diet (see graph).
Therefore, it is energy that is important, and if there is enough pasture, pasture is enough. If you have a feed deficit in early lactation, your focus should be on increasing the energy available to the herd, i.e. megajoules of metabolisable energy (MJ ME). The type of supplement used to achieve this is secondary and, therefore, supplement purchase decisions should be based on cents/MJ ME.
Starch-based supplements are better than fibre-based supplements for cow reproduction.
There are no reproductive gains in feeding early-lactating cows with a starch-based supplement compared with a fibre-based supplement.
Find out more about feed supplements, feed values (ME), feed storage and density, and the milksolids response to supplements at dairynz.co.nz/supplements
This article was originally published in Inside Dairy July 2019
*funded by dairy farmers through DairyNZ and by the Ministry of Business, Innovation, and Employment.