Managing large herds in pasture-based dairying systems presents unique challenges with implications for herd feed supply and milk production. A recent research project conducted by Agriculture Victoria researchers at Ellinbank, Victoria, set out to understand some of the issues.
Dr Martin Auldist and Dr Marlie Wright led a small case study to determine the potential impact on nutrient intake of cattle that walk long distances to the farm dairy each day and spend long periods of time off pasture.
"Feeding large herds on pasture often requires a larger farming area, with the consequence that cows must walk long distances to the dairy each day," Dr Auldist said.
"Then they also spend a long time at the dairy, waiting to be milked. The end result is that they spend several hours away from the paddock each day - you'd have to think it would affect their pasture intake.
"The other part of the equation is that there is a consistency to the milking order. In other words, it is often the same cows spending the longest time away from pasture, day after day. It's probably not surprising that the first cows are often the best producers."
Dr Auldist and Dr Wright designed a case study experiment to generate data about the extent of these issues, and to talk to the farmers about possible solutions. Three pasture-based dairy farms were chosen for study: one in Gippsland, one in the irrigation area of northern Victoria, and one in south-eastern South Australia. All farms were running more than 1000 cows, though not necessarily in one herd.
Dr Wright and the team visited each of these farms in spring to measure distances walked, time spent queuing at the dairy, and the time that the first and last cows reached the dairy and returned to the paddock.
"We also got a farm map so we could measure maximum distances walked and obtained milking records over a week, so we could look at the consistency of milking order and the relationship of milking order with milk yield," Dr Wright said.
The team also measured the pasture depletion that occurred in the time between the first and last cows reaching the paddock.
"We found that cows were spending up to 2.5 hours per day walking 10 kilometres or more to and from the dairy," Dr Wright said. "This amount of walking requires energy that equates to 3.5 kilograms of milk per cow per day, not counting the amount of energy required for walking around grazing.
"Some cows also waited up to 5.5 hours a day at the dairy before milking, while others didn't wait at all. When time at the feedpad was included, some cows spent up to 9.5 hours a day away from pasture."
On all farms, there was a consistency in the milking order but this was mostly due to the first and last cows. "The first cows always wanted to be first, and the last cows were always last," Dr Wright said.
"But the cows in the middle were much more variable - they didn't really care as long as they were in the middle somewhere."
When it came to milk yield, the first cows definitely held the advantage, producing up to 4kg of milk more than the last cows. "Presumably this is at least partly due to an increased opportunity to graze, though there might be other factors," Dr Wright said.
The results also showed that not only did the last cows back to the paddock have less time for grazing, but that between 19 and 29 per cent of pasture dry matter was already gone by the time they got to the paddock. "Presumably there was also pasture selection going on, so that the available pasture was also of lower nutritional quality," she said.
Dr Auldist said the study could have wider implications. "Although this study was originally aimed at owners of large herds, we think that the results have a much wider relevance," he said. "These kinds of issues with cow flow and time away from pasture can also be encountered in much smaller herds.
"We'd like to use our results as the basis for a study into better feed allocation on pasture-based dairy farms, irrespective of how many cows they have.
"There are still heaps of things we don't understand. Like what exactly is the effect on dry matter intake of spending that much away from pasture, is there compensatory grazing, and what is the cost of various mitigation options compared to the cost of doing nothing?
"Could we lift average farm milk production by reallocating feed resources by splitting herds, holding cows back, topping pasture to reduce selection, designing farms with more efficient fencing and laneway layouts, and so forth?"
These questions and more will hopefully form the basis of a future funding application to industry.D
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