“There’s a fundamental difference between grass-based systems and overseas where they generally feed total mixed rations,” Lincoln University’s Jim Gibbs stressed in his introduction to the 200 or so farmers and farm staff that turned out for the Ashburton event.
As the evening unfolded the panel of three wise men – Gibbs, DairyNZ principal scientist John Roche, and independent consultant Terry Hughes – expanded on that, answering dozens of questions, slaying many a marketing myth and sales pitch in the process.
“Without fail in research here and overseas, when you add straw to the diet of a milking cow there’s either no change in production or it goes down,” said Gibbs.
For example, a split herd trial in 2006 in New Zealand showed that offering 2kgDM/day of straw caused an “immediate and sustained” 3.5% loss in production. Even at a $4.50/kgMS payout and free straw, such a strategy would have cost Lincoln University demonstration farm $75,000 in lost production, he pointed out. “And of course straw isn’t free… Feeding straw’s a very, very expensive hobby.”
Gibbs’ frustration that some consultants and feed companies still recommend straw to stimulate rumen function was clear. “It’s a bit like a line from that Eagles’ song [Hotel California]: ‘They stab it with their steely knives but they just can’t kill the beast’!”
The ‘scratch factor’ of straw is just one of several stimuli to rumination and there’s no evidence of poor rumination among cows on grass-only or predominantly pasture diets, he stressed.
Watery faeces, another argument for adding straw, are just a consequence of the 100-120L of water/day a cow can be eating in pasture. Straw will firm the faeces, but it also sits in the rumen for up to 72 hours taking up space that could be filled with rapidly digested, high quality grass that would add to production, he explained.
Monensin’s place as a rumen modifier also came under fire, as most research quoted in “glossy brochures” is derived from TMR systems overseas, and often extrapolated to dairy from rumen research in beef feedlots.
“There’s been some pasture work but at best it’s equivocal…. The high flow through a pasture-based rumen makes it extremely hard to keep that antibiotic in there.
“Typically there’s no benefit in milk production. It does have a slight benefit in bloat reduction but if you’re in a bad bloat situation it’s not going to save you.”
Even where 3kg/cow/day of grain is fed there would be “very little difference” in rumen function so monensin-based products would still be of no benefit, he added.
“Over 6kg (of grain/day), possibly. But that question’s not really been put to the test. If the rest of the diet is still pasture then the probability of a benefit is still low.”
Roche referred to a December 2011 DairyNZ Technical Series article he’d penned on the matter. “The problem is we don’t really know what diets produce a positive response to monensin.”
Probiotics were dismissed as additives for adult cattle, though Roche conceded a response could be seen in calves “if they’re struggling for some reason.” At present responses are “hit and miss” but as technology advances, better targeting may make their use more justified, he suggested.
Hughes said the big thing to remember with rumen microbes is that the population that endures is the one driven by the feed source.
Allowing time for the rumen microbial population to adapt is why feeds such as grain or fodder beet need to be introduced gradually, stressed Gibbs.
But while everyone would have heard horror stories of cows dying from acidosis on fodder beet, in practice cases are very few considering the tens of thousands now wintered on the crop, and largely within farmers’ control, he said. Transitioning onto the crop is a case of “painting by numbers”, starting at 1kgDM/cow/day and building it to a full wintering ration over a fortnight. Transition to brassica, on the other hand, can be just three to four days as it isn’t so much a change of feed type from pasture, as managing the risk from anti-nutritionals such as nitrates and SMCOs, or lack of iodine.
