The intensive, high-input farm had been consistently superior throughout this period, peaking at 2.0kg milksolids (MS)/cow/day, compared with 1.72kg MS for the lower-intensity, low-input herd. This difference was attributed largely to superior condition at calving, leaving open the question of whether there had been some contribution from the brought-in feed component in the ration the high-input herd had been receiving.
The question then is, can this superior production/cow be maintained for the rest of the season, and if so how and at what cost? With the season still less than halfway through at peak lactation obviously if superior production trends made to that point can be continued, or better still enhanced, gains for the entire season will be substantial.
Obviously, in a perfect world the ideal would be for peak production levels until drying off, in other words a straight-line graph. However, unfortunately and inevitably, in the real world production will decline – King Canute couldn’t stop the tide coming in either – but the process of decline can be minimised and all summer and autumn management should be prioritised to this end.
Before discussing this, let’s look at the factors determining the timing and magnitude of the peak. There’s a commonly held belief that it is the onset of pregnancy that starts the drop-off in a cow’s milk production. This makes sense. In the natural world typically when a cow becomes pregnant she will have a weanable calf at foot, and because the survival of the species is the natural order of things, the cow will begin to switch her priorities from nurturing the calf at foot to supporting the foetal calf.
Consequently she begins to run down milk production and soon dries off completely. It’s a persuasive theory, with only one weakness – it is wrong. If we are to use the “back to nature” analogy the cow has to produce enough milk to feed one calf for only about 10 weeks. Over the years we have selected and bred cows to far exceed this humble target.
All the practical and scientific evidence is that, for the modern cow, early pregnancy makes no real nutritional demands, and it is only in the last two months that this will become significant. So the coincidence of peak lactation and becoming pregnant is just that – coincidence.
Coincidental
What is also coincidental at this time is the transition of pastures from the vegetative to the reproductive state, ie, the onset and development of stalk and seed head formation. There is also the advent of summer, with warmer weather and hotter temperatures. All these factors will work together to lower appetite, reduce the intake of digestible dry matter (DM), and thus with it, milk production.
Why?
First, temperature. We tend to overlook the fact that, generally, cows prefer temperatures about 2deg C lower than we do. So when we are feeling comfortably warm, a cow can be feeling too hot. We don’t like working under hot conditions and neither do cows.
Harvesting and digesting grass and producing milk are hard work, so when it’s hot the tendency will be to minimise this.
Exacerbating this will be the fact the fermentation of the large bulk of grass in the rumen will also produce significant heat, affecting body temperature.
Add to this pasture quality. Two factors of importance here are palatability and digestibility. Cows will eat more of the succulent, leafy pasture simply because it is tastier – that’s not rocket science. And in a double whammy, the ranker, stalky, seed-headed pasture will have a significantly lower digestibility, so for every kg DM consumed the cow will gain proportionately fewer utilisable nutrients. (The best indicator of this beginning to happen is the firming of the dung. Many farmers tend to think that sloppy dung in the spring – the eye-of-the-needle stuff – can be an indicator of animal health problems. It is much more likely to just indicate highly digestible feed. After all, if its feed was 100% digestible a cow would merely defecate water.)
These then are the key characteristics in managing and using summer and autumn pasture. Many times in December and January I’ve heard the statement, “I don’t know why they’re dropping so fast. They’re getting plenty to eat – they’re leaving plenty behind.”
Then they go into a nice, leafy hay or silage regrowth paddock and deck it – and production jumps overnight. (One thing that also shows is how much feed a herd leaves behind is a poor indicator of per-cow intake, unless of course it is accurately estimated and deducted from accurately assessed pre-grazing levels.)
Main weapons
The techniques and methods used to maintain pasture quality, post peak lactation, is an important subject in its own right . Generally the main weapons will be topping and grazing management, with the latter usually meaning harder grazing. (This also has the potential to be counter-productive and suppress milk production).
The big question then, if pasture quality is the best that can be obtained, is will continued feeding of supplements (ie, palm kernel) be economically justifiable and worthwhile?
The results to date at the demonstration farm, while possibly providing some useful pointers, raise more questions than provide answers. The figures from December 3 are:
- Production; MS/cow/day – high input 1.75, low input 1.64 – down from peaks in late October of 2.0kg and 1.72kg respectively.
- Body condition score (BCS) – high-input herd 4.7, low-input herd 4.5, down from calving levels of 5.5 and 4.9.
The low-input herd was getting 135 square metres (m2)/cow/day of pasture and consuming 16kg DM, while the high-input herd was getting 100m2 of pasture and consuming only 14kg DM. However, it was also eating 3kg DM of palm kernel.
The most significant data here is that showing the production gap is closing. A significant contributing factor to this could be that the past advantage of higher condition has now largely been milked off the high-input herd. The low-input herd has had 20% of its area cut for silage, with another 12.5% closed, so there’s plenty of good-quality pasture available, and being fed. But no silage regrowth paddocks have been available so far for the high-input herd.
On the other hand, it appears that the continuation of the palm kernel feeding for the high-input herd allows the cows to be grazed harder, while at the same time maintaining input. It would be fair to deduce then that the palm kernel is contributing usefully to the production of the high-input herd, and importantly, in doing so is not merely substituting for pasture to any significant extent.
If pasture quality continues to be superior on the low-input herd and the gap in production/cow continues to narrow, it would be reasonable to conclude that the most profitable option would have been to discontinue palm kernel feeding. However, if the high-input herd continues to be fed palm kernel and stays ahead in production, the question of whether this was because of the palm kernel or purely a response to the better earlier BCS and production remains unanswered. Hopefully at the end of the season, by studying trends we will have some better indications, but unfortunately we will still be far from definitive answers.
Brian Hockings is a member of the Stratford Demonstration Farm management committ
