Sally Peel, DairyNZ feed developer

Managing pasture allocation this spring

At this time of year, it’s difficult to find the time to monitor average pasture cover (APC). However, keeping a close eye on your cover allows to you to determine if there's a shortfall in feed. Regularly assessing your farm’s APC every 7 to 14 days will also allow you to get the best value from DairyNZ’s Spring Rotation Planner (see article on page eight), by monitoring actual APC against your target APC.

One of the aims of spring feed allocation is to have your APC at its lowest when pasture growth is expected to equal feed demand (balance date).

APC below target?

If your APC is below the target line on the Spring Rotation Planner, the quickest way to get back on track is to hold the rotation length and not speed up until APC is back on target. If you have insufficient feed for your milkers, consider supplementing dry cows and restrict their pasture allocation, or supplement milkers to achieve a consistent even-grazing residual.

If you’re anticipating a feed shortage, consider using nitrogen (see 'feed matters' article on page 20) or, if it’s profitable for you, supplements can help to build pasture cover by extending rotation length.

APC above target?

If your APC is above target, you may have the opportunity to speed up your rotation by increasing the area offered to cows, and/or removing supplement while ensuring cows are still grazing to a consistent and even grazing height.

Learn more about average pasture cover at dairynz.co.nz/APC

Common questions about supplements

Q: Will feeding supplements improve reproduction?
A: No, not if cows are at target BCS at calving and are adequately fed on pasture. Pasture is enough if you have enough of it.

Q: If I’m feeding supplements, can I stop doing so during mating?
A: Yes, if the energy supplied by pasture is adequate, there is nothing to fear (both from an in-calf rate or profitability perspective) from reducing or removing supplement during the mating period.

Q: Are there reproductive benefits from feeding a high-starch supplement during early lactation?
A: No, there’s no benefit to reproductive performance from feeding a starch-based versus a fibre-based supplement.

Feeding cows: is pasture enough?

Good-quality pasture provides a well-balanced feed for dairy cows, supplying them with energy, protein, lipids, vitamins and minerals. In fact, spring pasture offers enough protein to allow cows to produce up to 2.5 kilograms of milksolids per day (kg MS/day).

It’s true that cows fed a total mixed ration (TMR) – a method of feeding by blending many ingredients – will produce more milk than cows grazing pastures. However, most of the difference in milk production is due to the increased dry matter (DM) intake and reduced activity in a TMR system, and not the nutrient composition of the diet. So, if supplements are required for energy, they should be purchased on a basis of cents per megajoules of metabolisable energy (MJ ME).

It’s important to remember that the profitability of using supplements depends on both the revenue generated from the purchased feed and how much it costs.

Based on the last 10 years of DairyBase data, the average response to supplements is 80 grams (g) MS/kg DM supplement fed. However, this response will vary depending on how supplements and pasture are managed in the system. If your cows are grazing high-quality pasture to residuals of 1500 to 1600kg DM/ha, adding supplements to the diet will simply result in cows leaving more pasture in the paddock.

So, what is the cost of providing that supplement?

The cost of feeding supplements depends on the purchase price and method of feeding (e.g. in-shed versus trailer in the paddock). Farmers often overlook the additional costs of feeding supplements, and many use ‘margin over feed’ as a way of justifying these costs. However, this assumes the only cost of feeding supplements is the feed itself; it ignores other costs such as fuel, repairs and maintenance and labour. International and New Zealand datasets indicate the total cost to the system of feeding supplements is 1.5 to 1.8 times the purchase cost of the feed.

Getting ready for mating

Nutrition is important for getting cows in calf but that doesn’t mean feeding supplements pre-mating will improve herd reproduction. Research shows that feeding cows solely on good-quality pasture can achieve reproductive performance rates above industry targets. If there’s a prolonged energy deficit, plugging the feed gap can improve reproduction. However, the type of supplement – starch (e.g. barley or grain) compared with fibre (e.g. silage or palm kernel expeller) – makes no difference.

Low DM intake in early lactation is not the major cause of reproductive failure in New Zealand; body condition score (BCS) at calving is more significant. So, rest assured that, if your cows are adequately fed on pasture and you can’t justify the cost of supplementary feeds on the basis of increased milk production, this won’t affect your herd’s reproduction.

What about BCS?

Once a cow has calved, it’s very difficult to reduce the loss in BCS. Giving a cow more feed, whether pasture or supplements (or reducing milking frequency to once-a-day), has minimal impact on BCS loss until after four to five weeks of lactation.

Many farmers wrongly believe grazing cows can’t eat enough to meet their demand, and that supplements will help improve the energy balance. You must remember that a cow will only eat about 12kg DM/day in the first week post-calving, and its intake will slowly increase to peak at 10 to 12 weeks post-calving. Because milk production peaks earlier, at about six weeks post-calving, all cows will be in a negative energy balance during this period. The extent of the negative energy balance is primarily driven by genetics and BCS at calving, not feed type or amount.

The main determinant of BCS loss after calving is BCS at calving, which is influenced primarily by feed and cow management in late lactation and during the dry and transition periods.

For more information, check out the Feeding cows in spring book at dairynz.co.nz/spring

This article was originally published in Inside Dairy August 2018