Dairy nutrition May 2013

Dairy production model

The five systems of NZ dairy farming 1) all grass, self contained –No supplement fed to the herd, except supplement made on the milking area –No grazing off of milking area

2) feed imported either as supplement or grazing off and fed to dry cows (4% to 14% of feed imported) 3) feed imported to extend lactation and for dry cows (10% to 20% of feed imported) –Includes farms feeding 1-2 kg of meal or grain for most of the season

4) feed imported and used at both ends of lactation and for dry cows (20% to 30% of feed imported) 5) imported feed used all year (30% to 40%, but can be up to 55%) of feed

How do pastures grow Made up of grass and clover plants (usually ryegrass and white clover) In a pasture there are two processes taking place (growth and decay) Grazing management is the use of stock to harvest grass, thereby controlling growth and quality

Points to remember Net growth is the rate at which new leaves appear, less the rate of decay Grass leaves appear more quickly in spring (7 days) and more slowly in winter (30 days) Grass leaves die after 21 days in spring and 90 days in winter Dead leaves accumulate in the bottom of the pasture and reduce intake and quality (8 MJ ME)

Quantity Quantity of pasture is measured by: –Kilograms of dry matter per ha (kg dm/ha) Can be done in several ways: –Eye appraisal –Cut and dried –Plate meters –Electronically –By satellite –Based on production (12 kg dm/kg ms)

What is Quality Very digestible High in energy High in protein Easily harvested by cows (bite size) –Allows high feed intake –Allows high milk production

How do we assess quality Visually –Less than 20% dead material in base –Less than 10% seed head –More than 60% to 70% green leafy material Laboratory –Energy (MJ of ME over 12) –Crude Protein (22% early lactation, 16% mid lactation, 14% late lactation) –Neutral detergent Fibre (30% to 40%)

Management for quality –Keep the pasture in a wedge over the entire season (see overhead) –Graze the pasture consistently down to a low post grazing residual –During periods of growth exceeding demand, “increase” the stocking rate by dropping paddocks from the grazing round and conserving –Grazing round should be set at three times the number of days it takes for each new leaf to appear

Effects on milk production of quality for a 500 kg cow High quality pasture (12.5 MJ ME) –Intake will be 17 kg dm per day –17 kg X 12.5 MJ ME = 212 MJ ME –If 64 MJ ME required for maintenance, then 148 MJ ME available for milk (non pregnant, no weight gain) –If it takes 70 MJ ME per kg of MS, then production will be 2.1 kg MS (148/70=2.1)

Quality continued… Lower quality pasture (10.5 MJ ME) –Intake will be reduced to 14 kg dm (due to increased fibre, being slower to digest and filling the rumen—thus reducing appetite) –14 kg x 10.5 = 147 MJ ME –Maintenance is 64, so MJ ME available for milk production is 83 MJ ME –At 70 MJ ME per kg MS, then potential production is 1.2 kg (83/70=1.2)

Why feed supplements In early lactation to boost intake, so as to better meet cow requirements To improve body condition To overcome pasture deficits

Why continued.. As a carrier for other items, e.g. minerals To boost production above what is possible with grass alone To extend lactation

Best responses When the level of feeding is low (quantity) When the quality of pasture is low When high quality supplements are available at a reasonable price If supplement is easily eaten

In NZ energy is most common problem Dairy cows energy requirements are: –Maintenance –Pregnancy –Bodyweight gain –Lactation

What’s the true cost of supplements? Need to consider: 1) cost per kg of dry matter 2) utilisation 3) cost of machinery to feed out 4) cost of labour to feed out 5) production response