Feeding to increase milk protein

The dairy cow's production cycle can be divided into three stages:

First 80 days of lactation: The most important consideration is to minimise the energy gap between milk production requirements and the cows dry matter intake. This will minimise bodyweight loss and minimise the drop in milk protein content.
Mid-late lactation: Maximising dry matter intake of a high energy diet will maximise milk protein content and allow body condition to rise.
Dry Period: During this period the cow will rebuild her mammary tissue and replenish some of her body reserves prior to calving. The rumen should be conditioned to maximise dry matter intake as early as possible in the subsequent lactation.

Grass

The Northern Ireland climate is well suited to growing high yields of quality grass. Grazed grass is the cheapest feed available to the dairy cow. For farmers to maintain margins it is essential to optimise the use of grass.

Maximising the intake of quality grass throughout the season will boost milk yield and milk protein levels. The two key factors which impact on the performance from any grazing system are average grass cover and sward quality. Both are closely linked and good grassland management is required to ensure that adequate quantities of leafy grass are available. Target average farm cover should be in the region of 2500 KG dry matter/ha. This will allow a plentiful supply of grass to be offered to the cow whilst maintaining grass quality.

Ideal post grazing cover of 1600 kgDM/ha

Entry covers of 3500 kgDM/ha allow high grass intakes, promote energy intake and milk protein

Maintaining grass quality in mid season requires tight stocking in the spring to ensure dense leafy swards are available with minimum stem development. Table 1 illustrates the effect lax spring grazing has on protein production from the same swards grazed in mid summer.

Table 1. The effect of lax spring grazing on subsequent milk protein production

	Tight spring grazing	Lax spring grazing
Post grazing cover (KGDM/ha)	1500	2000
Protein (%)	3.30	3.22

Source: Massey University, New Zealand

On the other hand stocking cows too tightly in spring in an effort to maintain subsequent grass quality can reduce intakes and hence milk protein production. Allowing cows a plentiful supply of grass and removing any surpluses with dry stock or topping may be the preferred option. Target stocking rate should be four to six cows/ha depending on grass growth, with residual covers of around 1600 KG/DM/ha.

Supplementary Feeding

With increasing other hand stocking cows too tightly in spring in an effort to maintain subsequent grass quality can reduce intakes and hence milk protein production. Allowing cows a plentiful supply of grass and removing any surpluses with dry stock or topping may be the preferred option. Target stocking rate should be four to six cows/ha depending on grass growth, with residual covers of around 1600 KG/DM/ha.

Extending the grazing season

Research and first hand experience at Greenmount has clearly demonstrated that milk yield and protein content can be increased by allowing cows access to grazed grass in the early spring and late autumn periods. The benefits are most pronounced in a spring calving situation with increases in milk protein concentration of around 0.20 percent during the extended grazing periods. Smaller but still significant increases of 0.10 percent have been achieved with autumn calvers. (ARINI Hillsborough.)

Early turnout of a portion of the herd at Greenmount in 1998 was worth 88pence/cow/day.

At Greenmount, the grazing season normally starts in early March and extends to the end of November, depending on ground conditions and grass cover. Increasing the rotation length from September up to 60-70 days and expanding the grazing area ensures that cows have access to fresh grass late in the season.

Reseeding policy

To grow early grass and obtain high yields of quality grass throughout the season, a high ryegrass content sward is essential. The digestibilty of modern varieties is much higher than for non-sown species (up to five or more units of D value) and hence energy intake and milk protein production from ryegrass rich swards will be higher. Aim to keep ryegrass content at 60 - 70 percent across the swards.

Making high quality silage

Silage

The importance of silage quality

Cows calving during the autumn and winter period will produce a large proportion of their lactation from silage and therefore silage quality is vitally important for autumn calving herds. Silage quality during this period can have a dramatic effect on milk protein content. Table 2 illustrates the effect of silage quality on milk protein percentage. Increasing the D-value of silage from 62 to 73 increases milk protein concentration by 0.18 percent and at the same time increases milk yield.

Table 2. Effect of digestibility of grass silage on milk composition and yield

	D-value of silage (%)
	62	70	73
Silage intake (kg DM/day)	8.1	10.0	10.7
MILK COMPOSITION
Protein (%)	3.17	3.22	3.35
Fat (%)	3.68	3.68	3.77
Milk yield (l/day)	26.3	28.2	28.9

Source: ARINI, Hillsborough.

Research has shown that feeding rapid wilted (24 hours) silage can increase milk protein concentration by over 0.10 percent (Table 3). At Greenmount the target is to produce silage with a dry matter content of at least 25 percent, an ME of at least 11.5 MJ/KG DM and an intake value of at least 90. The aim is to achieve this by harvesting young leafy swards and wilting for up to 24 hours. Depending on ground and weather conditions tedding is carried out. With a large proportion of the Protein Improver Herd calving in the autumn, sufficient first cut silage is made to feed fresh calved cows over the entire winter period.

Table 3. The effects of rapid wilting on silage intake and milk composition and yield, results from 11 trials

	Unwilted	wilted
Silage intake (kgDM/day)	10.2	11.9
Protein (%)	3.27	3.38
Butterfat (%)	4.52	4.66
Milk yield (l/day)	20.7	21.2

Source: ARINI, Hillsborough

Additive

The choice of silage additive should be based on its ability to improve animal production under Northern Ireland conditions. Work at Hillsborough has clearly demonstrated that use of an effective additive can raise milk protein concentration by around 0.10 percent whilst also raising milk yield.

Alternative forages

In recent years there has been an increased use of alternative forages in Northern Ireland. The main alternatives are wholecrop cereals, forage maize, fodder beet and kale. The use of multiple forages tends to increase total dry matter intakes, but, this is not always accompanied by an improvement in milk protein percentage. High quality, high starch, maize silage, when it can be produced, generally results in improved milk protein concentration by 0.10 percent.

CONCENTRATES

Concentrate type/composition

The ingredient composition of the concentrate can have a significant influence on milk protein content. Increasing the level of starch in the concentrate, from cereals, has been shown to significantly increase milk protein content, see Table 4.

Table 4. Effects of increasing concentrate starch content on animal performance.

	Concentrate starch content(% DM)
	4	18	33
Milk Yield (litres/day)	26.8	26.5	26.4
Protein (%)	3.21	3.26	3.36

Source: ARINI, Hillsborough

The concentrates supplied by John Thompson and Sons Ltd for the Protein Improver Herd, are specifically formulated to balance the quality of silage being fed and the seasonal variation in grass quality. The concentrate contains high levels of starch from wheat and maize.

High quality concentrates, containing a balanced supply of both energy
and protein are important to ensure that milk protein content is optomised

The ration has been formulated to supply a readily available and balanced source of energy to the rumen micro-organisms to ensure optimum rumen function and maximise the production of microbial protein. This results in increased milk protein content. By-pass maize starch is added to provide an additional source of glucose in the blood supply to further increase milk protein production in the mammary gland.

Energy Density

Care must be taken to ensure that the starch levels are not excessive in relation to the total diet as this can depress intake due to digestive upsets such as acidosis. The use of excessive levels of oil in the diet should be avoided as this has been shown to depress protein as well as butterfat levels. Only high energy raw materials should be used in the concentrate to help maximise overall energy intake. This will produce the optimum supply of digestion end products for maximum milk protein production.

Protein quality

The ration formulated by John Thompson & Sons Ltd is a 20-21 percent protein ration, (depending on silage analysis) containing a high quality blend of protein sources which include soyabean meal and fish meal. The essential amino acid profile is tailored to ensure that the optimum level and balance of absorbed amino acids is achieved. Research work has shown that, of the end products of digestion, amino acids have the biggest effect on milk protein content. It is therefore essential that the amino acid flow to the small intestine and subsequent absorption at the mammary gland is maximised through microbial and by-pass protein in order to maximise milk protein content.

Concentrate Feed Level

Increasing the level of concentrate feeding increases milk protein content. This is largely due to the increased energy intake. On average, for each additional kilogram of concentrate offered per day, milk protein content was increased by 0.05 percent. (ARINI Hillsborough). This is an important fact to take on board when deciding on the economic optimum feeding level.

The level of concentrates required to support a specific yield will also be influenced by the quality and quantity of forage being fed. At Greemount Campus the Protein Improver Herd is fed to yield via a computerised in-parlour feeding system. Concentrates are fed at 0.4 KG for each litre of milk produced above that from forage alone. The level of milk production taken from silage alone is illustrated in Table 5.

Table 5. Production from silage for the Protein Improver Herd at Greenmount Campus

Year	96/97	96/97	97/98	98/99
Silage composition	1st Cut	2nd Cut	1st Cut	1st Cut
DM (%)	36	30	32	32
ME (MJ/kgDM)	12.9	1.0	10.4	10.6
Production from silage alone (l)	16	10	8	8

Depending on grazing conditions, up to maintanance plus 22 litres of milk are taken from grass during the month of May. This figure declines as the season progresses by approximately two to three litres/month depending on grazing conditions such that by October production from grass is limited to 10-12 litres.

Feeding to Genetic Potential

The level of concentrate required will be influenced by the milk yield of individual cows and the herd as a whole. The continued improvement of the genetic potential of the Protein Improver Herd means that there are more cows capable of yields over 7,000 litres. If these cows are not fed to their genetic potential, they will "milk off their backs". Cows which are fed to their genetic potential for milk yield will be more likely to meet their potential for milk protein production.

Out-of-parlour feeding

Feeding large amounts of concentrates containing high levels of cereals in two feeds in the parlour can cause digestive upsets which in turn reduces feed intake. Feeding concentrates on a 'little and often' basis via out-of-parlour feeders or complete diet feeders, can enable higher starch rations to be fed more effectively, particularly when fed at higher feeding rates. Table 6 shows the benefits of out-of-parlour feeding. Maximising starch intake and meeting the energy intake of higher yielding cows will help maximise milk protein content.

Table 6. Benefits of out-of-parlour feeding on milk composition.

	In parlour feeding	Out of parlour feeding
Total concentrate (t/cow)	1.33	1.33
Milk protein (%)	3.20	3.30
Milk butterfat (%)	3.85	3.95
Milk yield (l/cow)	5965	5903