Feeding The Dairy Cow In Spring

Researchers from Teagasc, Ireland, looks at supplementation requirements for feeding the dairy cow in Spring.
calendar icon 20 December 2011
clock icon 14 minute read

Summary

  • The grass intake of dairy cows in early lactation is low but increases by ~1 kg grass DM per week for the first two months, then intake levels off


  • Measurements of grass intake in early lactation indicate that, apart from the first month post-calving, the correct allowance of high quality grazed grass can supply sufficient energy to meet requirements


  • On a herd basis, the demand for grass in early lactation is dependent on stocking rate and calving pattern


  • In general across the herd the energy requirement is low in spring because freshly calved cows with a low energy requirement are entering the milking herd daily


  • Supplementation required on a herd basis should be calculated by comparing the herd requirement to grass availability in order to identify if a feed deficit is present


  • The milk solids response to supplementation is a function of a number of different factors, but the primary factor is the feed deficit – the greater the feed deficit, the smaller the substitution rate and the greater the response to supplementation

Introduction

Dry matter intake is possibly the single most important factor influencing milk production in dairy cows. Meeting the requirements of the animal by achieving the correct intake is crucial to ensuring good performance and health. Animals who experience a deficit in energy intake can reduce their energy output (milk production performance or weight gain) or attempt to bridge the energy deficit by mobilising body tissue (resulting in BCS loss). Both of these options are undesirable. The objective is to provide the animal with adequate nutrition to meet requirements, in the

cheapest way possible. In Ireland the grass-based system is the most profitable system. In this system grazed grass is the largest part of the feed budget. With variable grass growth conditions, grass intake and weather conditions in the spring it is possible that there may be an energy deficit at this time. The objective of this paper is to describe feeding the dairy cow in spring. Data from studies conducted at Teagasc Moorepark over the last number of years will be examined in order to identify the energy requirements and energy taken in, in order to ascertain if an energy deficit exists, and if so, how to bridge it. The size of the feed deficit is the primary factor affecting the substitution rate and the response to supplementary feeding. However, a number of other factors are also involved, including stage of lactation, genetic potential for milk production, grass availability and quality, and the quantity and quality of supplementary feed.

Dairy Cow Dry Matter Intake in Early Lactation

Figure 1 illustrates the grass dry matter intake of a cow in early lactation. These data are from measurements made at Teagasc Moorepark over the last five years (2007 to 2011 inclusive) on cows offered a grass-only diet. The data indicate the capacity of cows to consume grass in early lactation. The graph illustrates the low grass intake of a cow in early lactation, as shown by the low intake in weeks one and two, and then the increase of approximately one kg per week up to week eight. Intake then levels off. The graph also shows the greater intake of mature cows compared to first lactation animals. The first lactation animals consume on average 75 per cent the quantity of feed of their mature cow counterparts. Of course, most farms have a mix of mature and first lactation animals in the herd. The graph illustrates the average intake of cows in a herd with a 25 per cent replacement rate (i.e. 25 per cent first lactation animals and 75 per cent mature cows).

Figure 1. The grass dry matter intake of cows in early lactation

The energy value of feeds in Ireland is presented in the units UFL. One UFL is defined as the energy contained in one kg of air dry standard barley. Data from studies carried out at Teagasc Moorepark over the past 10 years (89 samples) indicate that the average UFL value of spring grass is 1.04 UFL/kg grass DM. This grass has a high feed value. So an intake of 10 kg DM grass is equivalent to 10.4 UFL, and an intake of 15 kg DM grass is equivalent to 15.6 UFL. There is variation around this value. The same dataset from Teagasc Moorepark indicates that the UFL value of spring grass can be as high as 1.13 UFL, but can also be as low as 0.84 UFL.

Dairy Cow Energy Requirements in Early Lactation

The energy requirement of a dairy cow in early lactation is composed of the energy required for milk production and the energy required for maintenance. In later lactation energy is also required to support pregnancy, to replenish any lost body weight and for growth. Energy requirements are also expressed in the units UFL. In early lactation the majority of the energy required comes from what is eaten by the cow, but a small proportion can also come from body fat mobilisation, which we see as bodyweight and body condition score loss. In early lactation the energy requirements of the cow change on an almost daily basis, due to the rapidly changing milk yield and milk composition.

Figure 2 illustrates the energy requirement of cows in early lactation. As in Figure 1, data are presented for a mature cow, a first lactation animal, and for the average cow in a herd with a 25 per cent replacement rate. In this case the mature cow is a 550 kg cow who loses 20 kg bodyweight between calving and week 11 and then from week 12 to 22 puts on 20 kg of bodyweight. This cow achieves a peak milk solids yield of 1.93 kg/d during week 8 of lactation. The first lactation animal is 450 kg bodyweight and achieves a peak milk solids yield of 1.46 kg/d.

Figure 2. The energy requirements of cows in early lactation

Comparing the energy required in Figure 2 with the intake in Figure 1 it can be seen that a deficit exists in the first month of lactation. This indicates that the cow is consuming insufficient grass to fulfil her energy requirements. As a result, in the example shown in Figures 1 and 2, supplement should be offered to the cow for the first month of lactation. It’s also clear from the graphs that the decision on whether to supplement or not will be influenced by both the grass intake (intake capacity of the cow) (Figure 1) and the energy requirements (milk production of the cow) (Figure 2). Typically, as the milk production increases so too does the deficit between energy supply and energy demand, increasing the requirement for supplementary feeding. Similarly, as the milk production decreases, so too does the deficit between energy supply and energy demand, reducing the requirement for supplementary feeding.

Supplementary Feeding

The quantity and type of supplement to be offered depends on the grass intake and the energy requirements. If high quality grass is available to meet the intake levels shown in Figure 1, then up to three kg of a high energy supplement (e.g. a high quality concentrate with a minimum of 0.94 UFL (fresh weight)) should be offered to meet the energy requirements shown in Figure 2. In general the crude protein concentration of grass is high and it is not necessary to offer a high crude protein supplement.

If there is insufficient grass available to meet the intake shown in Figure 1, then a higher level of supplementary feeding is required to meet the requirements shown in Figure 2. If grass is making up a very small proportion of the total diet then it is necessary to make up the feed deficit using a forage as well as concentrate (e.g. grass silage, maize silage, whole-crop). This maintains adequate fibre levels in the diet. This fibre must come from forage. The type of concentrate required depends on the levels of grass available. For example, if grass silage is being offered, in association with low levels of grass, it is necessary to offer a higher crude protein concentrate in order to maintain the total diet crude protein at an acceptable level.

If concentrate is being offered as a feed on its own (e.g. in the milking parlour at milking) then lower levels can be offered in equal proportions at the morning and evening milking. However, if greater than six to eight kg concentrate per cow per day is being offered in this way it is necessary to introduce a third feed. This is because large quantities of concentrate being eaten in a short amount of time can give rise to problems in the rumen (rapid drop in rumen pH). Special attention must be paid to heifers and early lactation animals being offered high levels of concentrate. This is because their total intake is low and the concentrate could be making up a greater proportion of the total diet than anticipated. This can lead to problems with low rumen pH and low gut fill. Concentrate feeding levels should be stepped up gradually over time to allow the rumen to adjust.

The Herd Energy Requirements in Spring in Early Lactation

Research from Teagasc Moorepark shows the importance of getting grass into the dairy cow early lactation spring diet. Maximising the amount of grazed grass in the diet boosts milk solids concentration and increases profitability while setting up the farm for subsequent rotations. The availability of grass should be the first consideration in the feed budget. In general across the herd the energy requirement is low in spring due to freshly calved cows with low energy requirements entering the milking herd daily. Calving pattern and stocking rate have an important influence on the herd requirement for grass in early spring.

Figures 3 and 4 illustrate the energy requirements of herds with different mean calving dates (21 February and 8 March) and at different stocking rates (1.6, 2.4 and 3.2 cows/ha). The herd has a 25 per cent replacement rate. The demand reflects the mix of animals in the herd – from those just calved to those calved a longer period of time. The data are expressed on an energy requirements per hectare basis for each week. As stocking rate increases there is an increase in the energy requirement.

For example, on 25 February, in the early mean calving date scenario, the low stocking rate has a requirement of 15 UFL/ha and the high stocking rate has a requirement of 29 UFL/ha. For the late mean calving date scenario, on 25 March, the low stocking rate has a requirement of 17 UFL/ha while the high stocking rate has a requirement of 34 UFL/ha. It’s also clear from the graphs that the earlier the mean calving date the earlier and greater the demand. This is because the earlier calving herd has a greater proportion of cows calved for a longer amount of time. This is illustrated by taking the example of the date on which the requirement of the high stocking rate reaches 40 UFL/ha. This occurs on 18 March for the early mean calving date, but not until 8th Apr for the late mean calving date.

Figure 3. The energy requirement per ha of the calved cows in the herd, depending on stocking rate, for a herd with a mean calving date of 21st February (herd composed of 25 per cent heifers and 75 per cent mature cows).

Figure 4. The energy requirement per ha of the calved cows in the herd, depending on stocking rate, for a herd with a mean calving date of 8th March (herd composed of 25 per cent heifers and 75 per cent mature cows).

Meeting the Herd Energy Requirements in Spring in Early Lactation

It’s desirable to meet as much of the herd energy requirements as possible from grazed grass due to the benefits on milk solids concentration and increasing the grass quality for future grazing rotations. The herd energy requirements (Figures 3 and 4) should be compared to grass availability on the farm. The availability of grass is a function of the farm grass cover and the current grass growth rate. Figure 5 illustrates two early spring grass growth rates, one high and one low. The high grass growth rate average from 5 to 19 March was 28 kg DM/ha/d. This is greater than both the low stocking rate requirement (15 UFL/ha) and medium stocking rate requirement (22 UFL/ha) in the late mean calving date system. This means that after the herd requirements are met, grass is still accumulating on the farm and farm grass cover is increasing. During the same time period, the low grass growth rate average was 12 kg DM/ha/d. This is less than the low stocking rate requirement (15 UFL/ha) and medium stocking rate requirement (22 UFL/ha) in the late mean calving date system. This means that if all the herd requirements are met from grass, then farm grass cover will reduce. Where farm grass cover and current grass growth rate can sustain the energy requirement per hectare, supplementary feeding above that required for the individual animal is not recommended. Indeed it could be detrimental as higher levels of supplementary feeding will cause a decrease in grass consumed giving rise to poor utilisation and Spring Rotation Planner targets not being met. Both of these could lead to reduced grass quality in subsequent rotations, with negative effects on animal performance. On the other hand, if the farm grass cover and current grass growth rate cannot sustain the energy requirement per hectare, then supplementary feed may have to be introduced in order to avoid a greater feed deficit in the future.

Figure 5. Grass growth in a good and poor year

Supplementary Feeding

Substitution Rate

When grass intake does not meet energy requirements, supplementary feed, often taking the form of concentrate, is offered. However, when supplementary feed is offered grass intake is reduced. This effect is known as “substitution”, because the supplement is substituting for grass. The substitution rate is primarily a function of the feed deficit - as the quantity of grass offered to the cow increases, the feed deficit is reduced and the substitution rate increases. On the other hand, if a low quantity of grass is offered, then there is a large feed deficit, and so there is a smaller substitution rate. Analysis of a large database of studies in Teagasc Moorepark (39 herds) was undertaken to establish the substitution rate observed with different herbage allowances. The results took into account studies conducted over the past six years and revealed that on average a cow offered a low herbage allowance (< 14 kg grass DM/cow/d) in spring had a substitution rate of 0.28 kg. But cows offered a higher herbage allowance (> 18 kg grass DM/cow/d) had a much higher substitution ate of 0.69 kg. Supplementing grazed grass leads to a reduction in time spent grazing, which reduces grass intake. The substitution associated with offering forages such as grass silage is much higher than with offering concentrate. Some studies suggest a substitution rate greater than one kg with grass silage. Forages are usually less digestible than concentrate and are slowly degraded in the rumen leading to greater gut fill. This leads to reduced time spent grazing and lower grass intake.

Milk Solids Response to Supplementation

The milk solids response to supplementation is defined as the increase in milk solids yield per kg supplement offered. There is a negative relationship between substitution rate and milk solids response to supplementation. A small feed deficit is associated with a high substitution rate and a low response to supplementation. A large feed deficit is associated with a low substitution rate and a high response to supplementation. In addition to feed deficit, the milk solids response is also dependent on a number of other factors including stage of lactation, genetic potential for milk production, pasture availability and quality, and quantity and quality of supplementary feeds. Analysis of a large database of studies in Teagasc Moorepark (39 herds) was undertaken to establish the immediate milk solids response to supplementation with different herbage allowances. The results took into account studies conducted over the past 6 years and revealed that on average a cow offered a low herbage allowance (< 14 kg grass DM/cow/d) in spring had a response of 0.046 kg milk solids per kg concentrate offered. But cows offered a higher herbage allowance (> 18 kg grass DM/cow/d) had a much lower response of 0.007 kg milk solids per kg concentrate offered.

Another set of analysis (1200 individual cow records over 11 years) was undertaken to establish the immediate milk solids response to supplementation by cows with different milk yield potential. The results showed that when cows were offered up to three kg concentrate, a cow with a peak milk yield of < 25 kg will produce 0.036 kg milk solids for every kg concentrate fed, but a cow with a higher peak milk yield of 25 to 30 kg will produce 0.041 kg milk solids for every kg concentrate fed. This indicates that cows with a higher genetic potential for milk production respond more to supplementary concentrate feeding. This is partly due to the fact that these cows have a greater feed deficit than lower milk production potential cows. When higher concentrate levels were offered the response decreased. There can be a carryover effect associated with concentrate feeding. The duration of this carryover effect depends on a number of factors including duration of concentrate feeding, quantity of concentrate fed and stage of lactation.

December 2011

© 2000 - 2023 - Global Ag Media. All Rights Reserved | No part of this site may be reproduced without permission.