Summer forage options for dairy heifers
Updated: Dec 22, 2019
A dairy heifer's first summer period is historically the first period where she begins to fall behind in growth rates due to low pasture quality and quantity.
Some work I did at LIC back in 2015/16 showed that 29.7% of heifers were below their target weight at 6 months which increased to 46.1% by 9 months and 66.5% by 12 months of age. Therefore, the summer period after 6 months of age is an ideal period to focus on how we can improve growth rates of dairy heifers.
Here are 3 studies on forages (other than pasture) for improving heifer growth over their first summer period. The forages included lucerne, pasture silage, leafy turnips or a chicory, plantain and clovers mix.
Lucerne with or without meal was a great feed source to improve heifer growth rates in a dry summer
A herb-mix of chicory, plantain and white clover was a promising feed source to improve heifer growth when managed appropriately
Leafy turnip is a forage brassica that has been used to sustain growth rates above 0.6 kg/d in dairy heifers over summer
The first of these 3 studies compared heifers that were fed one of three forages on a drystock farm in Masterton.
traditional ryegrass-based pasture + meal
lucerne + meal
conserved forages (herb-mix crop, pasture silage or pasture balage) + meal
Heifers in this study had an average birth date of the 8th August and the study started in February, which means heifers were about 6 months of age at the start of the study.
The first 2 weeks were a transition period (days -14 to day 0) where heifers were slowly transitioned from pasture onto either lucerne or the herb-mix crop (chicory, plantain, white and red clovers).
As can be seen in the graph below, heifers in the lucerne (grey) and crop (blue) treatments did not grow over their transition period, but the heifers that remained on pasture continued to grow.
The area allocated to the heifers for the crop was not large enough to sustain them over the whole summer period and drought conditions meant they needed an alternative. This alternative was to place heifers in a heavily grazed paddock (little to no pasture) from day 11 and to feed them pasture silage or balage for the remainder of the study. All heifers were still fed meal daily over the whole period.
From day 0 to day 20, the growth rate of heifers fed lucerne (grey) averaged 1.1 kg/d and the growth rate of heifers fed crop/conserved forages (blue) averaged 1.14 kg/d. Both groups grew faster than the heifers fed pasture (purple) that grew at 0.71 kg/d from day 0 to 20.
From day 20 to day 41, heifers that were fed lucerne maintained their fast growth rates (1.34 kg/d), whereas, the heifers fed crop/conserved forages fell back to a growth rate that was similar to heifers fed pasture (0.42 kg/d and 0.44 kg/d).
By the end of the study (mid-March) the heifers that were fed lucerne were the heaviest (188.6 kg) and had the most heifers above target weight (85% of the group). Heifers that were fed pasture were 167.9 kg and heifers fed crop/conserved forages were 170.1 kg at the end of the study.
Overall from treatment allocation (day -14) until the end of the study (day 41) the growth rates were fastest for heifers fed lucerne+meal (0.93 kg/d), intermediate for heifers fed crop/conserved forages+meal (0.61 kg/d) and slowest for heifers fed pasture+meal (0.55 kg/d).
In order to meet their target weight at the end of trial, heifers need to gain 0.67 kg/d. Based on the results from this study lucerne with the addition of meal was a great feed source to enable target growth rates to be achieved during a dry summer.
The crop mix with meal was a promising feed source, however, (as with any feed) there needs to be enough of it and in this study the dry summer had a huge effect on regrowth rates.
Feeding meal with pasture or pasture silage was not enough to meet the target growth rates in this study.
The second study was completed the year after the first study on the same farm using the same grown forages. This study was my honours project and was my very first taste of the research life.
This study was run slightly differently to the first study in that there was no meal or silage fed. The three forages were:
Traditional ryegrass-based pasture
Chicory, plantain and white clover mix "crop"
Same as the first study, heifers were about 6 months old at the beginning of the experiment, however, in this study there was enough forage to keep heifers on their treatments for 9 weeks over summer (Feb to April).
There was a transition period for the heifers grazing lucerne or the herb-mix crop this was from day -16 until day 0. Similar to the previous trial heifers fed lucerne barely grew over this transition period but grew faster once they were transitioned (average 0.99 kg/d for the first 6 weeks).
The heifers fed the herb-mix crop also grew pretty fast at around 0.9 kg/d for the first 6 weeks. The last 3 weeks of the study (days 42 to 63) growth slowed down for heifers fed lucerne or crop, to the point that the lucerne-fed heifers were similar in weight to the pasture-fed heifers on day 63. As can be seen in the photo above, the chicory was very stalky and overgrown towards the end of the study, which probably explains the slower growth rates in these heifers.
The heifers fed pasture grew at a fairly constant rate of about 0.5 kg/d throughout the summer period.
The week after the study ended, all heifers were grazed together on pasture (day 63 to 70). We decided to get a final weight after this week on pasture.
Why? Firstly, lucerne, chicory, plantain and white clover are known to have higher digestibility and lower neutral detergent fibre percentages (NDF) than pasture has, therefore, we would expect there to be differences in gutfill and passage rate.
During the study heifers were shifted once per week and were weighed once every 3 weeks at the end of their weekly break. This meant that the lucerne-fed heifers had consumed nearly all the feed available to them and had very little gutfill on weigh day. Conversely, the pasture-fed heifers were grazing what I would describe as standing hay and had a very high gutfill on weigh day.
By weighing all the heifers after 1 week on the same forage (purple band in the graph above) we were able to see what the heifers weighed when they had similar gutfill. As shown in the graph, the lucerne-fed heifers had a large spike in weight over that week, which most likely was from increased gutfill from eating the "standing hay" rather than increased live weight from eating pasture compared with lucerne.
Overall, this study showed that using lucerne or a mixed sward of chicory, plantain and white clover was able to improve growth rates of heifers during a dry summer compared with traditional ryegrass-based pasture.
An alternative to unrenovated ryegrass pasture for dairy heifers during summer could be a brassica. This third study compared heifers fed ryegrass-based pasture (purple) with those fed a leafy turnip (blue). In this study they used 'Hunter', but 'Pasja' is another common leafy turnip cultivar.
This study was run a little differently from the first 2 studies in that all heifers on both treatments grazed leafy turnip for approximately 6 weeks (Jan-Feb; blue shading in graph) followed by all heifers grazing traditional pasture for about 3.5 weeks (Feb-Mar; purple shading in graph) before being split into their 2 treatment groups for grazing on the 2 separate forages (pasture or leafy turnip) for around 7 weeks (Mar-May).
This gave the heifers in the leafy turnip treatment an opportunity to have prior adaptation and experience of grazing leafy turnip it also gave the researchers the opportunity to study growth of heifers when returning to pasture after grazing leafy turnip for a period.
Growth rates and live weights were similar for both groups during the blue and purple periods on the graph. Once the heifers were separated into their 2 groups, those that grazed leafy turnips (blue solid line) grew faster and were heavier than those that grazed pasture (purple solid line).
After the study ended, all heifers were grazed in one group and were monitored for subsequent growth up until 22 months of age.
Overall, using the forage brassica leafy turnip as a feed source to dairy heifers over the summer period enabled heifers to sustain growth rates over 0.6 kg/d over the dry summer period when pasture was not able to, likely due to low quality and/or supply.
These 3 studies showed that feeding heifers lucerne, a mix of chicory, plantain and white clover or a leafy turnip were all viable options to sustain growth rates above 0.6 kg/d during summer dry periods when traditional ryegrass-based pastures may not be able to.
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