Effects of milk allowance on growth and behaviour of dairy calves
Updated: Jun 5, 2020
This week's summary is of a study on milk allowance given to dairy heifers using automatic feeders and how the different milk allowances impacted growth (pre- and post-weaning) and grazing behaviour once on pasture.
Calves offered a higher milk allowance grew faster than those offered a lower milk allowance.
Calves offered less milk were unable to consume enough meal to match the dry matter intake of calves offered ad libitum milk.
Milk allowance offered to calves may affect the future development of grazing behaviours after weaning.
Three milk allowances were examined in Holstein×Jersey heifer calves:
low-allowance (LA; calves were fed milk replacer at 10% of initial live weight),
high-allowance (HA; calves were fed milk replacer at 20% of initial live weight), and
ad-libitum (ADLIB; calves were given ad libitum access to milk replacer).
All calves were provided with pelleted calf starter ad libitum and their intakes (both milk and pellets) were measured using automatic feeders.
Calves were weaned over 2 weeks from approximately 10 weeks of age.
As expected, calves given ADLIB access to milk consumed the most milk replacer (~9L per day), the HA calves consumed ~6L per day and the LA calves consumed ~3.5L per day.
Furthermore, calf starter intake was negatively associated with milk allowance. What this means is that as calves were offered more milk, they ate less meal - also pretty expected.
What is not as expected is that the total dry matter intake (milk + meal) was the lowest for LA calves (0.88 kg/d), moderate for HA calves (1.14 kg/d) and the greatest for ADLIB calves (1.38 kg/d). So the calves that were given less milk were not able to eat enough meal to match the intake of the calves that could drink as much milk as they liked.
This effect is shown very clearly in the figure below with meal intake in purple and milk intake in blue.
In the week after weaning, calves given a LA or HA of milk had similar dry matter intakes of calf meal (~1kg/day), both were more than the 0.8 kg/day that the ADLIB calves consumed.
Due to these different dry matter intakes, the live weight and growth rates were also different for each milk allowance group.
Heifers given ADLIB access to milk grew the fastest at 0.69 kg/day on average pre-weaning.
Heifers given a HA of milk grew on average 0.61 kg/day and those on the LA grew the slowest pre-weaning at 0.54 kg/day.
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In the week after weaning, calves in all groups had similar growth rates that were lower than in the pre-weaning period. However, the authors noted that there was a large amount of variation among calves within each group in post-weaning growth rate. What this means is that although the average growth rate appeared to be faster for LA heifers (0.46 kg/d) compared with the HA (0.33 kg/d) and the ADLIB (0.22 kg/d), there was a lot of overlap in growth rate among the groups, so overall they were not different.
The live weights over the course of the trial are displayed in Figure 2 below. As we can see, the heifers that were fed ADLIB milk grew the fastest (blue) and those offered a LA grew the slowest (purple).
The authors concluded that crossbred calves in NZ can consume more milk than is generally recommended (based on current recommendations of 10-20% of initial live weight).
Furthermore, the increase in milk consumption resulted in an increase in pre-weaning growth rate. Calves that had their milk intake restricted (LA and HA) to stimulate solid feed intake were unable to match the growth advantage of the unrestricted calves (ADLIB).
The second part of this study was using a subset of these calves (28 out of 198) to observe grazing behaviours in the post-weaning period.
As (most) cows in NZ live on a pasture-based diet, the ability of calves to successfully transition from milk to grazing pasture is very important for their future performance.
The authors expected that LA calves would have better developed rumens and that would lead to more time spent grazing compared with the other calves. This was not the case, as seen in Figure 3 below, the LA calves spent less time grazing (the day after introduction to pasture) compared with the HA calves, but a similar time to the ADLIB calves.
As mentioned in the first part of the study, the LA calves ate more solid feed compared with the other 2 groups, this may have made these calves less motivated to graze pasture. The calves were monitored for grazing behaviours between 8am and 4pm, perhaps the LA calves spent more time grazing overnight compared with the other groups?
What was not mentioned in the study (and is also very difficult to measure) were other variables that relate to grazing i.e. bite mass and bite rate as well as grazing time (Pasture & Supplements book, Ch 5).
Perhaps the LA calves were more efficient feeders? They did eat more solid feed before weaning, so maybe they were better able to get more pasture in per bite? Or maybe had more bites per minute than the other groups? These LA calves did spend more time ruminating than the other groups of calves, so maybe this was why?
Nevertheless, over the rest of the study, the calves in all three groups spent similar amounts of time grazing, ruminating etc. to each other. This peer-learning from each other is consistent with other studies and although doesn't help understand if different milk allowances made calves better or less able to transition to a grazing diet, it did show that there appeared to be no issues with feeding an ADLIB amount of milk to NZ calves.
The authors conclusions were that milk allowance may affect the future development of grazing behaviours of calves after weaning. However, this difference was only expressed immediately after calves were given access to pasture and was lost two weeks after.
Next up, I would love to see the costs involved for these three systems to help decide which methods may work better in different systems. It also would be good to see the long-term performance of these calves.
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Groenendijk M, Lowe K, Schreurs NM, Molenaar A, McCoard S, Luo D, Khan M 2018. Growth performance of crossbred dairy calves fed different milk allowances using an automatic feeding system. New Zealand Journal of Animal Science and Production 78: 21-25.
Groenendijk M, Lowe K, Schreurs NM, Khan MA 2019. Brief communication: Effect of pre-weaning milk allowance on post-weaning behaviour of heifer calves on pasture. New Zealand Journal of Animal Science and Production 79: 84-86.