Abstract
Simple SummaryThe climatic environment within calf housing can have an effect on calf health, but also on growth and performance. Calves have a lower threshold environmental temperature (lower critical temperature, LCT), below which can impact on the calf’s ability to maintain its core body temperature. This can cause the calf to partition more of its available energy into heat production and less into growth. The LCT decreases as the calf gets older. This year-long study followed 299 dairy-bred calves on one farm in Scotland from birth until approximately 28 days of age, and looked at the proportion of time for which the temperature was below the LCT for the individual calf, as well as the daily liveweight gain (DLWG; kg/d) of the calves during this time. For their first 6–14 days of life the calves were individually housed, and then subsequently group housed. Air temperature (°C), relative humidity (%), and wind speed (m/s) were recorded every hour of every day throughout the study, and calves were weighed regularly so that DLWG could be calculated. The study demonstrated that calves that spent a high proportion of their time below their LCT had a lower DLWG compared to calves that spent a low proportion of their time below their LCT.Calf housing is naturally thermodynamic, with interactions between various elements such as wind speed, air temperature, and humidity. This study investigated the effect of the proportion of time for which calves were exposed to effective environmental temperatures below their lower critical temperature (LCT) on their daily liveweight gain (DLWG) within their first month of life. This study used the naturally occurring climatic environment, whereas other such studies have been conducted under climatically controlled conditions. Air temperature (°C), relative humidity (%), and wind speed (m/s) were recorded within the calf housing from birth until approximately 28 days of age, with calves being health-scored and weighed at regular intervals. Calves were housed from birth until 6–14 days old in individual hutches, and then moved into group housing igloo pens. Whilst individually housed, calves that spent less than 32% of their time below their LCT had a DLWG of 0.06 ± 0.34 kg/d (mean ± SE) compared to calves that spent more than 97% of their time below their LCT, which had a DLWG of −0.19 ± 0.045 kg/d. When group housed, calves that spent less than 1% of their time below their LCT had a DLWG of 0.59 ± 0.18 kg/d, whereas calves that spent more than 28% of their time below their LCT had a DLWG of 0.53 ± 0.23 kg/d. The proportion of time for which calves were exposed to effective environmental temperatures below their LCT had a significant effect on DLWG when calves were individually housed. Therefore, exposure to effective environmental temperatures below the LCT can be detrimental to the growth of the calf in the early stages of its life.
Highlights
For the farmer, the main objective of rearing calves is to produce a healthy calf that is able to achieve target growth rates as economically as possible
As an alternative to using air temperature as the sole environmental parameter, this study aimed to examine the effect of the proportion of hours for which calves were exposed to effective temperatures below their lower critical temperature (LCT) on their daily liveweight gain (DLWG) for two management phases: the first days of life when the calf is in an individual hutch, and when the calves are moved into group pens
One calf was excluded from the data due to a missing birth weight, and 27 were excluded as they were older than 14 days when moved into the group housing igloo pen
Summary
The main objective of rearing calves is to produce a healthy calf that is able to achieve target growth rates as economically as possible. Calves in the UK are exposed to an environmental temperature that is typically below their thermal comfort zone (TCZ), with the most recent summary data available from the Met Office (from 1981 to 2010) showing that there is a mean annual maximum temperature of 12.4 ◦ C and a mean annual minimum temperature of 5.3 ◦ C [10]. The TCZ is defined as the environmental temperature at which the calf is not motivated to perform any thermoregulatory behaviour, and lies within the thermal neutral zone (TNZ) for the calf. The LCT is the point when the calf increases metabolic heat production to maintain thermal balance, which can be done by contraction of the skeletal muscles (shivering) or through non-thermogenic processes, such as increasing energy intake.
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